Study On Seismic Behavior Of Replaceable Steel Truss Composite Coupling Beams With Buckling Constrained Elements

Because of its high bearing capacity and lateral stiffn ess,the reinforced concrete shear wall structure is an anti-lateral force structural system which is widely adopted in high-rise buildings in China.As the “first line of defense” for the seismic fortification of coupled limb shear walls,coupling beam fi rst yields and consumes seismic energy to reduce the damage of shear wall limb when subjected to earthquakes.It is a very important energy-consuming component.However,the span height ratio of conventional reinforced concrete coupling beam is generally l ess than 2,and brittle shear failures are easily formed in the earthquake to form cross cracks.The deformability and energy dissipation capacity are poor,and it is difficult to repair after the damage.In this paper,three new kinds of replaceable steel truss composite coupling beams with buckling constrained elements are presented,namely,steel truss composite coupling beams with buckling constrained steel truss(SCB1),steel truss composite coupling beams with buckling constrained steel web(SCB2)and steel truss composite coupling beams with energy dissipating device(SCB3).The top and bottom chords in the proposed coupling beams are high damping concrete filled steel tube,the buckling constrained elements in the proposed coupling beams are constrained by a couple of precast high damping concrete plate.The top and bottom chords of the proposed coupling beams are pinned to the steel embedment in reinforced concrete walls;the buckling constrained steel truss of the SCB1 and buckling constrained steel web of SCB2 are connected to the steel embedment in reinforced concrete walls by using high strength friction bolts;the O-connectors are welded with the chords and constrained steel truss of the SCB1 and buckling constrained steel web of SCB2.The constrained steel web of SCB3 is only bolted to the chords using fish plates and high strength friction bolts.This paper combines experimental research and nonlinear finite element analysis to systematically study and analyze the seismic performance o f replaceable energy-dissipating steel truss coupling beam.The main research contents are as follows:(1)Quasi-static tests were carried out on steel truss composite coupling beams with buckling constrained steel truss(SCB1),steel truss composite coupling beams with buckling constrained steel web(SCB2)and steel truss composite coupling beams with energy dissipating device(SCB3).The three specimens were systematically analyzed for their crack distribution,failure morphology,bearing capacity,hysteretic curve,skeleton curve,stiffness degradation,displacement ductility,and energy dissipation capability.From the test results,it can be known that all the three specimens were plastically damaged in the steel truss webs and O-connector,and no damage occurred on the upper and lower chords and the reinforced concrete wall limb after tests.Both can meet the post-earthquake replaceable requirements;The SCB3 has the best load carrying capacity and deformation capability.The specimen SCB2 has the best ductility and energy dissipation capacity.The double-layer high-impedance concrete slab can effectively limit the out-of-plane stability of the steel web.The O-connector can enhance the energy dissipation capacity of the coupling beam.(2)ABAQUS software were used to numerically simulate the three coupling beam specimens,and the finite element model established by the finite element model was compared with the test results under the monotonic horizontal load.The results were in good agreement with each other,which demonstrated the finite element model established in this paper and the selected parameters are reasonable and reliable.(3)Based on the rationality of the finite element model,the influence of these factors on the bearing capacity,stiffness and deformability of the replaceable energy-dissipating steel lattice trussed coupling beam is explored by changing th e thickness of the steel web,the thickness of the O-connector,the steel web height,the number of O-connector,the steel web steel strength grades and chord section size.The simulation results show that the above factors have certain influence on the bearing capacity of the coupling beam,but the height of the steel web has the most significant influence.Increasing the height of the steel web is an effective method to improve the bearing capacity of the coupling beam;the up per and lower chord sections size has little effect on the bearing capacity of the coupling beam.A modified scheme of SCB2 was simulated by ABAQUS.The results show that the improved load-bearing capacity and stiffness of the coupling beam are significantly improved and the bearing capacity is higher than that of SCB3.It shows that the improvement plan works well.