Mechnical Performance And Reliability Assessment Method For Partial Cable-stayed Bridges With Corrugated Steel Webs

As a kind of relative novelty bridge structure,the number of partial cable-stayed bridges with corrugated steel webs(PCBCSW)is increasing gradually and meanwhile bring two kinds of requirements:(1)further investigation on the mechanical performance of PCBCSW;(2)the establishment of assessment method on the operation conditions.However,according to the summary towards the corresponding research status at home and abroad,in the current stage,the researches on the mechanical performance of key components,shear lag effect and performance assessment method,etc of PCBCSW are still insufficient,and the existing research achievements can not provide a better support for the design and maintenance of this kind of structure.It is necessary to conduct a further investigation on the mentioned issues by combining theoretical analysis,numerical simulation,model tests and field load test,etc.To investigate the mechanical performance of key components and completion state of PCBCSW,and then provide some references for the design and maintenance of this kind of structure,the push out tests were firstly conducted to study the shear performance and resistance calculation method of embedded connector with bolts(ECB).Then,the model tests,numerical simulation and field load tests were employed to investigate the shear lag effect of the box cross section of PCBCSW.In the last,the reliability based performance assessment methods were developed for the serviceability limit state and ultimate limit state of PCBCSW.The following conclusions are drawn as follows:(1)According to the push out test,the load-deflection curves of up folded plate,straight plate and down folded plate of the ECB are obviously different,specifically,the load-deflection curve of up folded plate has a hardening stage.The influences of bolts welded position,opening location on the shear resistance are explicated according to the analysis of contrast specimen.The approximate calculation method of shear resistance of ECB is proposed;(2)The most significant position of shear lag effect of corrugated steel web composite box section with four chambers under concentrated load is corresponding with the loading position,while it is the junctions of the adjacent two webs of middle web and the top plate for the uniform distributed load.The maximum shear lag coefficient of the box cross section increases with the increasing of wide span ratio,and decreases with the increasing of web thickness.The installation of diaphragm plate can weaken the negative effect of shear lag effect efficiently,more over,the solid diaphragm is better than the truss diaphragm.Further,the field load test data is employed to figure our the distribution of shear lag coefficient of completion stage of PCBCSW.The finite element simulation method of shear lag effect,whose applicability has been verified,is established;(3)For the Chaoyanggou Bridge,the actual eccentric load coefficient of top plate of the major span is a little lower than the theoretical value.For all the spans,the actual eccentric load coefficient of bottom plate is obviously higher than the theoretical value.For the corrugated steel web composite box section with four chambers,the shear stress of the most lateral two webs increases with the increasing of the height from bottom plate,for the interior three webs,the shear stress decrease firstly and then increases.The dynamic impact factor of PCBCSW increases with the increasing of vehicle speed.The dynamic impact factor of vehicle braking is a little lower than the normal travelling scenario.The dynamic impact factor of vehicle jumping is obviously higher than the normal travelling scenario.The former three modes of vibration of PCBCSW is vertical bending and the fourth order of vibration is lateral bending;(4)The mean value of vehicle load effect has the greatest influence on the reliability index of deformation of the main girder,and then the mean values of cable elastic modulus,cable cross section,concrete elastic modulus and elastic modulus of steel plate.The allowable deflection of the main girder shows a parabolic growth trend with the increasing of target reliability index.The deformation reliability index of main girder is 8.39 under design vehicle load.The measured characteristic value of deflection of main girder is around 47.5% of the allowable value,which indicates that the deformation performance of main girder of PCBCSW is satisfied;(5)The whole procedure of strength deterioration of steel strand cable can be divided into three stages: the protection of HDPE pipe,the duration of pitting corrosion and the development of fatigue crack.The fretting wear in the first stage in non-negligible for the whole procedure.The duration time percentages of the three stages are around 38.74%、12.47%、48.79%,respectively.The wear speed of wire increases with the decreasing of diameter,the increasing of contact force,the increasing of amplitude and the increasing of vibration frequency.On the other hand,the wear speed decreases with the extension of service time;(6)The time-dependent reliability assessment method for the critical components are developed by introducing the risk function based time-dependent reliability analysis method,and meanwhile by considering the deterioration model.For the critical component with safety level I,the target reliability index corresponding with reference period of 10 years is suggested to be 3.37,in which the differences of structural design and assessment,the individual risk criterion,social risk criterion,life quality index,and total cost optimization are considered.The reliability level of main girder is higher than that of the longest cable,for both of them,the reliability levels in the former 30 years are both higher than the corresponding target reliability index.Specifically,the cable should be paied more attention at the time point of 30 years.