Study On Shear Behavior Of Precast HSC Segmental Beams With External Tendons And Dry Joints

Externally prestressed precast high-strength concrete segmental beams(EDDJ-PHCSBs)with dry joints have become a preferred alternative for approaching the rapid construction,due to the lighter self-weight and the easier installation.In the existing research,there are many researches on the flexural performance of prestressed precast segmental concrete beams,and the research on its shear performance is relatively scarce.For prestressed precast segmental beams,its shear performance is relatively weak,which can not be ignored in bridge design.The strut and tie model(STM model)is a truss model abstracted from the continuous structural,which is composed of strut,tie rod and node to reflect the transfer of internal force flow.It is a commonly used tool to analyze the internal stress state of D-zone(structural zone with obvious nonlinear section strain distribution).In order to investigate the shear behavior of externally prestressed precast high-strength concrete segmental beams with dry joints,Based on National Natural Science Foundation of China——Direct shear failure mechanism and design theory of joint of precast segment UHPC beam(500170105),a series of experiments were carried out.Eight EDDJ-PHCSBs with dry joints were fabricated and tested to failure.For comparison purpose,one externally prestressed high-strength concrete monolithic beam was also tested.The primary experimental parameters,such as concrete strength,shear span-depth ratio,stirrup ratio,joint number and joint location,were adopted.Test results indicated that:(1)increasing the concrete strength or stirrup ratio can effectively improve the shear bearing capacity of the EDDJ-PHCSBs.(2)The shear span-depth ratio was shown to be inversely proportional to shear strength for all specimens.(3)The results also revealed that the joint number had some extent effect on the defection and stress of external tendons of EDDJ-PHCSBs with dry joints.(4)AASHTO 2017 and JTG3362-2018 were compared with the testing results.By calculation,the average ratio of the test results to the predicted values of AASHTO LRFDand JTG 3362-2018 is 2.125 and 1.36 respectively,and the standard deviation is 0.549 and0.316 respectively.(5)It is found that the calculation method of STM model specified in Appendix A of ACI 318-14 is not suitable for the EDDJ-PHCSBs with dry joints..The average value of the ratio of the test shear strength to the calculated value is 1.506,and the standard deviation of the ratio is 0.205.And the strength of the compression bar is far greater than the actual value,and the actual stress of the pull rod is far less than the actual value,which leads to the pull rod strength becoming the only factor determining the shear bearing capacity of the beam,which is not in line with the actual situation of the test.Finally,according to the characteristics of the actual failure mode of the test beam,a modified calculation method based on the Strut and Tie model is adopted.The formula proposed in this paper considers two kinds of failure conditions: concrete shear failure and steel strand fracture.The calculation results show that the average value of the test shear strength and the calculated value of the method is 1.04,and the standard deviation is 0.135.The results show that the formula can accurately predict the ultimate shear strength of the EDDJ-PHCSBs with dry joints.The calculation method can basically reflect the true failure mode of the specimen.