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Newsletter No 30 - April 2013

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Report Overview

This issue concentrates on competency and on issues identified on site. Statistics are collected from reports and one category is the stage of a project when a concern is identified. As shown in the pie chart almost a half of all events, 44%, are related to construction (34%) and temporary works (10%), with design accounting for 13%, and normal operations i.e. building or structure in use, 34%. Maintenance operations amount to 5% of the total and there are a few other minor categories. Lack of competency is reported to be a major reason for most of the safety-critical matters described below. It is very satisfactory to note that there is now a backlog of reports awaiting publication and in order to control this some reports will in future be added directly to the data base after anonymising rather than being included in Newsletters. Reporters will be told if this is to happen and lists will be given in Newsletters. All reports, together with expert comment from our panel of volunteers, are on the data base which is freely searchable. The growth of the CROSS programme depends on receiving reports and individuals and firms are encouraged to participate by sending concerns in confidence to structural-safety.

Overview of Reports in this Newsletter

297 New basements beneath existing properties

A reporter is concerned about the construction of some basements in London. He has reviewed two projects covering basement works in relation to Building Regulation checks on the structural aspects.

317 Chain hoist problem

A number of brand new proprietary hoists were being used during the progressive demolition of a gas holder says a reporter. One, a 20 tonne hand chain block was left under load over a weekend and afterwards one strand of the 6 strands of chain was found to be broken.

324 Lack of experience on steel column erection

Geometric constraints required that some column baseplates used a 2-bolt solution with the bolts located between the flanges of the UC sections. Notes on the drawings identified a temporary stability issue and said that the columns required propping until fully grouted. Several requests were made to the contractor to provide a method statement for erection but this was not provided and the reporter only noticed via a project webcam that the works had started.

327 Erecting reinforcement cages

A reporter asks about best practice guidance for the installation of pre-assembled reinforcement cages, as he can find very little guidance on the web.

357 Wall reinforcement cages collapse

A contractor says that he has experienced two cases of wall reinforcement cages collapsing.

315 Telecommunications towers and resin anchors

A telecommunications tower was held down by resin anchors which apparently passed their pull-out tests but failed 6 years later with little resistance in light winds. Although the prime cause of collapse was poor workmanship, there are many other issues.

321 Correct uses of concrete spacers

Concrete strip spacers are increasingly being used to support the bottom reinforcement in slabs says a reporter. They come in a variety of sizes to suit the required cover and generally are 1m in length. However if used incorrectly they can act as crack inducers. The problem, which is believed to be widespread, arises if when they are laid end to end in a continuous unbroken line and form a discontinuity in the structure.

359 Boom MEPW falls through precast planks

A high injury potential near-miss (near hit) incident occurred when a boom MEPW fell through such a floor at a point where there was a notched precast plank. The plank failed because of installation and quality errors which could potentially have resulted in the MEWP and operator falling through multiple floors of the structure.