Study On Seismic Behavior Of RC Non-planar Beam-thin Wall Joints

Frame-shear wall structures and frame-corewall structures are the most commonly used in tall building structures.In such structural forms,many joints are formed by a frame-beam connected to shear-wall in its out-of-plane direction. Compared with the coplanar beam-wall joint,stress distribution in this kinds of non-planar joints is more complicated.However,very few studies on non-planar joints have been conducted.The method for detailed design of non- planar joints is still not established up to now.Owing to the assumption that the non-planar beam-wall joints act like hinges,the non-planar coupling beams are often designed as simply supported beams and the possible out-of-plane bending of the walls is ignored during reinforcement detailing. Actually,it is very difficult to construct an ideal hinge between a concrete shear wall and a beam.While treating the non-planar joints as hinges would tend to underestimate the lateral stiffness and strength of the structural system,neglect of possible bending of the beams and walls near the joints in reinforcement detailing may lead to serious cracking of the concrete near the joints.In Technical Specification for Concrete Structures of Tall Building(JGJ 3-2002),a shear wall with concealed column is simply suggested as taking a reinforcing measure,but how to design this kind of joints is not mentioned at all.In the present work,the mechanical characteristics and seismic behavior of the RC non-planar beam-thin wall joints with concealed column have been carried out.The main contents are listed as follows:1.Based on the classical plate theory,the non-planar bending problem of the shear-wall subjected to non-planar bending moment at the joint is studied.The analytical solutions for stresses,internal forces,the rotational stiffness of the joint and strain energy of the wall are obtained.2.Based on equivalent frame model,equivalent bending width is introduced,which can be determined by the use of the equivalent principles for rotational stiffness or for strain energy.A detailed parameter study of the equivalent bending width is carried out to highlight the primary parameters and the impacting characteristic.3.Low reversed cyclic loading tests on four specimens of RC non-planar beam-thin wall with concealed column joints are conducted to investigate failure modes,ductility, hysteretic behavior,energy dissipation capacity and so on.Combing with elasto-plastic finite element analysis,influences of the concealed column breadth on seismic behavior are nailed down.And then the most reasonable concealed column breadth is obtained, which is defined as effective bending width.4.The calculation formulae for the out-of-plane flexural bearing capacity of the shear wall are proposed for two kinds of different failure modes.The results are compared with that from tests.5.The design method of concealed column of non-planar joints is provided. Moreover,methods on constructional and reinforcement details are suggested.