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906 Missing punching shear reinforcement

Report ID: 906

Published: Newsletter 58 - April 2020

Report Overview

Two separate engineers observed the omission of design punching shear reinforcement prior to slab pours on site.

Report Content

A reviewer for a professional membership institution was concerned to note that two candidates they recently interviewed reported an experience where, as a structural engineer monitoring the progress of their projects on site, they had observed the omission of design punching shear reinforcement in a slab pour about to take place.

Given that these two candidates were from different companies with different project experiences, the reporter feels it is worth reporting this in case it is a trend. One of the candidates was particularly experienced having visited many sites and said that omission of punching shear reinforcement is a 'watch-it' item within their team.

Comments

Issues about shear reinforcement in slabs, particularly flat slabs, have been around for many years and were highlighted by the failure of the Pipers Row Car Park. This multi-storey structure was built in 1965 and a 120-tonne section of the top floor collapsed during the night of 20th March 1997. An initial punching shear failure developed into a progressive collapse.

Designers should know that the critical connection on any flat slab is the shear resistance around its supports. Part of a structural engineer’s skill set is to know what to look for and to create a structure that is capable of being strong enough even before starting calculations. These skills are only acquired by practice (under supervision).

However, as such reinforcement is a critical factor in the safety of flat slabs, the importance of it being in place should be known to constructors and supervisors.

Designers of flat slabs should make it their business to conduct site inspections, or have them conducted, before concreting.

 

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Images

Pipers Row car park collapse; Attribution: Jonathan Wood, Pipers Row Car Park, Wolverhampton, Quantitative Study of the Causes of the Partial Collapse on 20th March 1997



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