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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 online feedback form.

David M 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]

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 Dentish [20/4/2017]

One item that is very relevant is 641 SQUARE HSS 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]

Ref Report 581 (CROSS Newsletter No 45) 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]

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]

I read item 614 relating to 3D Modelling (Newsletter No 45) and found that I recognised this issue; it 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]

With reference to CROSS Newsletter No 45 I was a little surprised that the commentary after the report 612 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]

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! 

Paul Bell [19/7/2016]

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]

There are a couple of interesting CROSS reports in the latest newsletter (Newsletter No 42) relating to bridgeworks. 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.

Correspondent [3/12/2015]

Comment on 'cost of scaffold design standard' (Newsletter No 40 Report 445): 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]

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 Perhaps consider making a revision to the alert that at the very least makes reference to this article?

Patrick Hobson [9/11/2015]

With reference to the reports on PV panels in Newsletter No 40, 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!

simon Willcox [3/9/2015]

I am currently studying for an MSc in Building Conservation at the Downland and Weald Museum. I have been trying to download your Report on the Apollo ceiling collapse reference 422. However I keep getting an 'error report. I would be grateful if you could send me a copy in pdf format. It will be of considerable use to me as part of my dissertation.

This error has now been corrected.

Tony Hutchinson [15/7/2015]

We were interested to see your comment in Newsletter No 39 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]

These comments are in relation to report 423 Temporary works design for basements in Newsletter No 39 and 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]

Regarding report ID:448 in Newsletter No 39 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.

Comment: Agreed - see the Newsletter for the original response.

 

Paul Bell [10/2/2015]

Dear CROSS, The photographs in report 482 (Newsletter No 37 January 2015) 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]

Newsletter 37 - 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]

I wish to draw your attention to that which appears to be an error in your SCOSS alert dated Sept. 2014. Preventing the collapse of free-standing walls - September 2014 Para. 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.

Comment

This is an interesting point and below is the response from one of our panel of experts.

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.

Malcolm Leighton [25/10/2014]

I note your September Alert (Preventing the collapse of free-standing walls) with great interest. I am currently, and have been for over the last year or so, drawing the attention of my local authorities to the importance of a better control of all freestanding walls. I have, as of last Thursday, been granted permission to give a one hour presentation to five decision makers of one Council. I was well received with a promise to raise the matter with the relevant County Council and for them to consider how to amend planning procedures.

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.

Response: we will look at this.

 

 

University [17/4/2014]

I would like to offer the comment below in relation to Report 435 Balcony strengths of blocks of flats - further experiences (Newsletter No 34 April 2014). 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]

I refer to the matter of under reinforced balconies (Newsletter No 34 - April 2014), where such reinforcement that exists is not where it should be. 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]

Report 320 (Newsletter No 33). 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]

Thanks for another thoughtful CROSS Newsletter (No 33). Report 341 Balcony collpase at block of flats 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]

It is quite troubling to see this trend of engineers not wanting to visit the site and work exclusively from architect’s drawings (Report 365 Newsletter No 33). 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]

Re report 348 Responsibilities of local authorities for possible 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]

The statement/question in this months structural safety report (Newsletter No 33, report 348):----"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. Kevan Latham (retired list)

Gordon Millington [15/1/2014]

358 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.

Simon West [5/11/2013]

I recently registered on your website and received the email with a link to complete the registration but I just get error messages when I follow the link and the link for the administrator. Is this an issue with the website or am I doing something wrong?

Andy [1/11/2013]

Great new website!

Peter Cunningham MIStructE [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]

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]

I've just read through the latest CROSS newsletter (No 31 July 2013) and came upon report 336 Modifications to a balustrade in a shopping centre. I noted some anomalies within it 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]

Re: Adjacent excavations in Australia Report (Report 360 Newsletter No 31).  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]

Regarding the concerns for stability for mezzanine floors (report 378 Newsletter No 31); 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]

Report 339 (Newsletter No 31) 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]

Report Cross 349 (Newsletter No 31) - 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]

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]

Failure of resin bonded anchors reminded me of an experience in the 60’s 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

Designer [23/4/2013]

This is a comment in response to Report 324 'Lack of experience in steel column erection' in Newsletter No 30.
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]

I read the latest issue with interest and as usual it raises important issues. I do however have one small problem and that is with CE marking. 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]

Many thanks for Newsletter No29, 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]

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]

I have read with interest the Cross Newsletter No 26, in particular Report 296.
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]

I'm just reading Newsletter No 26. The piece on cracking of RHS columns due to freezing (report 253) 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]

Regarding the report on Compatibility at RC column to slab joint (strong columns/weaker slabs) in newsletter no 26 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.

Dr Richard Barnes [4/5/2012]

Regarding CROSS Report 296 COMPATIBILITY AT RC COLUMN TO SLAB JOINT (STRONG
COLUMNS/WEAKER SLABS) there is a Concrete Society Advice sheet entitled High strength concrete columns and normal strength slabs available from:
http://www.concretebookshop.com/detail.aspx?ID=1192

Michael Crick [30/1/2012]

CROSS Newsletter No 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 266/280 PV panels on roofs 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)

Michael Crick [30/1/2012]

Newsletter No 25 Further to Report 287 on Concerns about PV installations, and the comments,I have done a straw poll amongst those here who have had PVs installed on their houses (admittedly a small sample) – 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]

In CROSS Newsletter No 25, January 2012, 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]

Thank you for the item in the CROSS Newsletter 24 concerning Report 244 'Failure of Epoxy Fixings due to High Temperatures'. 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]

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]

In Newsletter 23 (July 2011) you ran an item on water filled containers for ballast.

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]

Newsletter 22 includes Report 163 about freestanding walls. This 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]

In the CROSS Newsletter no 21, January 2011, there is a commentary (Report 216) 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 BEng (Hons) MICE [2/2/2011]

Dear CROSS,  I am somewhat surprised to read in the newsletter's first report (Newsletter No 21 report 216) 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.  <a href="/assets/uploaded/fck/File/SCI 7-05 installation of preloaded bolts.pdf">SCI guidance SCI 7-05</a> 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]

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]

I have just read the the report on the fall of bridge deck support in the latest newsletter (Newsletter No 21 January 2011 Report 216 ) and the comments about the appropriate bolts to use. Unfortunately the comments 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 C Eng M I Struct E [28/1/2011]

Ref: Cross 214 (Newsletter No 21 January 2011) 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.

Name withheld [20/10/2010]

I have just read Newsletter 20 and some of the issues raised in the Building Control article 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]

I was interested to read of the cases (in Newsletter No 19) 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]

Re: demolition of large panel structures, and lack of continuity 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.

J Gray [23/4/2010]

Newsletter No 18 contained a report: GAIN IN STRENGTH OF MORTAR SLOWER THAN CONCRETE (Report 177) and and a 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 public www. Useful information can be found on the Sustainable Concrete web site 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]

It is worth noting that (see Newsletter No 16 Report 158 - Substitution of Cold Rolled Hollow Sections) 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.

Eur Ing Robert Jones DM CEng FIStructE FCIOB FBEng MCMI Chartered Structural and Corporate Building Engineer

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