Study On Seismic Performance Of Reinforced Concrete Structure Considering Dynamic Effects

Reinforced concrete(RC)frame structures have been widely used in the domestic multi-story public buildings,and the seismic performance during their service period is closely associated with the national livelihood security and economic construction.Earthquake action in essence is a kind of cyclic dynamic load,on one hand the micro damage of materials under cyclic load results in the macro performance deterioration of members,on the other hand,the strain rate sensitivity of materials makes the behaviors of members under dynamic loading different from those under static loading,i.e.the dynamic effect.Although the seismic design theory and analytical method of RC structures have been rather mature,there is still a lack of provisions on the dynamic behaviors of RC members influenced by the strain rate effects of materials in current seismic code.Moreover,most of the available studies neglect the disadvantage influences of dynamic effect on the deformation capacity and performance deterioration of members.Therefore,for more accurate and reliable seismic performance assessment of RC structures,theoretical analysis and numerical simulation are carried out in this academic paper on the seismic performance of RC frame structures considering dynamic effects.The main research contents and conclusions are as follows:(1)Based on the dynamic loading test data of RC columns under seismic loading rate,the ordinary least square method and the Bayesian updating method are adopted to establish the determinate and probabilistic dynamic modified models,respectively.The DMC models are related to the main design parameters of members and the strain rate index and are capable of effectively reflecting the impacts of dynamic effect on the key mechanical properties of RC column members,i.e.the yielding strength,the maximum strength,the effective stiffness and the ductility coefficient.They can be further applied to dynamically modify the skeleton curves of members.The superiorities of the probabilistic DMC model over the determinate DMC model lie in its predictive accuracy,follow-up updateability and parameter randomness.(2)A macro hysteretic model for RC members is proposed which takes into account of the dynamic effects and seismic deterioration.The model can effectively reflect the different performance deterioration modes of RC columns under cyclic dynamic load,including the negative stiffness branch,the cyclic strength and stiffness degradation and the pinching effect.The static skeleton parameter can be determined by the empirical equations,while the corresponding dynamic skeleton parameter are obtained with the DMC models or the normalized proportional relationship of the feature point coordinates.The functional relations are established between the dynamic modified Park-Ang damage index and the degradation parameters,and the parameters are calibrated by test data.The accuracy of the hysteretic model is verified by comparing with the static and dynamic loading test curves.(3)Based on the proposed simplified calculating method for considering strain rate state of members,a dynamic concentrated plastic element model is established.The nonlinear dynamic analysis program for RC structures is compiled on the MATLAB platform.According to the calculated equivalent strain rate and the damage index values,the hysteretic model of plastic hinge can be real-time updated with dynamic effects and deterioration.The feasibility of the proposed method and program is validated by comparing with the measured results of shaking table test.The influences of dynamic effect on the seismic response,damage development and failure mechanism of RC frame structure are investigated.The numerical results show the dynamic effect has a significant influence on the structural seismic performance under large seismic intensities and its disadvantage impact should be sufficiently considered.(4)An analytical method for considering the uncertain dynamic effect in the seismic performance assessment of RC structures is developed.The uncertainties in probabilistic DMC model to the random structural parameters are investigated by parameter sensitivity analysis.Based on the interval predictions for dynamic behaviors of RC members,the calculated procedure of dynamic skeleton cluster is proposed,and probabilistic seismic demand and damage state of RC frame structure are numerically studied.The research results reveal that the randomness in structural parameters has a slight impact on the mean predicted value of DMC,but has an obvious impact on the dispersion in predictions.The major influential factors are the material strength,the axial ratio and the strain rate index,while the other factors have a minor influence.Moreover,the uncertain dynamic effect exerts a significant impact on the seismic performance assessment when the structure gets close to the collapse state.