Gantry Slipform

Bygging-Uddemann has harnessed the power of the innovative gantry slipform method for caisson projects, marking a departure from conventional techniques. Our journey towards excellence in concrete structure production led us to the realization that there exists a more efficient and cost-effective solution, tailor-made for the repetitive demands of caisson manufacturing.

The Gantry Slipform system

At the start of our concrete construction journey we used the standard slipform technique for numerous caisson projects. Over time, as we honed our expertise, we recognized the possibility of a more efficient and economical solution, particularly for repetitive concrete structures like caisson production.

This realization led us to the innovative Gantry Slipform system, which offers versatility in its execution. Whether it’s the onshore fixed gantry slipform, the onshore mobile gantry slipform, or the offshore gantry slipform on a floating dock, we’ve embraced these adaptable setups to revolutionize the construction landscape.

The main features of the Gantry Slipform method are as follows:

  • The slipform is never dismantled and reassembled during the progress of the production.
  • There are no jack tubes in the concrete and the yokes have extra high clearance, which simplifies the installation of rebars and block-outs.
  • The slipform decks are very spacious for good storing facility and best work conditions.
  • The need of cranes for the wall slipforming is very small.
  • Our standard Gantry Slipform System has truss spans of between 18 and 35 meters.

The most important benefits of using the Gantry Slipform method compared to a standard slipform solution for caisson production.

Cost comparison

Standard, or Traditional Slipform, requires a complete slipform assembly and dismantling for each caisson. The Gantry Slipform method on the other hand never has to be dismantled and reassembled during the complete production phase. Bygging-Uddemann used Standard Slipform for all caisson projects during the 60’s and 70’s before we developed the Gantry Slipform method. With the experience from using both types of slipform methods we have learned that the slipform cost for the Gantry Slipform method is the most economical solution on projects with more than approximately 30-35 caissons. See the diagram.

Jack tubes and yokes / differences

Traditional slipform requires continuous installation of jack tubes for the slipform jack to climb on. This operation disturbs the installation of rebar. With the Gantry Slipform method the slipform climbs on solid steel rods completely outside the caisson geometry and never interferes with the rebar installation. The jack rods will also last for the complete project.

Working conditions / material storing facilities

The Gantry Slipform method provides a very spacious working place since it provides two large work decks to operate from (Slipform Deck and Upper deck). The extra working space provides a much safer and effective working area since rebar material can be stocked in advance for distribution before the slipform starts.

Winches instead of construction cranes

There is no need for construction cranes with the Gantry Slipform method since all material is handled by winches supported by the gantry roof structure. The winches can haul material from the concrete lorries at the pick-up area directly into the caisson walls.

Keeping the same caisson geometry throughout the project

To be successful with a standard slipform set-up with many dismantling and reassembly operations its always very important to perform the set-up at assembly exactly the same throughout the project. With all the wear and tear involved with repeated re-assembly it can be difficult after a while to maintain the exact shape of the slipform shutters. The wall thickness can also vary, mostly it widens, which will cause higher concrete consumption.

Safety aspects to consider

Repeated dismantling and assembling always increases the risk for labour accidents with standard slipform. Safety precautions such as safety nets, hand railing, etc., are often neglected in a standard slipform after a couple of re-assemblies. Weather protection is very poor in standard slipform while the Gantry Slipform offers a permanent rain and wind protection which allows uninterrupted work during bad weather.

Summary:

In order to make a complete cost comparison between Gantry Slipform and Traditional Slipform following factors need to be considered regarding standard slipform.

  • Cost for assembly, re-assembly
  • Several cranes and other necessary extra site equipment (vibrators, lightning, etc)
  • Constant adjustments for accurate wall dimensions
  • Extra labour cost for steel fixing and concrete works
  • Final quality of caissons (risk for variation of measurements, wall thickness)
  • Additional work such as recovery of jack tubes and grouting (filling voids with concrete)
  • Labour “comfort” factors
  • Labour safety factors
  • Stops for bad weather conditions

Its our clear opinion, witnessed by many contractors with whom we have performed
caisson projects, that the Gantry Slipform method is superior in projects with repeated
concrete production such as caisson production. Not only in the economical aspect but also with respect to the final quality.

A visualization for which production method of caissons one should be choosing depending on how many caissons are to be produced.

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