Project Details
Project: Stair landing back propping for load-bearing masonry demolition
Location: Surry Hills, NSW
Sector: Commercial construction / structural alteration
Client: Buildcorp
Services Provided: Temporary works propping design input, equipment supply, installation
Equipment Used: Legend 50T Modular Propping System, hardwood timber sleepers
Project Overview
Buildcorp engaged Legend Hire to back prop a concrete stair landing at a Surry Hills project so the load-bearing masonry walls beneath it could be demolished. Once those walls were removed, the landing had no load path to ground. Legend Hire established an alternative load path using the Legend 50T Modular Propping System, founded on stacked hardwood timber sleepers to spread bearing pressure across poor, partially excavated ground. The system was assembled by hand in a confined sub-floor space, brought into firm bearing against the landing soffit, and verified before demolition commenced. The masonry was removed with the landing fully supported throughout.
The Challenge
The concrete stair landing was supported by the masonry walls scheduled for demolition. Remove those walls and the landing’s original load path to ground no longer exists. Back propping is the process of installing a temporary support system beneath a structural element to carry its loads before the permanent support is removed, and on this project it had to be in place, bearing correctly and verified, before the first course of brickwork came out.
Three constraints shaped the solution:
- Lost load path. The landing carries its own dead load plus imposed loads from stair traffic. With the masonry gone, every kilonewton of that had to be picked up at the soffit and taken to ground through a temporary system.
- Tight access. The work area beneath the landing was a confined sub-floor space with no route for plant or lifting equipment. Any propping system had to arrive in components a crew could carry in and assemble by hand, in position.
- Poor ground conditions. The prop bases sat over partially excavated, uncompacted material and exposed sandstone, ground with limited and variable bearing capacity. Placing a high-capacity prop directly onto that surface would have concentrated the entire reaction into a small footprint and risked local settlement under load. Settlement under a back prop is not a minor defect; it allows the supported structure to deflect at exactly the point in the works where it has no other support.
Engineering Considerations
Back propping over unprepared ground is a foundation problem as much as a propping problem. The prop itself is straightforward, the question is what receives the load at the bottom. With no slab available, stacked hardwood timber sleepers were used as sole plates beneath each prop base. Sleepers spread the point reaction over a substantially larger footprint, reducing bearing pressure on the ground to a level the material could accept, and provide a levelling and packing layer that lets props be set plumb on an irregular surface.
The Solution
Legend Hire supplied a back propping system built around the Legend 50T Modular Propping System, configured for the landing’s height and the site’s ground conditions.
The 50T system suited the site for two reasons. Its high axial capacity meant a small number of props could carry the landing without a dense grid in an already confined space. And because it is modular, assembled from pinned galvanised steel sections rather than delivered as a fixed-length unit, every component could be carried into the sub-floor area by hand and built up in position. No plant access required. The same characteristic made the system practical on confined-access column removal in Sydney, where poor ground and restricted access ruled out conventional propping.
Stacked hardwood timber sleepers were laid beneath each prop base to act as sole plates, distributing the reaction across the excavated ground and giving a stable, level bearing surface on material that offered neither. The same principle was applied at Hurstville, where hardwood timber sleepers distributed crane outrigger loads into a suspended carpark slab.
Each prop was extended and adjusted at the screw jack head to bear firmly against the underside of the landing, then checked for plumb and bearing contact across the full head plate before the system was released for demolition to proceed.
Installation was coordinated with the Buildcorp site team so that propping, verification and demolition ran in sequence rather than in parallel.
Equipment Used
- Legend 50T Modular Propping System: high-capacity modular steel propping providing the primary vertical load path, hand-assembled in confined access
- Adjustable screw jack heads: fine height adjustment for firm bearing against an irregular existing soffit
- Hardwood timber sleepers: stacked sole plates distributing base reactions across poor ground and providing a level bearing surface
The Outcome
The load-bearing masonry walls were demolished with the concrete stair landing fully supported throughout. The temporary system carried the landing’s loads to ground across unprepared, partially excavated material without measurable settlement at the prop bases, and the works were completed with no structural incident and no unplanned stoppage.