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AUS-1 Set-up of temporary works

Report ID: 797

Published: CROSS-AUS Newsletter 2 - July 2019

Report Overview

A correspondent was called onto site after the formwork for a slab collapsed during construction.

Report Content

A reporter who does inspections of temporary works was called onto site after a formwork collapse as the main builder required confirmation that it was safe to clear the collapsed portion.

The formwork contractor was setting up formwork for a slab using a proprietary system with main props supporting the ends of timber primary beams; timber secondary beams are then laid out on top of the primary beams before the deck is sheeted.

The correct procedure is to ensure that intermediate propping to the primary beams is in place before any additional loading is applied. In this event, it appears that the team doing the sheeting on top was unaware that the primary beams were not propped at mid-span.

The clear single span of the primary beam was over 4.0m (beam length was 4.9m). The workers were pushing a pallet of ply (at least 1 tonne) over the unpropped beam which snapped in two. At mid-span the bending moment would have been about 10kNm v/s 5kNm working capacity for the beam. The two workers pushing the pallet suffered serious injuries. Fortunately, no one was under that area at the time of collapse.

The reporter has since seen on other sites similar situations where a clear span of timber beams in excess of 3m occurs with the deck fully sheeted. Normally the form worker will give the all clear before the deck is loaded with construction material. In this case, the incident happened while it was still being constructed.

The reporter stresses that end users must be fully aware of any limitations when using proprietary systems as the member properties may be very different from conventional materials.

 

Comments

This report highlights the need for clear communication, consultation and co-operation between all parties involved in construction.

Pressure on contractors and sub-contractors for productivity can lead to short cuts being taken. Whilst the formwork sub-contractor may be tempted to put all his labour into getting the deck laid out to enable steel fixing to commence, and then redeploy that labour to install the intermediate props, the structural limitations of the system in the semi complete stage need to be recognised.

The project specification must cover the formwork standards as set out in AS 3610 and when a proprietary system is being used, the system supplier should have a documented installation methodology; and installers need to be inducted into that methodology and the limitations of the system during installation.

It is helpful if there is a nominated person on site (for example, the temporary works co-ordinator) who is responsible for supervising temporary works to ensure safe performance of those works.

 

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