Experimental Study On Seismic Behavior Of Reactive Powder Concrete Coupling Beams With Small Span-to-Depth Ratio

As the beam connecting the two walls in the inner plane of the shear wall structure and the frame-shear wall structure,the coupling beam is the key component to ensure the seismic performance of the common structural system in high-rise buildings.The coupling beam in the shear wall usually has a large beam’s depth and a relatively small span.In the high-rise civil buildings,the span-to-depth ratio of coupling beam is often less than 2.5,which belongs to coupling beam with small span-to-depth ratio.The coupling beam is often designed as the first seismic fortification line in the shear wall structure.In the seismic designs,the coupling beam theoretically yields before the shear wall limb,forming plastic hinge at both ends to dissipate energy and reduce vibration.But in fact,brittle shear failure is easy to occur in coupling beams with span-to-depth ratio in seismic action.Therefore,it is the key to improve the seismic performance,ductility and energy dissipation of coupling beams.In view of this important problem to be solved in engineering design,this paper designed six reactive powder concrete coupling beams and one ordinary concrete coupling beam for low cycle reciprocating loading test according to the relevant regulations in "Technical Regulations for Concrete Structures for Tall Buildings"(JGJ3-2010)and "Code for Design of Concrete Structures"(GB50010-2010).At the same time,the numerical simulation analysis of 10 test coupling beams was carried out by ABAQUS finite element software.The results showed that:(1)Reactive powder concrete coupling beams has better higher ultimate bearing capacity,higher energy consumption and slower stiffness degradation than ordinary concrete coupling beams.(2)The span-to-depth ratio and the characteristic value of stirrups are the main factors affecting the seismic performance of reactive powder concrete coupling beams.(3)When the span-to-depth ratio of the coupling beam is less than or equal to 0.8,the coupling beam will suffer from "Baroclinic shear failure",and the stress mechanism of the connecting beam is the barotropic bar mechanism.When the span-to-depth ratio of the coupling beam is greater than 0.8 and less than 1.5,the coupling beam will suffer from "bending and shear failure".There are three types of cracks: main oblique crack,secondary oblique crack and secondary oblique crack.(4)The edge longitudinal bar plays a major role in bending.Stirrups restrict the development of cracks in concrete.(5)The ductility coefficient of the RPC coupling beam with a span-to-depth ratio of 0.8 is 1.38,when the span-to-depth ratio is 1.5,the ductility coefficient is 1.6,which is increased by 16%,when the stirrup characteristic value is 0.028,the ductility coefficient of the RPC coupling beam is 1.42;When the stirrup characteristic value is 0.087,the ductility coefficient of the RPC coupling beam is 2.55,which is increased by 80%.(6)Increasing stirrup ratio and span-to-depth ratio can improve the ductility、reduce the stiffness degradation and increase the energy dissipation capacity.However,the stirrup ratio did not significantly improve the ultimate bearing capacity of RPC coupling beams.