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Scoss warns of structural issues in larger building design

NCE stock health and safety

The number of safety critical structural issues in larger building is a growing concern, according to safety body Scoss.

In its latest alert Scoss said that designers were not understanding “scale effects”, leading to specific issues which arise with increasing the size of a structure

Issues arise as clients and designers strive to build “lighter, bigger, taller and longer”.

Scoss said the evidence, although anecdotal, was supported by a “coincidental” Ciria report on design for movement in buildings, which included a number of case studies which provided supportive evidence to those points made in the alert.

In one example it said cracks within connections had arisen from repeated high stresses created by secondary moments at the end of long beams. It went on to add that this example led onto the validity of the modelling of longer span steel structures.

The report said it was aware of cases where very long span beams had been designated as simply supported by principal designers “without any comprehension of the detailing implications beyond specifying a set of loads to the connection designers”.

“Deficiencies become compounded because the longer the span, the higher the end reaction, and the higher the end reaction, the more bolts are required within deep connections,” the report said. “And the more bolts provided in deep connections, the more the connection is likely to behave as a fixed ended member whatever the design team have assumed.”

Scoss also raised issues with taller buildings not seen when designing low rise buildings, such as column elastic shortening and the potential for wind sway dynamic effects. It said “dealing with either of these topics is out with the skill set of many design teams” and suggested a need for caution.

While many of the effects were taken into account by analysis programmes, it said there was “limited experience” over what was an “appropriate” design.

Problems with thermal effects, notional live loads on large roofs, consideration of “whole building effects”, large frame construction and steel thicknesses and welding were also raised in the report.

In conclusion the body recommended that a “far better understanding of large structure performance” was needed.

“There are scale effects across several structural topics because of increases in height, span, and enclosed volume, which might well not be appreciated by the design community,” it said. “All effects cited in this paper have the ability to degrade safety.”

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