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Newsletter No 13 - January 2009

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Report Overview

In December 2008 the highly successful Fourth Forensic Engineering Conference was held at the Institution of Civil Engineers in London. Under the heading ‘from failure to understanding’ there were papers on many different collapses and concerns affecting structural and civil enterprises. Not only are there repetitions of types of failure, often a generation apart, but similar problems occur in different countries. There is great scope for learning lessons from such events but it was noticeable that there is no generally recognised way of categorising collapses and no common form of reporting on failures. The American Society of Civil Engineers has a programme for encouraging the teaching of forensic engineering and some universities in the UK are including modules on the subject. But as SCOSS has found, there is a great need from those in construction at every level for information on failures to be readily available and better ways must be established of disseminating this information. The idea, put forward by CROSS, of a database as a resource for practitioners was well received and will be developed in the coming months. When reports are sent to CROSS they are de-identified and categorised before they are considered by our panel of experts. In some cases reports are held back to find out if the are others of a similar nature so that they can be published at the same time. In some cases SCOSS carries out investigations into matters raised by reporters and until these are complete the reports are not published, and there are several topics that are pending. More reports are always needed and concerns about any structural or related matters will be most welcome and will help others to learn and avoid costly and un-necessary oversights, omissions, or mistakes. There is a report form at the end of this Newsletter.

Overview of Reports in this Newsletter

118 Issues for CDM co-ordinators

The lesson of many failures is that poor detailing and joint failure commonly precipitate serious collapses. These may arise as straightforward structural deficiencies as exemplified by the spectacular failures of the Boulevard de la Concord Bridge in Quebec (2006) or the Minneapolis Bridge (2007), or they may be exacerbated by deficiencies in maintenance or poor design that inhibits the ability to inspect and maintain.

123 Shop/domestic building collapse

The building was a two storey corner (end of terrace) property fronting a very busy, narrow major route in an area which is normally busy with pedestrians and traffic. On the ground floor there was a shop and there was residential accommodation above. Work had been in progress, without Planning or Building Regulations approval, for about a month to create a basement and loft conversion. A Building Control Surveyor visited the property and advised the builder to stop work until the permissions had been resolved. However, work continued.

125 Advice wanted by amateur builder

I am removing a supporting wall between the old exterior of the house and the new 'lean-to' extension. Because the 4-metre lintel will be fitted into the ceiling cavity I can't needle it but will be using 4 strongboys on the outside and 3 acros supporting the ceiling on the inside. I will also have a couple of temporary acros to use directly under the wall. The wall is a concrete block cavity wall.

126 Pre-cast concrete canopies in housing

A reporter wants a warning passed on to those undertaking surveys of houses. He says that pre-cast concrete cantilever canopies which are slender and monolithic with lintels over entrance doorways, particularly those constructed in the 1960's and 70's, can be vulnerable to sudden collapse.

128 House collapse

This is a case of collapse caused by a builder carrying out underpinning works.

132 Design wind loading for tower cranes

A report from a major contractor concerns wind loading on tower cranes.

133 Wind loads during construction

During construction the structure and associated temporary works are subjected to wind loading. This load case is typically short term and BS 6399 Part 2 allows for a reduction in wind speed where the load is of a temporary nature. What is not made clear in the code, but is in the supporting documentation, is that this reduction is based on the expectation that in times of high wind load the structure will not be in use, and therefore the consequence of failure is not severe.

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