Numerical Analysis Of Bearing Capacity Of Fabricated Beam-column Substructures Considering Bond Slip

The degradation or even destruction of the bond stiffness between the concrete and the reinforcement will reduce the bearing capacity of the reinforced concrete structure,and the bonding effect of interface between the new and old concrete of the fabricated structure will affect the bearing capacity under loading.The existing research focuses on the beam-column joints with symmetrical reinforcement,but does not consider the influence of the anchorage type of reinforcement on members or structures.Based on these characteristics,ABAQUS interface program is used to develop interface element for quantitative analysis of refined finite element model considering slip,and to discuss the influence of different parameter on the bearing capacity of fabricated beam-column substructures in this paper.Based on the finite element theory and ABAQUS interface program,the UEL（user element）interface bonding element is established in this paper.After properly simplifying the constitutive relation proposed by Eligehausen,the simulation results of interface bonding element are compared with the test data,and the results are in good agreement.Besides the results show that the peak strength of 90°hooked bar is about 90%of that of headed bar,and the corresponding slip amount is different through the comparison between 90°hooked bar,headed bar and test.By analyzing the influence of plastic damage model,the results show that the model has good accuracy and convergence when the expansion angle is 30°,the viscosity coefficient is 0.0005,and the element mesh is 0.0125m.Sixty-six fabricated beam-column substructures are established by ABAQUS in this paper.The analysis parameters include the thickness of cast-in-place layer of composite beam,the direction of load action,cast-in-place slab,the axial compression ratio of column,the stirrup ratio of column and the anchorage length of beam longitudinal bar.The results show that the yield load of the cast-in-place layer is about 30%lower than that of the cast-in-place layer in tension,and its peak load is only 85%;considering the floor compression,the effective flange width of 1200mm can be taken as the model;even if a certain anchorage length is reduced,the anchorage effect can be fully exerted by headed bar.The calculation formula of the basic anchorage length and the straight anchorage length in the Chinese,American,European and Japanese codes are discussed,It is considered that the calculated value of Chinese and European codes is required for the straight anchorage length between the 90°hooked bar and headed bar in American code.Compared with the maximum tensile stress of anchorage reinforcement,the results show that the maximum tensile stress decreases with the increase of concrete strength no matter the straight anchorage length,except for the calculation value of European code.Besides,it is necessary that the anchorage reinforcement should not be less than 0.4l_ab,which can basically ensure the yield of reinforcement and play the role of anchorage.