Improved quality assessment procedure for old truss bridges according to measuring data

In China, many steel truss bridges built at the beginning of the last century are still in service. These bridges have been integrated with the local culture, and demolishing them would be a great pity. Besides, most of them are located in urban centres and their century-old structures still carry heavy traffic loads. So the safety of these bridges are a serious concern for the local bridge management departments. But the existing evaluation method, which is based on experience, is unreliable.
This paper, taking Zhejiang Road Bridge in Shanghai as an example, illustrates an improvement to the evaluation method from the perspectives of traffic load, corrosion and fatigue. The characteristic parameters of traffic loads are first investigated to form a probability density function (PDF) and the traffic load effects spectrum is obtained from a Monte Carlo simulation analysis. Tensile tests on specimens with different degrees of corrosion are performed in order to analyse the effects of corrosion on truss structures. The fitted curve of test data and the degree of corrosion detected on truss components are used to estimate the residual loadbearing capacities of the bridge components.
Finally, the fatigue lives of the components are predicted in a study applying fracture mechanics. At the beginning of the study, the crack propagation rate and the fracture toughness are tested and the initial crack is detected using ultrasonic phased arrays. The stress spectrum based on numerical techniques obtained from the previous Monte Carlo simulation is then used to assess the residual fatigue life of each tension components.