Prevention And Control Of Structural Cracks On Column Monolithic Track Bed

Column monolithic track beds are widely used in track maintenance lines due to their simple construction and low maintenance workload.The main structure of the column monolithic track bed is composed of reinforced concrete columns and continuous beams.Due to the small size of the column and the dense arrangement of steel bars,the column inevitably cracks under the effects of concrete shrinkage,heat of hydration and temperature.In the later operation process,the cracks continued to expand due to the influence of external loads,and even threatened the safety of train entry inspection.In a subway maintenance line,the pillar monolithic track bed,during the construction process,thousands of pillars cracked to varying degrees,and even peeled off.Therefore,the research on the prevention and control measures of the pillar monolithic track bed structure can fundamentally prevent the occurrence of cracks and control the development of cracks,and play a better guiding role in the future pillar monolithic track bed structure design and disease prevention.It has important practical significance.In this thesis,the following research contents are carried out for the cracking of column monolithic track bed in a subway maintenance warehouse:(1)Aiming at the problem of cracking during the construction of a column-type monolithic track bed in an overhaul line of a subway warehouse,a numerical simulation of the cracks during the construction period was carried out,and the distribution of cracks and the width of the cracks under the influence of various factors during the construction period were calculated.The calculation results are compared with the actual measurement of the crack distribution of the subway maintenance line column,which verifies the correctness of the model and parameter selection.(2)Based on the analysis of structural design,concrete materials,construction and maintenance,the main influencing factors of the cracking of the column-type monolithic track bed in the maintenance line of a subway warehouse were clarified.Using the separation crack model,the effect of main influencing factors such as the arrangement of steel bars,steel fiber and concrete expansion agent on the prevention of column cracking was simulated and analyzed.On this basis,the preventive measures for cracks during the construction of the column were determined,and simulation calculations were carried out to prove the feasibility and effectiveness of preventive measures.(3)For the cracked columns during the construction period,the finite ele ment model of the column with preset cracks was established by using the em bedded crack model,the changes of the stress intensity factor at the crack tip in the operation period of the column under the combined action of the uplift force,the cooling load,the cooling load and the uplift force under different crack lengths were analyzed,and the crack propagation types and propagation conditions were predicted.The control measures of the cracks in the operation period of the column were put forward.