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Newsletter No 38 - April 2015
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Report Overview
Over half of the reports to CROSS are about events on site and this Newsletter has just that, with five of the eight featured reports describing issues that occurred during construction. Two are about design concerns and the other relates to an issue found in service. Sites can be dangerous and one of the reports is about a fatality that occurred outside the UK, but could happen anywhere, when a brickwork wall fell because some scaffold planks were leant against it. Another describes how an arrangement of precast slabs covering a shaft fell without warning due to a problem with reinforcement. A swimming pool roof fell when fixings, which were inadequate to start with, failed. Fixing failures are common and clearly not enough attention is paid to their selection, installation, or testing. Other reports are of bolt failures due to hydrogen embrittlement and stud failures through the use of unsuitable components. On the design front a report expresses another familiar concern which is that the outputs of computer analysis are not always correctly applied to the subsequently selected members of frames. Whilst some themes are recurrent the cases are always slightly different which demonstrates the need for constant awareness, continuing engagement at every level, and learning lessons from experience. Published reports are on the web site data base, along with others, which can be used as resource for learning from the experiences of others. As ever thanks are due to those who submit reports and the volunteer experts on the CROSS panel who review them. 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
505 Precast Concrete Cover Slab to Circular Shaft
The cover slab for a storage shaft was designed as an interlocking arrangement of seven precast concrete slabs with half joints between the individual units. When the slabs arrived on site they were lifted into place but approximately 10 minutes after the last slab had been placed, five of them collapsed into the shaft.
499 Failure of high strength studs
A reporter’s firm specified the use of M12 grade 8.8 threaded studs that were to be located in a tapped web of a parallel flange channel. The installation proceeded normally and the nuts were not over tightened. The firm then received reports that many of the studs were snapping overnight with the outer nuts falling onto the floor.
490 Bolt failures due to hydrogen embrittlement
A reporter recalls that in the 1970s he was working on bridge refurbishment project where a number of new, zinc electro-plated, bolts failed suddenly, often shortly after installation.
372 Understanding the difference between analysis and design
A reporter is becoming increasingly concerned about design practice and correct understanding of the difference between analysis and design and the linking of the two.
426 Swimming pool ceiling partial collapse
Part of a ceiling above a swimming pool collapsed, injuring 4 people. The ceiling was a double skin plasterboard false ceiling, supported off hangars which were screwed into timber joists above. The ceiling had been installed approximately 12 years previously, and showed no signs of distress before collapse.
476 Cantilevered brickwork - fatal collapse during construction
A blade of 270mm cavity brickwork in a temporary condition fell and killed a bricklayer after sixteen scaffold planks were leant against the wall on the side remote from the bricklayer.
448 Stability of terraced buildings
A reporter is concerned about a terrace of four buildings the third of which is being opened up. Two of the others have no cross walls on the ground floor and he notes that the spine wall in the last building has also been removed.
475 Backfilled cantilever brick wall
A 230mm cantilevered brick wall approx 1.6m high was built approximately 300 to 400 mm in front of a rock face. The space between the wall and rock face was backfilled (which was not the design intent) and it pushed the wall over.
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