Investigation Of Lane Load Disparities And Their Effects On Structural Performances Of Highway Bridges

Vehicle load is the main variable load of the bridge,its high time variability and spatial randomness are very important sources of risk for the safety and service life of the bridge.In the past thirty years,communications and transport in China have experienced explosive growth,the load model of the code system is usually applied to the performance evaluation of the bridge structure at a specific location,and often shows a large estimation deviation.It is necessary to establish a refined vehicle load model for evaluation and design based on the actual traffic load characteristics.The important characteristic of multi-lane road vehicle operation is to drive in different lanes by model,which makes the lane load significantly different,and this characteristic is not reflected in the existing code system,which may cause the deviation of the bridge vehicle load effect analysis.For this reason,this paper studies the multi-lane load characteristics of highway bridges,the performance of multi-beam structures under multi-lane loads,and the performance of integral box girder under multi-lane load.The main research contents and results include:(1)Based on the WIM data of one-way two-lane,three-lane and four-lane expressways in China,the characteristics of multi-lane trucks are described in detail from the perspective of lane selection behavior,traffic flow,load and vehicle weight correlation.Results have indicated that for the studied multi-lane WIM data,there are huge discrepancies between the lanes of truck traffic and truck weight,especially when the number of lanes is large.Heavy trucks basically drive on the two outer lanes of highway,causing inconsistent load on the inside and outside lanes.At the cumulative time interval of 5 s,the self-weight correlation coefficient of continuous trucks exceeds 9%,which indicates that trucks tend to drive in rows with a small but never negligible probability.(2)Based on the multi-lane load characteristics,this graduation thesis analyzed the typical multi-beam concrete bridges like two-lane,three-lane and four-lane slab beams,T-beams and box structures so as to calculate the bearing capacity and fatigue performance of multi-beam bridges accordingly under the ultimate load and equivalent load effects of multi-lane truck loads.Results show that huge differences are shown in the traffic load effect and reliability index of each main beam in the same bridge,and the difference is even more significant when the number of lanes increases,the span decreases,or the crossbeam connection is weak.In this difference,the load response of bridge components in the slow lane is usually larger than that in the fast lane,and the safety and fatigue reliability levels are lower.It should be emphasized that component performance differences should be taken into consideration in the design or evaluation of multi-girder bridges,so that each main beam member can achieve the required uniform target reliability under the actual multi-lane truck load.(3)Taking a box beam bridge as an example,a probabilistic reliability assessment framework concerning both multi-lane traffic load growth and structural resistance degradation is established,whose core is to update the finite element model based on the bridge detection data,and establish a traffic growth model and time-varying resistance degradation model.The implementation process and effect of the evaluation framework were even explained in detail through a project case and results show that during the reference period,the reliability index of the bridge's mid-span section and the section at the support decreases year by year as the service life increases,but it still has sufficient safety reserves and does not need to be reinforced.