ABSTRACT:In recent years, traffic loads and vehicle speeds on both existing steel and concrete bridges have increased to provide fast and sufficient transportation service in China. Chinese government and bridge engineers are paying more attention to the structural fatigue life, service safety, maintenance intervals and the ability to improve capacity of such infrastructure. To study evaluation methods using modern technologies to achieve economical maintenance and extend the sustainable service life, a deterministic evaluation approach was proposed in this paper based on investigation of linear fatigue-damage accumulation theory and fracture mechanics, in which the fatigue failure behaviour of existing steel and concrete bridges was reflected. According to the stochastic fatigue failure mechanism of existing bridges, the member fatigue reliability assessment models were proposed using probabilistic fracture mechanics. Furthermore, based on a Monte-Carlo method, a fatigue reliability analysis program was developed to calculate member fatigue failure probability of existing bridges. The deterministic and probabilistic assessment methods proposed in this paper were applied to evaluate typical existing steel and concrete bridges. According to assessment results, the deterministic and probabilistic remaining fatigue life, safe inspection intervals and maintenance strategies were determined, which can avoid fatigue failure accidents and reduce the life-cycle cost of these bridge structures. INTRODUCTIONExisting steel and concrete bridges are aging and experiencing increased levels of fatigue deterioration due to increased demands in traffic volume, vehicular weights and environmental corrosion. As a result, the service safety of existing steel and concrete bridges is declining. In recent years, bridge engineers are paying more attention to the actual fatigue life, service safety, maintenance intervals and load carrying capacity of such infrastructure. Researchers devoted to develop effective evaluation methods, and then provide structural behavior prediction for existing steel and concrete bridges, which can make reasonable maintenance and management decisions to ensure the structural safety [1-5].To acquire reliable fatigue life evaluation technique, this paper proposed deterministic and probabilistic evaluation approaches, which reflect fatigue failure behavior of existing steel and concrete bridges. According to the stochastic fatigue failure mechanism of existing bridges, the fatigue reliability assessment models for member were proposed using probabilistic fracture mechanics. Furthermore, based on a Monte-Carlo method, a fatigue reliability analysis program was developed to calculate member fatigue failure probability of existing bridges. To verify the effectiveness of proposed evaluation approaches, five typical existing steel bridges and concrete bridges were selected as case studies. Continuous dynamic monitoring technique was adopted to acquire real fatigue stress spectrum, in order to evaluate the real fat...

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The existing concrete bridges are often required to carry an increasing volume of traffic, higher speed and heavier trucks, so the bridge owners pay more attention to the actual fatigue damage and service safety of such structures. In this paper, Acoustic Emission (AE) sensors are used to monitor and evaluate the fatigue and damage of Yaoxian Bridge, which is the first field AE monitoring using Physical Acoustics Company equipment and sensors in China existing concrete bridge. This AE sensor has fine frequency bandwidth of interest to bridge monitoring, which is applicable to local cracking and damage positions and can monitor fatigue cracks and damage in close-range. In the field inspection, healthy monitoring was conducted at several locations, including the box concrete girder webs, bottom plates and deck plates using AE sensors. Based on AE monitoring data, the fatigue and damage conditions of box concrete girders was analyzed in order to propose theoretical basis and the rational advices for Yaoxian Bridge maintenance.