Study On Seismic Behavior Of Energy Dissipation Joint Frame In Steel-engineered Bamboo Composite Structures

In recent decades,engineered bamboo products have emerged as an alternative of traditional building materials for their pronounced advantages,i.e.abundant bamboo resources,long history of bamboo and wood structure,and the increasingly mature production technology.They also provide a new channel for solving the current serious ecological problems and ensuring the sustainable development of national economy.However,there is some problems exists when using engineered bamboo prouducts as perpendicular bearing components,such as the excessive creep of columns in bamboo-wood frames compared with concrete and steel structures.In this paper,a composite frame made up of steel columns and engineered bamboo beams is proposed as an effective solution.Therefore,the connection between the steel column and engineered bamboo beam becomes an utmost aspect of steel-engineered bamboo frame.Researches with variable parameters have been made to explore appropriate design methods of the joint as a reliable connection.Among them,a semi-rigid joint made up of a steel hinge and a pair of top and seat brackets to carry shear force and moment from the end of the beam is presented by Zirui Huang,Southeast University.In this way,the joint can serve as a frame connection as well as an energy dissipation device.Low cyclic load experiments for 9 joints were conducted in Nanjing Forest University,and the results revealed that the joint can not only provide sufficient strength and stiffness to meet the requirements of serviceability,but also show satisfactory capability of energy dissipation with a proper design.On the basis of the horizontal low-cycle reciprocating load test of the new energy-dissipating joints,a simplified trilinear skeleton curves are constructed,in which the characteristic values can be gotten by the finite element simulation in ABAQUS and theoretic derivation.While the hysteretic rules of a single loop turn out to reversed S-shape,which can be modeled by a concave hexagon.In this paper,the characteristic values of the simplified skeleton curves and parameters of the concave hexagon are obtained by theoretic derivation and Genetic Algorithm respectively.Then a restoring force model,comprised of a trilinear skeleton curve and hysteretic restoring rules of the energy-dissipation joint,is proposed.In order to verify the rationality and validity of the joint restoring force model,a bamboo-steel hybrid moment frame with a novel energy dissipation connection was tested.It was found that hysteresis loops of the frame with energy dissipation joints show less pinching than that of frames with dowel-or bolt-type connections;by proper designing,the damage and failure of the frame can be restricted in the EDPs(energy dissipation plates)of connections,whereas virtually no damage was observed in the other components of the frame;the connection can provide more than 10 % damping for the frame after the yielding of EDPs.The skeleton curve and hysteretic behaviours of the composite frame were studied and compared with the solid model in ABAQUS and the macroscopic element model in Open SEES,respectively.The hysteretic characteristic curves of cyclic load simulation results were compared and the following conclusions can be reached:(1)The proposed restoring force model,made up of a simplified trilinear skeleton curve and a concavehexagon hysteretic rule,can be used to determine the hysteretic behavior of energy dissipation joint in steel-engineered bamboo frame.(2)The seismic behaviours of the joints in the new energy dissipation joint frame test is the same as that in the joint test: the earthqukes energy is dissipate by the buckling of the energy dissipation paltes of the joint,and the damage and failure of the frame can be restricted in the EDPs of connections,whereas virtually no damage was observed in the other components of the frame;(3)The hysteresis loops of the frame with energy dissipation joints show less pinching than that of frames with dowel-or bolt-type connections,and the connection can provide more than 10 % damping for the frame after the yielding of EDPs.(4)The solid model in ABAQUS can basically simulate the mechanical behavior and failure mode of the new energy dissipation joint frame of steel-engineered bamboo composite structure system,but the computation efficiency and accuracy is not good enough to meet the needs in actual projects;(5)With the parameters and typical points of the restoring model inputed in Open SEES,the simulation efficiency and computation accuracy can be greatly increased.The established restoring force model can be used for the elastoplastic analysis of the steel-engineered bamboo structure.