Study On The Health Monitoring And Early Warning System Of Precast Segmental Simply-supported Box Girder

The existing highway bridges,due to prolonged exposure to overloaded vehicles,as well as a lack of maintenance and management,can develop various types of damage,leading to a reduction in their carrying capacity beyond expectations and a significant decrease in safety during use,becoming a significant threat to traffic safety.Therefore,it is possible to utilize a bridge health monitoring system to continuously monitor the carrying capacity and safety of bridges during their service life,provide timely warnings for bridges that fall below code requirements or exceed preset alert thresholds,and enable timely intervention by bridge maintenance and management authorities to enhance bridge service safety.However,existing bridge health monitoring systems often directly apply monitoring parameters and alert thresholds specified by codes,lacking specificity for structurally unique bridges.Additionally,their threshold designs may not precisely match the dynamic characteristics of real-world engineering.As a result,during actual monitoring,they may either trigger frequent alarms due to low alert thresholds,resulting in the waste of human and material resources,or have reduced sensitivity to changes in bridge carrying capacity and structural damage due to high alert thresholds,exacerbating bridge aging.This paper,based on the "Intelligent Monitoring and Early Warning Technology Research for Large-Span Bridges in Jilin Province" project conducted by the Jilin Provincial Transportation Planning and Design Institute,focuses on the practical engineering context of the monitoring system for the Songhua River Bridge in Wujintun,Jilin City.It conducts numerical simulation analysis and early warning mechanism design for the prestressed concrete simply supported box girder bridge with bonded joint segments.Using the response surface method and modifying the finite element model based on the stress,strain,deflection,crack,and natural frequency data obtained from static and dynamic load tests,the occurrence and development of bond interface cracks in prestressed concrete simply supported box girder bridges with bonded joint segments under loading conditions were verified.Crack damage scenarios were established based on the bridge’s structural form,and a separation crack model was selected and validated as the damage simulation approach in this paper.The sensitivity of the bridge’s ultimate carrying capacity and modal frequencies to different crack characteristics was analyzed.Latin hypercube sampling was used to determine samples with different crack damage characteristics.Response surface analysis methods were employed to establish relationship models between ultimate carrying capacity and crack damage characteristics,first-order frequency and crack damage characteristics,and first-order frequency and ultimate carrying capacity.The support vector regression algorithm was used to eliminate temperature effects from monitoring data,which can also be applied to eliminate the effects of other factors such as humidity.The acquired data was denoised using the EMD wavelet thresholding algorithm.Considering the types and locations of bridge monitoring sensors,a fourlevel early warning mechanism was established for the Wujintun Bridge.Strain alert thresholds were set at specific measurement points based on load combinations,the most critical load conditions,bridge structural yield points,and prestressed steel yielding points.Based on existing research on bridge modal frequencies,code requirements,and the bridge’s first-order frequency and ultimate carrying capacity relationship model,a first-order frequency alert threshold was established for this bridge to detect decreases in its ultimate carrying capacity.