Research On Crack Resistance Of Inclined Section Of Prestressed Concrete T Beam For Heavy-haul Railway

With the increasing demand for heavy-haul transportation of bulk goods over these years,China’s heavy-haul railways continue to develop towards long formations,large axle loads and large transportation volumes.Under the repeated load of heavy-haul trains,existing heavy-haul railway bridges designed according to China Railway Standard Live Loading will experience diagonal cracks in the web of commonly used span prestressed concrete T-beams.The appearance of diagonal cracks will affect the safety and durability of the bridge structure.Therefore,it is urgent to analyze the causes of diagonal cracks in the web of commonly used span prestressed concrete T-beams for heavy-haul railways,in order to provide experimental and theoretical basis for the risk assessment of diagonal section cracking in heavy-haul railway concrete beams.This thesis adopted a combination of theoretical analysis and model experiments to study the stress law,crack fatigue strength and fatigue damage analysis method of inclined section concrete of prestressed concrete T-beams for heavy-haul railways.The main research work and conclusions are as follows:(1)The stress law of prestressed concrete T-beam diagonal section concrete has been analyzed.Considering the influence of three factors: principal compressive stress,principal tensile stress ratio,and upper limit of principal tensile stress by combining theoretical derivation with analysis of existing scholars’ experimental results,the diagonal section crack resistance fatigue equation has been established.The CortenDolan nonlinear cumulative damage theory was selected as the calculation criterion for the cumulative damage of concrete on the inclined section of prestressed concrete Tbeams for heavy-haul railways.At the same time,a method for analyzing the damage of concrete on the inclined section of prestressed concrete T-beams for heavy-haul railways under fatigue loads was proposed.(2)Based on the crack resistance test of oblique section of four concrete model beams,the damage law of concrete in the oblique section of the model beam was explored and the applicability of the fatigue damage analysis method for prestressed concrete T-beam oblique section concrete proposed in this paper was verified.Based on the experimental results and analysis,it can be concluded that when the inclined section was not cracked,the strain of the stirrup was relatively small under fatigue load,and some parts were still in a compressive state.Before and after the cracking of the inclined section,the stiffness of the reinforced concrete beam decreased significantly,while the stiffness of the prestressed concrete beam changed less.The comparison between the results of the model beam diagonal section crack resistance test and the diagonal section fatigue damage theory calculation show that the proposed fatigue damage analysis method for concrete beams has good applicability and can be applied to predict the static crack resistance strength of diagonal sections.(3)It is carried out that the fatigue damage analysis of the 32 m beam inclined section of the Zhuan Qiao 2059A/B in the Chinese Drawing of Datong-Qinhuangdao railway by using the fatigue damage analysis method of concrete with inclined section verified by tests.The excessive thickness of ballast has an adverse effect on the crack fatigue strength of the inclined section.The crack resistance design strength of the 32 m beam diagonal section of the Zhuan Qiao 2059A/B in the drawing number meets the requirements of the current railway code.However,based on the damage analysis method of the concrete beam diagonal section proposed in this thesis,considering the combined action of increased operational dead load,the main compressive stress and the repeated load of the heavy-haul train,there is a significant risk of cracking in the32 m beam diagonal section of the Zhuan Qiao 2059A/B.Therefore,it is recommended that the railway code put forward higher requirements for the crack resistance strength of the heavy-haul railway diagonal section.There are 58 pictures,70 tables and 90 references.