CROSS Safety Report
Inadequate end bearings for transfer beams
This report is over 2 years old
Overview
Whilst advising a steel fabricator on tendering for a transfer structure steel frame, a reporter's firm noticed a serious design error with the bearing pressures at the supports of a transfer beam.
Key Learning Outcomes
For civil and structural design engineers:
-
Connections can often be the weak link in structures and attention to detail is required to ensure what is designed can be fabricated
-
Careful consideration is required for connections, particularly at interfaces between different materials. The role of tolerances should not be overlooked.
-
An attribute of ‘safety’ is to assure that the design is not disproportionately vulnerable to minor error
Full Report
Find out more about the Full Report
The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.
Whilst advising a steel fabricator on tendering for a transfer structure steel frame, a reporter's firm noticed a serious design error. The structure comprises an irregular arrangement of large steel beams supported by steel columns and, at the building perimeter, bearing on to a reinforced concrete (RC) wall.
The beams support a slab and several stories of stud framed residential flats above. End reactions were shown on the drawings, with up to around 1,000kN design load specified for the bearing on the RC wall. The bearing detail was clearly shown and comprised beams resting on a recess cast in the RC wall. The specified end bearing was 100mm. A simple calculation showed the bearing pressure to exceed twice the permitted maximum value.
Can inadequate bearing design lead to failure?
Experience has shown bearing design to be a common cause of major structural failure, with inadequate provision for tolerance often cited as an issue. In this case were the works to be constructed as designed, tolerance issues could make an already bad situation much worse, with a reduction in bearing to 75mm being a distinct possibility even without unusually lax site control.
Experience has shown bearing design to be a common cause of major structural failure, with inadequate provision for tolerance often cited as an issue
Of particular concern is the fact that this defect was part of a structural design passed by a certification scheme; it thus illustrates the shortcomings in that process. As the 13th Biennial Review of SCOSS (The Standing Committee on Structural Safety) pointed out, independent third party peer review is the gold standard in structural checking and the alternative of occasional sampling of in-house checking does not give the same degree of safety.
Submit a report
Your report will make a difference. It will help to create positive change and improve safety.
Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.
Feedback
No feedback has yet been published for this page.
Expert Panel Comments
Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
As ever, safety is often dependent on attention to detailing and this report illustrates how the safety of a large structure can be jeopardised by inadequate attention to supports.
Five common themes emerge in such situations:
It is frequently connections that are the weak link in any structure
There are frequent problems at interfaces between different materials (here steel and concrete)
There are frequent problems when the designer of a connection has been tasked with developing an ‘impossible connection’ because the structure has not been adequately conceived/designed ignoring practicalities of fabrication/connection
The role of tolerances is often overlooked
An attribute of ‘safety’ is to assure that the design is not disproportionately vulnerable to minor error
As ever it is essential that there is adequate quality control in place to ensure all design criteria are met.