What Is The Principle Of Prestressing Tension?
Prestressed tensioning is to add tension in advance in the component so that the prestressed component bears the compressive stress, and then causes a certain deformation to cope with the load on the structure itself, including the load of the component’s own weight and wind load, snow load, earthquake load, etc. Generally, steel strands, tensioning jacks, anchor plates, and wedges are used for tensioning.
The prestress adopts the two-end symmetrical simultaneous tensioning, tensioning force, and elongation dual control method and the lifting and pressing of the jacks at both ends, line drawing, elongation measurement, and pad insertion are carried out together. After the jack is in place, first fill the main cylinder with a little oil to make it tight, so that the prestressed steel strand is stretched straight. When the steel strand reaches the specified initial stress σ0, stop the machine to measure the original gap and draw a line as a mark.
The tension sequence of the steel strand is calculated and determined based on the following factors: one is to avoid excessively large eccentric stress on the cross-section of the member during tension, no tensile stress is generated at the edge of the concrete, and the other is to calculate and compare the batch prestressing force. The third is to minimize the excessive loading of the beam body to prevent the beam body from cracking or serious deformation. After comprehensive comparison, the two-stage force transmission anchoring method is used for tensioning, that is, the T beam concrete strength is up to After 90%, the first stretch the N1-N4 steel strands anchored to the beam end, grouting the channels of the 4 steel strands, and then store the beams. In order to reduce the creep rate of the T beam, anchor the beam on the top of the beam. The N5-N7 steel strand is stretched and grouted before the beam is erected, and then the beam is erected.
Another advantage of using the two-stretching process is first to stretch a part of the steel strands, apply a lower prestress to the beam body so that the beam body can bear the load of its own weight, and move the beam out of the production beam position in advance, which can greatly shorten the life cycle of the production pedestal and speed up the construction progress.