Analysis Of Durability And Study On Reinforcement Technology Of General Speed Railway Low-height Slab Beam Bridges

During the early construction and development of China's railway,in order to meet the requirements of clearance of span and to adapt to various purposes such as plain,a large number of low-height slab beams were adopted in some areas.This design effectively reduced the web thickness,but inevitably reduced the vertical stiffness of the bridge.The early-built low-height slab beam bridges have a service life of 50 to 60 years.Under the influence of severe climate factors in northwest China,the upper cantilever slab of the bridge is in a state of freeze-thaw cycle for a long time,and the lower part of the upper flange slab of the bridge gradually shows phenomena such as steel corrosion and concrete spalling.In recent years,the speed of railway trains has been increasing and the axle load of trains has been increasing year by year.Under the repeated action of live load of railway trains,due to the problems of low rigidity,large deflection and low concrete strength in the early construction process of the low-height slab beam itself,after a certain degree of deterioration of the beam body,the mid-transverse cracks in the beam bottom span of the low-height slab beam gradually appear,and gradually extend to the structural cracks of the web slab,which cause great hidden dangers to railway traffic safety.Therefore,this paper investigates the durability problems of low-height slab beams,analyzes the damage mechanism in combination with the influence of atmospheric environment conditions in northwest China,and proposes reasonable and effective maintenance methods and reinforcement methods for the damage of local components of railway bridges,which has become an urgent task to be solved.Based on the scientific research project "Research on Assessment and Maintenance Technology of Rib-slab Damaged Bridges",this paper conducts an on-site investigation of some low-height slab beams in northwest China.Combined with the characteristics of climate and environment,it proposes that railway departments should pay attention to the durability of bridges.Through finite element calculation software,it proposes the maintenance limit of cantilever slabs,and proposes a new reinforcement method for low-height slab beams with excessive deflection.The main research contents are as follows:(1)According to the example of lanzhou,a representative city in the cold region of northwest China,the number of freeze-thaw cycles in different temperature ranges was calculated.Combined with the previous theoretical results of freeze-thaw cycles,according to the damage mechanism of freeze-thaw on concrete,the relationship between the freeze-thaw cycles in different temperature ranges and the freeze-thaw cycles of standard rapid freeze-thaw tests is analyzed,and the standard rapid freeze-thaw cycles that the damage degree of freeze-thaw cycles on concrete in Lanzhou area can reach on average every year under natural freeze-thaw conditions are obtained.Through the natural exposure freeze-thawtest of concrete,the difference between natural freeze-thaw and laboratory rapid freeze-thaw test on freeze-thaw damage of concrete is compared.(2)Based on the research of freeze-thaw damage by a large number of scholars,the bearing capacity reserve of cantilever slab of low-height slab beam bridge deck is theoretically analyzed,and the interface loss state of deteriorated cantilever slab of bridge deck under freeze-thaw environment is analyzed by finite element method,so as to put forward a safe maintenance limit for cantilever slab maintenance.(3)Based on the analysis of the bonding mechanism between the new and old concrete interface.Through the production of Z type concrete specimens,the influence of different planting bar restoration on the shear resistance of the bonded flour is considered.It provides better parameter values for future concrete interface repair design and achieves the best repair effect.(4)The disease of a 3-8m low-height plate beam was investigated,the deflection was measured on site,and the bearing capacity and deflection reserve were analyzed theoretically.Aiming at the problems of excessive vertical deflection and insufficient rigidity,the reinforcement scheme is discussed,the advantages and disadvantages of different reinforcement schemes are analyzed and compared,and the applicability of various reinforcement schemes is put forward.According to the field investigation of a low-height slab beam,the reinforcement method of vertical steel support is proposed.(5)The vertical deflection of the deteriorated beam is analyzed through numerical simulation,and then finite element simulation is carried out for different reinforcement methods,and the reinforcement effects of each reinforcement method are compared and analyzed,providing theoretical basis for the selection of reinforcement schemes for low-height slab beam bridges.