CROSS Safety Report
Steelwork connection design
This report is over 2 years old
A reporter is concerned that on small domestic projects, steelwork fabricators are appointed who do not have the expertise to design connections or prepare fabrication drawings.
Key Learning Outcomes
For civil and structural design engineers:
Connections can often be the weak link in structures and attention to detail is required. These should be designed and detailed by a suitably qualified and experienced engineer.
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
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A reporter was particularly interested in report 378 on the design of steelwork connections. The reporter has worked as project engineer on many projects and has also worked for steelwork fabricators designing connections for them on hundreds of projects. It is undoubtedly true, in their experience, that steelwork designs sent by project engineers to contractors are sometimes deficient. However, on commercial projects, the responsibilities of the parties are usually defined by National Structural Steelwork Specification (NSSS) and the parties usually make some effort to work to this document.
Of greater concern to the reporter is what happens on small domestic projects. Although the architect may refer to NSSS in his specification, they frequently award contracts to small builders whose steelwork fabricators do not have the expertise to design connections or prepare fabrication drawings.
The architect may also not provide enough information on his drawings to enable the steelwork to be set out or the levels agreed (hence some of the connections cannot be designed and some of the fabrication drawings cannot be prepared). On such projects they frequently find that:
- although they ask to see fabrication drawings, none are received, and;
- they are not invited to site to check the as-built structure
What often happens is that they are asked to design critical moment connections and the rest is sorted out on site between the architect and the builder without any reference to the structural engineer - obviously a highly unsatisfactory situation. This is presumably driven by the desire of the architect to save costs and the reporter’s firm only then gets involved if something has gone wrong. The reporter would be interested to know if other engineers are worried about such issues.
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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.
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This illustrates very well the situation of a safety-critical industry being allowed to operate in a piece-meal manner. Indeed, the architect is open to legal action should there be a significant problem involving harm to persons, for not identifying the hazard of inappropriate delegation, and for failing to engage a competent constructor.
It is prudent for the structural engineer to ensure his appointment is fully qualified, but even so, he also has obligations to identify hazards and mitigate risks (e.g. by recommending suitable supervision) arising from his design, and pass on this information.
As regards site visits, a key attribute to safety is confirming that what parties thought was being built was actually built. The client should employ a steelwork contractor with the right skills to design and fabricate the steelwork. BCSA’s website can assist parties in identifying a steelwork contractor with the correct range of technical and commercial skills required for the job.