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THE Top Tip – Height Clearances and Road Slopes

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Self-propelled modular transporters (SPMTs) can carry some of the heaviest loads in the world and are widely used to transport bridge sections. In order for a successful and smooth operation involving SPMTs and bridge installations, it is essential to identify any height limitations that could impact the process. Heights that must be considered during a SPMT bridge installation are:

  • • Nominal road level.
    • Actual bridge underside height. The lowest point usually occurs at a crash protection beam or something similar, and not typically the main bridge itself. Check at any rivet or bolt head locations on the bridge underside.
    • Overall height of the transporter and packing. This figure needs to include any timber, plywood shims or packs. Additionally, check for actual physical section sizes, not just nominal dimensions, as well as any bolt heads or lifting eyes.
    • Transporter stroke. Make sure to check on any limits imposed by the PPU(Power Pack Unit) location.

In addition to considerations above, it is important to recognise that roads under bridges are rarely flat. In most cases, the road level is lowered as it approaches a bridge and quite often dips in the middle, as well as the sides (to allow for drainage). Height adjustments will therefore need to be made to accommodate an uneven ground. The slope of the road needs to be considered as every millimetre difference in road level is a millimetre removed from the available transporter stroke. If the dip is too great underneath for the available trailer stroke, then look at filling the dip to return the road level back to within the trailer stroke.