Research On Temperature Dependence Of Isolation Bearings And New Fully Precast Frame Structure System

The western region of China is characterized by harsh climatic conditions,dense distribution of seismic zones,frequent strong earthquakes,and abundant ecologically sensitive areas,which make it difficult to carry out long-term high-intensity construction.The economic development of these places is severely restricted by traditional construction methods.Therefore,it is an urgent task in the engineering field to develop a structural system with low-carbon and fast construction,good seismic performance and repairability.To solve this problem,this paper proposed a new dry-connection precast concrete frame structure system with fast assembly,convenient disassembly and reliable performance,and adopting the developed rubber bearing base isolation technology to improve its seismic performance and ensure its seismic function recoverability.The temperature dependence of the rubber bearings was studied,and a prediction method for the mechanical properties of the bearings at different temperatures was proposed.A new type of dry-connection precast beam-column joint was proposed,and static tests and numerical simulations were carried out to study the seismic performance of the joint.A 1/2 scaled test model of the new fully precast frame structure was designed and produced,and the shaking table tests of seismic isolation and anti-seismic conditions were carried out;the finite element model of the precast seismic isolation frame structure was established,and the seismic performance analysis and seismic vulnerability analysis considering bearing temperature dependence were presented.On the basis of experimental research and numerical analysis,a performance-based design method considering the bearing temperature dependence was proposed for the isolation precast frame structure system.The main contents and conclusions are as follows:1.An experimental study on the temperature dependence of rubber bearings was carried out,and the temperature influence coefficient function method was proposed to predict the bearing mechanical properties.Taking the lead rubber bearings and natural rubber bearings with a diameter of 200 mm as the research objects,the compression shear tests were carried out at temperatures ranging from-30°C to 20°C and shear strains ranging from 100% to 300%.The test results show that the equivalent stiffness,yield force and post-yield stiffness of the lead rubber bearing are significantly affected by temperature,and all increase with the decrease of temperature.The temperature dependence of the equivalent stiffness of the natural rubber bearing is also significant.On the basis of the test results,the temperature influence coefficient function of the mechanical parameters is proposed by the nonlinear regression analysis method,which can accurately predict the mechanical properties of the rubber bearings at different temperatures.2.An experimental study on the temperature dependence of the rubber bearing considering the effect of loading speed was carried out,and the rheological model reflecting the dynamic mechanical characteristics of the rubber bearings at different temperatures was established.Cyclic shear tests(CS),single-step relaxation tests(SR)and multi-step relaxation(MSR)tests at-30°C,-10°C and 20°C were carried out on lead rubber bearings and natural rubber bearings,respectively.The hysteresis curve of CS test,the stress time history curve of SR test and MSR test were compared respectively.The results show that the shear stiffness and hysteretic energy dissipation,instantaneous stress and equilibrium stress of the bearings all have significant temperature dependence.A fractional derivative rheological model was established to represent the loading velocity-dependent behavior of rubber bearings.3.A box-type concealed corbel dry-connection precast beam-column joint was proposed,the results of quasi-static test and numerical simulation show that the seismic performance of the beam-column joint is good.The test results show that the cracking story drift ratio of the precast joint is larger,the cracks on the concrete beam body are less when the joint fails,and the plastic deformation is concentrated on the connectors.The hysteresis curve of the precast joint is asymmetric,and the positive and negative bearing capacities are 37.3% and80.4% higher than the design value,respectively.The numerical simulation results show that,with the increase of concrete strength grade,the initial stiffness of the precast beam-column joint increases,the yield displacement decreases,and the yield load and bearing capacity increase significantly.The anchoring length of the column embedded part has a great influence on the trend of the skeleton curve.When the length increases from 150 mm to300mm,the yield load and peak load increase by more than 10.1%.The influence of anchoring length of beam embedded parts is also obvious.When the steel of the concealed corbel and the beam top connector changes from Q235 to Q345,the yield load and bearing capacity of the joint increase by more than 9.5%.When the bolt/nut strength grade changes from 8.8 to 10.9,the increase of positive yield load and peak load is greater than 9.2%;the increase of negative yield load and peak load is greater than 12.6%.4.Shaking table tests of the dry-connection precast frame structure and the corresponding isolation structure were carried out.The results show that the precast isolation frame structure can meet the seismic requirement of high seismic intensity areas.The 1/2 scaled model of the dry-connection precast concrete frame structure was designed and produced,equipped with lead rubber bearings.Shaking table tests were carried out for the isolation and anti-seismic conditions respectively.During the test,the superstructure of the isolation model was dominated by overall translation.After loading,only a few micro-cracks appear on some concrete beams,and the overall seismic performance is good.The response of the seismic model gradually intensifies with the increase of earthquake intensity,and the damage gradually accumulates.With the increase of seismic intensity,the acceleration of the top of the seismic model increases rapidly,and the displacement response of each layer shows an increasing trend.While the acceleration of the isolation model changes relatively slowly,the displacement of the isolation layer increases significantly,and the floor displacement of the superstructure increases slightly.The maximum story drift ratio of the isolation model and the seismic model under the rare earthquake of 8 degree are1/428 and 1/133,respectively.Under each condition,the acceleration attenuation coefficient of the first floor of the isolation model is greater than 0.31,and the shock absorption effect is remarkable.The new fully precast isolation frame structure has excellent seismic performance,which can achieve the performance target of no damage under medium earthquake and repairable under large earthquake.5.The seismic performance of the precast frame isolation structure was evaluated by finite element analysis,the effect of temperature variation on seismic performance of precast isolation structures was revealed.The Opensees finite element model of the dry-connection precast frame isolation structure is established,and the validity of the model is verified by comparing with the shaking table test results.Seismic performance analysis and seismic vulnerability analysis considering rubber bearing temperature dependence were carried out.It is found that the natural vibration period of the isolation structure decreases approximately linearly with the decrease of temperature.The decrease in temperature will lead to a decrease in the shock absorption efficiency of the isolation system.From 30°C to-20°C,the average increase of the acceleration at the top of the structure under the action of20 seismic waves is 20.0%,the average increase of the maximum story drift ratio is 25.0%,and the average increase of the damping coefficient is 23.6%,the average increase of bearing force is 25.9%,and the average decrease of bearing displacement is 24.5%.The seismic vulnerability analysis of the isolation structure at-20℃,20℃ and 30℃ shows that the transcendence probability of the story drift ratio of the superstructure increases with the decrease of temperature,and the transcendence probability of the maximum displacement of the bearing decreases with the decrease of temperature.The probability of exceeding the maximum tensile stress of the bearing increases with the decrease of temperature.The seismic vulnerability of the isolation structure increases with the decrease of temperature,and the horizontal deformation capacity of the bearing plays a leading role in the vulnerability of the isolation system.6.A performance-based seismic isolation structure design method considering the temperature dependence of bearing performance is proposed.Taken the story drift ratio limit and the maximum displacement of the isolation layer as the performance objectives,the temperature influence coefficient function was used to represent the change of the mechanical properties of the isolation layer within the design temperature range,and the equivalent two-degree freedom model was used to simulate the synergistic response of the isolation layer and the superstructure.A performance-based design method considering the bearings temperature dependence was proposed.This method is suitable for the rubber bearing isolation system.After iterative calculation,the key parameters of the isolation layer and the floor shear force distribution of the superstructure can be determined,and the design of the isolation structure system can be completed.A simplified design and check calculation method of the dry-connection precast beam-column joint and the design method of fully precast frame structure system were proposed,which provide a theoretical basis for the engineering application of dry-connection isolation precast structure system.