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Newsletter No 20 - October 2010

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Report Overview

The theme of this issue is the need for robustness. The Institution of Structural Engineers Practical guide to structural robustness and disproportionate collapse in buildings to be published in November 2010 will emphasise the importance of this aspect for both design and construction and will be of value to all engineers. Many collapses start with the failure of relatively minor components, such as fixings, and result in disproportionate damage and in risk to life. Achieving robustness is not difficult and usually not expensive but it does require a consideration of what might happen in various circumstances and the risks incurred. For example loads may not be precise, differential movements and secondary effects may produce unexpected stresses, weathering and corrosion may affect hidden components, and one in a series of fixings may fail and trigger a progressive collapse. The good designer, the good builder, and the good regulator need to be always aware of the need for robustness. To make the SCOSS and CROSS programmes as effective as possible reports are needed on a continuing basis - so if you have a concern, or know of an incident that involves structural safety, then please contribute. Details of how to do so are on the CROSS website as are all of the Newsletters. In addition to the confidential reporting facility there is a Feedback section which provides a forum for any subject related to structural safety. Reports are edited to remove names and identifying details and are printed in normal text in the Newsletters. Comments from the panel of experts are printed in green italics. Reports together with comments are on the data base.

Overview of Reports in this Newsletter

220 Architects and construction firm fined after worker falls to his death (news)

An architect's practice and a construction company involved in a development have been fined a total of £195,000 following a fatality on the site. The builder pleaded guilty to breaching Section 3(1) of the Health and Safety at Work etc. Act 1974 for failing to safely manage subcontractors working for it.

210 Design deficiencies in calculations submitted to a Local Authority

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 his area over the last five years within a predominantly rural Council. A third of the projects represent more serious risks to longer term safety.

212 Do Building Regulations apply to repairing a collapsed building?

The building in question is mid 19th century mill with cast iron frames spanning 8.0m at 3.3m centres and jack arch floors. It has three storeys and a roof and is 24m wide by 67m long and was subject to a fire which resulted in the sudden collapse of part of the interior structure.

151 Divided design responsibilities

Having sized the lintels (to support 5m height of blockwork) the firm were then asked by the contractor to confirm the overall stability of the walls. It transpired that the brickwork sub-contractor had taken on a "works package" from the management contractor. The sub contractor had apparently assumed design responsibility for their portion of works such that; wind posts had been sized and located by the wind post company and lintels were to be sized by the lintel company’s advisors (the reporter’s firm). "Overall" responsibility appears to have been apportioned out to individual parties rather than having one structural consultant onboard to pull all the various aspects together.

173 Thermal effects on long span concrete car park beams

While in the Gulf a CROSS correspondent received a report from an engineer in his company who had visited a car park built with a system using long span precast hollow core units. The pattern of cracking in the supporting beams showed that solar radiation was causing the units to bow upwards with the rotation at the ends forcing the supporting reinforced concrete L-beams to crack through friction at the bearing - contact was concrete-to-concrete with no provision for movement. The structure was three years old and had progressively worsened during each summer.

181 Canopy collapse due to snow

During bad weather conditions in the winter of 2009 a school's canopy collapsed. Luckily the school was closed at the time and no pupil or member of staff was injured.

182 Glass panel fixings failure

A double-laminated glass panel measuring approximately 1x1.5m fell from a first floor balcony, striking four people who were standing on the ground floor.

Structural Engineering Failures: Lessons for design by Dr Niall MacAlevey - Book Review

This is a well written book that will appeal to all engineers and especially those who have an interest in failures and collapses. The author has collected examples from the past 100 or so years and summarises, in categories, the failures of 50 bridges and buildings from around the world. The names of some of the projects will be familiar to the more experienced practitioners but not to the younger members of the profession, and the reasons for many of the failures will not be well known.

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