Study On Safety Monitoring Parameters And Evaluation Methods Of Small And Medium Span Concrete Girder Bridge During Operation Period

Under the combined effect of long-term effects of load,environmental erosion,material aging,fatigue effects and other unfavorable factors,in-service small and medium span bridges will inevitably appear structural damage and resistance attenuation.How to ensure the safety of the operation of a large number of small and medium span bridges is an important challenge faced by the bridge maintenance department.In order to make up for the inadequacies of traditional bridge inspection methods,the application of safety monitoring in small and medium span concrete girder bridges has been increasingly affected by the practice of long-span bridge safety monitoring in recent years.However,scientific research,technical specifications,and engineering practices for bridge monitoring at home and abroad are mainly concentrated in the area of long span bridges.In view of the many differences in live load response values of small and medium span bridges during operation period,safety monitoring systems and warning thresholds constructed based on existing experience are not fully applicable to small and medium span bridges.This article takes Chongqing Municipal Science and Technology Commission project "Study and Application of Practical Safety Monitoring Technology for Medium and Small-Span Highway Girder Bridges Based on Live Load Characteristics" and the Chongqing Highway Bureau Traffic Science and Technology Project "Research and Application of Applicable Security Monitoring System and Assessment Technology for Mid-sized Bridges".it mainly completed the following tasks.(1)The commonly used methods for condition assessment and warning threshold setting for bridge safety monitoring are analyzed,and their applicability for large-span bridges such as long-span girder bridges is analyzed,and the proportion of live-load bridges and monitoring values The other aspects are obviously different from the characteristics of long-span bridges.Currently,commonly used method based on static monitoring during operation period and monitoring value changes under dead load status to evaluate bridge status is not applicable to the safety monitoring of small and medium-span bridges.(2)The medium and small span concrete girder bridges with common spans,typical bridge widths,and design loads were selected and their constant live-load effect ratios were calculated and analyzed.It was found that the ratio of live load effects to total effects was generally between 30%and 60%.The large-span bridges,which are significantly larger than the dead-load effect,are significantly different from the effects of dead-load and live-load effects.It is proposed that the safety monitoring of medium-and small-span bridges should be based on the live-load response monitoring values during the operation period.State Assessment.(3)The most commonly used simple-supported T-beams and hollow slab general-purpose diagrams for medium-and small-span concrete bridges are chosen as research objects.The stress and deformation laws under the action of contraction,creep,live load,and gradient temperature during the operation period are calculated and analyzed.The selection of safety monitoring parameters for medium and small span bridges and the proposed layout of measurement points are recommended.For small and medium-span bridges with health monitoring systems installed after years of operation,the effects of shrinkage and creep on data processing can be ignored,but the effects of gradient temperatures must be considered.(4)Analyzed and elaborated the composition of the safety monitoring system for medium and small span concrete girder bridges and the principle of suitable sensor selection.It is recommended to use the quasi-dynamic or dynamic monitoring system as far as possible,and use two methods to carry out the safety monitoring of two typical small and medium bridges.System design and practice.(5)Based on the principle of extracting live information from wavelet technology,the actual monitoring engineering data was analyzed;using the distribution law of stress and deformation test coefficients of a large number of small and medium span bridge load tests,taking into account the impact of the integrity of monitoring data,based on the actual structure The setting of warning threshold for live load response characteristics.