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Newsletter No 21 - January 2011

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Report Overview

CROSS is very pleased to announce that the Highways Agency has implemented Confidential Safety Reporting in its procedures in Interim Advice Note 136/10 (see page 2). This relates to structures of any kind on the Highways Agency Motorways and Trunk Road Network and is an important step in the development of the scheme. SCOSS has recently issued two alerts: the first is Timber framed buildings in fire situations: the role of the designer following a number of severe fires in timber framed buildings during construction. The second is: Temporary structures: Saddlespan type tents which highlights the need for adequate engineering input for specialised temporary structures. In this issue are more reports on serious concerns that have been sent to CROSS and from which lessons can be learned by the engineering community. The first is the fall of part of a bridge due to the use of the wrong type of bolts and is another example of the importance of choosing the right fixings. The second is about the deflections caused by pouring concrete onto permanent metal decking which can affect the safety factors of primary and secondary beams and connections. There are then three reports on defects during construction which were caused by ignorance or negligence and were spotted by engineers on site. How many defects are not seen or are ignored and result in lowered levels of safety or serviceability? Internet search engines offer a huge resource for finding out about any subject and when directed towards building collapses they find a daily catalogue of disasters often with a death toll attached. These are mainly from areas of the world where there are limited controls on building, many of the structures have not been properly designed or constructed, and defective materials may have been incorporated. Vigilance is required everywhere and ways of publicising concerns are a way of maintaining and bolstering standards. CROSS needs reports all the time so that lessons can be learned and if you can contribute please do so.

Overview of Reports in this Newsletter

205 Role of approved inspectors

A reporter’s firm is involved in a partially built project, worth £6m, where there is defective work and the builder has gone into liquidation. The project is 2-3 storey building in the health care sector and has load-bearing masonry walls and floors spans of up to 9m. The reporter and the client have sought the information that they would normally expect be lodged with the Approved Inspector concerning the structural design.

209 Risk in notching timber studs

During the construction of a block for student accommodation a reporter found a couple of locations on an external 4th floor wall where the load-bearing studs had been notched well past permissible depths.

214 Need for licensed builders

Certain building operation should only be carried out by licensed qualified builders says a reporter. He believes that the creation of a basement below an existing building is far too complicated and dangerous for the incompetent operatives that abound in this industry.

215 Permanent formwork to slabs

The advantage of permanent formwork to slabs is that it can remove the need for temporary falsework and formwork. However, designers of structural frames usually leave the specification of the sheeting to the contractor and do not specify what propping is required when the concrete is placed. In turn, the people responsible for procurement within the contractor go out for quotes to specialist suppliers of the sheeting. The suppliers typically do not know the deflections of the steel frame under dead load so assume zero deflection and specify sheets over one, two or three spans.

216 Fall of bridge deck support due to bolt over-tightening

A 7 tonne steel frame designed to temporarily support part of a bridge deck during bearing refurbishments work fell from height as it was about to be lowered some 21m to the ground. An operative who was standing on the frame at the time of the dangerous occurrence suffered minor injuries, inflicted by his safety harness as it arrested his fall.

217 Defect on site deliberately covered up

The site level had to be raised which allowed reinforced concrete pile caps and ground beams to be constructed above ground level. At one end the formwork was struck within a couple of days and fill immediately placed to form the founding layer for the ground slab. During the compaction of the fill, which was done by a subcontractor, part of the ground beam was damaged by a roller.

223 River Crane bridge failure (news)

During the evening of Saturday 14 November 2009, the foundations of a Victorian bridge carrying the railway over the River Crane in West London failed without warning, causing part of the bridge to subside. A total of 21 trains crossed the failing bridge between the first report and closure of the line.