Study On Fire Resistant Performance And Post-fire Seismic Performance Of New-type Precast Concrete Frame Joints

Compared with traditional cast-in-place concrete buildings,prefabricated buildings have the advantages of fast construction speed,low labor demand and environmentally friendly.The development of prefabricated buildings is conducive to solving the problem of the current population aging situation and the strict environmental form in China.It is a main direction for the future development of China's buildings.The vigorous development of prefabricated buildings is now included in the national “13th Five-Year Plan”.The current research on fabricated buildings is mainly devoted to the development of splitting and connection forms with reasonable mechanical properties,convenient construction and less wet work.However,the research on fire resistance and fire damage of fabricated buildings in the prefabricated buildings is relatively less.In the development process of the prefabricated cast-in-place and dehumidification operation in the prefabricated building connection joint,the components with faster heat transfer and heat transfer such as steel and bolts are often used for connection,and these materials accelerate the structure under the action of fire.The heating rate is therefore necessary in the research of the fabricated joint,it is necessary to study the fire resistance of the assembled joint and the seismic performance of the assembled joint after the fire.In this paper,based on the previous research literature on the thermal properties of building materials,use the Abaqus finite element analysis software is used to study the fire resistance and fire resistance performance of a new type of fabricated joint fire.The following work has been done:(1)Using ISO-834 standard rising(lowering)temperature curve,the temperature field of the assembled joint under fire and after fire is analyzed,and the law of temperature rise and fall inside the joint during the whole process of fire is studied.It is found that the node is affected by the heat exchange rate with the environment during the fire action.The fire area on both sides rises faster than the single-sided fire area,and the angular positive angle area rises faster than the negative angle area.The bolts connecting the core area of the joint is heated up and plays a role of heat transfer under the action of fire.(2)Based on the current "Fire Test Method for Building Components" and "Code for Fire Protection of Building Designs",the sequential fire-force coupling is used to analyze the fire endurance of the joint under fire and set the column axial compression ratio,eccentricity,beam load ratio,concrete protective layer thickness,bolt diameter are analytical variables.In the process of simulation analysis,the failure modes of all joints are failure of the beam deformation to reach the f fire endurance,and the fire endurance can meet the specification requirements.When the node is close to failure,the deformation speed of all nodes increases sharply,and the node reaches a fire limit failure with certain abruptness.Among the analysis parameters,the increase of axial compression ratio,eccentricity and load ratio is an unfavorable condition for the fire resistance of the joint.The increase of the bolt diameter and the thickness of the concrete protective layer is an advantageous condition for the fire resistance of the joint.In the unfavorable condition,the axial pressure The influence of axial compression ratio and eccentricity is large.In favorable conditions,increasing the thickness of concrete protective layer has better effect on improving fire resistance.(3)Extract the historical maximum temperature of each unit node in the fire during the temperature rise and fall of the fire.According to the loading method recommended by the Code of Practice for Building Seismic Test,the node with the normal temperature after the fire is loaded by the low-cycle reciprocating loading of the beam end.The normal temperature joints are loaded to study the effects of different fire durations and axial compression ratios on the seismic performance of the joints after fire and compared with the cast-in-place joints.It is found that the seismic performance of the joints is reduced after fire,and the assembly is under the same fire time.The performance of the joint is reduced more than that of the cast-in-place joint;the influence of the increase of the axial compression ratio on the seismic performance of the joint is the same before and after the fire;the longer the fire of the same fabricated joint,the more the ultimate load and the energy consumption decrease.But the ductility is in this paper is study decreased slightly first and with the increase of fire time within the range of fire duration.