STUDY ON CALCULATION METHOD OF SHEAR CAPACITY OF WET JOINTS IN CLOSURE SECTION OF PRECAST CONCRETE SEGMENTAL BRIDGES

Precast concrete segmental bridge (PCSB) closure section usually adopts the wet joint form of cast-in-situ concrete, and the width is generally 10 cm-20 cm. The longitudinal regular reinforcement is not continuous, which is the vulnerable part of the structure. In order to study the performance of the wet joint of the closure section of PCSB under cyclic loading, six wet joint specimens of the closure section are tested considering four factors: loading method, interface treatment method, setting regular reinforcement and prestress level. The results show that the failure patterns of wet joint specimens in closure sections have similar characteristics, the new and old concrete joint surfaces close to the loading point crack and expand rapidly upward, and then the cracks extend to the loading point with the increase of the load; the concrete in the compression zone is crushed, the specimens are damaged and lose the bearing capacity. Compared with the specimens under monotonic loading, the stiffness of the specimens under cyclic loading decreases significantly, and the cracking load decreases by 14.7%; the roughening of precast section end faces can improve the bonding effect of the new and old concrete interface and delay the cracking of the specimen; compared with the specimen with slight roughening, the cracking load of the specimen is increased by 10.3% after careful roughening; the reinforcements installed in the wet joint has little effect on the mechanical properties of the specimen; when the prestress level increases from 6 MPa to 8 MPa and 10 MPa, the stiffness of specimens increases by 21.9% and 32.8%, the shear strength increases by 9.9% and 6.6%, respectively, but the ultimate displacement decreases by 5.6% and 11.4%, respectively. The ratios of the test values to the calculated values of Chinese design code JTG 3362−2018 are between 0.86 and 0.97, and the ratios to the calculated values of US design code AASHTO LRFD are between 0.81 and 0.99. This paper suggests that the shear reduction coefficient of the wet joint shear strength calculation formula of the closure section for JTG 3362−2018 is 0.85, the shear reduction coefficient of wet joint in closure section for AASHTO LRFD is 0.8.