Research On Seismic Behavior And Design Method Of Self-lock Plug-in Joints In Modular Steel Construction

Modular Steel Consturction（MSC）is a novel type of construction,in which the baseic units is room modules instead of structural components.For the induaral construction,modular steel construction is an ideal type of structure due to the exceptional advantages,e.g.,efficiency,quality,lower cost and environmental advantages.However,previous joints require extra operation spaces for connection and cannot be adopted for middle joints in modular steel construction.Besides,it is difficult for these joints to direct load-transfering and reuse.Limitions about the section profiles of beams and columns exsits for these joints.Regarding this condition,a novel types of joint,plug-in self-lock was proposed in this study.Experimental study,numerical and therotical analysis were conducted.Investigations on the seismic behavior and design method were made as following:（1）A novel type of plug-in self-lock connector was proposed,and investigations of the behavior of the connector under tensile and shear load was made.This demoutable connector needs no extra opertation spaces,and can allow manufactural errors.Also,the connector can be demounted with extra unlocking device.Based on experimental study and FE analysis,the behavior of the connector under tensile and shear load was investigated.Load-displacement relationship,strength,deformation and failure modes of the connectors were gained.Effect of the area of the stud,the ring-teeth and the sleeve was evaluated.The test results showed that there was no initial slip under tensile load.The failure mode was the fracture of the stud.The connector strength was almost the the strength of the minimum section of the stud.The friction mechnisim worked well.The FE results showed that the potential failure modes of the included the tensile and shear fracture of the stud,the fracture of the ring-teeth and the failure of the sleeve.The minimum section area of the stud determined the strength of the connector directly.The unfavorable fairlure modes,i.e.,the fracture of the ring-teeth and the failure of the sleeve,can be avoided with proper construction measures and details.Based on the test and analysis results,design method and calculations of strength was proposed.Reccomendations about construction measures and details were given accordingly.（2）Based on the connector in the second chapter,a novel type of self-lock joint were proposed for modular steel construction.This type of joint can be adopted as conrner,side and middle joint,and can be easily disconnected for reuse and recycling.Axix load can be transferred directed through this joint.There is no limitions about the sections of beams and columns.The connecting and unlocking function of the joint was validated through the functional test.Experimental study on seismic behavior of the plug-in self-lock joint was conducted.A test consisting of 11 full-scale specimens was designed and conducted.The seismic behavior of the joint under monotonic and cyclic load was investgated.Moment-drift relationship,failure modes,strength,stiffness,ductility and energy dissipation was gained.The effect of the beam section types,structural details for seismic design at the corners,diameters of the stud and assembling holes,the unlocking devices was evaluated.The results showed that the plug-in self-lock joint can be defined as full-strength semi-regid joint according to Euro Code 3.The stiffness of the joint is about 80%of the regid-joint limitation.The strength of joint region is higher than that of the connected beams.Thus the failue mode of the joint is the fracture of the section at the root of beams.The ductility coeficients of the joints are about 2.7～3.1.The joints exhibit exceptional energy dissipation capabilities with the maximum equivalent viscous damping coefficient of 0.30～0.45.The unlocking device will decrease the inintial stiffness by 15.0%.The diameter of the stud,assenmbling hole and the thickness of the connecting plate will not have significant effect on the strength and stiffness.（3）FE models of the joints was developed and numerical analysis was conducted.Detailed FE models which can simulate the internals,including stud,cone-shaped latches and sleeve,were developed.The mechnisim of the joint was gained and the factor effect analysis was conducted.The effect of the thickness of joint boxes,the diamerter of the stud and the constructional details and mearsures was discussed.The results showed that the joint can transfer the moment verticaly,but cannot transfer the moment horizonally.The mechnisim of the side or middle joints was same as that of the corner joints.The connecting plate can only transfer the horizontal force,but cannot transfer the moment.The side joint can be simplified as two connecting corner joint;the middle joints can be simplified as two orthogonally-placed side joints.Thus the side joint can be simplified as two connected corner joint,the middle joint can be simplified as four groups of orthogonally placed side joints.The effect of stud diameter is not significant.The thickness of the joint boxes have some effect on the strength and initial stiffness of the joint.When the side thickness of the joint boxes is doubled,the strength and initial stiffness increase by 2.6%and 6.0%respectly.The unlocking device will not effect the strength,but will decrease the initial stiffness by about 10.0%.For the joint without joint boxes,the strength and initial stiffness are 11.4%and 10.2%lower than that of regular joints.Compared with rib stiffener,cover plate can increase the strength and initial stiffness by about 9.2%.The RBS joint can protect the weld,but decrease the strength and initial stiffness by 12.5%and 5.5%respectly.（4）Therotical analysis were conducted about the seismic behavior of the plug-in self-lock joint.Based on the experimental and analysis results above,a simplified mechanical model was developed.The connection between the modules can be simplified as a spring hinge,of which the stiffness is K₀.This simplified mechanical model can be used in the structural calculation of the modular steel construction.Equations for the stiffness and strength in elastic and inelastic stage was proposed.Validations among the simplified mechanical model,experimental and FE analysis results were made.The maximum error for strength and initial stiffness is about 14.9%and 10.6%respectly.The results showed that the simplied mechanical model were with excellent accuracy,and can simulated the behavior of the plug-in self-lock joint.Based on the simplified mechanical model,design method of the joints was proposed.Recommendations for the design of the joints were given accordingly.