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HeavyTorque Issue 1 - ESTA and The Heavies



A special Europe-wide working group of heavy transport and engineering experts is developing a new best practice guide for the operation of self-propelled modular trailers, or SPMTs, in a move to raise safety standards and reduce the number of accidents.

The work is being organised by ESTA – the European association of abnormal road transport and mobile cranes. ESTA created the working group following concerns expressed by a number of clients just over two years ago. They were worried that some SPMT loads had tipped over, even though the existing operating rules and stability calculations had been precisely followed. ESTA – whose members include the UK’s Heavy Transport Association and the Construction Plant-hire Association – has also commissioned the consultancy Euro-Rigging to develop a common mathematical model that could be used throughout the industry and that would better take into account the full range of forces affecting an SPMT and its load.

David Collett, ESTA president and managing director of Collett & Sons, said: “The work is presenting us with some new considerations and new ways of looking at operating SPMTs. We will see the final outcome later in the New Year. We have been working on this for a couple of years now and it is really challenging the way we have done things in the past.” He added: “ESTA’s approach is to improve safety at all levels. We are aware that there have been accidents involving SPMTs and we need to understand how they have come about, and improve the working practices that we have. “Currently, there is no best practice guide. The work is on-going, and we are attempting to formalise a way forward.”

Collett stressed that the final report would not cover every eventuality: “We are not aiming to produce a recipe book for every circumstance, but a starting point. “The purpose is to produce a baseline from which to codify how to use SPMTs, but when you need to go beyond that baseline, to carry out a more difficult or complex project then, a more detailed engineering solution will be required.”

Collett also emphasised the importance of the work to ESTA, its members and their clients. “When an accident happens the fall-out can be monstrous.” Of course, there is the issue of personal safety, and that is terrible. And on top of that, a whole project can be threatened and the consequential losses can be huge. “At the same time, in some markets an increasing amount of work is being done by SPMTs, they are becoming the norm, and yet there are no guidelines at all. Nothing currently exists, and that is what we are addressing.”

The working group involves senior engineers and representatives leading user companies, manufacturers and clients. Members include Collett, Fagioli, Goldhofer, Kamag, Mammoet, RDW (the Dutch Department of Road Transport), Sarens, Scheuerle, Shell, Wagenborg Nedlift and The Works International.

Euro-Rigging’s senior lead engineer Andre van der Steen, said that an important part of the project involved adopting a full three-dimensional approach, taking into account all of the forces affecting an SPMT’s stability. This means paying particular attention to the elasticity or stiffness of the system and the progressive effects of trailer deformations. Van der Steen said: “The most important stiffness is the surface or the soil you are driving on – perhaps a roll-on, roll-off ramp, for example.

“The second is the stiffness of the tyres. Roughly half of the total stiffness is generated by the stiffness of the tyres.” Oil and hydraulic pressures are also important, along with other forces such as external wind loadings, of course. So there are a great many forces involved.” He added that monitoring the complete route to be taken was essential. “Speed can affect the capacity of the trailer, and you can decrease speed for areas of softer soil.” Van der Steen stressed that although the work is based on complex mathematical models, the aim is to produce simple guidelines that will be practical and easy to use.

“With an SPMT trailer there are the same amount of “elasticity related” variables as for a crane. Yet there are currently no load charts for trailers.” ESTA president David Collett concluded: “This is the most expensive piece of work ESTA has ever carried out and we want to spread it as far and wide as possible.”

Main image: ESTA wants to make sure every job goes as well as this one. Sarens’ award-winning movement of the famous Pippi Longstocking house in Muiden.


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