CROSS Safety Report
Architect conducts structural design of sway frame for domestic project
This report is over 2 years old
A reporter looked at a project recently where the drawings had been produced by the architect, including a structural design.
Key Learning Outcomes
For all built environment professionals:
It is important to recognise and know the boundaries of your expertise and work within the limits of your competence
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A reporter looked at a project recently where the drawings had been produced by the architect, including a structural design. This showed a steel frame within a gable wall to create a new 5.2m wide opening using two No. 152x89 universal beam (UB) posts per end with a 203x102UB supporting the inner leaf and 178UB supporting the outer leaf (but both beneath the floor/new lean-to roof).
There was a note to say that the beams were designed as fully restrained. The method of restraint turned out to be with proprietary galvanised mild steel straps at 800mm centres. The reporter considered that the beams should be 2 No. 203x133x30UBs minimum as the lateral restraint was inadequate. Also, the foundations for the posts were inadequate.
The reporter knows of quite a few architects who do this. They apparently use online programmes to do the design and just submit the calculations which include disclaimers at the bottom of each sheet. They cannot understand why building control pass them and why the Institution of Structural Engineers (IStructE) are not doing more to prevent it? He wants to know what he should do about this?
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Restraints are only as good as the component stiffness to which the restraints are added. SCI Publication P360 Stability of Steel Beams and Columns provides guidance on the determination of buckling resistance of beams and columns. There is a tendency amongst some to think that small structures are not worthy of ‘proper design’, but any number of failures show this to be untrue.
In the case reported here, it is possible to envisage excessive beam deflection, beam twist under eccentric loading, falling of masonry post buckling, global side sway of the frame in or out of plane, and so on. Unfortunately, as we all know, building control have finite resources, and this presents real risk. CROSS have made their opinions known to the current consultation on building regulation and its enforcement.
A few years ago, a court in Italy fined a software house for claiming that their programmes could design seismically resistant buildings. Unqualified persons, including architects, should not design structures, although there is nothing about this in the building regulations. It is a basic principle that those who are registered professionals know the boundaries of their expertise and constrain themselves to work within their limits of competence.
It is not uncommon for architects (and surveyors) to undertake structural design on what they consider to be minor elements of a building, but without sufficient training to properly understand the concepts. In addition, they rarely have any appreciation of the dangers their lack of knowledge can cause. The matter will be raised with the Royal Institute of British Architects (RIBA).
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