Study On Seismic Performance Of Prefabricated Limestone Powder-slag Concrete Frame Structure With Dog-bone Pre-embedded Steel Bone Connection

In recent years,the government has put forward higher requirements for the construction industry to achieve the carbon peaking and carbon neutrality goals and pursue sustainable development.The organic combination of green building materials and prefabricated buildings not only greatly improves labor productivity and construction quality,but also reduces construction pollution and saves resources and energy.It can effectively achieve the goal of high-quality development of the construction industry.PC(Prefabricated Concrete)frame structures have advantages over traditional construction industries,such as high construction efficiency,good building quality,and low environmental pollution.The structure itself is clear,stable,reliable,and easy to standardize construction.The theory of PC frame structures is also relatively mature compared to other structural forms.The connection between components in PC frame structures is crucial in the entire structural system,and its performance will directly affect the overall reliability of the structure and the failure mode of the structure under seismic action.Mineral admixtures such as limestone powder,slag,etc.,can effectively improve the performance of concrete while also having good environmental and economic benefits,which contributes to promoting the process of sustainable development.Based on extensive research by scholars,this thesis proposes a dog-bone type preembedded steel bone connection node to protect the core area of the node in the frame structure,improve the ductility and energy dissipation capacity of the frame structure,and applies it to the overall frame structure in combination with limestone powder-slag concrete.Three types of frame structures were designed for different seismic intensity zones.For each type,a reinforced concrete(RC)frame structure and a precast concrete(PC)frame structure were constructed and tested.The seismic performance of the material and the node in the frame structure,such as hysteresis curve,skeleton curve,bearing capacity,stiffness,ductility,and energy dissipation,were analyzed through physical tests and ABAQUS finite element simulation analysis.The influence of different parameters in the frame structure on its load-bearing performance was also studied.Based on the experimental and numerical simulation results and their characteristics,design methods and construction requirements for the dog-bone type pre-embedded steel bone connection prefabricated limestone powder-slag concrete frame structure were proposed.The main conclusions and innovative achievements of this thesis are as follows:(1)The limestone powder-slag concrete frame structure has good seismic performance.Its failure mode is beam end bending failure.The test results show that the limestone powder-slag concrete hysteresis curve is full and has good ductility and energy dissipation capacity.The skeleton curve undergoes the elastic stage,yield stage and ultimate stage,and has good stiffness.(2)The seismic performance of the dog-bone shaped pre-embedded steel connection PC frame structure with limestone powder-slag concrete is slightly better than that of the cast-in-place limestone powder-slag concrete frame structure.The PC frame structure has less cracking in the joint core area and precast beams,and no concrete spalling.The hysteresis curve of the PC frame structure is full and "humpshaped," with excellent energy dissipation capacity and slight "pinching" in the later stage.The bearing capacity of the PC specimen is equivalent to that of the RC specimen,and the stiffness is slightly lower than that of the RC specimen.The degradation of the bearing capacity and stiffness of the PC specimen is comparable to that of the RC specimen,and the ductility coefficient can meet the requirements and is better than that of the cast-in-place RC frame structure.(3)For the dog-bone-shaped pre-embedded steel connection PC frame structure designed for different seismic intensities,i.e.,different concrete strengths and different reinforcement modes,increasing the concrete strength and increasing the reinforcement ratio within the range of specifications can improve the bearing capacity of the PC frame structure and enhance the stiffness when upgrading the concrete strength grade.However,it does not have a significant effect on the mechanical behavior of the entire PC frame structure in the elastic stage,and it has no obvious effect on the degradation of bearing capacity,stiffness,ductility coefficient,and energy dissipation capacity."(4)Through ABAQUS finite element simulation,the reliability of the physical experiment was verified,and it was found that the development trend of the skeleton curve of the finite element simulation model was basically consistent with that of the physical experiment specimen,experiencing the elastic stage,yield stage,and ultimate stage,and the two had roughly the same bearing capacity.However,the initial stiffness of the finite element simulation model was much different from that in the physical experiment,and there was some discrepancy between the material constitutive model used in the simulation and the actual material.(5)In this study,the effects of axial compression ratio,dog-bone joint size,material strength,and bolt pre-tightening force on the mechanical performance of the dog-bone prefabricated steel-concrete composite frame structure were investigated using finite element simulations in ABAQUS.The skeleton curves of the model were obtained by applying unidirectional loading,and three stages including elastic,yield,and strengthening were observed.Within a certain range,the increase in vertical load could significantly enhance the model’s bearing capacity,yield strength,and initial stiffness,while also slightly increasing the bearing capacity degradation coefficient.The improvement in concrete strength level could significantly enhance the ultimate bearing capacity of the prefabricated specimen and had a certain effect on the degradation of its bearing capacity.The improvement of steel strength level in the connection area had little effect on the bearing capacity of the prefabricated specimen.Applying pre-tightening force could effectively prevent the occurrence of bolt slippage under seismic loads,and improve the energy dissipation capacity.However,with the increase of bolt pre-tightening force,the model’s bearing capacity showed a trend of first increasing and then decreasing,but the change was not significant.The reliability of the physical experiment was verified by ABAQUS finite element simulation,and the simulation model showed a similar trend to the physical experiment specimen in terms of the development of the skeleton curve,except for a large difference in the initial stiffness due to the discrepancy between the material constitutive models used in the simulation and the actual materials.(6)In this study,a design method and construction requirements for the assembly of limestone powder-slag concrete frame structures with dog-bone pre-embedded steel connections were proposed.Design methods were provided for the reinforcement inside the prefabricated beams,the connection of the steel bar grouting sleeve,the connection of the steel plate and concrete in the transition zone,the size of the weakened part of the node,and the connection of the beam-column connection bolts.Construction requirements were also proposed for the assembly of the dog-bone pre-embedded steel connection limestone powder-slag concrete frame structure.