Research On Evaluation Method Of Capacity And Durability For Hollow Slab Bridges Based On Damages

Nowadays,a large number of hollow slab bridges have been in-service for many years since they were built in the early stage of highway projects.Due to a series of factors such as poor construction quality,material degradation and environmental erosion,different kinds of damages are formed in hollow slab bridges over service time,exerting an irreversible impact and endangering the bearing capacity and durability of bridges.With the increased traffic volume,structural damages in many hollow slab bridges become a potential threat to the national highway.Therefore,it is of great necessity to study the influence of various damage forms on the service performance of hollow slab bridges.Based on the existing damage data,a scientific evaluation method for the capacity and durability of the existing hollow slab bridges is proposed.In this study,on the basis of the reconstruction project of Hefei-Wuhu highway,typical damaged hollow slab bridges are selected for the following research:First of all,main damage forms and causes of hollow slab bridge are summarized.Based on the quantitative investigation,the characteristics of damages such as "hinge joint damage","structural crack" and "bearing damage" are analyzed,and their spatial distributions are first obtained.Secondly,in order to evaluate the transverse load-distribution of bridges sample with typical damages,the load test that works in various measurement environment is designed,and evaluation index of the hinge joint damage,which can measure the transverse distribution of the hollow slab bridge,is proposed.After the load test of the sample,the transverse load-distribution is analyzed by comparing the theoretical values under the non-damaged state.Then,based on the theoretical and measured relative displacement of the hinge joint,the evaluation indexes of each hinge joint are calculated.Combining the evaluation indexes with the results of the transverse distribution,the rationality of evaluation index of hinge joint is explained in the quantitative evaluation of the transverse load-distribution.Thirdly,it is difficult to quantitively evaluate the durability of internal conditions of bridge structures.Therefore,based on the cutting test of hollow slab,a durability evaluation system of the hollow slab bridge is proposed by combining AHP with fuzzy theory.Based on data of cutting test,AHP is applied to establish a hierarchical model of durability evaluation and obtain the weight of each level.On this basis,the fuzzy synthesis vector of each level is determined by using fuzzy theory,and then evaluation index of the safety and durability is finally obtained.Then,in order to deduce the ultimate capacity and its reduction coefficient without reaching the failure state,a calculation method is proposed through the law of material degradation or existing test data.The correctness of this method is verified by the data of a slab failure test in the existing literature.Finally,the correlation models between damage index and index of transverse load-distribution,durability or ultimate capacity are built.By taking the above indicators as the input and output,neural network training is carried out to establish the quantitative relationship.At the same time,the training data is supplemented by the finite element model.A bridge engineering case is selected to verify the applicability of the correlation model.The results show that trained neural network system based on damage is reasonable and can be used to evaluate the capacity and durability of hollow slab bridges.