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Newsletter No 22 - April 2011

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Report Overview

Events in Japan and in New Zealand show the cataclysmic consequences of earthquakes on people, infrastructure, and structures. As the world becomes more crowded and complex more of its citizens will be at risk from the effects of extreme occurrences; some natural and some man made. A confidential reporting scheme such as CROSS is not going to be sent information about the aftermath of an earthquake, but the principle of searching for the precursors of larger failures must be relevant. There will be many lessons to be learned from the catastrophes of the last few months and if these can be analysed, stored, disseminated, and particularly if they can be used as reminders, then the severity of the effect of future events may be reduced. In this Newsletter there are two significant reports about the design principles for very tall and unusual buildings and the comments from our panel of experts emphasise the need for proper analytical procedures and the importance of robustness. There are the reports about; falsified documentation, the failure of fixings used to connect a scaffold to a structure, a scaffold which did not meet design criteria, the question of errata in manuals, and once again the design of free standing masonry walls. A SCOSS Alert - Snow loads on agricultural and other building structures (March 2011) has been issued following snowfalls in 2010, and in the early part of 2011, which caused a significant number of agricultural and associated buildings in Scotland, and a small number in the North of England, to partially fail or to collapse. The likely causes include the build-up or drifting of snow on roofs, the age of the buildings, weaknesses in original design or construction, and lack of maintenance. Prolonged periods of snow deposition and very low temperatures were experienced which contributed to snow compaction and increased snow densities. In some cases, snow depths of 50-60cm on roofs have been reported. CROSS needs reports all the time so that lessons can be learned and if you can contribute please do so. Reports are edited to remove names and identifying details and are printed in normal text in the Newsletters. Comments from the panel of experts are printed in green italics. All reports together with comments are on the web site data base.

Overview of Reports in this Newsletter

235 Concern about design principles for tall buildings

A reporter raised questions about very tall and complex reinforced concrete structures that incorporate combined transfer systems some of which may be supported on corner columns. The reporter’s question highlighted a common concern which is that in the case of accidental damage to, or removal of, any key structural element, such structures may not have adequate redundancy to redistribute the loads without collapse.

238 Design of tall asymmetric structures

A reporter has touched on the topic of analysis and design of the structural systems for tall buildings which are asymmetric and may be irregular in plan. These might have a concrete core and an external steel frame with floors spanning between core and frame. Tall buildings which are complex in plan raise interesting issues concerning the methods of analysis that should be used, and there is conjecture that a first order linear analysis may not represent the structure adequately. It has been argued that non-linear geometry effects should be included so as to provide a better representation of the behaviour of the structures.

230 Defective imported scaffold ties

On a contract where multi lift access scaffolds had been installed for a period of up to 18 months in an exposed coastal location, it was found by a reporter on one of the regular inspections that some of the scaffold ties had failed. The ties, including the anchor bolts had been installed in accordance with the scaffold design and load tested in accordance with TG4:04. The anchor bolts had been sourced from a reputable supplier. The failures were first identified when several heads of the screw anchors used for fixings into both concrete and brickwork were found broken off and lying on the scaffolding.

226 Verification of inspection documents

For steel products such as heavy plates, inspection documents/inspection certificates as per EN 10204 represent an important element for ensuring quality control along the different processing stages from the receipt of heavy plates until the finished product.

219 Deficiencies on access scaffold

Investigation by a reporter’s firm into an access scaffold on a refurbishment contract on a city centre site brought to light a number of deficiencies which rendered the scaffold outwith its design parameters. The system was further compromised in that the basic components were a system scaffold, but the various add-ons made it a designed scaffold requiring more careful input and proper calculations prepared by and approved by competent personnel.

211 Check for errata when using manuals

A reporter from an international firm of consulting engineers noticed an alert on a global internal knowledge networks about an errata in an AISC manual.

163 Building control and the design of a free standing wall

A client wanted a garden wall 2m high, and a reporter referred to the OPDM leaflet (see comments below) which states that for the region in question the height of a freestanding wall should be brick 328 mm thick to resist wind loads.