Project: Mobile crane back propping on suspended slab
Location: Sydney, NSW
Sector: Residential construction / remediation
Services Provided: Temporary works engineering, equipment hire, installation support
Equipment Used: Legend Titan Props, concrete footing pads
Duration: Long-term (extended hire)
Project Overview
Our client, a Sydney contractor required a long-duration back propping solution to safely operate a small mobile crane on a suspended concrete slab. Without temporary support, the slab’s load capacity could not accommodate the crane’s point loads. Legend Hire engineered a back propping system using Legend Titan Props bearing onto purpose-poured concrete footings excavated to rock. The system transferred crane loads through the slab into stable ground, allowing the crane to operate safely above for the duration of the works.
The Challenge
The client needed to position and operate a small mobile crane on a suspended concrete slab, a structure not originally designed to carry concentrated crane loads. Several constraints shaped the brief:
- Load transfer risk: the suspended slab could not safely carry the crane’s point loads without temporary structural support below.
- Poor ground conditions: the bearing layer beneath the slab was unsuitable for direct propping. Soft fill required excavation down to rock before any load could be transferred.
- Long-duration requirement: the props were needed for an extended period, meaning the solution had to be cost-effective over time, not just for a single lift.
- Site access: restricted working space typical of an established residential site.
The Solution
Legend Hire’s engineering team designed a back propping arrangement to transfer crane loads from the suspended slab through to a stable bearing layer:
- Excavation to rock: the area beneath the slab was excavated down to competent rock to establish a sound founding level.
- Concrete footings poured: purpose-sized concrete pads were poured on rock to act as bearing footings for each prop, distributing load and preventing differential settlement.
- Titan Props installed: Legend Titan Props were positioned evenly beneath the slab, spaced to suit the design load and span. Titan Props were selected for their high working load capacity (up to 128 kN), suitability for long-duration hire, and adjustability to the slab soffit.
- Load path verified: the propping layout was engineered so loads from the crane above transfer through the slab, into the props, and down through the concrete footings to rock.
The result is a complete, engineered load path from crane → slab → props → footings → rock.
Equipment Used
- Legend Titan Props: heavy-duty adjustable steel props rated to 128 kN working load, suited to long-term suspended slab support.
- Cast-in-place concrete footings: engineered bearing pads founded on rock to eliminate settlement risk.