Working Stress Tests Of Prestressed Tendons In Ground Anchorage

Prestressed strands of ground anchors are widely used in the reinforcement, building excavation and structural reinforcement. Service load is an important factor in the safety of prestressed structures ,and service load detection is necessary.Paper focus on the research of two service load detection methods: the lift-off test and non-destructive test based on acoustoelasticity theory. First, the detection mechanism of lift-off test is given; the inflection point method and the insert method are compared. Inflection point method is verified by experiments. Service load can be caculated as the average of the upper and under of the load - displacement curve's turning section. When the service load is 75% of the ultimate load of the prestressed strand, the detection error is about 2%.Paper analysis the theory of non-destructive test based on acoustoelasticity theory, and get the relation between wave velocity and service load. Dispersion has been taken into the consideration of the choice of the exciting wave in test. Wave's frequency is suggested be lower than 200kHz. The laboratory tests show: with the service load of the prestressed strand increases, the wave propagation velocity becomes lower. Tests show that taking the commonly used equipment into service load detection in the engineering application is feasible. Based on the application of existing projects, the possible service load detection method is illustrated, according to theoretical studies and experimental results. Issue needed to be further discussed is point out.Based on the theory of wave propagation in continuous media, the discrete element software PFC2D is taken to simulate elastic wave propagation. In simulations of the wave propagation in granular media, waves reflect at the interface. Using the non-linear contact model, the wave propagation velocity in granular media is related with the pressure in the media.The simulation of wave propagation in continuous media in PFC2D needs to get the relation between numericl model's contact stiffness and the continuous media's macro-stiffness. Paper tries to get the relations. Also, the viscous damping is used in the simulation of single degree of waving system. The viscous damping ratio calculated in the software is compared with the ratio in theory. Paper derived motion equation of local damped single degree of system.