Comparative Research On The Global And Local Sensitivity Of Seismic Fragility Of Unreinforced Masonry Structures

The masonry structures have a long history,and are widely used in many applications,but are easy to be severely damaged in earthquakes.Therefore,accurate seismic fragility analysis is essential for engineering applications.Due to the high discreteness of structural parameters and the strong nonlinearity of seismic response,it is necessary to consider the uncertainty of structural parameters by using the appropriate sensitivity analysis methods in seismic fragility analysis.The computational efficiency of local sensitivity analysis（LSA）is high,but the global consideration of parameters is lost.The global sensitivity analysis（GSA）is more accurate,but the calculation cost is greatly increased.Thus,the application in the structural field is still in its infancy.In this paper,a comparative study is conducted on the sensitivity analysis of structural parameters to seismic vulnerability of typical unstiffened masonry structures with 3～6 storeys.The multi-dimensional spatial distribution and correlation of structural parameters are considered in the GSA based on elementary effect（EE）,and the computational efficiency is improved.Therefore,it is introduced into the sensitivity analysis of masonry structures.A method of seismic fragility analysis is proposed based on the EE and IDA called EE-IDA.The equivalent frame model of an unreinforced masonry structure is established by OpenSees.The seismic fragility analysis based on the elementary effect and IDA（or the LSA and IDA）is conducted considering nine structural uncertainty parameters.The sensitivity of structural seismic fragility against the above parameters is compared,and the sample of the local sensitivity analysis is adjusted accordingly.The comparative study in different sensitivity analyses for damping ratio is carried out using 4 unreinforced masonry structure models composed of 3～6 storeys.The correlation of parameters has little effect on the sensitivity of the damping ratio.The complex GSA can be replaced by the reasonable sampling of LSA whose theory is easy.Further work of sensitivity analysis is conducted considering several parameters which have strong influence,including the density ρ_m,shear strength f_vo,tensile strength f_t,and compressive strength f_m.The interaction of the relevant parameters of structural uncertainty can be ignored.For most structural parameters,the local sensitivity values are a good substitute for the global sensitivity values,especially for the damping ratios,after changing the samples.There is a great difference between the sensitivity values of f_t and f_m,which can lead to the strongest nonlinear change of the median of the seismic fragility curve.When correlation and nonlinearity of parameters are weak,LSA is a good substitute for GSA due to the higher computational efficiency if the sampling is reasonable.