| At present,the annual output of construction waste in China is more than 2 billion tons,the pollution is serious and the utilization rate of resources is low,so the environmental protection and regeneration technology needs to be improved urgently.On the other hand,the traditional construction industry with high energy consumption and high pollution is also eager to transform to the industrialization of prefabricated construction.It is of great strategic significance to promote the sustainable development of China’s construction industry to apply the construction waste recycling resources to the assembly building,which can not only reduce the environmental pollution,but also save the consumption of raw materials.The results show that it is a promising green recycling technology to make recycled concrete from construction waste.However,researchers at home and abroad focus on the application of recycled concrete in non load-bearing products and components,lack of research on recycled concrete load-bearing components,rare reports on the seismic performance of prefabricated joints of recycled concrete,seriously limiting the application and promotion of recycled concrete in prefabricated buildings.Therefore,in this study,the recycled concrete fabricated frame cross joint is taken as the object,and nine nearly full-scale beam column joints(divided into three groups according to the replacement rate of recycled aggregate of 0,50% and 100%)are designed and manufactured by adopting the fabricated reinforcement structure of multi spiral stirrup and one stirrup combination.Each group of specimens includes three joint types: cast-in-place,semi assembled and fully assembled).Through the pre compression frame joints Based on the quasi-static test of horizontal loading,the seismic performance of this new type of assembled beam column joint is discussed,and the calculation model of shear capacity of the joint is put forward.The main research contents and conclusions are as follows:(1)In this paper,the quasi-static test research of the multi spiral stirrup concrete fabricated frame joint and the traditional stirrup cast-in-place joint is carried out,and the seismic performance of the new stirrup fabricated beam column joint and the traditional stirrup cast-in-place joint is compared and analyzed.The results show that,compared with the cast-in-place joints with traditional stirrups,the multi spiral stirrup concrete fabricated beam column joints have better seismic performance;for ordinary concrete,the cumulative total energy consumption of the new stirrup semi fabricated joints and fully assembled joints is 30% and 16% higher than that of the traditional stirrup cast-in-place joints,respectively.In addition,the function cost ratio of the new type of stirrup recycled concrete fabricated joint is higher,and compared with the traditional stirrup cast-in-place joint,the steel consumption of the multi spiral stirrup fabricated beam column joint can be reduced by about 13%.(2)Based on the experimental study of the recycled concrete composite joints with multi spiral stirrups under axial compression and horizontal low cycle repeated load,the influence of recycled aggregate content on the seismic performance of the new composite joints is analyzed.The results show that the influence of recycled aggregate on the seismic performance of the multi spiral stirrup concrete assembly joint is small.With the increase of the replacement rate of recycled concrete,the seismic performance of the new stirrup recycled concrete assembly joint is generally decreasing,but it is not linear with the replacement rate of recycled aggregate.When the recycled aggregate content is 100%,the reduction of displacement ductility coefficient and cumulative total energy consumption of multi spiral stirrup concrete fabricated joints are less than 10%,which can meet the seismic design requirements.(3)The influence of different assembly types on the seismic behavior of recycled concrete beam column joints with multi spiral stirrups is discussed.The experimental results show that the seismic performance of the semi assembled joint is slightly better than that of the new type stirrup recycled concrete fully assembled joint;when the replacement rate of recycled aggregate is 100%,the displacement ductility coefficient and the cumulative total energy consumption of the semi assembled joint are 5% and 1% higher than that of the fully assembled joint,respectively.(4)Based on a series of quasi-static tests,the failure mechanism of the cross joint of the recycled concrete assembled frame is explored.The research results show that the new stirrup fabricated beam column joint and the traditional stirrup cast-in-place joint both have bending failure at the beam end,and their failure process is similar,roughly going through four stages: initial crack,yield,limit and failure;under the action of horizontal low cycle repeated load,the slip between the beam longitudinal reinforcement and the concrete is increasing,and the bonding interface between the two is damaged,and the main crack runs through the joint,The concrete in the compression zone of the beam end is crushed,resulting in the loss of bearing capacity of the joint;compared with the ordinary concrete fabricated beam column joint,the crack development of the recycled concrete fabricated beam column joint is more concentrated,but the failure process and failure mode are similar as a whole.(5)Based on the truss model,the shear capacity formula of the joints in the code for seismic design of buildings(GB50011)is modified by introducing the reduction coefficient of recycled concrete,and the calculation method of shear capacity of the beam column joints with multi spiral stirrups is proposed.The results show that the modified shear capacity model proposed in this paper is in good agreement with the test results;when the replacement rate of recycled coarse aggregate is 100%,the strength reduction coefficient of recycled concrete for calculating the shear capacity of this kind of joint is suggested to be 0.85. |
PDF Full Text Request