Study On The Fatigue Of Orthotropic Steel Decks Under The Action Of Vehicle Loads

Orthotropic steel deck(OSD)has been the preferred form of bridge deck for longspan bridges such as suspension bridges and cable-stayed bridges.However,the frequent fatigue problem have seriously affected the usability,durability and safety of bridges.Although the steel-UHPC lightweight composite deck(LWCD)system can greatly improve the fatigue performance of OSDs,the risk of fatigue cracking cannot be completely eliminated.Studies have shown that vehicle loads are the primary external cause of fatigue of OSDs.In this dissertation,the fatigue performance of conventional OSDs(COSDs)and LWCDs under the action of vehicle loads was investigated through theoretical analysis and numerical simulations.The major research work and conclusions are as follows:(1)A analytical model for the fatigue truck suitable for the fatigue analysis of OSDs was established.The concept of revised equivalent stress range(RESR)considering both the magnitude and number of stress range cycles was proposed.Effects of factors including the road surface condition(RSC)and vehicle speed on the RESR of fatigue details in OSDs induced by vehicle loads were studied.The applicability of the dynamic impact factor(IM)for the fatigue design and evaluation of OSDs adopted in the AASHTO specification was discussed.The results show that the effects of vehicle dynamic impact on the fatigue damage of both COSDs and LWCDs are not significantly different.RESRs of fatigue details in OSDs fluctuate significantly with the change of vehicle speeds when RSC deteriorates,but this phenomenon does not follow a clear pattern.RESRs of fatigue details increase with the deterioration of RSC,and the maximum increase can exceed 80%.The IM recommended by the AASHTO specification may result in an underestimation of the effect of vehicle dynamic impact on the fatigue damage of OSDs if the RSC is poor(class of D)or very poor(class of E).(2)The deterioration model of RSC during the service life of bridges was determined based on its main influence factors.The fatigue performance of COSDs and LWCDs was evaluated from the perspective of fatigue reliability based on a threedimensional vehicle-bridge couple system.The accuracy of the fatigue life of OSDs evaluated based on the deterministic analysis was discussed.And effects of the pavement maintenance cycle and vehicle overloading on the fatigue life of OSDs were studied.The results show that the fatigue life of OSDs evaluated based on the deterministic analysis would be overestimated by 65%～110%if the very poor RSC is considered.The fatigue life of OSDs can be extended by 40%～75%if the pavement maintenance could be undertaken before the RSC deteriorates into the very poor condition.Compared with the COSD,the fatigue life of OSD in the LWCD can be greatly extended and is less affected by overloaded vehicles.(3)Local finite element(FE)models of a COSD and an LWCD were established.The effect of stress reversals on the fatigue life evaluation of OSDs was studied from infinite-life and finite-life perspectives.A convenient and efficient vehicle loading scheme was proposed to obtain the maximum stress range of fatigue details in OSDs.The rationality of the transverse position distribution of vehicles in the current specifications was discussed.The results show that the most unfavorable stress reversal experienced by fatigue details in OSDs may be generated by vehicles passing from two critical transverse positions in a same lane.The maximum stress range of fatigue details obtained by three typical wheel paths may be underestimated by more than 40%.The transverse position distribution of vehicles recommended by Eurocode 3 may be overly conservative,and it is recommended to adopt the transverse position distribution of vehicles recommended by BS 5400 if the measured data is not available.The fatigue life of OSDs could be overestimated by 95%if the effect of stress reversals is ignored.(4)The potential effect of autonomous vehicles on the fatigue life of OSDs was evaluated based on the FE analysis.A scheme to extend the fatigue life of OSDs by optimizing the transverse distribution pattern of autonomous vehicles was proposed and its feasibility was verified.The results show that the effect of autonomous vehicles on the fatigue life of COSD is more significant than that of LWCD in most cases.The presence of autonomous vehicles may lead to a 51%～210%increase in the fatigue damage of most fatigue details in OSDs in the most unfavorable case.The fatigue life of OSDs can be effectively extended by adopting the uniform distribution or bimodal Gaussian distribution as the transverse position distribution pattern of autonomous vehicles.Specifically,the fatigue life of most fatigue details in the COSD can be extended by more than 86%in the most favorable case.This dissertation aims to conduct an in-depth study on the fatigue performance of COSDs and LWCDs under the action of vehicle loads,so as to address the deficiencies in the current fatigue design and evaluation methods of OSDs and provide references for the design,evaluation,and maintenance of OSDs.