Study On The Performance Of Me-dium-bearing Steel Pipe And Con-crete Arch Bridges Based On Load Tests

Since the 21 st century,more than a hundred bridge collapses have occurred in China,resulting in huge loss of life and economic damage.With more than 40 per cent of bridges in service,it is essential to study the performance of old bridges.Load testing is an important tool for studying the performance of bridges.This paper outlines the historical development of tubular concrete arch bridges and optimises the existing non-destructive testing methods for bridges.The theory of bridge modelling and load testing is explained by taking a medium-bearing steel pipe concrete tied arch bridge as the object of study and load testing as the research method.By using the Ling Feng Bridge as the actual engineering background,a Midas Civil finite element model is established and dynamic and static load tests are carried out to analyse the deformation of the bridge model under static load and the dynamic characteristics of the bridge during traffic to obtain theoretical data,and to compare the theoretical and measured data and then analyse the actual load carrying capacity and working condition of the bridge.The main findings of the study are:(1)Midas Civil was used to establish a frame type model for the main bridge of the Ling Feng Bridge,and six loading conditions were identified through the internal force influence surface with three levels of loading.The maximum positive bending moment was 352.8 k N·m,the maximum boom increment was 609.4 k N and the maximum negative bending moment was-1210.3 k N·m for the off-loading design load,and the maximum positive bending moment was293.0 k N·m,the maximum boom increment was 502.1 k N and the maximum negative bending moment was-1156.3 k N·m for the medium-loading design load.(2)Centre loading and eccentric loading of the span section and pier section were carried out in the static load test to output the stresses under each condition.The strain calibration coefficients ranged from 0.63 to 0.84,the deflection calibration coefficients were 0.74 to 0.78 and the boom tension calibration coefficients were 0.81 to 0.85.Their residual strain values ranged from 0.00% to 12.50%,their residual displacement values were 6.55% to 10.90%,their residual boom tension values were 5.57% to 9.44% and their residual displacement values were6.55% to 10.90%.The strain,deflection and boom tension calibration coefficients all meet the requirements of not more than 1 in the Specification for Load Testing of Highway Bridges(JTG/T J21-01-2015),indicating that the bridge has a high load carrying capacity.(3)In the dynamic load test,the bridge environmental vibration test and the unobstructed traffic test were carried out,and the results were obtained for dynamic analysis with the actual measured data.The theoretical structural fundamental frequency of the bridge was 1.121 Hz and the impact coefficient of the bridge was calculated to be 0.05.The measured maximum impact coefficient of the main bridge under the unimpeded traffic test was 0.04 at speeds of 30km/h and 40 km/h.The measured impact coefficient was less than the calculated value,indicating that the actual bridge structure has good dynamic performance.(4)The model sensitivity analysis was carried out to investigate the effect of different parameters on the self-oscillation frequency.After modifying the model to study the deflection and strain under working conditions,the maximum calibration coefficient for deflection is0.793 and the maximum calibration coefficient for strain is 0.90,both of which are less than 1.The stiffness meets the requirements,but the calibration coefficients are smaller than before the modification,which indicates that the safety reserve is sufficient and reflects the structural condition more realistically,further indicating that the modified model method is feasible.