The Fatigue Life Assessment Of Existing Reinforced Concrete Highway Box-girder Bridge Based On Sub-model Method

With the rapid development of China's highway transportation,as a main form of highway bridges,the existing highway reinforced concrete continuous box-girder bridge with variable cross-section plays a vital role in China's highway transportation.The existing highway reinforced concrete continuous box-girder bridge with variable cross-section is likely to cause fatigue damage to the dangerous part of the bridge under the long-term action of the vehicle load,which is a serious threat to the safety of the bridge.Therefore,it is particularly necessary to study the fatigue life of the existing highway reinforced concrete continuous box-girder bridge with variable cross-section under the action of vehicle load.In this paper,taking an existing highway reinforced concrete continuous box-girder bridge with variable cross-section as the engineering background,the fatigue life assessment of which under the marshalling fatigue vehicle load is studied.According to the existing domestic and international research status of fatigue life assessment for existing highway reinforced concrete continuous box-girder bridge with variable cross-section,combined with the actual research situation of this paper,the research focuses on the following aspects:Firstly,the fatigue vehicle load spectrum is studied,and the marshalling fatigue vehicle load is obtained;the existing highway reinforced concrete continuous box-girder bridge with variable cross-section is analyzed to determine the location of bridge which is prone to fatigue failure: box girder web of 1/4 span segment and box girder floor of midspan segment;use of critical plane method is proposed to evaluate the multi-axial fatigue life of the web,and the fatigue life of the steel bar is evaluated based on the S-N curve and the Miner linear cumulative damage theory;the flow chart of fatigue life evaluation of the existing highway reinforced concrete continuous box-girder bridge with variable cross-section is presented.Secondly,based on the engineering background in this paper,the finite element model of the bridge shell is established.Aiming at the location of bridge which is prone to fatigue failure,adopting multi-scale analysis method based on sub model method,the entity model without/with cracks of box girder web in 10 m segment before and after 1/4 span cross section belonging to the third span is set up.While the entity sub-model with cracks of box girder floor in 12 m segment before and after mid-span cross section of the third span is also established.The response of the shell model and sub-model under the action of marshalling fatigue vehicle crossing bridge along a single lane and two lane is analyzed so as to determine the fatigue risk point of web concrete.Finally,the critical surface method is used to calculate the cracking life of the web concrete dangerous point in the multi-axial fatigue stress state.Basing on S-N curve and Miner linear cumulative damage theory,the fatigue life of stirrup at web crack and longitudinal reinforcement at floor crack is evaluated to obtain the fatigue life of the bridge.The effects of marshalling fatigue vehicle with different speeds on the fatigue life of the bridge are analyzed and compared.In summary,aiming at the location proned to fatigue failure of existing highway reinforced concrete continuous box-girder bridge with variable cross-section this research has conducted the analysis and proposed the fatigue life assessment method for the bridge.It has certain economic and social benefits for the fatigue life prediction of existing highway reinforced concrete continuous box-girder bridge with variable cross-section as well as the prevention of serious accidents.