The majority of mobile cranes are supplied with standard “as travels” crane outrigger support pads. The total surface area of these pads is less than 1m² / outrigger.
A typical example would be the 900mm diameter Nylacast mat providing 0.64 m² of load spread area.
It is common practice (under BS7121) for Crane Appointed Persons (AP) to be provided with evidence of the ground bearing capacity for the proposed crane hard-standing positions.
Individual company procedures vary. Ultimately, the AP must ensure the imposed crane outrigger loadings will not exceed the hard-standing capabilities. This is to avoid potential outrigger support failure and overturning of the crane.
The typical standard “as travels” mats are often considered by AP’s as being of inadequate area to ensure the ground bearing capacity is not exceeded.
Permissible ground bearing capacities exceeding 40 Tonnes / m² are relatively uncommon. It is often closer to 20 Tonnes / m² or less.
Typical Applied Outrigger Loads (Actual Predicted Type e.g. LICCON)
|Example Crane Size||Typical Outrigger Load||Typical Standard ‘As Travels’ Mats||Pressure Beneath Mats|
|30 Tonne AT Crane||20 Tonnes||760mm Diameter||44.5 Tonnes/m²|
|80 Tonne AT Crane||35 Tonnes||900mm Diameter||54.7 Tonnes/m²|
To reduce the pressure applied beneath the mats to more realistic / achievable levels, the outrigger loadings need to be distributed over a larger crane pad area.
Traditional increased size mats are constructed of either box section steel or large timber sleepers bolted together. Both are very heavy and can be difficult to install / move around on site to alternative crane stand positions. Critically, they can also prove difficult to source to pre-determined dimensions, hindering the process of forward planning for the AP.
To install these mats, the site would often need to provide plant to off-load / install the mats, often without detailed consideration of the method and associated risks (balancing on forklifts, pushing around with excavator buckets etc). Alternatively, the mobile crane may need to short rig and install its own additional mats on short rigged duties, temporarily using the “standard” outrigger support mats and risking overloading the hard-standing.
ALIMATS, the number one choice for Crane Outrigger Mats across the UK
The ALIMATS system is a purpose designed / engineered product, specifically developed to spread outrigger loadings from mobile cranes and other site plant.
It is a unique modular interlocking system, with each individual module measuring 1740 x 580 x 60mm (1.0m²) and weighing 38kg. Three interlocked modules form the base layer, and two interlocked modules placed on top at 90º to those beneath complete the 3.0m² pad. Five modules / 3.0m² pad, 20 modules per crane.
ALIMATS offer unique benefits and are exclusively manufactured by Brilliant Ideas Ltd.
- Strong – Purpose designed interlocking multi-mat system with a 500 tonnes / m² compressive design strength, backed up by physical testing and Finite Element Analysis demonstrating its capabilities in the fully rigged application.
- Significant reduction of applied pressure onto hardstands / reduced crane hardstand bearing capacity requirement (Could save significant ground-works costs associated with improving the bearing capacity to suit “standard” construction plant mats).
- Not reliant on additional site plant to move / set up on site.
- Ease of site set up – 38kg / module. Easily hand lifted into position by two people, ideal for multi stand operations.
- No need for mobile cranes to short rig to lift / place its own increased size mats. This is often not addressed on the Lift Plan / should be considered to avoid increased pressures exerted in the temporary short rigged state.
- Safety textured finish – Aids purchase at mat interface and between the ALIMATS layers.
Summary of Reduced Pressure Beneath Mats Using ALIMATS
|Example Crane Size||Typical Outrigger Load||Applied Pressure Using Typical Standard ‘As Travel’ Mats||Applied Pressure Using Alimats|
|30 Tonne AT Crane||20 Tonnes||44.5 Tonnes/m²||6.7 Tonnes/m²|
|80 Tonne AT Crane||35 Tonnes||54.7 Tonnes/m²||11.7 Tonnes/m²|