With about 60,000 homes required per year to house the current numbers of houseless families in India rapidly growing population, it makes sense that people are turning to precast and prefabrication as a way to meet the demand of the country.
The connection of precast commands on construction sites has always been a difficult challenge due to manufacturing tolerances and the need to transfer loads through the structure; even more so when you factor in a require resilience to a seismic event. Precast components are inherently stiff, so it is essential that the connection components are robust enough to allow the structure to absorb the energy of the earthquake while providing enough robustness to avoid collapse.
State – of – the – Art Technologies
This type of system is traditionally used in the bottom of a column or well as a means to connect on to starter bars protruding from the foundation. Although they might often be designed as a pin connection, the reality is that this will transfer moment from the foundation into the wall or column and should therefore always be made of a ductile material that does not compromise the ductility of the steel reinforcement that it is coupling together. To that end, the coupler should always be of a ‘’bar break ‘’ type where there is a considerable factor of safety between the bar failure and the coupler failure capacities.
Wire Rope Loopboxes
Wire rope loop boxes are prefabricated components with a constant rebate geometry and 1 or 2 high strength wire rope loop. Loop from adjacent elements then overlap during the installation of the panels and are secured using a reinforcing bar and a high early strength grout to complete the connection. Further information about the detailed of these components can be obtained from the author, but it is not part of the scope of this paper.
Shear Dowel System
The shear dowel system is always a challenge as they generally require very tight tolerances to ensure effective load transfer, so system without grout and oversized holes are almost impossible.
But by keeping the grouting to a minimum , one such technology – Invisible Connection – has revolutionised the use of precast all throughout Northern Europe ; it is a patented system, with its origins in Norway, to connect precast concrete without use of corbels or steel angles, and is used extensively throughout Europe due to the independently tested and certified European technical Approval that provides engineers with peace of mind about the capacities .
TSS and RVK for the precast slab to wall connection; TSS where the slab is to be left with an exposed concrete surface finish and RVK where the slab will have a secondary floor covering. For simplicity, we will focus on the TSS version in this paper although further information on the rest of the range is available from the author.
The TSS is cast into the slab and recess is cast into the precast or in-situ poured concrete wall. Additional items are available to ensure that lateral movements in Earthquakes do not result in the unseating of these dowels.
What Is Traditional Technology?
Traditionally, precast slab such as stair landings used to be supported by steel angles bolted to the wall or via a concrete corbel. Installation of angles is slow, requires a high degree of accuracy, ties up the crane with costly hook-time and can only be used on straight walls. The creation of corbels is time-consuming and will only be economically viable in large quantities to ensure adequate reusability of the mold.