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Newsletter No 19 - July 2010

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Report Overview

BP oil rig disaster – lessons to be learned for the construction industry The dominant issue on safety is of course the disaster in the Gulf of Mexico which has transcended the technical press to become a matter of international concern. It is an extreme example of a low probability incident which has enormous consequences. It is likely to change the way in which such operations are conducted in the future, it will change safety regimes, and it will influence the practice of risk analysis in all engineering disciplines. This is a defining event. The Tay Bridge disaster and other bridge collapses are reminders of the way in which bridge design has changed, Ronan Point changed thinking on robustness, the football stand disasters in the 1960s changed for ever the design of stadia. To learn from past events and to keep that information for future generations of engineers is vital. To pick up pre-cursers of major events and then use proper reporting schemes to generate alerts is a valuable aid to safety. The Swiss Cheese model which is often used to illustrate risk shows that there are usually several influences which coincide to transform a hazard into a failure. It is when deficiencies in Plant, Processes and People coincide that failure occurs. Indeed the application of these three Ps to risk analysis is a SCOSS mantra. Influence of CROSS A primary objective of CROSS is to use data from reports to influence change and a good example is the effect of a report in Newsletter No 18 on unstable concrete bocks. The issue of inferior concrete blocks has been discussed in the relevant BSI Product Standards technical committee and the aggregate block industry has been made aware of the situation. The issue is usually the use of furnace bottom ash as the aggregate (whether of quality assured nature or not) and the limit to proportion of ash used in concrete block mixes. At the moment the BS EN for aggregate masonry units does not limit proportion.

Overview of Reports in this Newsletter

152 Scaffold collapse and slipping clips

These photographs have been sent in by a reporter and show a scaffold that collapsed onto a parking area. Luckily, he says, only 11 vehicles were damaged, and no people were injured.

169 Dangerous modification to a column

A reporter was requested to visit a warehouse to inspect work carried out to a column that was constantly being hit by a fork truck. The Client had commissioned a 'design & build' contractor to remove the lower section of the column and support the higher section out of the path of the forklift with a cantilever.

175 Unsuitable underpinning

The consulting engineer for this site proposed to underpin the party wall to depth of 3.8 metres using 325 mm thick mass concrete. A simple glance at the details showed that there was insufficient vertical load to maintain stability under lateral load from the retained height of soil.

187 Network Rail bridge collapse (news)

A train carrying kerosene, gas oil and diesel, came off the rails south of Stewarton on 27 January 2009. Six of the 10 wagons came off the rails during the incident and some caught fire. Power lines were also brought down and the nearby A735 was closed. It took the emergency services several hours to bring the fire under control.

189 Retaining wall concerns and the stance of a local authority

A reporter was asked by a Client to assess a retaining wall built on their boundary by a neighbour who had erected a new dwelling. Of reinforced concrete block work construction the wall is about 2.75m high at its highest point and retained the Client’s land. From a visual inspection the wall appeared sound. However, a review of the calculations and a typical section, gave serious concern for its strength.

196 Undermining shallow foundations

The problem is a tendency for existing shallow footings to be exposed and possibly undermined during the process of reducing levels for the proposed new floor. This appears to occur more regularly on sites underlain with clay soil where a suspended floor is proposed for the extension.

204 Split responsibilities on temporary bracing of steelwork

A project is supported by numerous steel columns which start at ground floor level. Because of various site constraints, several columns are kinked at upper floor levels; the resulting horizontal forces are taken back to a substantial concrete core through the floor beams or slabs. The second floor slab is post tensioned concrete and the contractor decided to erect the steel first and install the second floor slab later, when the steelwork and concrete subcontractors would not interfere with each other.