| In recent years,our country’s energy and environmental pressures have increased,and labor costs have increased,which has accelerated the transformation and upgrading of the construction industry.The main structure of the construction industry is cast-in-place reinforced concrete,which has good integrity and can meet the needs of seismic fortification.However,the problems of castin-place concrete structures such as excessive wet work on site,large loss of building materials,and low resource utilization are not in line with current sustainable development strategy.Thus,prefabricated buildings have been vigorously promoted in my country due to the advantages of fast construction speed,less construction waste,and guarantee of construction quality.The key difference between prefabricated building and cast-in-place structure lies in the connection of components,and the comprehensive reliability of the connection directly affects the overall performance.Compared with the relatively mature equivalent cast-in-situ monolithic structure using wet connections,the assembly structure adopting dry connection greatly reduces on-site wet work and saves high labor costs.However,the stiffness of most dry connections is relatively lower than that of equivalent castin-place connections,and the lateral stiffness and damping ratio of the structure are insufficient,which restricts its application range.Based on the above background,this paper take the semi-rigid prefabricated concrete connections as the research object,and studies the final failure modes and failure mechanisms of 15full-scale beam-column connections through experimental methods.Not only the design theory of semi-rigid prefabricated concrete joints is established,but also the low-cycle fatigue theory is combined to provide early warning of connection failure.It is of great significance to promote the development of prefabricated concrete structures in the direction of safer,more controllable and higher reliability.Based on the above considerations,the main research contents and conclusions of this paper are as follows:(1)The experiment plan was formulated,and the static and pseudo-static tests of semi-rigid precast connections and cast-in-place connections were carried out.According to the existing conditions of the laboratory,the connection size was reasonably designed.According to the purpose of the test,we make a reasonable plan for connection loading and measurement.The test results show that the semi-rigid prefabricated connections often fail when the concrete at the beam end is crushed under monotonic and reciprocating loads;the semi-rigid prefabricated beam-column connections have good deformation and high bearing capacity.After reasonable design,It can achieve the same performance as the cast-in-place connection.(2)The design theory of semi-rigid prefabricated concrete connections was proposed,and the simplified modeling design method were verified.The material performance parameters are brought into the theoretical design formula,and the design load obtained is compared with the ultimate bearing capacity of the experiment.There is not much difference between the two,which verifies the accuracy of the theoretical design formula.Simplified modeling of semi-rigid prefabricated joints in XTRACT also simulates the actual bearing capacity of joints,which can be used as an effective method to assist theoretical design.(3)The semi-rigid prefabricated concrete connections have been tested on different ground motion excitation and parameterization.In the experiment,different loading protocols were used to simulate different ground motion excitations,and the important connection dimensions of semi-rigid prefabricated concrete connections were changed,and reciprocating loading experiments were carried out respectively.The results show that partial amplitude loading can give full play to the seismic performance of semi-rigid connections.Sudden peaks are more detrimental to the performance of semi-rigid precast concrete connections than progressive peaks;Because the size change of welding seam and corbel of semi-rigid precast concrete connection has a great influence on the performance,it is necessary to strictly control is required when designing the joints.(4)A low-cycle fatigue life prediction model for semi-rigid precast connections based on cumulative damage theory is proposed.The test data is reprocessed to determine the basic information of fatigue failure of semi-rigid prefabricated concrete connections.Based on the Miner cumulative damage criterion,the variable-amplitude loading displacement is subjected to constantamplitude processing.The traditional fatigue life formula is transformed,and the fatigue life curve of semi-rigid connections is fitted with the constant-amplitude fatigue loading failure information.The fatigue life prediction method was successfully applied to welded steel frame joints,which verified the feasibility of the method. |
