Secondary Anchorage Of Fractured Strand And Flexural Performance Of Post-tensioned Concrete Beams Under Secondary Anchorage

Post-tensioned prestressed concrete structures have been widely used in bridge structures due to its high cost efficiency,strong span capacity and light weight.However,corrosioninduced strand brittle fracture is easily to occur in the local insufficient grouting region of bellows under the coupling action of imperfect grouting process,adverse environment and sustained load,which seriously affects the safety performance of corroded prestressed concrete structure.Therefore,the present study takes PT beams with strand fracture as the research object,and focuses on secondary anchorage of fractured strand and residual flexural performance of PT beams under secondary anchorage.The main research works are as follows:(1)Secondary anchorage of fractured strand and prestressing force loss are investigated.The strand fracture test was designed.The mechanism,prestressing force and transfer length of secondary anchorage are investigated by analyzing the data of anchor cable gauge and strain gauge after strand fracture.Based on the cracking load method,the residual prestressing force of PT beams after strand fracture is evaluated.The results show that fractured strand can be reanchored in concrete to form the new prestressing force by the interfacial force between the fractured strand,grouting,bellows and concrete.When the length of fractured strand exceeds the transfer length,the prestressing force generated by secondary anchorage decreases little compared with the initial prestressing force.The residual prestressing force loss of PT beams after strand fracture is related to the strand fracture positions.With fracture position moves from anchor region to the mid-span region,the prestressing force loss increases gradually until the prestressing force is almost completely lost.(2)Degradation rule of flexural performance of PT beams under secondary anchorage is clarified.The static load test was carried out on PT beams with strand fracture.The effect of strand fracture positions on crack development,load-deflection response,ductility,failure mode and flexural capacity was analyzed.Based on failure section transfer principles,a method for calculating the flexural capacity of PT beams after strand fracture is proposed.The accuracy of calculation method is verified by the experimental data.The result shows that the degree of flexural performance degradation is related to the strand fracture positions.With fracture position moves from anchor region to mid-span section region,the flexural performance of the PT beam deteriorates continuously.When fracture position locates in mid-span section region,the flexural performance of PT beams will degrade to be similar to that of ordinary reinforced concrete beams.(3)The finite element simulation model for calculating the flexural performance of PT beams with strand fracture are established.Based on COMSOL Multiphysics software platform,considering the influence of new prestressing force generated by secondary anchorage of fractured strand on flexural performance,the finite element simulation models for calculating the flexure performance of PT beams with strand fracture are established.The calculation accuracy of the simulation model is verified by comparing the load-deflection curve and the concrete equivalent plastic strain calculated by simulation model with the test measured values.The results show that the simulation value is in good agreement with the experimental value,and the simulation models have good calculation accuracy.Based on the established finite element model,a simulation App for efficiently evaluating the flexural performance of PT beams with strand fracture is developed.