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Beresford’s

The largest precast concrete installation specialist in the UK

ALIMATS®

Interlocking Aluminium Crane Mats & Outrigger Pads

Hole Covers

Temporary Safety Hole Covers for Construction

Instant Pipe Shutter

Alternative Shuttering Method

Levelling Shims

Stacker Packers, our engineered levelling shim with a high compressive strength

Pole Driller

Safe, fast and cost-effective drilling

Safety Net Recovery System

Construction’s Fastest Inflatable System

Shutter Clip

Permanent shuttering solution for hollowcore unit ends

SLAPP Clamp

The safe lightweight block moving system

BI Ainscough Crane (2)

January 10, 2022

Outrigger Materials and Performance – Finite Element Analysis

Most outrigger mat materials perform well under compression load but to perform as intended the tensile strength of an outrigger mat is also critical. The suitability of the outrigger mat used is determined by:

• The size of the mat being suitable to distribute the load to the ground at a stress level less than the ground bearing capacity
• The strength and integrity of the mat and its ability to evenly distribute the load exerted by the outrigger

We’ve recently carried out a simple point load test utilising Finite Element Analysis software on several mat modules capable of being manually handled, to compare the stiffness and load bearing capability of the various materials.

Here’s what we tested:

MaterialBeam SpanPoint LoadMax Deflection
ALIMATS® (Aluminium)1.5m10T24mm
Single Sleepers (Timber) D40 Oak1.5m10T88mm
Ultra-High-Molecular-Weight Polyethylene (Plastic) UHMW-PE1.5m10T972mm

The tests showed the amount of deflection and stress build up within each mat material, with startlingly different results when it came to deflection. Deflection or ability to adjust to the ground has both benefits and disadvantages so selecting the right type of material for the job is critical.

It’s clear from our research that some manufacturers and distributors of outrigger mats are promoting the compressive strength of the material, even though all outrigger mat materials have high compressive strength. A far better question to ask is: ‘are they capable of safely spreading the outrigger load horizontally before distribution to the ground? Which is related to the stiffness of the material.

We don’t understand how we’re in an industry where in many cases an outrigger mat area is calculated above all else, while their make-up is largely ignored – especially when you consider different materials perform very differently. This doesn’t happen within other design procedures, for example, a beam size is designed in tandem with the material.

We believe that going forward outrigger mat manufacturers and distributors, including ourselves, declare a Safe Work Load (SWL) for each configuration. We have already done this on a handful of our configurations and plan on completing this project next year across our range. In our opinion, the only way to do this is via Finite Element Analysis, as physical testing would not be viable on full outrigger configurations. But for this process to be credible, it has to be visible to designers, therefore transparency of design assumptions are essential. This point is extremely pertinent to the UHMW-PE system, as it promotes a higher SWL as the mat area increases, which defies Physics.

By adopting the SWL approach, when the outrigger load is calculated along with the outrigger mat area, selecting a suitable outrigger system would thereafter be seamless, with available Safe Working Loads from outrigger mat manufacturers.

To view and download our specifications and drawings for cranes and MEWPS, please click here – or contact us to find out more about our FEA testing – we’re happy to share.

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