Calculation and Analysis of Load Test Safety Control for Through Tied-Arch Bridge with Single Bearing Surface

Abstract

This paper attempts to evaluate the actual carrying capacity and guarantee the operation safety of Qin Bridge, Ningbo, China. Considering the structural features of the bridge, reasonable field load plans were prepared to realize load test safety control of long-span through tied-arch bridges with single bearing surface (SBS-TTABs). The internal force, stress, and deformation control under different working conditions of static load were calculated, and compared with those measured in static load tests. After that, the natural vibration, and damping features of the target bridge under impact and bumping were explored through pulsating test, barrier-free driving test, and bumping test. The results show that the maximum deflection and strain measured on the midspan section and arch rib section were both smaller than theoretical values, the calibration coefficients of deflection and strain fell in 0.60-0.88 and 0.48-0.88, respectively, indicating that the overall rigidity and strength of the bridge meet relevant code. Under the test loads, the maximum relative residual deflection and the maximum relative residual strain at each measuring point were 12.98% and 11.76%, respectively. Both were below the 20% threshold specified in JTG/T J21-2011. It shows that the bridge span has excellent elastic recovery ability. In dynamic load tests, the fundamental frequency measured by driving test agreed with that measured by bumping test, and the vibrations were smaller than the theoretical values. This means the main span has stable vibration features. Overall, the target bridge has sufficient capacity to withstand Urban-A level vehicle load, under normal use conditions, and the bridge structure belongs to the safe state.