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Newsletter No 41 - January 2016
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Report Overview
A report last year was about high local winds in a city centre causing damage to temporary works. This generated interest in the SCOSS Committee so an Alert: Wind Adjacent to Tall Buildings was published in December 2015. Although the Alert was prompted by concerns regarding the design of temporary structures, it is noted that wind around tall buildings can lead to unpleasant, and sometimes dangerous, conditions for pedestrians. Aggregating a number of reports, whether they are on matters sent confidentially to CROSS or from other material, to produce a SCOSS Alert is part of the Structural-Safety system. Ian Fleming wrote: “Mr Bond, they have a saying in Chicago: 'Once is happenstance. Twice is coincidence. The third time it's enemy action'.” At Structural-Safety the third time means that an Alert may be needed. The first report in this edition is about a near miss involving pre- cast and in-situ concrete from which a number of lessons can be learned. After the next article on wind problems there is a case about defects during construction and the relationship between an engineer and a client. Then comes an example of the problems that can arise at the interface between steelwork and concrete encasement. Moving on to demolition a reporter voices concerns about flat slab structures when unexpected shear failure adjacent of a column can precipitate general failure. Another has concerns on the way in which a mansafe system was designed without recognition of structural principles and which was found during a third party review. Finally a building control officer found a bug in a proprietary software programme. The success 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
529 Risks from off-site manufacture and hybrid construction
A reporter was recently investigating a ‘near miss’ involving concrete construction in which pre-cast and in-situ concrete were used in combination. This type of construction offers efficiencies and, as in this instance, can reduce the number of man-hours worked at height. It is growing in popularity. It does however bring its own risks, and these need to be understood. The works under investigation comprised a circular shaft 20m in diameter and 20m deep, which required an L-shaped shelf or balcony some 5m from the top.
506 Wind problem in city centre
A reporter is dealing with temporary works for sub-contractors working in and around the centre of a major city. He has experienced a spate of wind related incidents where structures which have been designed in accordance with normal practice using current codes have suffered damage and he feels that there is an issue which needs to be investigated and discussed so that Engineers dealing with structures in the vicinity of tall buildings and groups of tall buildings are fully informed.
515 Roof constructed without structural input
A reporter wants to highlight the problem of builders working off plans provided by an architect or surveyor and assuming that section sizes shown on drawings actually work.
517 Flaws with partial encasements around steel columns
A structural assessment found that steel columns encased in concrete to mid-storey height were heavily corroded directly above the top of the encasements.
523 Shear failure during demolition
A number of buildings being demolished ‘top-down’ have suffered from partial collapse during demolition, says a reporter.
527 Wrongly designed safety system
A reporter is a checking engineer for the client on a tall building. If tenants of the building wish to make structural alterations, they are obliged to send the reporter the details of the proposed changes and he reviews the effect on the main structure. One tenant introduced a stair between two floors. This meant that there was a double-height section of facade to keep clean adjacent to the stair, and so a "mansafe" system was proposed.
538 Failure to check designs produced by software
A reporter works as a Building Control Officer and recently checked some block work wall calculations for a new office building that had been undertaken using proprietary design software. He noticed a regular error appearing that returned a value of zero for the effective plan area when performing the check for the minimum area required.
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