RC Structural Hybrid Simulation With Model Updating Of Material Constitutive Law

It is extremely essential to study the seismic behavior of structures to improve their safeties,due to the grave casualties and economic losses caused by seismic disaster.One of the means for studying the structural seismic performance is hybrid simulation which isolated the key components,which are tested as physical substructure,from the reminder of the structure which is the numerical substructure.In this way,the limitation of testing site,loading equipment,and funds budget for large-scale specimen can be solved to a great degree.However,for large complex structures,it is unrealistic to take out all the critical components as physical substructures for that the number of the components exhibiting nonlinear behavior will significantly increased.Hence,the accuracy of the numerical substructure faces increased challenge.To hybrid simulation,the numerical substructure is constructed based on the existing constitutive models in finite element software.Hence,this paper will emphasize on updating the parameters of the existing constitutive models after the finite element model of the structure is modelled.To this day,most hybrid simulations with model updating focus on updating the parameters of component constitutive model(story shear model)leading to large modelling errors and the unknown detailed responses of the structure.Moreover,for reinforced concrete(RC)component,there is no generalized constitutive model that contains the factors of the size of the RC member,boundary conditions,axial compression ratio,and the volumetric stirrup ratio,etc.However,the component constitutive models in narrow sense are different for various RC members results in difficulty in updating the parameters to numerical substructure,hence limitation of applying the hybrid simulation with model updating.In addressing this challenge,this paper goes from the perspective of material level which is the foundation of finite element model and proposes the hybrid simulation based on identification and updating the parameters of the concrete constitutive model.The main work and results are concluded as follows,1.In order to make the updating of the concrete constitutive parameter be more universal,the conditions for realizing model updating are clarified through defining the constitutive parameter and unconstitutive parameter.The unified constitutive models of unconfined and confined concrete are derived from the existing uniaxial concrete constitutive models by introducing the volumetric stirrup ratio as unconstitutive parameter.2.Based on the principle of Kalman filter,the relation of the recursive least square estimation,the Kalman filter and the unscented Kalman filter is explicated to make the principle of unscented Kalman filter more understandable.The precision of unscented transform(UT)based on the scaled symmetric sampling method(SSSM)is analyzed;the influences of determining the coefficients in the SSSM on the estimation of mean and variance are discussed;and the values of the coefficients are deduced,for one dimension random variable case,when the estimations of the mean and variance reach the fourth-order precision.Aiming at model updating in hybrid simulation,the source codes of OpenSees are developed and the parameter identification method embedding the OpenSees is proposed to solve the problem rased from taking the restoring force as the measurements.3.The proposed identification method and hybrid simulation based on updating the concrete constitutive parameters are respectively validated through a monotonic loading test on an RC column and a model updating hybrid simulation on an one-bay-one-span RC frame.The results show that the convergence values of each parameter under various experimental cases are close to each other with a small variance,which indicates that the proposed identification method embedding OpenSees is robust and reliable.Comparing to the standard hybrid simulation,the accuracy of the proposed hybrid simulation with model updating is significantly improved.Under the same seismic loading,the damages of the specimens are different between the standard and model updating hybrid simulation.The standard hybrid simulation may underestimate the earthquake-resistance of structures leading to the waste of structural capacity.4.Apply the proposed hybrid simulation updating concrete constitutive parameters to the RC continuous rigid bridge with tall thin-walled piers.It concludes that the convergence speed,the robustness and the reliability still behave quite well.Contrasting to the simpler structure,the improved accuracy of a large complex structure is even greater.Moreover,the accuracy of the numerical substructure can be greatly increased even though the model error is increased.By tuning the initial values of constitutive parameters,the negtive influence of model error is decreased to further improved the precision of the numerical substructure.From the observation of specimens,it is found that the failure mode of this thin-wall hollow section pier is bending-shear type with the tensile rupture of the stirrup.This infers that the affect of shear can not be ignored.