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CROSS Safety Report

Design deficiencies in calculations submitted to a Local Authority

Report ID: 210 Published: 1 October 2010 Region: CROSS-UK

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Overview

A Local Authority Building Control manager has sent a list which gives twenty nine of the more serious design review queries raised by the building control structural checking process over the last five years.

Key Learning Outcomes

For civil and structural design engineers:

  • A quality assurance system within your organisation, that includes the internal checking of calculations, can help prevent safety issues from occurring

  • Competent supervision of design by experienced personnel can allow less experienced engineers to develop a feel for the right solution

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A Local Authority Building Control manager has sent a list which gives twenty nine of the more serious (and most typical) design-review queries raised by the building control structural checking process in their area over the last five years. This is within a predominantly rural council.  A third of the projects represent more serious risks to longer term safety.

It is interesting to note, says the reporter, that all but two of the designers whose work was incomplete in some way, were Chartered Engineers and members of either the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). The suggestion from other quarters would seem to be, says the reporter, that it is only amateurs producing beam calculations who pose any real danger.

They continue: ‘Please understand, I am in no way criticising the status, qualification or technical excellence of a Chartered Engineer.  I am, however, making the point that in a commercial world, where time is money, there is no real substitute for a genuine, independent third party check.’

From the detailed facts provided the following have been extracted:

Type of building

 

 

Problem

 

 

Materials involved*

 

new build

12

 

dangerous structures

10

 

steelwork

 

13

 

 

modifications and conversions

 

17

 

design defects

9

 

timber

7

      other 10   masonry 5

 

 

 

 

 

 

concrete

4

 *May be more than one material involved 

 

 

 

Of the 13 steelwork cases 4 were new build and 9 were modifications and conversions whilst of the 4 concrete cases 3 were in foundations. Nine examples were from sole practitioners, 13 were from what are described as small practices, 5 from medium sized practices, and 2 were from ‘top 10’ practices.

Some quotations from the report:

  • New 35m span portal. Secondary moments in bracing connections, out of plane buckling restraint to main stanchions - too far from haunch and missing in some locations, fitted stiffeners designed (in calcs), but not on drawings, un-tied bases adjacent to service trenches

  • Loft conversion. 254 UC section primary beams seated on timber head-plate spreader with only single stud adjacent. No stud continuity to foundation level

  • New school hall. Gable end wall panel unrestrained - vaulted roof. No buttressing or wind posts - remedial work required

  • Timber framed warehouse. Post and beam structure provided with only 50% of required wind bracing

  • New public office building. Load bearing masonry design - 15m square. Engineer shows no buttressing walls or wind posts - inner skin 100mm. Also, no overall designer (as required by BS) - trussed rafter design, bracing details and girder fixings all inadequate

Expert Panel Comments

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These demonstrate that problems can occur whatever the material used and whether or not the designer, or at least the person submitting the scheme, is qualified. This is not the usual view which is that unqualified persons are most likely to get it wrong, and it would be interesting to know how many of these examples had proper checking before submission.

CROSS has previously recommended that calculations have a front sheet giving the fundamentals of the design assumptions and a brief description of the structure so that those who check know what to look for (see SCOSS Biennial Report 16 Appendix C).

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