Study Of Model Updating And Seismic Reliability Of Self-anchored Suspension Bridge With Super-wide Girder

Self-anchored suspension bridge(SASB)is competitive in the design scheme of small or medium span bridge due to its advantages such as attractive appearance and high adaptability to constructuion site.Especially with the fast development of domestic transportation infrastructures,SASB has been widely used in China.But,because of the cables of SASB are anchored in the main girder,this self-balance system which is different to normal suspension bridge makes the performance of the structure,especially the main girder,extremely complex.Furthermore,modern bridges ordinary enlarge the width of girder or expand the vehicle lanes to improve the traffic throughput and alleviate the transportation pressure,the increase of the ratio between width and span results in more complexity of the structure and the response of the bridges.Hence,the researching of the performance,the response and mechanism of SASB with super-wide girder fills up the empty research area of this bridge type,improves the situation of the advanced development and the hysteretic research and provides scientific basis for the expansion of the application of SASB with super-wide girder.Based on an in-service SASB with super-wide girder and the breakthrough point of safety assessment of the in-service bridge,two difficult problems are focused and settled during the research of SASB with super-wide girder.Firstly,the establishment of detailed and effective finite element model of super-wide girder,namely model construction and updating.The detailed model can be used to avoid both poor accuracy of single or double spine girder model and low efficiency of solid model.The accurate finite element model provides the foundation of performance analysis and condition assessment of SASB with super-wide girder.Secondly,perform accurate and highly effiective seismic condition assessment of SASB with super-wide girder.The problem of low accuracy and efficiency of seismic reliability assessment of complex engineering structures is solved.This proposed technique used in seismic reliability assessment provides the security of SASB with super-wide girder.It should be pointed out that the research contents and methods of SASB with super-wide girder are universe and can be reasonablely applied in other large and complex engineering structures to provide experience and reference.The main research contents and results are included:(1)A 3-D detailed model method and experiment validation of SASB with super-wide girder.Because the requirement of the model is already not meted by the ordinary model method,based on software of ANSYS and shear-flexible grillage method,a 3-D FE grillage model method of the bridge was proposed,which increases the simulation accuracy of the model through subdividing the wide girder;The ambient vibration test and static test with vehicle loading under finished state were introduced and implemented,the comparisons between the results of model and test are made,including the vibration frequencies and shapes of girder,displacements and stresses of typical cross-sections,the mechanism of the bridge was explained.The results show that,the vibration frequencies of girder of the initial model are smaller than the experiment,the differences are mostly over 25% and the largest one is up to 38.85%,but the MACs of vibration shapes are mostly over 95%;From the static performance of the girder,the distribution of vertical displacement of girder of initial model is totally different with test results,but the calculated change trends of displacements and stresses of typical sections under vehicle loading conditions are close to test results,this reveals that the initial 3-D detailed model at least reflects the change regular of static performance under vehicle loading;This model method is validated by the comparison between test and the initial model that it can reflect the real distribution of stresses of cross-sections;The big difference between them shows the significance of model updating of this SASB with super-wide girder.(2)Research of SASB finite element model updating based on Gaussian white noise mutation particle swarm optimization(GMPSO)method.Finite element model updating problem is practically a nonlinear optimization problem with constrained conditions,the PSO was introduced to solve this optimization problem to improve the disadvantage of more iteration number needed in most used updating issues;The deficiency of standard PSO and lots of advancements implemented in PSO were explained,the performances of the modified PSOs were comparied;The model updating technique based on GMPSO was then proposed and the updating process with each reasonable coefficients was defined,the feasibility of this model updating technique was then verified by the application to model updating of a damaged simply supported beam and the high efficiency was validated by the comparison with model updating technique based on Genetic Algorithm(GA)which was frequently used in other model updating issues;Finally,based on the GMPSO model updating technique,the initial model of SASB with super-wide girder was updated and then verified by both dynamic and static experimental data.The results show that,the GMPSO was proved having better global searching ability and higher efficiency by test functions example;The updating results of model updating methods based on GMPSO and GA are consistent,but the former method needs less iteration steps,the feasibility of model updating method based on GMPSO is validated;In the application of GMPSO to model updating of SASB with super-wide girder,the objective function is suggested as the combination of the static performance and the frequencies to obtain better updating results.(3)Research of SASB finite element model updating based on hybrid method of Gaussian white noise mutation particle swarm optimization(GMPSO)and meta models.The polynomial meta model,Kriging meta model and BP neural network meta model were explained and based on those meta models,the new model updating technique integrated by Gaussian white noise mutation particle swarm optimization(GMPSO)was proposed to improve the efficiency of direct GMPSO applied in model updating of engineering structures with high variable dimensions and complex structures,like SASB with super-wide girder;The updating process was defined and the feasibility of this new technique was verified by the application to model updating of a damaged simply supported beam,meanwhile,the accuracy and efficiency of different meta models were compared with each other;Finally,based on the model updating technique with the best meta model combined by GMPSO,the initial model of SASB with super-wide girder was updated and then verified by both dynamic and static experimental data.The results show that,using GMPSO with meta models to solve model updating problem of complex engineering structures obtain quite accurate finite element model with higher efficiency compared to direct GMPSO method;The model updating method based on BPNN-GMPSO has better updating results and higher efficiency than other meta models;The same result that he objective function is suggested as the combination of the static performance and the frequencies to obtain better updating results in complex engineering structures.(4)Research of hybrid method for seismic reliability assessment of complex structures.The subset simulation(SS)method,explicit time domain method(ETDM),power spectrum of random earthquake loading and its discretization method were all explained;The deficiency of subset simulation and its application to seismic reliability with small failure probability and high dimensions was put forward and to alleviate this disadvantage,advanced subset simulation was introduced and to improve the efficiency of solving seismic reliability of complex engineering structures with high dimensions,a hybrid method integrated with the advanced SS,ETDM and BP neural network algorithm was proposed and this method successfully separate the low randomness of structural parameters and high randomness of earthquake parameters;The application of this hybrid method to solve the seismic reliability of a 3-D frame structure was implemented to verify the accuracy and efficiency of this new method and the results were compared with the direct Monte Carlo simulation(MCS).The results show that,the value of seismic reliability of the new hybrid method is close to that of direct MCS and its efficiency is much higher than direct MCS;No matter the randomness of structural parameters are considered or not,the hybrid method can always obtain the accurate seismic reliability of this frame structure with high efficiency,and the smaller the failure probability of the structure is,the higher efficiency this hybrid method has;This hybrid approach is quite applicable and provides the probability to assess the seismic reliability of the complex engineering structures with small failure probability and high dimensions.(5)Seismic reliability assessment of the self-anchored suspension bridge with super-wide girder based on the new hybrid approach.The structural performance under deterministic earthquake loading was analyzed and the sensitivity of the parameters such as Young's modulus of materials,density,geometric dimension of sections,et al.to the dynamic responses;Based on the proposed hybrid approach of SS-ETDM,the seismic reliability of the SASB with super-wide girder having deterministic structural and temperature parameters was implemented,considering the random earthquake loading with the Shinozuka's equation;Based on the proposed hybrid approach of SS-ETDM-BPNN,the situation of randomness of the structural and temperature parameters was considered combined with the variability of earthquake loading,under that the seismic reliability of SASB with super-wide girder was analyzed;Based on hybrid approach,the sensitivity of structural and temperature parameters to the seismic reliability was conducted and according to the sensitivity results,the thorough evaluation of seismic reliability of the SASB with super-wide girder under specified conditions of coupling of parameters was implemented.The results show that,the compressive tress of key cross-sections instead of displacement becomes the criteria of failure in the seismic reliability assessment of SASB with super-wide girder;the hybrid method of seismic reliability assessment can be successfully applied to complex engineering structures even under the 3-D earthquake loading;The efficiency of the new proposed hybrid approach has higher efficiency than direct MCS method in solving seismic reliability assessment of complex engineering structures;The thorough assessment of seismic reliability of this SASB with super-wide girder reveals that it has quite safety in random earthquake loading,which means the failure probability of this bridge structure is small enough and it has conservative structure,especially under randomly frequent earthquake loading.