| Precast concrete segmental bridges (PCSB) have the following advantages:rapid construction speed, small effect on surrounding traffic, easy control in quality, wide span adaptation, etc. PCSB can satisfy the need for rapid rhythm in contemporary bridge construction. Combined with external prestressing technique, PCSB have good technological rationality, durability and economy. Joints are the weak parts of PCSB, the mechanical behavior of which has an important impact on forced state of the whole bridge in both serviceability limit state and ultimate limit state. The direct shear failure of joints has higher probability of occurrence in engineering practice. However, the study on shear mechanism and shear strength of joints are not nature in theory, there is no uniform understanding yet. Therefore, this paper studied the direct shear performance of joints in PCSB.Considering normal stress level (2MPa,3MPa, and 4MPa), joint type (dry jiont, epoxid jiont), joint structure (flat joint, keyed joint), size of keys (30mm,50mm) and inserted reinforcement (regular reinforcement, FRP reinforcement) as test parameters, this paper designed 14 specimens for shear test of joints in segmental concrete beam. Through experimental research of each specimen, crack development law, failure mode and shear strength of different types of joints were obtained. By comparing the test results of different types of joints, the effects of various parameters on the shear performance of joints were summarized.In this paper, the existing formulas for direct shear capacity of joints were summarized. Through comparing the formulas with test results obtained in this article, the applicability of these formulas was discussesed. Based on the experimental and theoretical analysis, the paper proposed direct shear failure mechanism of various types of joints. Based on the friction theory, the direct shear capacity formula for plat dry joint was given; On basis of the data obtained in flat epoxid joint tests by M. M. Bakhoum and Xiangming Zhou, the direct shear capacity formula for plat epoxid joint was given with the method of linear regression analysis. As to keyed joint, the paper put forward the failure mode of keys-inclined compression failure. Combined with theory of mohr’s stress circle, shear resistance of concrete keys was deduced. Furthernore, the formulas to estimate the shear capacity of keyed joints were given. According to the shear-friction theory, the direct shear capacity formula for joint strengthened with inserted reinforcement was given. Finally, the formulas proposed in this paper were verified by results of direct shear tests obtained by author and other scholars, and it is proved that the proposed formulas have good applicability.In this paper, the finite element analysis model of each test specimen was established with ABAQUS finite element analysis software. Through comparing the finite element analysis results with test results obtained in this article, it is proved that ABAQUS can simulate the experimental procedure with good accuracy.In this paper, problems that may be encountered in application of shear capacity formula for keyed joints to PCSB were studied. Paper discussed how to take the value of shear failure area and sliding friction area in box girder section. The changes of stress in prestressing tendons caused by beam bending and prestress loss were studied. Pointing at the stress increment in section due to the changes of stress in prestressing tendons, the paper carried research on both dry joint and epoxid joint. Finally, the modified direct shear capacity formulas for keyed joints in practical bridge engineering were proposed. |
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