Research On Seismic Behavior Of Precast Recycled Concrete Beam-column Joints

With the acceleration of urbanization,the annual output of construction waste in China is increasing day by day.The comprehensive utilization of recycled solid building waste materials is of great significance for realizing sustainable development and building a resource-saving and environment-friendly society.The development and application of recycled concrete technology can not only save the natural aggregate resources,but also reduce the environmental pollution caused by waste concrete,which brings vitality to the recycling and efficient utilization of waste building materials.According to China's national economic and social development plan,in the next few years,we will vigorously develop green buildings,requiring the construction of new urban buildings to reach 50% of the total number of green buildings.We will implement the green building industry chain development plan,and promote energy-saving green building materials and prefabricated buildings.In addition,prefabricated building is a green construction method vigorously promoted by the state at present,and the application of recycled concrete in beam and column joints of prefabricated frame structure is a combination of energy conservation and emission reduction with green construction,which has important scientific significance and engineering application value for promoting China's sustainable development.For this reason,this paper adopts the method of combining theoretical analysis,experimental research and numerical simulation to study the seismic performance of the new type of prefabricated concrete beam-column joints of full size,so as to provide some theoretical basis and experimental data for the application of regenerated concrete from construction waste in prefabricated joints.The main research contents and conclusions are as follows In this paper,the seismic performance of the new type of assembled regenerated concrete beam-column joints is studied by combining theoretical analysis,experimental research and numerical simulation.The specific contents and conclusions are as follows:(1)Based on the skew strut-truss model and the tension strut-compression model,considering the influence of the content of recycled aggregate of cons truction waste on the deterioration of concrete,and introducing the reduction coefficient of recycled concrete,the calculation formula of the shear capacity of the beam-column joints of the precast recycled concrete frame was proposed.The results show t hat the modified simplified tie-bar model is in good agreement with the test results,and the difference between the calculated value and the test value is about 10%.Compared with other models,the modified simplified tie rod-press rod model is more secure.When the concrete is mixed with 50% recycled coarse aggregate,the shear capacity of the beam-column joints of the precast recycled concrete frame decreases by about 7%-15%.(2)In this paper,the pseudo-static test of fully assembled regenerated concrete frame beam and column joints under axial pressure and horizontal low cyclic loading is carried out,and the seismic performance of the new type of joints is discussed.The results show that the ductility coefficient of recycled concrete joints Q2 and B2 is about 4.1.For the full assembly node,the addition of recycled coarse aggregate can significantly reduce the ductility coefficient of the node.The ductility value of node Q2 is about 89% of that of node Q1.For semi-assembled joints,the ductility coefficient of recycled concrete node B2 is about 111% of that of node B1,and the ductility coefficient is improved.The ductility coefficient of node Q1 is about 124% of that of Node B1,indicating that the ductility coefficient of component can be impr oved more by full-assembly splicing than by semi-assembly splicing for prefabricated ordinary concrete joints.(3)The energy consumption index of each joint component is studied.The cumulative energy consumption of recycled concrete joints Q2 and B2 is a bout 84.3% and 89.1%,respectively,compared with that of ordinary concrete joints Q1 and B1,indicating that the addition of recycled coarse aggregate can significantly reduce the energy consumption capacity of joint specimens.For ordinary concrete joint s,the cumulative energy consumption of Q1 is about 110.9% of That of B1.The connection of the beam end sleeve can effectively improve the energy consumption performance of the joints.The cumulative energy dissipation of the two recycled concrete joints was not significantly different,but the total assembled joints were still slightly higher than the semi-assembled joints.(4)By carrying out the pre-loading of the beam-column joints and simulating the damage of the semi-assembled concrete frame beam-column joints under the action of a major earthquake,a quasi-static test was carried out to investigate the seismic performance of the semi-assembled concrete frame beam-column joints under the action of a major earthquake.The results show that after a big displacement yield load,low cycle reciprocating loading experiment was carried out again,component of energy dissipation performance significantly,and its ultimate load corresponding energy dissipation of hysteresis loop back about 60% of the same node for the same period,cracks are no longer along the regional development of plastic hinges on both ends,but on the edge of the core composite layer near;However,the prefabricated concrete joints still have a high safety reserve after a major earthquake,and the residual bearing capacity is about 75% of that before the loss.(4)Based on the above quasi-static test results,an accurate nonlinear finite element analysis model of assembled regenerated concrete beam and column joints is established,and the influence of parameters such as the amount of regenerated aggregate and assembly mode on the seismic performance of the joints is analyzed.The results show that the addition of recycled coarse aggregate will change the failure mode of the node under the low-cycle reciprocating action.With the increase of the replacement rate of reclaimed coarse aggregate,the failure mode of the node develops from the bending failure of the beam end to the core failure of the node.The aseismatic performance of the beam and column joints is degraded to a certain extent by the increase of the replacement rate of recycled coarse aggregate.With the same replacement rate of recycled coarse aggregate,the damage degree of the core area of the fully assembled node is more serious than that of the semi-assembled node,but the failure mode of the node is basically unchanged.