4 Levels of Back Propping To Support Compromised Concrete – Brisbane

Problem

A construction company completing a new build in Brisbane City did a crack test on concrete columns that had been poured. Instead of the concrete being at an expected strength of 80MPa, the results showed it was around 40MPa, meaning that the columns were not strong enough and needed to be demolished and formed up again before the client could continue with the rest of the build. This was a major issue for the client, and without quick rectifications, it could have had major impacts on the project schedule.

The columns being formed up again needed to support substantial loads (3220kN and 3849kN), so Shore Hire recommended multiple props and hydraulic pre-loading to maintain the integrity and level of the slab above without deflecting. To add further complexity to the temporary works design, a clearance of 750mm around the columns was also needed so the client could complete the demo and rebuild works.

In order for the client to continue with the build they needed full confidence that Shore Hire’s props could support the loads specified, which we were able to demonstrate through ample technical data and direct liaison with our own and the client’s engineers. Another challenge was that this was happening under the ground floor slab, and extended down to the B4 basement level, meaning that four levels of back propping were required.

Solution

To address the client’s needs, we engineered and installed four levels of our heaviest duty modular prop – the Shore Prop 1000, with five props per column to account for the major loads.

Once we installed all of the propping down to the lowest ground slab, we used our new hydraulic casing units to pre-load the props in the upper levels to the heavy loads specified by the client’s structural engineer. This pre-loading allowed the client to begin their works without risking any movement of the ground floor slab.

In total, 40 Shore Prop 1000s were installed for this project, allowing the client to continue pouring slabs, while the necessary rectification works were completed.

Shore Hire’s innovative solutions and propping design approach allowed the client to carry on with the project safely with minimal impact on their schedule.

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