Quick Search

Recent Feedback

Recent feedback submitted to Structural-Safety is shown below. If you would like to contact us regarding any aspect of the scheme, please use the Submit Feedback form.

Fahed Maida [19/11/2020]

Feedback on report 845 Weld de-specification

Our experience is that in some cases, the structural engineer for the frame (not for connections) does not size up welds. The choice of weld type as partial pen would only make sense if it is reducing fillet weld size (the alternative would be large fillet weld size with risk of so many passes leading to cost and overheating). If the frame structural engineer has not sized up the weld, they would not be able to recommend partial pen over fillet.

With regards to full pen, I have only come across cases where fillet weld won't be recommended when fatigue is a risk. Unless this is a concern, I can not see why a frame structural engineer would insist on it.

As an observation, I feel it would have been worthwhile mentioning in the report that structural engineers should not over specify. We are seeing cases of specifications for projects with small sections sizes but the structural engineer still includes a statement such as 'minimum fillet weld of 8mm' when some web thicknesses on the project are only 6mm to 8mm.

Thanks a lot for the great work.

Daniel Munday [6/11/2020]

Feedback on report 971 Workmanship in domestic buildings

This report highlights the need for inspection under The Building Regulations. Very often domestic work is unsupervised apart from the builder's own control - which is likely to be variable, unprofessional and not independent. I admit I am biased toward Local Authority Building Control, but I have seen and heard of private Approved Inspectors relying on builder's photographs for steel beams and even foundations. The fault in this report would not have been picked up or rectified unless properly inspected.

Brian Duguid [15/10/2020]

Feedback on report 968 Execution not matching design assumptions

An observation; could this have happened if the structural frame designer had also been responsible for the connection design? It seems to me self-evident that the division of responsibility common in building works has played a part in the error here. The frame designer did not assume an eccentric connection, and a connection should not have been designed that permitted eccentric loading.

Andy Thompson [14/10/2020]

Feedback on report 940 Fire in multi-storey car parks

You may or may not be aware of the fire in the Car Park at the Tesco at Douglas, Cork, in (I think) August 2019. The structure has had to be partially demolished and remains closed; with particular impacts as the car park is on the roof of a large shoppint centre. I have no professional association here beyond being a regular visitor to Cork for other Civil Engineering reasons. Doubtless there will be parallels to be drawn.

Robert Lye [1/10/2020]

Feedback on report 958 Roof collapse at primary school

Regarding this report which I have just read in the latest copy of Building engineer magazine, it states that in current codes for flat roofs with access for maintenance only, should be designed for an imposed load of 0.6kN/m2. This is correct, (unless taken as a small roof for which there are different criteria), and then goes on to say that it is "considered that the dead load from both the existing and new coverings were within this allowance". This is incorrect as the roof construction loads are considered as construction, or dead loads, and therefore should be checked independently.

The imposed loading allowance is for, it is generally accepted, snow or maintenance assuming spreader boards are used. If the weight of the new roof covering was taken as part of the imposed loadings, then this would mean that the overall allowable imposed loading was reduced and possibly that the roof could not accept its designed loads and was therefore liable to be overstressed.

The information within the report is therefore, in my opinion, misleading and may possibly lead to further incidences such as this, if misread or misunderstood.


CROSS Response

The CROSS report has been updated to reflect the views of this feedback.

Mark Blanchette [23/9/2020]

Feedback on report 905 Consequences of low professional fees

This report reminded me of the John Ruskin Common Law of Business:

“It's unwise to pay too much, but it's worse to pay too little. When you pay too much, you lose a little money - that's all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do. The common law of business balance prohibits paying a little and getting a lot - it can't be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that you will have enough to pay for something better.”

John Collins [28/8/2020]

Feedback on report 926 Emergency motorway lane closure during concrete repairs

Something struck me about the repair. Once the concrete has been removed, the bars are no longer bonded to the concrete and there is no longitudinal shear transfer between them. As such, there is no strain continuity over the whole of the beam section; the bars act as a tie across the bottom of a concrete beam rather than directly engaged in flexure by dead loads.

As such, when the concrete was hydro-demolished the dead load moment across the section would have redistributed. When the repair was installed, the state of the bars being not engaged still exists; having the concrete in place no longer suddenly causes the bars to become engaged by the dead load moment causing the whole section to enter flexure.

To return the whole section back to one of flexure would likely require dead load to be jacked out of the beam, then the beam allowed to bend back down into its original dead load deformed condition. If the above has not been addressed, there is a risk that the section capacity is significantly less than may have been considered in the assessment. Has this been considered by the designer?

Gavin Kerr [15/7/2020]

Feedback on report 899 Glazing design and horizontal barrier loading

There are numerous facade engineers working on the consultancy side of the construction industry who can advice on glass, glazing system, curtain walling systems that need to resist lateral loads, and reliance does not need to be made on the sub-contractor installing the element in question. Not only is the strength of the glass an issue, but consideration needs to be given on how the glass will fail, will it fail spontaneously due to other causes, does it comply with building regulations in terms of safety glass an so on. CWCT (Centre for Window and Cladding Technology) Technical Note TN 99 - Design of glazed barriers is a good place to start for guidance on the matter.

John Grant [15/7/2020]

Feedback on CROSS Newsletter 59

Building control in England is significantly different from the practice in Scotland. I believe it is important, necessary even, if only by a footnote, that references to the Building Control function, duties and powers will often be different between England and Scotland. Experienced structural engineers in Scotland (carrying authorisation) will be aware of this.

John Gill [27/4/2020]

A lesson from the Covid-19 Work At Home will be that many more professionals will be confident in using virtual meetings and reviews. This will allow specialist contribution to design reviews and other safety critical milestones in the design process 'from the office' whereas previously the time taken to travel to a face to face meeting discouraged key parties attendance. A 'positive' report developing good practice in design reviews, distance attendance and contribution would be excellent. I addition, the ability of Microsoft Teams to be used to record Design Reviews should be considered in terms of data protection and privacy vs openness and vital future records.

Philip Jepson [15/4/2020]

Feedback on report 889 Dangerous substitution of lintels on domestic projects

This is a very common type of issue that occurs on domestic projects. Builders very often substitute components that are different to those specified on the drawings. A typical example in my experience is joist hangers. They seem to think that a joist hanger is just a joist hanger with no regard or understanding of the reason why a particular type is specified. When questioned the reply tends to be "that's just what they had at the builders merchants". Or they say that they have definitely installed the type specified when very clearly they haven't.

David Ramsay [15/4/2020]

Feedback on report 882 Post-tensioned slab failure

In the photo showing the damaged anchor location, I can see no evidence of anti-bursting reinforcement at the anchorage location. I would expect something in the order of 12mm bars at 250, links or U-bars. It may be there but just not evident on the photo?

David Brown [4/2/2020]

Feedback on report 866 Portal frame design and fabrication

The report in portal frame construction highlights a number of issues, particularly with agricultural buildings. Designers should note the 2013 amendment to BS 5502-22 which requires design to Eurocodes. There are now only two building classes, so designers should expect less relaxation than allowed by the previous standard.

In my opinion, the situation with agricultural buildings (and similar) is often much worse with frames formed of cold rolled members, supplied by companies who simply do no design at all. If design is completed, connections are generally assumed to be rigid in analysis (which they are not) meaning overall frame stability is compromised and the moments around the frame are quite different to those assumed. Restraints to the inside flange are often not provided. At the eaves level, a torsional restraint is often not provided, meaning the fundamental verification of the members is not valid, in addition to the spurious design bending moments. A summary of the concerns with this common type of structure can be found in New Steel Construction of April 2015.

Anonymous [20/1/2020]

Feedback on report 866 Portal frame design and fabrication

This feedback is from a fabricator who regularly designs portal frames. They are accredited to the highest standard for design, and fabrication (EXEC 4) with full QA and safety accreditations. However, they are not members of BCSA. They say that BCSA are a trade organisation which does a lot of good in the industry, but their members are not the only competent fabricators. The suggestion in the CROSS Panel comments that clients should use a competent contractor are of course correct, but BCSA is not the only method used.


CROSS Response

The CROSS Panel comments on the report have been updated to incoporporate this feedback.

Kevin Dentith [15/1/2020]

Feedback on Report 617 Structures at risk from scour and erosion

Further advice on assessing the risk of scour at bridges can be found in the revised BD97 to be released in Spring by Highways England as part of the DMRB review. The impact of debris on scour is considered; accumulations of debris is an increasing problem at many bridges. Scour is also a topic at the Bridges 2020 conference in March.

HSE BIM 4 Health & Safety Working Group [8/1/2020]

CROSS Report 789 Temporary stability of steel frame building - Feedback from the HSE BIM 4 Health & Safety Working Group

This CROSS report was raised as a concern typical of those encountered in the steel fabrication and erection industry by the British Constructional Steel Association (BCSA) and steelwork contractors. The question was put to the BIM 4 Health & Safety Working Group - how can BIM make a difference and improve safety in these cases?

At a meeting in December 2019, the Working Group considered this case, and others, where for example additional steel, unplanned for at (contractor) tender stage, is required to brace a structure in its temporary state during erection. Who should be responsible for identifying the need for and carrying out the design of the bracing and for planning the insertion, management and often more challenging, the removal of this bracing safely?

The Working Group considers that 3D visualisation of erection sequences is both practical and valuable in informing duty holders of the risks to be treated, and safe systems of work which should be employed. Good practice examples already include method statements which incorporate drawings of sequences of erection, using suitable software. The use of 4D sequencing goes a stage further because it requires planners to consider, and then model, the steps between the temporary state and the permanent state of the structure.

More fundamentally, BIM facilitates collaboration between the client, design teams and contractors. The Principal Designer (PD) on a project has an explicit responsibility under CDM 2015 to identify foreseeable risks, and to liaise with the Principal Contractor (PC) in order manage these according to a hierarchy of control. Issues which affect stability of steel structures in the temporary state will always be significant. Part of the PD role is to evaluate steelwork design to ensure that stability can be properly maintained during both construction and when in operation. The software and digital design tools used in BIM enable more detailed assessment of the design to be carried out earlier in the project, and enable more effective scrutiny by the PD.

In considering the role of BIM, and the guidance contained in PAS 1192-6, the Working Group offers these recommendations of good practice:

  1. Clients must set out arrangements, in partnership with the PD, to ensure that the PD, design teams and contractors collaborate from the outset and specify which safety critical sequences require 4D models or visualisations for planning and assessment purposes.
  2. Designers should provide information and instruction (CDM 2015 Reg.8(6)) to ensure stability of temporary states to the PC (CDM 2015 Reg.19), especially the need for additional elements of design, through notation or links attached to models. The Client, advised by the PD, should specify the detail required in 3D or 4D models. The PC (CDM 2015 Reg.19) must ensure that they are content with the level of design, sequencing and method information provided by the design team to ensure stability at all stages. The PC must take up any concerns or suggested changes/improvements with the PD to ensure that deviation from the arrangements proposed by the designer is analysed and agreed at an early stage.
  3. Cat II or Cat III temporary works as defined in BS 5975 and any other “safety critical” temporary works should be fully designed as part of the permanent works design with the Client, advised by the PD, specifying the 4D sequencing required. In order to achieve this, early contractor involvement will be essential.
  4. Less complex temporary works should be considered to a proportionate level during the permanent works design, with sufficient information communicated to assist later stage temporary works designers, taking into account the capability and experience of contractors, as specified by the Client.
  5. All temporary works should be subject to specific design and planning reviews by the PD and PC.
  6. As constructed records shall record agreed sequencing to help facilitate future de-construction as appropriate.

For CROSS report 789, adopting the collaborative approach set in PAS 1192-6 and utilising 3D or 4D models would have provided those involved with the opportunity to actively communicate the need for the design and use of temporary bracing during erection, and therefore significantly reduce the risks and subsequent consequences that occurred.

Raymond Pearson [17/10/2019]

Feedback on Report 680 Late detection of flange/web splitting on steel beam

It was stated that a Notified Body issues the Welding Certificate. In the Milan 2016 meeting of the SG17 Committee that oversees BS EN 1090-1, it was stated that it is not the responsibility of the Notified Body, but the company to produce one or instruct the Notified Body to do so on its behalf.

Ben Hutton [17/10/2019]

Feedback on Report 857 Fire resistance of multi-storey car parks

This report raises a valuable point as to whether the current Approved Document B fire resistance ratings are enough to achieve the robust design of fire-resistant car parks, however it presents element Fire Resistance Ratings as being the same as the Structural Fire Resistance.

This is an important distinction to make in my view as the common misconception of the rating system is that the fire resistance rating (i.e. R30) means that the structure is designed to allow collapse after 30 minutes of fire exposure, this is not the case. From my understanding, Approved Document B provides the fire-resistance rating of a structural element based on the length of time that it performs satisfactorily in the standard furnace test. i.e. a resistance of 15 minutes means that the element in question will resist the standard furnace test temperature curve for a minimum of 15 minutes before failure under a predefined set of loading conditions. This is not to say the same element will resist a real fire for 15 minutes before failing but is simply a way of standardising fire resistance testing and specification across the industry.

The true length of time a structure may last during a fire is related to the individual temperature – time relationship of the individual fire which, in turn relies on the quantity of fuel available to a given fire. This leads to a structural failure time that may be higher or lower than the resistance rating obtained by the standard furnace test.

It is conceivable that the misconception that a fire resistance rating relates directly to the length of time before structural collapse could result in the dangerous scenario that firefighters are given false information on the overall fire resistance of a structure. This article provides a good overview of this topic: Structural fire resistance: Rating system manifests crude, inconsistent design.

Jim Dickie [16/10/2019]

Feedback on Report 730 Collapsed scaffolding

Knowledge as to whether the scaffolding was a modular system or tube and coupler would be useful. My limited knowledge of the latter is that a properly designed scaffold has a high factor of safety which is recognised by scaffold erectors. Torque levels in fittings depend solely on the erector; piecework payments and late in the day tiredness can result in torque levels that are too low and possibly even fittings that are not tightened. Scaffold geometry changes due to movement as a consequence of poor erection can jam any loose fittings and possibly create sufficient structural integrity.

Peter Everett [29/7/2019]

Feedback on Report 844 Defects in tapered thread reinforcement bars for coupling

The photograph of the defective threads look like they may have been stripped or cross threaded. If this is a photo of the bar after the coupler has been removed, then it could be that the threads were cut correctly but became damaged when the coupler was attached. If that is the case, then 100% sampling of the threads before the couplers are attached might not address the problem - the threads on the bars would be OK but would become damaged once the coupler is attached and concealed. Maybe the coupler needs to have a slot in the side so the threads can be inspected in-situ?

Adam Noakes [2/7/2019]

Feedback on Report 764 Hidden defects in railway masonry arch viaducts

I recently read with interest the Report 764 Hidden defects in railway masonry arch viaducts on this Structural-Safety website. My intention with this feedback is mainly to add detail to the following statement in the aforementioned report: "It is understood that the railway arch sell-off is supported by robust measures to ensure that the asset management inspection and assessment requirements for the loadbearing railway arch structures can be met. The new regime will of course need to demonstrate this will remain the case."

Upon reading the report, and the quoted statement above in particular, I was rather surprised. To my knowledge there is no explicitly "new regime" for the safety-related management of property sales to third parties, or of third party access, or of structures that are wholly or partly owned or managed by a third party.

Rather, my experience is that the means and methods by which Network Rail manage these risks are not new, but have been in place for many years, all under the scrutiny of the Office of Rail Regulation (now Office of Rail and Road). Network Rail have the power under the Railways Regulation Act 1842 to a enter third party premises if required following an emergency or in order to prevent an emergency developing. The right of access granted by the 1842 Act is also highlighted on Network Rail's webpage Buying a property next to the Railway.

The 1842 Act guarantees that Network Rail has a means of obtaining access to ensure the safe operation of its infrastructure. There is therefore no realistic prospect, for example, that a 125 lease could prevent Network Rail from performing essential structural examinations. Nevertheless, use of the 1842 Act is rare as it is usually unnecessary.

Instead, access for examination is routinely arranged with the cooperation of third parties, as part of Network Rail's standard infrastructure management regime. For the masonry arches noted in the aforementioned report, the relevant Network Rail standard is NR/L1/CIV/032 The Management of Structures. This standard, the current issue of which has been in place since 2009, has clear provisions and robust infrastructure management requirements for both Outside Party structures (wholly owned by another organisation, for example road overbridges) and Shared Structures (where ownership and/or responsibility is shared between Network Rail and a third party, for example occupied viaduct arches).

NR/L1/CIV/032 also requires up-to-date information on ownership of property close to the railway be maintained, for use in routine management or emergency. In addition, Network Rail property sales are subject to a comprehensive Property Clearance Process under standard NR/L2/PRO/001, which has also been in place since 2009. Prior to authorisation of any property sale, asset and maintenance protection engineers will undertake a technical and safety review to ensure that a proposed sale will not prejudice Network Rail's ability to safely operate and maintain the railway. This will include having a clear plan in place for the management of any infrastructure assets that remain relevant to railway operation, regardless of their ownership or occupancy.

My view is therefore that the existing systems and processes for managing risks related to third party access are well-established and robust, provided they are followed properly and good records and communication between the relevant parties is maintained throughout the life of the assets. I hope you find this information to be of interest and relevance.

Mark Griffiths [24/4/2019]

Feedback on Report 789 Temporary stability of steel frame building

I agree the CDM Regulationss place a duty on the Principal Contractor. I consider that, in addition to this, the Principal Designer's duties extend to temporary works designs, even though this is during the construction phase. The Principal Designer should ensure that all designers comply with their duties and ensure cooperation between designers. This applies not just to permanent works designers, but to temporary work designers too.

David Ambrose [23/4/2019]

Feedback on Report 607 Settlement of driven piles

I've had experience where H-Piles were founded in mudstone. The piles just about achieved the recommended set, but, unfortunately, as water tracked down the steel /soil interface it softened the footing of the pile section and could have caused a notional failure. We discovered that if you returned to the pile some days later, the piles could be 're-driven' to achieve the set and provided the required load capacity. The construction of the pile cap was undertaken without any further delay and by covering the piles prevented further water ingress. Despite some protestations that H-Piles were not not suitable for mudstone, this minor additional work meant that the most cost-effective and quickest piling solution could be used in areas with sedimentary rocks. The integrity of the steel piles is easily demonstrated (unlike cast insitu piles).

Paul Owen [14/3/2019]

Feedback on Report 298 Props to large excavations

Looking at the prop detail where is extends to the wall above the wailing beam, I agree that when it is resolved statically, the force at the top of the prop will be very high. The question then however is with what level of localised deformation the wall can take. The prop can only push into the wall a very small amount before the wailing beam 'kicks in' and prevents further horizontal movement. If it is a sheet-piled wall, I would imagine this would simply suffer some localised small deformation around the top of the prop which wouldn't even be noticeable. If the wall is concrete, however, some localised crushing may occur which might need repairing after the props are removed.

Andy Beeton [18/2/2019]

Feedback on SCOSS Alert: Effects of Scale

I applaud the 'Effects of Scale' article and would say that it reflects concerns that I have felt for many years and which, largely, have fallen on deaf ears.

I would though like to mention my belief that there is another issue, not mentioned, that should come under this heading. Designers, often more accustomed to smaller scale structures, are routinely designing structures with at least one and often multiple levels of transfer structures. This is often driven by architecture that arises from mixed use developments and, commonly, car parking modules conflicting with residential or commercial modules. The result is often something that would fall a long way short of any exhortations about robustness, collapse resistance and direct load paths. If you have a failure in a transfer structure, the spread of collapse could be catastrophic, so the issue is serious.

Designers sometimes attempt to address the issue by applying prescriptive and highly simplistic tying rules that pay lip service to the problem, at best. The potential for disaster is compounded still more by designers who manipulate, or stretch to breaking point, the disproportional collapse categorisation and strive to obtain a client-favourable interpretation. The guidance is clear but is not being implemented, I fear.

Therefore, much clearer and perhaps a more explicit and robust statement on disproportionate collapse should be made and the issues that flow from that spelled out in no uncertain terms. It is my view that the rules in the AD's (number of stories, basements, mansards) are misused and we would be better off saying that the rules should apply to all structures. Structures of modest height, say 4-5 storeys, can still be quite large and extensive and, especially if non-robust structural forms exist in them, may present a potential for great loss.

Andrew Smith [17/1/2019]

Feedback on Report 757 Lack of method statements on domestic projects

On the domestic alteration projects I work on, if there's any significant structural demolition entailed I produce 3 drawings of the structure that is to be altered; as existing noting any structural defects, after demolition showing where I consider temporary support should be provided and the capacity it should have, and as altered. I back this up with a requirement that the contractor submit their own proposals for temporary supports and a method statement for this work as part of their tender. Sometimes this ends up with me designing the temporary supports, for which I obtain the clients' agreement. This procedure is generally successful in getting the contractor to take the issue of the stability of the incomplete structure seriously and to think through how they get from what's there now to what's to replace it.

Ian Browne [19/11/2018]

Feedback on SCOSS Alert: Effects of Scale

Thank you once again for an excellent and appropriate SCOSS Alert.

I feel it should be highlighted, however, that the deflection effects on the long spans you illustrate are in fact even more sensitive to length than you advise. Whilst it is correct that deflection is proportional to (span)^3, in the cases you highlight, the main loading (especially the construction loads) are all UDLs. As the overall load applied by a UDL is itself a function of the span, then for UDLs, deflection is in fact proportional to (span)^4.

The significance of this is often overlooked and is compounded by the presentation of many standard formulae, for example, the Steel Designers’ Manual: Simply-supported UDL deflection, say, is given as 5WL^3 / (384EI), where W = wL (w being the UDL). Although obvious to experienced engineers, and for those with the time to review such things, the significance of this can often be overlooked in time-pressed design houses, leading to the examples you describe in your Alert.

Cecilio Monang [15/11/2018]

Feedback on Report 793 Street sign collapse causes fatality

My feedback would be a suggestion and its up to you if it is feasible/acceptable. According to the report the cause of failure is due to strong winds. In this regard, I suggest that a post to be constructed should be done by an Engineer by computing the size of weld base on maximum wind speed or the strongest wind and selecting the size of material and type of electrode to be use and also providing access hole for welding the joint inside and at the same time for future maintenance.

Alasdair Beal [7/11/2018]

Feedback on SCOSS Alert: Effects of Scale

The issue of concrete ponding on long spans was considered in detail in my paper Floor slabs, lasers and levels in Concrete September 2011. Unfortunately, despite support from some of the main steel sheeting manufacturers, I have been unable to persuade anyone to address the issue properly in specifications. In practice it is only the good sense of some specialist contractors plus a fair degree of luck that has prevented major disasters.

Brian Bell [7/11/2018]

Feedback on SCOSS Alert: Effects of Scale

Your Alert on the Effects of Scale is excellent and extraordinarily comprehensive. Congratulations to the author(s). Other associated topics might include fatigue-induced cracking and destruction of marine structures from wave-loading; cyclical flexure of thick members or tensile loading of hangers under vehicular loading; fatigue-induced cracking of testing equipment (fully loaded for 20m cycles); all of which I have encountered. How far can RC design for shear be extrapolated? I am sure I am not alone in having designed slabs over 3.5m thick for large span tunnel roofs, largely based on rules derived from test on 0.35m thick specimens or shallower. Have we stacked up serious problems for posterity?

Timothy Pope [18/10/2018]

Feedback on Report 714 Unsafe removal of some internal walls

The report suggests that the individuals concerned are construction professionals. If this is the case, they are bound by the Code of Conduct of their Professional Institution. For the IStructE, Item 2 of the Code of Conduct is to "have regard to the public interest as well as the interests of all those affected by their professional activities". If nothing else, a complaint against the property owner should be raised to investigate if professional standards were breached.


CROSS Response

You make a good point and it is a reminder to all members of Professional Institutions to ensure that they follow their Code of Conduct. It is also worth noting that there are also many individuals working on construction projects who are not members of Professional Institutions.

Michael Hann [17/10/2018]

Feedback on Report 781 Quality of design and construction of major bridge structure

Surely the real problem here was of dis-aggregating the design and there being no one controlling mind. Presumably the Cat 3 check was done before the project went to site. It is a common problem that design and build contractors take designs and amend them to suit sub-contract suppliers offers, or worse, to suit commercial pressure to reduce costs. Because of the chasm in the industry between designers and site, and with no effective supervision, site personnel are becoming more and more likely to have insufficient design experience to know when this is safe or, worse still, when to refer such matters to a designer. This will only be solved when a single designer signs off every detail including any change howsoever caused from start to finish of a project.

Tim Viney [17/10/2018]

Feedback on Report 793 Street sign collapse causes fatality

It is difficult to tell from the report but is the correspondent sure that the damage was not due to fatigue? Given the 'whipping' of tall lamp standards visible due to vortex shedding you can observe in high winds, I wonder if it was cyclical loading which caused the failure? I also note that the Highways England Design Manual for Roads and Bridges permits only 'tubular or rectangular hollow sections to BS EN10210' or rolled sections to be used for traffic signs.


CROSS Response 

The reporter states that a fatigue crack was present in the post, with the fatigue crack initiating at the unfused edge of the transversely welded channel. However, the reporter does not provide details to state if it was cyclical loading which caused the fatigue crack.

Robert Thomson [9/8/2018]

Feedback on Report 735 Inadequate design of cantilever glass barriers - Newsletter 50

I'm not sure that SCOSS is the appropriate venue for such a discussion. As noted in the editor's comments, there will be disagreement regarding the interpretation, particularly as pretty much every cantilever glass balustrade I have seen would not meet the reporter's recommendations. That is not to say they are incorrect, but a general report like this should take place in a way that there could be discussion within the industry. If there is a problem then it needs to be talked about openly. A letter in Verulam say might provide more opportunity for response and reflection.


CROSS Response 

Thank you for the feedback. We have several reports about glass elements in buildings and there is certainly a diversity of views about how these should be designed. This has already been raised within IStructE for further consideration. 

Your feedback will be published and, of course, please do write to Verulam if you want take the discussion forward. We are always keen to promote debate and are also careful not to be prescriptive but to raise safety awareness for practitioners.

Ralph Maudlin [1/8/2018]

Feedback on SCOSS Alert: Building a Safer Future - July 2018

I am a former MIStructE and was until 1986 a GLC District Surveyor in London. I applaud the report and its aims and am glad that it pulls no punches. However: Who is going to devise the new rules and draft the new legislation? The "race to the bottom" started with the introduction of the 1985 Building Regulations and the subsequent abolition of the Greater London Council. The wealth of expertise in its specialised fire regulations department and its world renowned scientific department were fragmented. At the same time the statutory status of the District Surveyor, the chief building control officer was extinguished. Thus at a stroke a well established system of control, administered by properly professionally qualified and trained personnel was removed. The regulations were then diluted with the abolition of Section 20 of the former Building Acts (Amendment) Act 1939, which could (in the view of the commentator) have prevented the disastrous Grenfell Tower fire. Unless the expertise of the fast disappearing group of DSs who formally ran the system is harnessed, I see no hope of the recommendation ever being effectively implemented.

Nick Kramer [14/7/2018]

Feedback on Report 713 The role of District Surveyors - Newsletter 49

Regarding District Surveyors I started work in 1975. One essential difference between the system of building control in London and elsewhere in England and Wales was that the London system only approved construction. Outside London building plans could be approved in advance. This may seem a minor distinction but it did affect developers in obtaining funding, as construction in London was perceived as financially riskier as the plans could not be signed off in advance. As well as the District Surveyor's knowledge and experience compared with BCO's as described in the report, many other beneficial aspects of the London Bye-Laws were lost with the changes in 1985.

Anonymous [6/7/2018]

Feedback on SCOSS Alert - Fire in Multi-Storey Car Parks - February 2018

You should focus on fire load in split level Multi-Storey Car Parks (MSCPs), with unprotected steel and no sprinklers. These MSCPs are doomed to collapse, and the designers are ignoring the fact that fire spread between cars will happen and the underlying fire tests from 1980s involves small cars in windy conditions. If the car park in Liverpool was a split level open car park, it would have collapsed.

Major UK steel stockholder [2/7/2018]

Feedback on Report 740 Common use of S235 cold rolled steel instead of S355 hot rolled steel

A major stockholder of structural hollow sections was surprised to read the CROSS report 740 in Newsletter No. 50 about the availability of hollow sections. They carry a large range of sizes and lengths in EN10210 S355J2H and EN10219 S355J2H. However, in their experience it is not uncommon for general steel stockholders to not be aware of product availability outside their own ranges, and to not be informed about the grades available. The stockholder says that they deliver all over the UK and Ireland and wanted to take the opportunity to set the record straight that the products are readily available.

Stephen Axelsen [29/5/2018]

Feedback on Report 683 Corrosion causes collapse of steel floodlight mast at football club - Newsletter 50

I don't think this identifies one of the key issues, as it is about the approach to mast and tower structures within sports grounds, and how they are singed off, as I have seen a number of structures which are not properly maintained, or have even been modified by the grounds keeper. I think it requires a step back to identify the reason it has got to this point. I think there may well be a bigger problem here, and classic of the person signing off just does not understand the implications.


CROSS Response 

Your feedback discusses the importance of proper maintenance and controlling modifications. The reporter did discuss the importance of maintenance in their report, which is copied below.

Advice from the reporter to other clubs is as follows:

  • Your maintenance regime for floodlighting masts at your ground should include a risk assessment for internal corrosion of steel tubes.
  • A check for internal corrosion should be carried out by a suitably qualified person where internal corrosion has been assessed as a significant risk.
  • Your maintenance regime should include a check for cracking around any openings in tubular steel masts.
  • Your assessment of the structural adequacy of the floodlighting masts at your ground should include an assessment of the adequacy of any strengthening around openings in tubular masts.

John Haines [18/4/2018]

Feedback on Report 665 Lack of masonry wall ties - Newsletter 50

Regarding the comment about "As Constructed" drawings in Report 665, the CDM Regulations state that as-built drawings should be considered for inclusion in the H&S File. It's not difficult to think of situations where such drawings would be necessary and errors in them could result in failure. I consider that for any but the simplest structures, accurate as-built drawings are essential and Clients need to recognise this as part of their responsibility for the adequate management of the project.

Chris Evans [18/4/2018]

Feedback on Report 634 Contractor installs incorrect steel grade - Newsletter 50

The statement that the duty of care lies with the TWC to ensure the design intent is transferred to the final as-built construction is considered misleading, if not legally incorrect. The duty of care and contractual responsibility lies with the Principal Contractor and ultimately the Client. IF the steel fabricator (sub-contractor) substituted a lesser material (S235 in lieu of S275) then under CDM they have become Designer. Under statute law and contract law they become liable for any loss or injury caused thereunder. The TWC is NOT a CoW nor an RE and is not there to protect the PC or Client from their own inadequacies in terms of QA/QC. The role of the TWC is difficult enough without pushing additional liabilities upon them, especially where there is an ongoing lack of TWCs with the commensurate knowledge of civil/structural design as suggested by the TWf in their suggested competencies of a TWC.


CROSS Response

We understand that the statement you are referring to is the CROSS Panel's comment below on Report 634 Contractor installs incorrect steel grade.

"This is a Golden Rule in temporary works management (BS5975 refers), where the Temporary Works Coordinator has a stated duty to ensure that design intent equals constructed manifestation."

'Design intent' in this statement refers to the design intent for the temporary works design. It does not refer to the design intent of the permanent works design. As you rightly say, it is not the TWCs responsibility to ensure that the design intent of the permanent works is transferred to the as-built construction. Section 10.1 of BS 5975 below is what the CROSS Panel were referring to.

10.1 Work on site should be the subject of careful direction, supervision and inspection to ensure that the temporary works is constructed safely in accordance with the design and specified materials, and that only when all checks have proved satisfactory is the works loaded, used, maintained and then dismantled in accordance with the design documentation and method statement.

Chris Bolton [18/4/2018]

Feedback on Report 665 Lack of masonry wall ties - Newsletter 50

Re 678 Architect conducts structural design of sway frame for domestic project I understand (but have no direct evidence) that the only reason 'Architect' is a protected title is because, at the time the law was made, Structural Engineering wasn't a profession and Architects were responsible for structural aspects. Logically, the protection should now be transferred to SEs. Secondly, the reporter notes " can’t understand why Building Control pass them" - so far as I have been able to find out, there is no legal duty on Building Control other than to 'approve plans'. They don't certify that the design meets Building Regs. Given their limited resources, this needs to be made clear to anyone who submits plans.


Phil Reeves [10/1/2018]

Feedback on Report 703 Inadequate structural design for domestic properties - Newsletter 49

This is the classic example where it should be a legal requirenment to have a chartered engineer carry out structural design. Can the Institution comment as to why this is not yet the case?


CROSS Response

Making it a legal requirement for a chartered engineer to be responsible for structural design may well improve the quality of design, but the Institution do not set the law and can only advise those who do.

Jonathan Prew [10/1/2018]

Feedback on Report 703 Inadequate structural design for domestic properties - Newsletter 49

From the description of the problem it sounds as if there could be a breach of the Construction (Design and Management) Regulations 2015 in terms of competency of the Designer. In which case perhaps this should be reported to the HSE for investigation.

Angus Holdsworth [10/1/2018]

Feedback on Report 703 Inadequate structural design for domestic properties - Newsletter 49

I look forward to reading the CROSS newsletter, as they give an interesting and thought-provoking insight into the industry. However, on this occasion, I was concerned to read the following:

 “Building Control bodies are under extreme pressure on fees, and are not on site all the time, so it is not a surprise that they miss things on occasion.”

It is simply not acceptable to use this as an excuse for missing an issue. If a commercial organisation tried to use lack of fees as an excuse in this manner CROSS would have no issues pointing out why this is wrong. It is of note that if you search for fees on the portal you find the following from ID 190 makes this exact point “However, strictly it is not fees per se which determine the legal position but if a professional takes on a job for nothing he or she carries all the responsibilities regardless. The formal position is clear. The Client must ensure that he or she appoints competent parties, adequately resourced. The engaged party has a reciprocal responsibility and the CDM-C also plays an important role in this instance. Those appointing professionals so far below typical market rates should ensure that they have suitable qualifications and insurances.”

In short if you accept the job you accept the responsibility.

At the start of my career I worked in a consultancy that undertook design reviews for building control and the fees were indeed tiny. This didn’t stop a full and thorough review being undertaken, and nor should it.

I look forward to your response.


CROSS Response

Thanks for your observations on what is very much a topic of current interest. You may have seen it already but the following report by Dame Judith Hackitt contains a number of comments about Building Control and their role.

Building a Safer Future - Independent Review of Building Regulations and Fire Safety

Building Control do not have responsibility for quality control and generally do an excellent job given their limited resources and funding. As a consequence of the Hackitt report however there will be searching questions and probably recommendations for change.

Andy Beeton [3/11/2017]

I regularly read the newsletters and reports and find that I often have seen the same shortcomings and errors reported. I think it would be a good idea, which might help with your feedback and possibly to spot 'trending' issues if you had some kind of 'me too' button.

CROSS response

Thank you for this idea which we will look into when next updating our web site.

Detecting trends is an important part of our work and we use the information from reports to compile statistics and in deciding upon subjects for Topic Papers and Alerts.

Geoff Fletcher [17/10/2017]

I'm always interested to see courses promoting Forensic Engineering but I find they frequently seem to confuse Failure Modes & Effects Analysis (FMEA), which is certainly a worthwhile field of study, with actual Forensic processes which by definition imply legal & Court disciplines. The TU Delft course "Forensic Engineering : Learning from Failures", as advertised via the home page, seems to follow this trend as I find no reference to legal matters in the Syllabus. Distinctive aspects should include (at least) primary duty to the Court, rules of evidence, receiving legal instructions, implications of adversarial cross-examination, reputational risk.

David Ramsay [31/7/2017]

I was interested to read about the "recent" problems in Pinner with potential collapse of chalk mines. There was no reference to an excellent series of publications Chelsea Speleological Society Records (CSS) which includes an extensive database of natural and manmade underground features in the southeast of England. CSS has been recording these since the 1950's. About thirty years ago I visited chalk mines at Pinner with the CSS group and descended into chalk mines in the area. My memory is vague but I recall it was entered by ladder through a manhole. This was just one of many mines recorded by the group in the area. Their details are here http://dev.chelseaspelaeo.org/index.htm

Ron Watermeyer [31/7/2017]

Feedback on SCOSS Alert - Sudden Loss of Ground Support

I enjoyed your loss of ground support alert. In South Africa we have found in certain types of ground formation that in a study of 650 events over the 20-year period in a particular area, 643 (99 %) were found to be directly attributable to leaking services or humans negative influence i.e. water ingress as being the trigger. The attached paper presents a unique study of an area of before and after mitigation measures which illustrates the point. SCOSS should perhaps stress the avoidance of water ingress.

Kevin Dentith [20/4/2017]

Feedback on Report 641 Square Hollow Section (SHS) expansion due to freezing

We have experienced quite a bit of this in Devon which at first may be a surprise as the South West is a very temperate climate – however as can be seen at the moment we are experiencing relatively high daytime temperatures which can create condensation inside the HSS on bridge parapets and the following clear nights can lead to sub zero temperatures. A number of years ago when the mesh was replaced on one of our most significant bridges in North Devon water was found to spurt out at pressure such was the volume of water inside – potentially highlighting a hidden defect due to corrosion.

Peter Symmons [10/4/2017]

I was/am well aware of SCOSS & CROSS but was not aware that Structural-Safety had been formed. When did this take place?

Comment from Structural-Safety: The group name Structural-Safety was introduced several years ago to rationalise operations. For a description of the difference, see the About Structural-Safety page on our website.

Colin Baird [14/2/2017]

I would like to see some reporting from those involved in the Edinburgh schools masonry collapse which raised serious concerns about building standards. The issues that resulted in the problems and the extent of the condition needs to be understood.

Nick Kramer [7/2/2017]

Feedback on Report 581 Requirement for CDM Safety Files to be transferred

As a working structural engineer I am disappointed that there is not stronger action from HSE. We are often working on altering existing buildings that were built after CDM's introduction, and the Health and Safety File is not provided. On Design & Build we are very far down the food chain and any query produces shrugs. I feel this aspect strongly as it adds uncertainty and risk and probably cost to the work, that should not be necessary. I have a strong suspicion that the H&S File exists somewhere, but inertia and ignorance is denying the designers and contractors sight of the information. This is an area where a few well publicised prosecutions could provide significant safety benefits.

Robin de Jongh [4/2/2017]

Feedback on SCOSS Alert - Structural stability/integrity of steel frame buildings in their temporary and permanent condition

As a practicing structural engineer and former learning professional, I would commend the distribution of the SCOSS Alert Structural stability/integrity of steel frame buildings in their temporary and permanent condition but question the efficacy of including such a long list of “learning points”. Multiple learning points can serve to water down and ultimately lose the impact of the message. The clear outcome of the alert could have been a warning that site welding or re-work is inherently dangerous, and needs to be carefully procured, managed, and checked. The new CE marking law requiring steel fabricators to be at least Execution Class 2 for any site welding should help us out here, but is not widely implemented (if at all) and I would suggest a note in the next newsletter advising all structural engineers and project managers to insist on seeing evidence of EC2 certification from any steelworker engaged to do site fabrication or modification of steelwork. Leaving aside that little note of caution, I love reading the reports and newsletter, and thank you and the team for all the hard work!

Correspondent [30/1/2017]

Feedback on report 614 Columns missing due to 3D modelling

This issue is something I have been debating and discussing with our own BIM manager for a while. It is my view that engineers have become too remote from the current 3D software, as it is far more complex than the 2D cad in which we were able to dabble. It means that there is less engineering input to 3D models than there would have been with traditional drawings.

In effect the model is owned by someone skilled in operating the software rather than skilled in engineering. Despite having been involved with 3D drafting for the best part of 18 years I now find it very difficult to check 3D model output. I usually need to look at 2D drawings, which are vulnerable to error if they are sliced through the model at the wrong point, because they potentially don’t show features above or below the model slice. This is particularly true if there are changes in level or angle to a floor. There is also increased risk of error due to the fact that each element of a model now has to be given attributes, for example the concrete grade for columns. This might previously have been covered by a single note on a drawing whereas now the attributes of each column at each floor must be checked.

I have also noticed a recent trend where clauses are inserted into our contracts, which legally enforce the pre-eminence of the model over the 2D drawings and other aspects of the contract. I view this as dangerous, particularly as it is the drgs that engineers tend to check, not the model. I always seek to have such contract clauses deleted. I offer these thoughts not as a luddite trying to turn the clock back; I see many positives working in 3D and I am wholly in favour of adopting new ways of working. It is the inevitable future that 2D drawings will in time disappear. My fear is that in the transition period [which we are currently in] we have the tools and ability to produce models, but not the expertise or protocols to check them adequately or at least to the same standard as was common in the 2D world. We are currently looking at ways to improve this; but we are not yet there.

Angus Cormie [30/1/2017]

Feedback on report 612 Number of near misses and the regulatory regime

I was a little surprised that the commentary after the report didn’t mention SER (Structural Engineers Registration) and the benefit that brings to design assurance (This sytem operates only in Scotland at present). Perhaps the next report could back refer. The points made are very relevant, as are the post report discussion, just the missing SER link!

Darell Morcom [14/12/2016]

Feedback on SCOSS Topic Paper - Reflective Thinking

I was very pleased to see your paper on reflective thinking as it is such an important thing. I have found a few methods of achieving reflective thinking on structures. The first is to draw schemes by hand and try and trace over existing drawings and proposed schemes (or the very least draw them yourself in CAD). It is a very important method to make sure you (not someone else) have understood the context, the existing and proposed. It works as the slower speed of tracing and the hand eye coordination helps understanding of what the questions are, but also with the understanding of suitable structural proposals. It allows many creative and relevant schemes to emerge as the 3D nature of forces and design is also clarified in this way. The second is an important piece of advice I was taught by more than one very experienced senior engineer at well know and creative engineering companies who tend to work on difficult structures. It is: " we need to sleep on that! " It was meant very literally and I often use this motto and go to bed! It really works as the mind reflects whilst the body is asleep. I think an addendum to your note would be useful as it is not complicated but sound advice. Of course proper reviews are important! 

Reuben Richardson [10/9/2016]

Feedback on report 253 Freezing splits galvanised RHS columns

Regarding splitting, I have seen it with columns that even have drainage holes. That have plugged up with corrosion over time. Also long term I have seen hollow sections that look okay on the outside but are rotting on the inside significant loss of thickness with drain holes plugged up aswell. I know it says cleaning out of holes is a requirement but I doubt it happens in practice.

Chris Bolton [16/8/2016]

I'm interested in finding any reports on failure of handrails but am finding inconsistent results from the search tool. Entering "fall" finds Report 373 'Polyethylene pipework handrails'. I would have expected a search for "Handrails" to find this report, but it finds nothing. I don't know how many other reports there might be that mention "Handrails" but aren't picked up. Is the search function working properly (possibly the index needs to be updated?)

Paul Bell [19/7/2016]

Feedback on CROSS Newsletter 43

I am a big fan of SCOSS/CROSS. However I feel that in the Newsletters the gap between theory/expectation and reality/practice is much wider than appreciated. For example in Newsletter No 43 Report 561 it states that “owners of structures over and under roads and railways have an obligation to inspect and maintain these structures in accordance with the procedures set out by the operator of that infrastructure”. How many of the countless owners in question know anything about this? What are these procedures (excuse my ignorance)? In 580 it says “many contracts include an obligation to produce ‘as built records’. Is this true?

John Collins [14/4/2016]

Feedback on CROSS Newsletter 42

There are a couple of interesting CROSS reports in this Newsletter. Report 387 "Importance of bearings" struck a particular chord given our recent work replacing the Humber Bridge main span bearings and involvement with emergency works at the Forth Road Bridge just before Christmas: both of which are examples of seized bearings. A reporter wonders "whether any systematic study on the overall issues of bearing assembly and associated requirements has been done". This is very similar to what I was trying to write about in our upcoming CIRIA Report "Hidden defects in bridge components". I really struggled to find good references to cite. The last seminal publication on the subject was Lee's "Bridge Bearings and Expansion Joints" (1994). Clearly time for an update.

In our draft CIRIA report we suggest that bridge bearings and expansion joints require research to provide "up to date review on their current general condition and value to be gained by rolling cycle of replacement": in the absence of UK guidance I quote some German statistics in our report instead.

Some minor comments on report 387:

· Thelwall Viaduct is on the M6, not M62. This is a bridge which also features in our upcoming CIRIA report, though with very little detail: not much has been reported in the public domain due to legal restrictions which is a real pity. The wider industry could learn a lot from knowing more?

· Whilst the CIRIA guide quoted is useful, C543 Bridge detailing guide is perhaps more applicable for this particular area.

Anonymous [3/12/2015]

Feedback on report 445 Cost of design standard for scaffolding

Comment on cost of scaffold design standard; it is not necessary to buy the TG20 suite of documents. All the relevant information for analysis, design and safety may be found in the following national standards which are freely available: BSEN1990 BSEN12811-1 BS5975 or on the HSE website.

Chris O'Regan [3/12/2015]

Feedback on SCOSS Alert - Wind Adjacent to Tall Buildings

I read the CROSS alert on low level wind effects near tall buildings with some interest. It’s something I have always tried to raise awareness of within our profession as I do not believe it is given the attention it deserves, so well done for creating the alert on it. My only comment on it would be the lack of real world examples cited in the alert. The BBC wrote an excellent piece about it earlier this year that described a series of examples where high winds around the base of tall buildings has led to injuries and sometimes even death. Here’s a link to it: http://www.bbc.com/news/magazine-33426889.

Patrick Hobson [9/11/2015]

Feedback on report 519 PV panels blown off roof

As a practising Building Control Surveyor, I would appreciate an authoritative guidance note on the fixings for these panels. However, from my point of view, it still leaves us with a problem when carrying out an inspection on this type of work, as on many occasions, by the time we are called out to do an inspection, the panels have been fixed and the contractor has left the site, so access to inspect the fixings up a sloped roof is virtually impossible!

Tony Hutchinson [15/7/2015]

Feedback on report 510 Policing of CE marking on steelwork

We were interested to see your comment about the lack of enforcement of CE Marking of structural steel. We have over 100 frame manufacturers as members who have all been accredited to CE Mark to BS 1090.1. They report that they are competing against other frame manufacturers who are undercutting them on price because they are not accredited to CE Mark their structural steel. Trading standards when told are taking very little action and DCLG are not being helpful. In the agricultural market this is a serious safety concern, because there is no Building Control and no third party check of the frame manufacturer's design. We also believe that many non-accredited frame manufacturers are designing to 35 year old load tables. The different design methods allowed causes confusion in the agricultural market as there is often no professional to check that the correct standards are being used. We are concerned that if we have heavy snows again or very strong winds, more agricultural buildings will collapse as they did a few years ago, (See CROSS reports on snow load collapses) when we were very lucky that no one was hurt. Any pressure you can bring to ensure there is more enforcement of CE Marking will be welcomed. Tony Hutchinson FIoR National Secretary Rural & Industrial Design & Building Association www.ridba.org.uk

Paul Follows [15/7/2015]

Feedback on report 423 Temporary works design for basements

These comments are in relation to the matter of what represents an "unknown". I'd say that it is possible to know "unknowns" in as much as I can know that I don't know the water level and flow rate (ie if the sand and gravel will wash into an underpin bay.) I can know that I don't know the structure on the other side of the wall. The job of an Engineer is to define the problem and solve it. That includes defining the information that is needed to solve the problem. If the "unknowns" are not presented at Tender Stage then the Engineer has not carried out the activities for which they are responsible. Also as I understand it,within CDM, designers have a responsibility to design out risks within reasonable cost ranges. Don't design a three metre deep trench fill foundation if mini piles remove the safety risks at minimal increase in cost. I also believed that designers are required to provide Tender Stage Health and Safety risk assessments that describe the risks, how they have been designed out, plus any residual risks and hazards remaining (eg beams designed as cantilevers that need loads applying on the main span before the cantilever end.) For example the lack of knowledge of a structure to be underpinned and lack of knowledge of the structure directly adjacent to the underpinning (that could fall in the excavation and kill someone) are unknowns that the designer is aware of. The potential problems associated with those unknowns could be designed out in the design stage by a considered and responsible designer. Or they could highlight the unknowns to the tenderers. Failure to determine the risks (design parameters) and failure therefore to try to design out the risks at design stage could cause a designer to fail to exercise their duties under the CDM regs? It also knowingly puts the winning Tenderer in the position to have to pass around a "hot potato" to temporary works designers when contractual and time pressures are being forced on them.

Derek Garwood [5/6/2015]

Feedback on report 448 Stability of terraced buildings

The statement regarding the involvement of a structural engineer is misleading. Where there is a structural engineer involved, even if appointed for only one unit within the terrace, it is the structural engineers responsibility to ensure that with the removal of the wall there is sufficient stiffness remaining to support the proportion of the side sway loading attributable to that unit.


Paul Bell [10/2/2015]

Feedback on report 482 Unbraced temporary props

The photographs in this report are misleading. It should be pointed out that Strongboys are being used with the Acrows clearly bending. I do not permit Strongboys on site in an attempt to make builders aware of their problems. It is also not clear that the Good Building Guide photo is an example of bad practice not good. It would be useful to have a reference to the particular BRE Guide. How should the props be braced? It is easy to brace them in one direction but not so easy in the other.

Anthony Gill [14/1/2015]

Feedback on report 443 Post-fixed RC anchors - erroneous assumptions leading to unsafe design

Why should a specialist steelwork connection designer be tasked with the design of a concrete/steel interface? Surely this responsibility belongs fairly and squarely with the principal structural designer - after all he is being paid by the client for his design and a fundamental part of his design is the interface between different materials.

Malcolm Leighton [26/10/2014]

Feedback on SCOSS Alert - Preventing the Collapse of Free-standing Walls

I wish to draw your attention to that which appears to be an error in your SCOSS Alert. Paragraph 3 states 'if this is an adopted highway' whereas 1980 Highways Act Section 66. Part IE+W+S+N.I. Highway Authorities and Agreements Between Authorities states... H(2)Outside Greater London the council of a county [F2or metropolitan district] are the highway authority for all highways in the county [F2or, as the case may be, the district], whether or not maintainable at the public expense, which are not highways for which under subsection (1) above the Minister is the highway authority.


CROSS response

This is an interesting point and below is the response from one of our Expert Panel Members.

This is a grey area, and hinges around whether it is a ‘highway’ or not. There is no definition of ‘highway’ other than in common law.  Some unadopted roads become highways through dedication and acceptance, others would not be defined as highways.  The query is seemingly correct in part, because an unadopted highway may be subject to highway authority control but some unadopted roads are not highways and so would not.

Aaron Knight [15/9/2014]

Hello, I really like the site but one frustration is the inability to click on the subjects "under consideration" to read more about them. Is there any chance of having these link to an article in future? Thank you for your time.



Anonymous [17/4/2014]

Feedback on report 435 Balcony strengths of blocks of flats - further experiences

Placing steel reinforcement in the wrong position in a cantilever reinforced concrete slab subjected to gravity loading is symptomatic of a clear lack of understanding of structural behaviour. There is no simpler beam, and one which as a teacher, I can use to illustrate the importance of the proper position of steel reinforcement in RC members. I have actually shown the picture of a collapsed balcony previously posted in Structural-Safety and asked students to identify the possible reason for the collapse. I was disappointed to realise that still a few students were unable to guess the obvious reason. Structural-Safety provides excellent examples of things that can go wrong when we do not pay attention to detail or when the construction industry lacks a proper design-implementation process to guarantee structural safety. Any decent structural engineer could have detected this conceptual mistake had he/she been asked to inspect the reinforcement before concrete was casted. Now attention must be placed on the strengthening of these defective balcony slabs whose strength is virtually dependent on the bottom bars acting as cantilever steel members with very small cross sectional area (but if poor bond exists then not even that strength mechanism will be able to develop its full capacity!). The worst case scenario is that the expected lack of ductility of these defective balcony slabs can trigger a progressive collapse which could have dramatic consequences (e.g. people having a balcony party during summer). 

Nick Eckford [17/4/2014]

Feedback on report 435 Balcony strengths of blocks of flats - further experiences

As a newly started Graduate Engineer in 1965 with a major contractor I was set on a site where an estate of buildings such as you describe were being constructed. I was sent up to observe the casting of just such a slab with balconies that you describe. The reinforcement for the cantilever was on rod spacers to get it at the right level. I observed the gang concreting the slab stamping down the top steel so that it was effectively in the bottom. I pointed out that this was top reinforcement and should be set up within the slab. I was told, in no uncertain terms that I will not repeat here, that I was an ignorant trainee and to get lost. I reported that back to the senior Engineer. The upshot was that all the completed balconies on the estate were load tested. The best design can be defeated by ignorance and presumption on site. Supervision is necessary to get what you require.

Tim Griffiths [25/1/2014]

Feedback on report 320 Lifting an unbalanced load

This report suggests that all lifts where the suspension point is below the centre of gravity are inherently unstable and should not be used. This is not correct. The diagram does not even show an unstable lift unless the combination of lateral load and lifted weight are way outside what could normally be expected. My main concern is that by stating that the point of application of the lift should have been above the centre of gravity the report infers that no lifting should be carried out where the suspension point is below the centre of gravity of the load. This is not something that I would like to appear in contractors' site procedures manuals as a rule of thumb because it is likely to lead to more problems than it solves. There are clearly a very small number of circumstances where the geometry of the lifting points can lead to instability but, as with fork lift truck lifting, I think that it is probably more important to consider the base to height ratio and the weight to horizontal load ratio and resulting moments than focussing on the height of the centre of gravity relative to the suspension point. These issues have clearly been considered on these lifts which appear to have been successful: My opinion is that the majority of lifts are self stabilising rather than just some and that centre of gravity vs lifting point level should not be given precedence when looking at a lift.

John [20/1/2014]

Feedback on report 341 Balcony collapse at block of flats

This describes a form of ductile failure. I think the "all at once & nothing fust" of Wendell Holmes is now well discredited, although one could (unfairly?) describe that as an accountant’s method/principle. (v. the "wonderful one-hoss shay", as described in an old design book).  Report 365 Alterations to existing buildings with no site visits brings to mind an experience that I had. Report 411 Quick & cheap design calculations: –astounding, perhaps should not be. See BSI news:- BS 7000-4:2013 Design Management Systems: Guide to managing design in construction. I am often reminded of the tragic Aberfan principle/fallacy, including – Nothing gets done until there is a tragedy – often, sadly, loss of life. There was a very similar tip collapse to the Aberfan landslide, a few miles away during WW2. Witnessed by a lone cyclist, I seem to remember from the parliamentary report. And one of their other conclusions, that all necessary knowledge was available, but not to those responsible for the tip. A tragic case of door-shutting after the horse.

Chris O'Regan [20/1/2014]

Feedback on report 365 Alterations to existing buildings with no site visits

It is quite troubling to see this trend of engineers not wanting to visit the site and work exclusively from architect’s drawings. The response by Structural-Safety is correct in that engineers must attend site where they are proposing to carry out alterations as they have to understand and appreciate the condition of the existing structure and what it is made out of in order for them to develop a sensible and appropriate design solution. Additionally it is also prudent in the interests of due diligence that structural engineers should attend site during the works to ensure that their designs are being constructed in accordance with their specifications for and behalf of their client. To think neither of these actions is occurring due to a squeeze on fees is troubling to say the least.

Geoff Fletcher [17/1/2014]

Feedback on report 348 Responsibilities of Local Authorities for possibly dangerous structures

I have applied what I was told by an experienced engineer many years ago (and have since passed on to juniors); if you ever see something about which you have safety concerns you must write it down and must send it to someone whom you believe may have responsibility / be able to help. Re report 304 Partial collapse of suspended ceiling - I believe a bigger issue for the other cited cases (Boston Big Dig & Sasago Tunnel) is that of management of progressive (or "cascade") collapse mechanisms. They are usually entirely foreseeable and thus a responsibility (& liability?) for the Designer, and just an extension of the principle of redundancy & alternate load paths. A simple measure to at least contain the scope of such a failure could be to introduce discontinuities along a structure - to act as a "structural fuse" one might say. Some widespread design review & checking of existing structures might be called for.

Kevan Latham [15/1/2014]

Feedback on report 348 Responsibilities of Local Authorities for possibly dangerous structures

The statement/question in this report "A related question is whether a chartered engineer has an obligation or duty to act if he/she sees something that is, in their opinion, manifestly unsafe? The answer will depend upon legal circumstances, Institution codes of conduct, and ethical considerations. Views on this too will be welcome." Well this is my view - Once you have decided that there is something to say then do something about it quickly ! Don't sit and think about what to do --just do it. It is no good bleating afterwards that 'I knew there was something wrong' - an engineer is part of society and his knowledge is important in that society. What is so called 'correct procedure' or 'PC' is rubbish thinking in my mind -- just think about common sense and the folk who are involved in the problem that YOU see - it does not matter who has checked it or it has a certificate - just get involved and be PERSISTENT in a polite way. Remember --- that you are not finding fault with anyone -- that's not your responsibility - you are making sure that what you see wrong is put right --that is your responsibility - without any doubt.

Gordon Millington [15/1/2014]

Feedback on report 358 Offshore tower failure

I am surprised there is no mention of fatigue failure of the bolts. I have experience this no several structure subject to dynamic load where the bolts have not been properly torqued up to reduce cyclical loading.

Peter Cunningham [23/10/2013]

These reports make for spine chilling reading, particularly the ones relating to small scale domestic work. However, I find the responses advising that a “competent” steelworker and structural engineer "should" be employed as being completely pathetic. We all know the essence of construction, particularly at domestic level, is for the lowest cost with scant reference to competence of builders and avoiding paying for any supervision. Our industry continues to operate on this “amateur” basis…until something goes wrong…and then we shake our heads wonder why? Our professional institutions, with their refusal to stand up for fee levels which can provide a responsible level of service, plus the legal framework for construction, which allows the public to be exposed to incompetence and danger, are the chief culprits here. This website, whilst very interesting, does not address the underlying commercial causes of the problems reported and therefore could be more effective.

Mike Kirkham [22/10/2013]

Feedback on report 393 Steelwork connection design

Up until a few years ago I used to design steelwork connections for a fabricator on large projects in the UK. I have given up doing this because I felt that potential dangerous practices were going on. This is my experience not with just one engineer but with several different practices. I would receive a stick diagram from the main job engineer together with moments and shear forces at the joints. The mangitude of the forces was always given but rarely the direction. Whenever I had queries or concerns I was always put through to a junior engineer who quite often didn't have the knowledge or experience to understand my question let alone give me an answer. Whenever I tried politely to ask for someone more senior I was told that they were the project engineer. In a number of other jobs I was involved in the main job engineer designed the beam and stick main frame and lift core etc (usually concrete) but anything like a penthouse steel frame or a balcony was put out to tender as design and supply. This was better in a way as least we were being paid to do the main design of the structural elements but I often wondered if the client was paying twice for this design. I suspect that at least some of these consultants were set up with a limited number of senior people to be the client interface and to attend site meetings with the main work being done by inexperienced graduates pumping numbers into design frame packages with the whole process almost automated. I can see that this would be a very efficient and cost effective way of working. My feeling rightly or wrongly was that they were relying on the likes of me to pick up major design errors. Here are 3 problems that arose on different jobs Main job engineer showed a large main beam revised to rise verticaly up and over a large opening and then back down again. no moments were shown only shear forces Main job engineer designed main beam to act compositely with decking but large opening over first third of span meant that composite action could not take place in this portion of the beam. Beam would have theoreticaly collapsed under full live load (this is so similar to your example). Had a job with cruciform fin plates on top of cloumns supporting laminated beams. Main job engineer had designed column laminated beams as a sway frame in the wind and specified large moments to be transferred through a joint which has virtualy no stiffness in the plane of the applied moment. A large number of failures of structures are related to connections or parts of connections. Its very rare for a main structural member itself to fail. I find it bizzare therefore that so liitle attention is given to teaching connection design either at university or in the consultants office.

Chris O'Regan [20/7/2013]

Feedback on report 336 Modifications to balustrades in a shopping centre

 I have noted some anomalies within this report that may need to be addressed; principally the differentiating between 'toughened' and 'laminated' glass, which is not very clear. These are not strictly speaking two different types of glass, as it is possible to have laminated toughened glass. One is a single monolithic sheet while the other is a series of sheets of glass of any type stuck together using an interlayer, typically PVB but can also be ionoplast or EVA. Additionally the installation of laminated glass in balustrades is preferable than a single sheet of toughened as in their post failure condition they tend to remain within their supporting frame. A single sheet of toughened however will shatter into small cubes that initially form fist sized clumps until they impact onto a solid object. It may have also been prudent to cite the CIRIA guide to glazing at height in the report as it discusses balustrades at length as well as BS 6180: 2011, which is the code of practice for barriers in buildings.

Peter Rutty [18/7/2013]

Feedback on report 360 Adjacent excavations in Australia

This situation is addressed explicitly by BS EN 1997-1:2004 (Eurocode 7) - see 9.2(1)P, 5th bullet point.  The clause is a principle for which there is no alternative and must be followed.  A designer working in the UK, and using currently applicable codes (EC7 is the the only standard applicable now), will have to address this situation appropriately.  Personally, this is one of the good things about EC7 - it provides comprehensive check lists telling designers what they shall and should consider - not necessarily analyse - and this seems to have been lost in the discussion that's focussed more on the issues of design cases, partial factors and analysis.

Andrew Dawber [17/7/2013]

Feedback on report 378 Stability of tenants' mezzanine

The SCI has published documents about how stability of these frames should be handled. It is possible to design a mezz floor with no bracing and with over-sailing beams. However the columns must be designed as vertical cantilevers with fixes bases. This can significantly increase column sizes however.

Andrew Dawber [17/7/2013]

Feedback on report 339 Further concerns about competence

I completely agree with this reporter, and the problems he highlights are ones I have encountered many times. It seems to have got worse lately. I think the recession has a lot to do with it. During good times general consulting engineers are happy to let steel fabricators design steel structure for them. However during recessions they want to hold on to as much work as they can; even when they can't handle it properly. Young inexperienced (and cheap) engineers are being given projects which are beyond their limits of knowledge.

Richard Herrmann [17/7/2013]

Feedback on report 349 Error in proprietary design program

The (often complete) reliance on proprietary software and common lack of checking is a grave concern. We have identified similar problems with propped retaining walls designed by a well known software package. Why not name the software package to assist identification of areas of potential problems??

Derek Bishop [31/5/2013]

I am looking for information on Building Information Modelling (BIM) as it would relate to Civil; Structural Engineers as part of a design team. My interest in the subject is related to Health and Safety issues in Construction and how, for example, the use of Structural Safety information could or would be fed into the system and the role of the CDM Co-ordinator in a structure designed and constructed under BIM requirements. Any information on this as it may relate to Structural-Safety will be welcome.

Howard Caroline [29/4/2013]

Feedback on report 315 Telecommunications towers and resin anchors

It is my understanding that most, if not all, Commercially available Off The Shelf (COTS) resin anchor systems rely largely upon a mechanical bond after being set. The liquid resin will flow in to and out of the internal surface depressions of the hole, albeit at a microscopic level. If installed correctly, the resin will then act in shear and continue to perform until a traditional cone failure occurs in the base material. The rougher the internal surface of the hole the better. For this reason diamond cored holes undertaken by rigid track mounted coring machines are likely to be a higher risk due to the smooth internal surface that is created. Resin anchors do not rely upon chemical bond alone. I do concur with the majority of this article.

Alan Hill [25/4/2013]

Feedback on report 315 Telecommunications towers and resin anchors

Failure of resin bonded anchors reminded me of an experience in the 60s with MIG welding wire drive feed rolls where repeated and unexplained failure of the epoxy joint between the Bakelite centre and the steel outer occurred. The loading of the joint was shear combined with fluctuating compression with every rotation of the roll. Fatigue was not identified at the time but it now seems it was the most likely cause. I believe it is clear work need to be done on fatigue strength of resin bonded joints.

Anonymous [23/4/2013]

Feedback on report 324 Lack of experience on steel column erection

Design responsibility of steel to concrete connections. It is common pratice for main consulting engineers to design steel frames but leave it to the steel fabricator to design the connections. Design engineers working for steel fabricators tend to be very good at designing the steel connections but their knowledge can be very limited when it comes to concrete design. This presents a problem when it comes to designing steel to concrete connections. This may be column to foundation or steel beam to concrete beam. The Steel Industry Guidance Notes has a document SN51 01/2011 that describes how the design responsibility works. Basically the main consultant provides the loads, the steel fabricator proposes a suitable connection detail and then the main consultant should confirm the adequacy of the anchorage. Recent experience has led me to believe that the vast majority of consulting engineers do not believe it is their responsibility to confirm the adequacy of the anchorage. They believe their responsibility ends when they have submitted the loads. In the vast majority of cases this does not represent a problem but where we have braced bay columns with high uplifts and then site constraints mean the concrete edge is close to the bolts then potentially it can be a problem. The solution to the problem is a bigger base or steel reinforcement to the base that will aid the pullout forces. Both of these factors fall outside the control of the steel fabricator. It is my belief that in most projects neither the steel fabricator or the main consulting engineer are checking this potential problem properly.  I am an engineer who specialises in working for steel fabricators and I am happy to admit my knowledge of concrete is limited. I have tried raising this issue several times but get chastised for it. Main consulting engineers simply tell me that connection design is not their responsibility and they seem quite happy to walk away from the issue.

Chris Murgatroyd [21/1/2013]

Feedback on report 284 False CE certificates

It should be noted that CE marking is simply about permitting the movement of good around Europe, including imports. CE marking is not quality or safety related. In fact EN 1090 for structural steelwork is basically a self-certified system. If one takes steel fabrication as a typical example neither the NSSS (CE marking version) or EN 1090-2 will be acceptable for delivering either a quality product or one that can be assumed to be safe. We will also not have a uniform approach across Europe and I am sure it will be exploited in the Far East. So it should be noted that CE marking is fairly pointless from a purchasers point. It is only of use for the movement of goods.

Geoff Fletcher [21/1/2013]

Feedback on CROSS Newsletter 29

Many thanks for this Newsletter, another excellent read and take my encouragement for CROSS and your work. Perhaps it's an old joke for you over there but I can use that line from Report 284 about 'CE standing for Caveat Emptor' in some major presentations coming up focussing on engineering for precast design & construction (with acknowledgement to CROSS of course!). Report 229 re divided responsibilities reminds me of new legal regulations rolling out across Australia (terms proposed by the Federal Govt to be passed in each State parliament) covering safety in precast construction wherein aside from a lot of 'shoulds' there are only 2 'musts'  there MUST be consultation where design responsibilities are staged or divided, and designers MUST eliminate construction risk from their design if reasonably practicable. So both of these must be verifiable as part of discharging obligations. As a profession we need to be much better at seeing, communicating and selling the value of what we offer & do - and that it's a smarter & more certain spend than the alternative of risking untold litigation when things go wrong.

Eric Dickson [21/12/2012]

Absolutely top notch Newsletter and website about safety, so informative and you are a credit to the construction industry ten out of ten.

Harold Stocks [23/10/2012]

Feedback on report 333 Falsework support to a bridge – a near miss

There seems to be confusion about Roles and Responsibilties. The Temporary Works Co-ordinator makes sure that the TW design is carried out by a competent person and determines the design brief. This is to ensure  that the design does not adversely affect site operations. The Temporary Works Designer carries out the design, issues preliminary drawings and recieves  comments from the Temporary Works Co-ordinator. Following this he revises the design and re-issues as a Construction Issue document. Following the installation of the TW the ONLY person who can issue the Permit to Load is the Temporary Works designer. This follows a mandatory site inspection.

Roderick Chisholm [8/5/2012]

Feedback on report 296 Compatibility at RC column to slab joint - strong column/weak slab

I read this report with interest.
1. This deals with the compatibility of the concrete at column/slab junctions where the column concrete is of a characteristic strength much higher than that of the slab and where the slab is cast over the column head.
2. This is a common occurrence in tall buildings design.
3. The ACI Code 318 gives empirical guidance, stating that if the column concrete characteristic strength is limited to not more than 1.4 times the slab characteristic strength then the full column strength can be used. This removes the problem of having to cast a small area of the 'column strength' concrete along with the much larger area of the 'slab strength' concrete.
4. For example, slab concrete C37 can be used with column concrete C37 x 1.4 = C52
5. The example quoted, C85 column concrete and C37 slab concrete would seem extreme. It would benefit from having larger columns (with lower strength concrete) and higher strength concrete slabs at lower levels which are presumably the critical levels. C55 column concrete, C40 slab concrete would be satisfactory. For a given load the column area would be only about 35% greater with C55 concrete.
6. Although it appears that this ACI 318 concession will apply well to interior column/slab junctions, where the concrete at the column head is confined all around, edge and corner columns have less confinement if the slab is flush with a column face. It would be logical to provide additional "containment" reinforcement, extending to the column face, within the slab thickness. Where the slab extends beyond the column face by a full anchorage length then the edge or face column can be treated as internal.
7. The condition about tensile stresses in the top of the slab will occur for any concrete strength. If there is concern about this, simply continue the column links through the depth of the slab. This should provide sufficient confinement to the weaker slab concrete where it passes over the column head. In geographical areas of even medium seismicity it is common practice to provide links at close centres (eg 100mm c/c) for a short distance below and above the column/slab intersection.
8. This situation is referred to in the Concrete Society Publication 'Guide to the Design of Concrete Structures in the Arabian Peninsula', 2008, Section 7.8.4.

Chris Bolton [7/5/2012]

Feedback on report 253 Freezing splits galvanised RHS columns

This report is interesting, but I wonder if freezing is the only cause? The second photo (of a non-galvanised section?) shows cracking in the middle of the side, not at the corners. I would expect freezing to cause bending in the spans before enough tension developed to split the corner. My suspicion is that the corners may have been cracked in the galvanising (Liquid Metal Assisted Cracking) and the freezing has just opened them up. On cold rolled RHS, the corners are work hardened so vulnerable to LMAC. If I remember right, LMAC was first observed on the corners of RHS - they were posts for motorway barriers and had split from the end like banana skins. The cracks were not initially obvious but the posts would not fit in their sockets.
Any other comments on this phenomenon will be welcome.

Jørgen Munch-Andersen [4/5/2012]

Feedback on report 296 Compatibility at RC column to slab joint - strong column/weak slab

I would like to draw attention to the fact that the robustness of a column-slap structure increases very significantly if the columns are continuous and the slaps rests on plinths. This could ensure that failure of a slab does not drag the column with it.

Richard Barnes [4/5/2012]

Feedback on report 296 Compatibility at RC column to slab joint - strong column/weak slab

There is a Concrete Society Advice sheet entitled High strength concrete columns and normal strength slabs available from:

Michael Crick [30/1/2012]

Feedback on CROSS Newsletter 25

Report 276 Licensing of temporary structures

I could not disagree with some of the comments however I would expect the duties under the Occupier Liability Act 1957 to apply with the authority being the occupier or controller of the premises and hence holder of any duty of care. The items are certainly structures, are of metal or similar and are non-domestic and are constructed in the 'furtherance of a business' or in line with 'the conduct of their undertaking'. The people who erect and maintain them are at work therefore I would expect the Health & Safety at Work Act 1974 to apply including regulation 3(1) would apply. Although not necessarily notifiable, the construction (Design & Management) Regulations 2007 wherein designer duties under Regulation 11 would apply together with contractor duties under Regulation 13. It would seem that where there is concern there should be sufficient legislation in place to allow the serving of a Dangerous Structure Notice under the building Act 1984 Armed with this information it would seem reasonable for a level of encouragement be given to have matters rectified.I do not advocate a legislative approach in the first instance and usually seek co-operation and discussion but it is nice to know the law should there be a need to encourage when, on occasion, those that can, and perhaps should, do something claim they cannot.

Reports 266 PV solar panels and 280 Loading from solar panels

I am currently working with a large energy organisation on installation of PV panels and cn confirm that not only is a part of the process the need to carry a structural survey on the roof for ability to take both positive and negative pressure loads but also on a number of sites, roofs have required strengthening or been excluded from the programme. (I commend this company on ensuring such checks are carried out). The issue of snow load adds a further issue in that panels can cause a dam effect under slight thaw and instead of the snow sliding off it can be retained against panels and re-freeze overnight to ice. This not only increases dead-loads but at a point of thaw when the ice melts to a sufficient thickness to pass beneath the panel, has the potential to slide off in a single sheet of significant size and weight therefore the accessibility to persons by doors or paths beneath has to be considered. Such systems etc. will remain an issue as so much of the controlling legislation refers to 'non-domestic premises'. 'furtherance of a business' and 'at work' which so often do not apply to residential properties. (albeit civil law may)

Roger Davies [30/1/2012]

Feedback on report 287 Concern about PV installations

Further to this report and the comments, I have done a straw poll amongst those here who have had PVs installed on their houses (admittedly a small sample) and in no case was it treated as a material alteration and consequently the structure has not been assessed for the additional load. One of the manufacturer / installers of the ‘hot water panel systems’ that we have contact with had the same view. I would also have concerns about the design of fixings particularly the uplift case. I think that as most of these systems are installed under Competent Persons schemes that in practice the Local Authorities take a relaxed attitude particularly as it is considered to be a good thing on sustainability grounds.  My personal experience is that triggering a request for structural justification for a material alteration is far less likely than a material change of use. When I put an extra floor on an existing building it was the coincidental material change of use that was used by the Local Authority to request more information I suspect that is because the definitions and requirements are better defined and wider in scope. Please keep up the good work in producing these reports, they are useful triggers for raising items for our Engineers to think about.

Nick Clarke [26/1/2012]

Feedback on CROSS Newsletter 25

In this Newsletter, reports 266, 269, 280 and 287 refer to PV installations. Several BRE publications give guidance relevant to these reports: Digest 495 Mechanical installation of roof-mounted photovoltaic systems 2005 Digest 489 Wind loads on roof based photovoltaic systems 2004 Information Paper 8/11 Photovoltaic systems on dwellings: key factors for successful installations 2011 These are available from www.brebookshop.com In addtion, there is the NHBC Foundation publication (written by Paul Blackmore, BRE) NF 30 Guide to installation of renewable energy systems on roofs of residential buildings 2011 This is available from www.nhbcfoundation.org

Geoff Fletcher [14/12/2011]

Feedback on report 244 Failure of epoxy fixings due to high temperature

Thank you for this report. A comment I would offer re this mobile phone tower failure incident is that in addition to questions of what was the temperature of the epoxy grout material and the receiving concrete substrate at the time of installation, note that just about ALL installed chemical anchoring products start to lose strength once they get to about 80degC. Even if installed within the stated temperature limits, a black tarmac covered concrete roof with a steel threaded anchor element embedded into the epoxy might attract, hold and conduct high temperatures into the epoxy on a sunny day & possibly for some time after that when storm conditions gather. On that basis I would think a mechanical anchor is a better potential solution.

Kubilay Hicyilma [7/11/2011]

Feedback on report 244 Failure of epoxy fixings due to high temperature

I was reviewing some drawings and had reservations about epoxy anchors in tension in high thermal conditions, so it was timely to comes across the fact that CROSS had noted this in the Newsletter No 24, October 2011. I will use this to help make my point, so that the detail is properly thought through.

Mike Crick [23/7/2011]

Feedback on report 255 Use of water filled containers to anchor temporary structures

I have similarly had problems of vandalism and a solution for temporary ballast was to place 2m dia manhole rings on visqueen and then fill with gravel. Can all be done with JCB 3, small tractor or similar but provides a vandal resistant 10 tonne balast block. On completion the ring can be lifted by same as it is light and will slide over gravel. Gravel can be recovered clean and re-used.

Same basic system, all quickly achievable with small plant but vandal resistant. My use has been mainly for temporary road closure barriers that cannot be easlily removed but principle is the same.

Nick Clarke [7/6/2011]

Feedback on report 163 Building control and the design of a free-standing wall

This report refers to the ODPM leaflet which can be downloaded from the websites of many councils, though oddly not from any government website, as far as I can tell. This leaflet refers to two BRE Good Building Guides (13 and 14), which provide much more detailed advice on the topic than the ODPM leaflet. There are in fact several BRE Good Building Guides and Good Repair Guides about freestanding walls that will be of interest to a professional readership, as opposed to the householder, who the ODPM leaflet is aimed at: GBG 13 Surveying brick or blockwork freestanding walls (1992) GBG 14 Building simple plan brick or blockwork freestanding walls (1994) GBG 17 Freestanding brick walls - repairs to copings and cappings (1993)  GRG 28 Repairing brick and block freestanding walls (2000) This can be purchased through www.brebookshop.com. Nick Clarke IHS BRE Press, Garston, Watford WD25 9XX 01923 664170 GBG 13

Ian Smith [3/2/2011]

Feedback on report 216 Fall of bridge deck support due to bolt over-tightening

This report includes a commentary on the failure of a group of M16 grade 8.8 bolts that connected a stub bracket to the web of a steel beam. The bolts had been excessively tightened by the erector, using an air-powered torque wrench. The fact that the grip length (and hence the thread length within the grip) was short was cited as one reason for the over-tightening of the bolts. The recommendation follows that 'critical connections should be checked by an external consultant and that critical connections must use HSFG bolts with load indicating washers or TCBs' (attributed to HSE). While the external checking of critical connections is seen as being a good recommendation, the effective banning of the use of 'untorqued' bolts in all critical connections is seen as misguided, particularly if (as appears to be the case here) the bracket had a single load application and thus fluctuating stress at the base of the thread was not a design consideration. The logic behind this recommendation appears to be that an HSFG bolt will not be broken by a air-powered torque wrench. In practice this is known to be wrong. If the wrench used is too big, then an HSFG bolt can be broken and it is down to the skill of the erector to ensure that this does not happen. Erectors have been using air wrenches to tighten (not to torque) for many years and, if they are experienced, this method has been seen to be safe and very cost-effective. SCI Advisory Desk Note AD302 is topical, which in turn refers to the NSSS 4th edition stating 'Bolts may be assembled using power tools or shall be fully tightened by hand' (this referring to non-preloaded bolts). The AD302 document, however, is concerned more with under-tightening bolts than over-tightening, though it does contain the caveat 'Ordinary bolts particularly those specified to BS 4190, should not be torqued to the values used for preloaded (HSFG) bolts because they have thinner nuts than preloaded bolts'. Other European countries, and the builders of mechanical installations in the UK use grade 8.8 bolts with (usually) grade 10 (but not HSFG) nuts under conditions of controlled torque to create bolted connections that work in the same way as those which the bridge industry uses HSFG bolts. The fact that the nuts used in such connections are significantly smaller than the HSFG variety means they use lower torque values and achieve similarly lower axial preload in the shank of the bolt. The lower torque values are demanded because of the danger of stripping the nut' thread due to excess hoop strain in the nut if the same torque is used as would be the case for an HSFG bolt. It has also sometimes been the practice to apply a grade 10 nut to grade 8.8 bolts when loaded in tension. Experienced erectors will, when tightening 'untorqued' bolts, either reduce the torque limit on the wrench, or throttle back on the air supply. The use of an air-powered wrench is not something for untrained erectors. The comments in Report 216 that experience and site control are necessary are therefore welcome. However, the effective banning of non-preloaded bolts from critical connections due to a single incident of improper site action is less appropriate - good guidance on the safe operation of air-powered wrenches would be a more useful tool.

Brian Duguid [2/2/2011]

Feedback on report 216 Fall of bridge deck support due to bolt over-tightening

I am somewhat surprised to read that the HSE recommends use of load-indicating washers or tension control bolts in place of calibrated torque wrenches. All three methods are prone to the risk that they can apply the incorrect bolt strain, and as a result the part-turn method has been traditionally preferred in the UK.  SCI guidance SCI 7-05 gives more details of the problems with the other methods, but essentially they are all prone to creating an incorrect strain in the bolts, due to uncertainties in the thread friction, and the load indicating washers have the additional flaw of introducing a corrosion-prone crevice into the steelwork.

John Carpenter [2/2/2011]

Feedback on report 214 Need for licensed builders

I agree with Peter Hyatt's suggestion that full plans are desirable for a wider range of work than currently catered for by the Building Act. The sophistication and complexity of basement (and loft) constructions were perhaps not envisaged when this was drafted. This is a subject under review by the Department of Communities and Local Government.  Recent research work for the Health and Safety Executive (HSE) explores how closer co-operation and effectiveness could be achieved between Building Control, which does visit site during the construction phase, and the HSE. There are now arrangements in place between the Building Control Alliance and HSE to allow this to happen (http://www.buildingcontrolalliance.org/2010/09/hse-bca-sign-new-agreement-to-improve-health-and-safety-on-construction-sites/).  Notwithstanding, it is not correct to say that safety legislation, and CDM specifically,  does not apply to domestic alterations. It applies in full, with the sole exception of the client, who, if a householder, has no duties. Whether duties are discharged is another issue!

Mike Banfi [28/1/2011]

Feedback on report 216 Fall of bridge deck support due to bolt over-tightening

Unfortunately the comments on this report do not reflect the current bolt standards. HSFG bolts used to be specified to BS 4395. That is obsolete and has been superseded by BS EN 14399 (High Strength structural bolting assemblies for preloading). There is a grade 8.8 bolt to this standard. Therefore it is not so much the grade of bolt that was wrong but the fact that they were to the wrong standard.

Peter Hyatt [28/1/2011]

Feedback on report 214 Need for licensed builders

Local Authority Building Control are entitled to request additional information, including structural calculations, in connection with Building Notice applications and, in my experience, often do so.  Approved Inspectors are not allowed to issue a final notice if they are aware that the works do not comply with the Building Regulations (according to Direct.gov.co.uk) and are entitled to withdraw the Initial Notice under these circumstances.  This action would re-assign the Building Control function to the Local Authority, which has enforcement powers.  There would appear to be only limited instances where Building Control can require Full Plans applications and these relate to means of escape and building use.  It would appear that 'ordinary' residential projects do not fall into this category, even for relatively complex underpinning and basement construction.  There would seem to be a good case to make for an amendment to the Building Act to require Full Plans applications for all works involving, say, substantial demolition, underpinning and the construction of basements - maybe in other situations, too.  This might particularly apply to residential alterations and refurbishments, carried out for the private owners of the property, where many of the rigors imposed by the CDM regulations are not applied.  There might also be a separate case to be made to extend the categories under which the full CDM regulations do apply, to include substantial structural works to privately owned residential properties.  It would seem to be a complete anomaly that some of the most challenging building works, at risk of being  undertaken by small contractors without adequate experience or resources, are excluded from much of the relevant health & safety controls.

Anonymous [20/10/2010]

Feedback on report 210 Design deficiencies in calculations submitted to a Local Authority

Some of the issues raised in this report resonate with what I and colleagues have been discussing recently. In my experience, engineers do not carry out sufficient checking. I would go further and say that some, especially sole practitioners and small firms, rely on Building Control as their checking engineer. I think it is often the case that Building Control do not have the resources to carry out proper checking themselves and I know of cases where the commercial structure of how checking is sub-contracted out to consulting engineers by Building Control is not viable (e.g. contracts for checking let on ridiculously low hourly rates). One might see this as an argument for self-certification but my experience of working in such an environment saps still furher my confidence that checking is properly carried out. In this case, firms check and certify their own work (actually they employ certifiers) when they are under certainly no less commercial pressure to issue their design than when they were being checked by Building Control. In the case of 'self-certification', the certifiers are audited but our experiences of this does nothing to reassure. Audits seem to have focussed on minor or secondary issues such as the certifiers failure to specifically cerftify nailed fixings of domestic stud partitions and not looking at the certifiers' competence and dilligence in a broader sense. My belief is that independent review is a better system and should perhaps be mandatory.

Henry Dalton [4/8/2010]

Feedback on CROSS Newsletter 19

I was interested to read of the cases in this Newsletter in which:
1) An engineer proposed to underpin a wall with mass concrete without allowing for the bending moments (and therefore tensile stresses) which would arise due to soil (and water?) pressures, and
2) A local authority failed to take action regarding a defective retaining wall.

Two years ago we were asked to design underpinning works to form a basement under a building. On one side of the building no soil would be retained (since there was an adjacent basement) and we specified mass concrete. On the other side about 3 m of soil was to be retained and we specified reinforced concrete. Unfortunately the builder used mass concrete where reinforced concrete was required. Although the Building Control Officer is fully aware of this he has taken no action to force the owner to take remedial work.

George Mathieson [30/4/2010]

Feedback on report 186 Collapse of Large Panel System (LPS) buildings during demolition

I remember working on this after Ronan Point, when many large buildings were being strengthened, mainly to introduce continuity between panels. General practice at the time was very poor in many cases, and I remember thinking at the time that a lot of the continuity reinforcement or bolting that we were designing would only add minimal strength in practice. Nothing I have seen since has caused me to change my mind on this. Demolition of any large panel building needs to be approached with great care, and a basic assumption that continuity is likely to be severely lacking should guide the work.

Anonymous [23/4/2010]

Feedback on report 177 Gain in strength of mortar slower than concrete

This issue can be addressed with the use of a rapid hardening cement. Not to confuse hardening and setting, the two are independent and can be designed separately.

Final hardness/strength is often taken at 28 days, but continues indefinitely at a slowing rate.  It is quicker at higher temperatures. Many modern cements gain substantial strength in much less time. Match testing can be done when strength on loading is important. Strength is a function of water/cement ratio for mortar as for concrete.

There are numerous specialised cements/mortars, and Contractors accustomed to using them.  Any of the larger firms' Intranets should refer, and it is impressive what can be found on the web. Useful information can be found on the Sustainable Concrete website: http://www.sustainableconcrete.org.uk/main.asp?page=140.

Alasdair Beal [8/2/2010]

Report 166 (Newsletter No 17 assets/uploaded/fck/File/CROSS Newsletter 17[1].pdf) concerning the collapse of a freestanding boundary wall misses the main problem with these walls, which is that they are not covered by Building Regulations (unless they form part of a building), so their construction is unregulated. Therefore local authority building control officers have no authority to do anything about the design or condition of such a wall unless someone reports it as a dangerous structure (by which time it is usually too late).

Brian Bell [4/1/2010]

To supplement Allan Mann’s points (see previous Feedback item), I would add that active signalling may be considered in conjunction with passive structural resistance where catastrophic loss of a bridge span caused by a low probability event may be accepted in some cases as being too expensive to avoid completely. While it smacks structurally of giving up the ghost or throwing in the towel, actually it is a pragmatic solution to a very difficult matter, particularly in low income economies where a remote bridge may be crucial to a locality and be heavily trafficked in the dark or in very poor visibility (e.g. monsoon conditions, which can wipe out a bridge in a very short time.) The principle need not only apply to bridges, of course. Below is a reference to a system which is a high-tech variant of the weighted fusible string low-tech solution: either can be deployed in most parts of the world.

If de la Concorde Overpass (30 Sept 2006: http://en.wikipedia.org/wiki/De_la_Concorde_overpass_collapse ) or I-35W (1 Aug 2007: http://en.wikipedia.org/wiki/File:35wBridgecollapse.gif ) had failed during the hours of darkness, the loss of life could have been substantially greater. 

 Bridge Collapse Detection System in Texas

James Justin Mercier, Eligio Alvarez, Juan Marfil, Mark J. Bloschock, and Ronald D. Medlock,

Texas Department of Transportation:

The Texas Department of Transportation (DOT) installed a collapse detection system on the Queen Isabella Memorial Bridge that will detect a span collapse and warn motorists to stop. The system consists of a fiberoptic cable that carries a current under the bridge deck for the 2½-mi length of the bridge. A span collapse will break the current, initiating flashing red lights to tell motorists on the bridge to stop, closing gates at each end of the bridge to keep additional cars off, and sending alarms to Texas DOT and local law enforcement to notify them of the event. 

(6th International Bridge Engineering Conference, July 2005, Boston , Mass. )

Allan Mann [15/12/2009]

All engineers will have noted the collapse of the bridges in Cumbria recently. Whilst there has been some discussion on the causes (possibly scour) there are wider safety lessons to be learned.

1. The death of the policeman was precipitated by a sudden collapse. It is a fundamental target of structural engineering that any failure will be foreshadowed by signs of distress to give warning. The question therefore is how fast was this collapse, would there have been signs of distress (from this failure cause) and if not, does that suggest the margins of safety against (whatever caused the failure) need to be increased?

2. A second attribute of safety is that of assessing sensitivity. We all know there have to be best assumptions about loading conditions etc. And we all have heard that this was an 'exceptional event’. But in industries where statistically possible events (albeit rare) can occur yet the consequences are severe, the aim is still to preserve a safety margin (maybe > 1.0) against extreme events. The target being to survive short of catastrophic collapse. What is not acceptable is to have a rapid change of state consequent on a marginal exceedence of design conditions. To assess this, sensitivity studies are called for. Has anyone looked to see if these failures were explainable by undue sensitivity to the presumed accuracy of the design events?

3. In safety related plant it is always an objective to have the design ' inspectable'. Numerous failures have occurred with bad consequences simply because it was impossible to verify plant/ structure condition. Was the source of failure (say scour) such that the condition was impossible to verify? There is absolutely no point in fretting whether the bridge superstructure state is Ok to stress levels (where the consequence might be cracking) and spending scarce resources verifying this 'accurately'; if a catastrophic failure can be precipitated at foundation level but can't be verified in the field.

4. All failures are regrettable. But as is well known whenever there is a near miss the wider question should be what is the risk to the remaining structures? After serious bridge failures in US and China we know surveys predicted many thousands of bridges were at risk. It is commendable such surveys are being conducted in Cumbria to assess bridge state there. But surely these flooding events can happen in any county. What is the vulnerability of the UK bridge stock elsewhere? How much will an assessment exercise cost (however crude) against the full costs of a single bridge replacement? For all these reasons, a full and open enquiry into the bridge failure causes is merited.


Derek Bishop [26/10/2009]

Feedback on report 158 Substitution of cold rolled hollow sections for hot rolled hollow sections

It is worth noting that an alteration to the design (including specification) by 'another' person should be considered under Regulation 11 (ss 3 & 4) of the Construction (Design and Management) Regulations 2007 whereby the Buyer takes on the duties of the 'Designer' and should consider the risks to health and safety (in the construction process and use (of the structure)) that may arise from the alteration to the original specification.

Investigation, should a failure occur, could identify the reason for the failure and at what stage the change in the original specification took place and who was responsible for making that change.

Robert Jones [29/9/2009]

May I welcome this development of the CROSS site and hope that it makes it easier for more colleagues to report situations where the safety of persons could be compromised. There is no statutory record of dangerous structures and “near misses”, CROSS is the only national register in existence as Dangerous Structures legislation is discharged locally with no other national record. Too often small issues that can lead to disaster are ignored, I had to rebuke a builder today for building a blockwork core off a first floor slab, before the supporting ground lift had been constructed under. An email to his office has had to confirm my concerns, and request support be provided, as I could be liable under section 3(2) of the HSW Act.

I feel privileged to be an Engineer and feel I have a duty to the public at large and my profession, so I seek to discharge that duty of care diligently, and would encourage colleagues to do likewise and support CROSS and the Institution in making buildings safer places. This might seem a little bit altruistic, but I regularly come across Engineers who would never dream of undertaking any action for fear of becoming involved.

Email Updates

How to Report

Online submission:
Submit by post: