New Construction Technique To Build Concrete Shells
Have you seen how a domed concrete structure is built?
If there aren’t many structures with concrete domes that you see in your community, it’s because it’s difficult, tedious, and time-consuming to build. Concrete dome construction usually demands a wooden structure or form work that would support and hold the concrete firmly in place during the hardening period.
New Dome Construction Technique
A new system has been devised by the scientists at the Vienna University of Technology – one which allows concrete shell structures to be “inflated” and girded together using a steel cable. The new system or technique is called the “pneumatic wedge method” or “balloon method” which is likened to peeling an orange and lying its skin flat on a table. Only it’s in reverse – starting with a flat surface and then bending it to a shell. This technique does not require any expensive support structures which is often the reason why builders stay away from dome-shaped structures or large concrete shells.
How It Works
Laid out alongside each other on the ground are a number of flat rebar placed on top of a plastic air cushion – deflated, where concrete will be poured and allowed to harden. What results is a series of flat concrete slabs which will be attached with steel cable and metal beams, to link them together.
Inflated Air Cushion Creates Dome-Shaped Structure
When the concrete becomes hard, the deflated air cushion will be inflated. As air fills it, the slabs are lifted up from the ground at the center and pushed together from outside, causing them to bend in order to take the shape of the dome and form a sustainable concrete shell. The steel cable is tightened around the concrete segments in order to snug the slabs in against one another. The connecting metal beams ensure that they are following one movement. The slabs will then have edges in wedge-shape that cause them to interlock securely with the slab next to them.
Getting The Right Geometric Shape Is Critical
When the dome shell is lifted up, the inflated air cushion will be allowed to deflate and gradually be removed, including the beams and steel cables. The hardened concrete will have some cracks resulting from the bending while the air cushion is being inflated. But said cracks don’t affect the structure’s stability because each concrete segment holds the others in place if the right geometric shape is achieved. This observation came from Prof. Johann Kollegger, the project co-leader. The final step is applying a layer of plaster to cover the entire dome to add more strength and to hide those tiny cracks.
Savings On Time, Materials And Construction Costs
A test was done on the new dome construction system and results showed that a 2.9 meter high concrete dome took approximately two hours to build. Kollegger said that constructing shells measuring up to 50 meters in height should be doable. This new technique once perfected should significantly reduce the costs of constructing domed buildings by half, not to mention the savings in time and materials. The new construction technique also renders timber structures obsolete so it’s a good environmental attribute. The construction technique also eliminated the need for stud bolts to fasten the studs forming the support for the concrete dome.
A trial design has been commissioned by the Austrian Federal Railways for a wildlife overpass using this new construction technique.
Will this new technique start a new trend in dome-shaped structures?