Seismic Experiment And Theoretical Study Of New Type Of Precast Concrete Frame Beam-Column Joint

Assembled building can effectively reduce the generation of various construction wastes from the source,which is essential for the progression of construction industry towards low-carbon,green,energy-saving and environmental protection,and is a significance measure in attaining the target of Carbon Peak and Carbon Neutrality for China.At present,the beam-column joints of prefabricated buildings are generally classified as dry and wet connections,where the dry connection technique with the highest assembled ratio is yet immature,and its mechanical behavior and failure mechanism under seismic action require improvement.In current paper,a novel type of bolt-connected precast concrete beam-column joint is innovatively proposed,which is divided into rigid,semi-rigid and weakly rigid joints according to the different grades of bolt strength.The low-cycle reciprocating loading test,three-dimensional numerical simulation and theoretical analysis of the high-strength,ordinary and low-strength bolted joints are systematically carried out.And the design and calculation method for such joint is proposed subsequently.The research outcomes offer fundamental experimental and theoretical backing for the national key research and development project "Key Technology of Industrialized Building Design",with considerable basic theory and engineering application value.The primary research outcomes and innovations of the thesis are as follows:(1)To study the seismic performances of the novel precast concrete beam-column joints connected by high-strength bolts,ordinary bolts and low-strength bolts,low-cycle reciprocating loading tests are carried out on foot-size joints,and the effects of bolt strength on the joint performance are investigated.The low-strength bolted joint presents small rotational stiffness and poor energy dissipation capacity.The joint is damaged under reciprocating loads,while the beam and column remain intact.For ordinary bolted joint,the rotational stiffness is small but the energy dissipation capacity is good.The joint exhibits semi-rigid under reciprocating loads,and the joint remains intact when the beam is damaged.For high-strength bolted joint,due to the application of pre-tightening force,a certain increase in the rotational stiffness and a decline in the energy dissipation capacity is attained.The joint shows rigid and remains intact despite the damage to the beam.Generally,both ordinary bolt and high-strength bolt connection joints satisfy the seismic requirements of "strong column and weak beam" and "strong joint and weak member",thereby holding impressive practical value and potential.(2)A comparison of beam ends equipped with and without haunched plates demonstrates that the addition of haunched plates boosts the overall bearing capacity of the precast beam.The setting of beam-end haunched plates makes the failure of the low-strength bolted joint manifested as bolt failure.The failure of the ordinary bolted joint still occurs in the beam when the haunched plates is set.The haunched plates induce the main penetration cracks to extend outward from the column edge when the beam is damaged,thus significantly improving the bearing capacity of the joint.This finding provides reasonable new thoughts and strategies for the construction of the precast dry joints.(3)On the basis of the low-cycle reciprocating loading test,a three-dimensional numerical simulation of the novel precast beam-column joint is conducted.The open-hole section of the column in the core area of the joint primarily experiences the compressive stress along the screw axis applied by the bolt in the horizontal direction,and the local stress concentration is generated at the hole.Through evaluating the alteration of joint stresses brought about by the hole-opening rate,the control requirements of the hole-opening rate are suggested.During the normal working stage,the bolts of the semi-rigid joint display a linear force distribution,with the bolts closest to the corbel exhibiting the least tensile force and the bolts furthest from the corbel presenting the greatest tensile force under the action of negative bending moment at the beam end.This conclusion serves as a basis for the calculation assumptions and analyses for the theoretical calculation and design method of such joints.(4)Considering the failure mechanism of the novel precast beam-column semi-rigid joint with ordinary bolts and low-strength bolts,the force analysis of the semi-rigid joint is conducted,and the "equivalent method" for determining the initial rotational stiffness of the beam-column joint is proposed and verified by comparison,which addresses the difficulty with the internal force calculation of such precast structures.A mechanical analysis model for the core area of the precast concrete beam-column joints is proposed,the calculation formulas for the shear force and bending moment in the core area of such joints are derived,and a complete design methodology is formed.This lays the foundation for the design and engineering application of the precast concrete structures equipped with such joints.