Seismic Performance Of Friction Dampers Reinforced Glulam Bolted Joints With Cracks

In recent years,in order to achieve the requirements of low carbon and green building,the application of wood structure has been widely concerned.The beam-column structure is a common structural system in modern wood structure,and in this kind of beam-column structure,the steel plate-bolt connection is often the first choice.However,a large number of studies have found that steel plate-bolt connection joints are prone to produce low stiffness due to machining accuracy,and wood is sensitive to the external environment because of its hygroscopic property.When temperature and humidity change,cracks are prone to occur,and the appearance of cracks will affect the mechanical properties of joints.However,China is in the area of frequent earthquakes,the existence of cracks will also affect the seismic performance of joints and the whole frame.In this paper,through experimental research,finite element simulation and other methods,the seismic performance of joints with cracks and the lateral force resistance performance of glulam beam and column frame are analyzed according to the idea from local joints to the whole frame,and the reinforcement design of joints with cracks is carried out based on the friction energy dissipation principle.The seismic performance of crack joints reinforced with friction energy dissipating device and glulam frame reinforced with this device are studied.It provides reference basis and design scheme for considering the influence factors of cracks and seismic performance in practical engineering design.The main research contents and conclusions are as follows:(1)Monotone and low-cycle reciprocating loading tests were carried out on glulam bolted joints with different initial crack numbers and positions to study the influence of cracks on the seismic performance of the joints.The results show that with the increase of the number of initial cracks,the initial stiffness,bearing capacity and ductility of the joints will gradually decrease,and the initial stiffness,maximum bending moment and ductility coefficient of the test joints decrease by 25%,14% and 30%,respectively.When the number of cracks is the same,the change of the initial crack location also has a certain influence on the node stiffness,whether there is an initial crack at the bolt row on the tensile side has a great influence,and the energy dissipation capacity of the point with only cracks at the bolt row on the tensile side is worse than that of the node with cracks on the tensile side and compression side at the same time.In addition,the failure mode of joints will change from ductile failure to brittle failure due to the existence of initial cracks,which can not meet the requirements of seismic design of structures in practical engineering.(2)A kind of friction energy dissipation reinforced joints was proposed.Low-cycle reciprocating loading tests were carried out on the cracked joints reinforced with friction energy dissipation devices with different high-strength bolt pretightening forces to study the seismic performance of the strengthened joints.The results show that the mechanical properties of the strengthened joints are greatly improved.The initial stiffness and ductility coefficient of the strengthened joints are 2.44 and 2.3 times of those of the unstrengthened joints,respectively,and the maximum bending moment is 79% higher than that of the unstrengthened joints.In addition,there is no initial crack expansion in glulam joint area,indicating that the friction energy dissipation device can effectively suppress wood cracking in joint area,give full play to the ductility of bolts,and improve the failure mode of glulam joint to a certain extent.At the same time,by comparing the reinforced joints with different high-strength bolt pretightening forces,it can be found that within a certain range,the greater the pretightening forces applied,the higher the initial stiffness,bearing capacity,ductility performance and energy dissipation capacity of the joints are.(3)In order to study the influence of cracked joints on the lateral force resistance of glulam beam-column frame,single-layer single-span frame and two-layer two-span frame were designed for reference,and the influence of cracks on the frame with different span number and the influence of cracks at different node positions on the frame performance were compared and analyzed.Analysis shows that: The existence of joint cracks will reduce the lateral stiffness and bearing capacity of the frame.When only cracks exist at column foot joints,the lateral stiffness of single-layer single-span frame decreases by 10.9%,two-layer two-span frame decreases by 5.5%,and the bearing capacity of single-layer single-span frame decreases by 16.9% and two-layer two-span frame decreases by 6%.This indicates that with the increase of the span of frame layers,The weakening effect of cracks on lateral stiffness and bearing capacity of the frame will be reduced.However,cracks at different joint locations have different influences on the performance of the frame.When only the column foot joints have cracks,the weakening effect on the performance of the frame is greater than that when only the beam-column joints have cracks.When both the column foot joints and the beam-column joints have cracks,the weakening effect on the performance of the frame is the greatest.(4)In order to study the influence of friction energy dissipating devices on the seismic performance of glulam frame reinforced with cracked nodes,a single single-span frame reinforced with friction energy dissipating devices was designed,and the seismic performance of unreinforced frame and reinforced frame was compared and analyzed,as well as the influence of different pre-tightening forces applied by friction energy dissipating devices on the seismic performance of frame.The analysis shows that the elastic stiffness and maximum bearing capacity of the reinforced frame are 91% and 36% higher than those of the reinforced frame with the same crack,and the stiffness and energy dissipation capacity of the reinforced frame are also significantly improved.The greater the preload value is,the greater the stiffness and energy dissipation capacity of the reinforced frame are.There is no initial slip in the initial stage of the reinforced frame,and its failure mode is also improved,from the original failure caused by sudden drop of bearing capacity to ductile failure with a certain yield stage.These results indicate that using friction energy dissipating device to reinforce the cracked frame can effectively improve the stiffness,load-bearing capacity and energy dissipation capacity of the frame,and also optimize the failure mode of the structure and improve the safety performance.