Residual Prestress Detection Technique Research And Application For Prestressed Members Of High-piled Wharf

Residual prestress is one of the important indicators of prestressed concrete components. It is a necessary work to find a way to detect the residual prestress more accurately and conveniently, both for the performance evaluation, design of repairing and strengthening work of existing concrete structures and design of new structures. In this paper, the residual prestress of a beam in a high pile wharf is detected by hole-drilling method, based on finite element analysis. The following works are involved.1. The relationship among residual prestress, hole depth, plate size and the prestress disturbance beside the hole, in the model of prestressed concrete thin plate. The disturbance value is independent of prestress, increases with the growth of hole depth, and decreases with the growth of the plates size.2. A model of prestressed concrete beam is established based on general finite element ANSYS, with birth-death element method and 2 times loading method. Release of stress beside the hole is studied in Simulation drilling at the prestressed concrete beam without external load, By changing the drilling parameters which is diameter and depth. It is found that when diameter and depth are both 50 mm, the calculated stress and measured stress are in good agreement which is 100mm away from center of the hole. Therefore, the diameter and depth of drilling are both 50 mm and the strain gauge affixing point is 100mm from hole center at the bottom of the beam, and the direction of which is the axial stress direction of the beam. This conclusion is instructive for the Detection of residual prestress prestressed beam.3. Residual prestress of existing prestressed concrete track beams in high-piled wharf is conducted by hole-drilling method.4. The maximum cracking load of prestressed track beams is calculated according to the residual prestress detected, then health assessment about the track beam is done through calculating the envelope diagram of the portal crane moving. The envelope show that the most unfavorable position are cross 1 and cross 8, but it did not exceed the maximum of cracking load, so the track beam is safe when the portal crane normal working. And it can be determined that the position of the hole should be cross 1 and cross 8, because the two cross most likely to be fatigue failure and cracking.