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Newsletter No 5 - February 2007

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Report Overview

It is over a year since the first Newsletter was published and more than 60 reports have been given covering over 20 topics. This issue has reports on Responsibility for change, Balconies and balustrades, Hidden corrosion leading to failure, Timber frames, and Grades of steelwork. These represent a wide range of concerns that have affected structures and give experiences from which other engineers can benefit. SCOSS (the Standing Committee on Structural Safety) will publish its biennial report in early summer 2007 which will contain an analysis of the reports so far and give recommendations for actions that may be taken to make best use of the information gathered. During the year CROSS plans to increase the number of reports made by contractors, and the engineers who work for them, to extend the applications of the scheme. In December 2006 there was an International Symposium in London on Confidential Reporting Systems with representatives from schemes in Health Care, Aviation and Railways. CROSS is unique in that there are no other systems that deal with structures. The longest running scheme is ASRS (http://asrs.arc.nasa.gov) which has been run by NASA for the last 30 years and has received 750,000 reports on matters of aviation safety in the USA. After a slow start the number of reports climbed steadily and the scheme has become a major influence on the aviation industry worldwide. Key features of ASRS are to: be non-judgmental and promote an attitude that things can be fixed, be seen by all sides of the industry as an honest broker, have stakeholder participation to provide advice and guidance, analyse and evaluate the subject matter and provide feed back. It has been established that people are willing to share information if they are assured that their identities are protected and there are no disciplinary or legal consequences. CROSS is modelled on CHIRP (www.chirp.co.uk), the UK aviation and maritime system which is closely related to ASRS and NASA, and thus has a distinguished pedigree. We have a long way to go to approach the success of these schemes so more reports are needed both on topics already covered and on new topics.

Overview of Reports in this Newsletter

50 Responsibility for change

During the construction of two three storey blocks of flats with masonry walls and pre-cast concrete floors, the contractor requested that he be allowed to substitute an alternative make of steel lintels for those specified by the structural engineer. This was agreed and a change order was issued.

51 Stability of timber frame construction

When checking calculations an engineer has noted that a common defect appears to be related to the design for overall stability. Stability is provided by timber framed racking walls sheathed in OSB (Orientated Strand Board) providing in plane resistance to lateral loading. Often the presence of large numbers of doors and windows means that external walls have insufficient racking resistance to provide overall stability on their own.

61 Balustrades in public buildings

A reporter had a concern regarding a timber balustrade in a showroom. It was only 900mm high made out of 50mm x 100mm timber framing screwed down to the 38mm chipboard floor of a mezzanine. The reporter had told the owner on many occasions that the balustrade was totally inadequate but no action was taken until Building Control officers agreed to tell the building owner to make modifications to improve the balustrade.

62 Timber truss

The reporter has been dealing with an application where the engineer involved discovered proprietary timber girder trusses 400mm deep and spanning 7.5m @ 1.2m centres with glued joints. Some of these joints have come loose.

63 Facade failure

The building in this report is a church built as a composite masonry structure with granite cladding on the front façade.

69 Unstable building due to modification work

A SCOTCROSS report relates to an old 4 storey building undergoing modifications.

43 Grades of steelwork

A reporter says that engineers seem reluctant to specify the grade of steel. Even when prompted, some fail to request anything other than just S275 – failing to mention JR, J0, or other grades.

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