Study On Lifting Load Grade Of Small And Medium Span Skew Bridge On Highway

Facing the increasing traffic load flow,the existing bridges confront a tremendous challenge of upgrading the load grade.Firstly,this paper compares the vehicle loads of the new and old general specifications of highway bridges,and studies their effects on different span bridges.Based on the upgrading load project of a hinghway,the sensitivity of small and medium span skew bridges of upgrading the load grade is analyzed by grillage model.Through systematic calculation,test and analysis,23 pre-stressed concrete hollow slab skew girder bridges on this line can meet the requirements of operation load to elevate highway-class I,which have been designed with steam-20 and hanging-100 loads,and the following results are achieved.1.This paper compares the vehicle loads of 89,2004 and 2015 codes.The renewal of the new and old codes has less impact on bridges over 50 m in span,but greater impact on small and medium-span skew bridges.Therefore,when existing bridges lift operational loads,the risk of small and medium-span bridges is greater than that of long-span bridges.2.Based on the orthogonal grillage model,the sensitivity analysis of lifting load grade of small and medium-span skew bridges with different spans,different inclinations and different bridge widths is compared.The bigger the span of the bridge is,the more advantageous the load grade is;the bigger the inclination of the bridge is,the more advantageous the load grade is;the wider the bridge is,the more advantageous the load grade is.So when the bridge lifting load,in addition to paying attention to the size of the span,the influence of geometric parameters such as slope and bridge width on the lifting load should also be considered.3.The bearing capacity of medium and small span skew bridges is studied by means of finite element calculation and testing after lifting load grade.If the stiffness contribution of accessory members is not taken into account,the calculation result has a big difference with testing result,even the internal force calculation fails to pass,but the test result tends to be safe.It shows that the calculation model of medium and small span skew bridges without considering the stiffness contribution of ancillary members can not be used to guide the calculation and test of the lifting load of bridges.4.According to the result of internal force calculation and test,the load-lifting calculation model of medium and small span skew bridges is revised.It should not be considered of contribution of deck pavement for skew bridges with span over 20 m,while carried out different thickness of deck pavement with different beam height with span below 20 m.Crash barrier is should be considered to side gider with all medium and span skew bridges.Based on the modified model,the load grade can be lifted when middle and small span skew bridges pass the internal force calculation,and the test verification coefficient is between 0.6 and 0.9;if not,it can not be lifted.