Research On The Mechanical Properties And Seismic Design Method Of Detachable Steel-concrete Composite Beam

With the rapid development of China’s economic level and the steady progress of urbanization construction,the conflict between the traditional cast-in-place building and the natural environment has become increasingly apparent.How to achieve the assembly,demountable and rapid recovery of the use function of the building structure,and achieve the harmonious coexistence of the building and the nature has received more and more widespread attention.In order to meet the concept of green and sustainable development of building structures,this paper proposes a demountable steel-concrete composite beam with replaceable connecting members,and studies its mechanical performance and seismic design method.The main research contents and conclusions are as follows:(1)A demountable steel-concrete composite beam is proposed.Its components include prefabricated concrete slabs,profiled steel beams and replaceable connecting members.The replaceable connecting members are composed of fastening nuts,concrete plugs,gaskets and high-strength bolts.ABAQUS software is used to carry out finite element analysis on the push-out of replaceable connecting members and the test of composite beams.The results show that the composite beams have three performance levels of "demountable,replaceable and anti-collapse",and the replaceable connecting members can concentrate the damage and realize the rapid recovery of the use function of the composite beams.(2)The finite element analysis of the shear performance of the replaceable connecting members is carried out.27 push-out beam specimens are designed with the diameter and strength of the bolt,the size and strength of the concrete plug,and the strength of the concrete slab as parameters.The results show that the diameter and strength of the bolt and the size and strength of the concrete plug are important factors affecting the shear performance,and the influence of the bolt diameter is the most significant.When the diameter increases from 10 mm to 24 mm,the ultimate shear capacity increases by 329.6%;Increasing the diameter and strength of bolts can significantly improve the demountable performance of connecting members;Increasing the size and strength of concrete plug effectively delays the damage of connecting members and significantly improves the replaceable level of connecting members;Based on the finite element simulation results,considering the influence of concrete plug strength,bolt diameter and strength on shear bearing capacity,a formula for calculating shear bearing capacity of replaceable connecting members is proposed.(3)The finite element analysis of the flexural performance of the demountable steel-concrete composite beam is carried out.27 composite beam specimens are designed with the strength and width of the concrete slab,the strength of the steel beam,the diameter of the longitudinal reinforcement,the size and strength of the concrete plug,and the diameter and strength of the bolt as parameters.The results show that,except for the size of concrete plug,the other parameters can improve the flexural performance of composite beams to varying degrees,and the strength of steel beams has the most significant impact.When the strength of steel beams is increased from Q235 to Q420,the ultimate flexural capacity increases by 42.7%;The demountable performance of the composite beam increases with the increase of the diameter and strength of the bolt,and the replaceable performance level increases with the increase of the size and strength of the concrete plug.(4)Taking the strength and width of concrete slab,the strength of steel beam,the diameter of longitudinal reinforcement,the size and strength of concrete plug,the diameter and strength of bolt as the research parameters,the seismic performance of demountable steel-concrete is analyzed by finite element method.The results show that the composite beam can realize the rapid recovery of the use function after the earthquake;The increase of steel beam strength can significantly improve the strength and stiffness of composite beams,but will reduce the seismic energy dissipation capacity of composite beams;The ductility of composite beams increases with the increase of concrete slab strength and longitudinal bar diameter;Based on the results of finite element analysis,the formulas for calculating the bearing capacity of composite beams under positive and negative bending moments in the existing codes are modified,and the seismic design method of demountable steel-concrete composite beams is established.