Generally, fatigue has not been considered as a key problem in the design of reinforced concrete bridges. Until the 1960s, reinforcement was mild steel and the stresses permitted in the steel bar and the concrete were such that fatigue and fracture failure was believed to be impossible. With the developments of reinforced concrete structures, higher working stresses were permitted and, in particular, high yield reinforcing bars were introduced. Design rules were issued to control cracking and to prohibit welding of reinforcement unless the risk of fatigue was negligible. In recent years, great deals of researches have been carried out, leading to a better understanding of the fatigue behaviors in concrete structures. Some studies showed that fatigue could occur in reinforced concrete structures in combination with other causes of deterioration. In the past eight years, considerable increases in traffic intensity and wheel loads have caused obviously fatigue damage in reinforced concrete structures in China. Some reinforced concrete bridges were damaged seriously, leading to the whole bridge collapse sometimes because of overloading and oversize trucks. So how to evaluate the fatigue safety of existing reinforced concrete bridges is an urgent problem in China. In the current paper, the assessment models of existing reinforced concrete bridges based on S-N curve and fracture mechanics approach were proposed considering the effect of overloading and oversize trucks. Finally the assessment method based on S-N curve and in-situ monitoring data was applied to a case study bridge.

Since the first application of steel orthotropic deck in bridges, engineers have shown great interest in the popularization of steel decks, based on their various advantages like light-weight, high capacity and so on. However, because of their complex configurations, repeated loading, and stress concentration, many details of steel orthotropic bridge decks are fatigue-sensitive. Recently, considerable increase in traffic volume and wheel loads has caused a number of fatigue cracks in steel orthotropic bridge decks in China. For example, bridge engineers have detected thousands of fatigue cracks in steel orthotropic deck on the main box girder of Humen Bridge only ten years after opening to traffic, which is the first modern suspension bridge with the main span of 888 meters in China. So the bridge owners pay more attention to evaluate the locations of fatigue damages. In current paper, the standard section of the real bridge deck was simulated and a kind of typical fatigue cracks was selected to analyze their fatigue life using S-N curve, the fatigue damage analysis was carried out on the longitudinal ribs to deck plate connections. The fatigue damage analysis results were consistent with the observations from real bridge decks.

The effective stress range (ESR) and the number of stress cycles (NSC) are two key parameters in fatigue damage evaluation. The inaccuracies in predicting remaining fatigue life can be attributed to either one of these two parameters. A sensitivity analysis is described to address the effects of four cycle-counting methods on ESR and NSC for various fatigue details, which including rain-flow counting (RF), mean-crossing-peak counting (MCP), level-crossing counting (LC) and simple-range counting (SR). Using field monitoring data under normal traffic of Wei River Bridge, the comparative results of four methods showed that RF was more conservative than MCP and SR. The relationships between RF and other three counting methods were determined in the form of a correlation coefficient and a linear regression line. Therefore, values obtained for ESR and NSC by MCP, LC and SR can be converted to values for RF, which is used for comparison and transformation of fatigue life evaluation results using different cycle-counting methods.

A scaffolding system is a temporary structure that is commonly adopted on construction sites. As steel scaffolds are modular members manufactured with fixed dimensions, the total height of a scaffolding system seldom fits the headroom of a building when scaffolds are set up in multiple stories. This results in a difference in elevation, i.e. gap, between the top of the scaffolding system and the ceiling slab. In addition, scaffold configurations may need to be adjusted if the interior of a building has inclined planes on the ceiling slab or stairs on the ground. This study shows that the gap between the scaffold and the ceiling slab can be eliminated by altering the lengths of adjustable base jacks or adjustable U-head jacks. When the ceiling slab is inclined, it is suggested that a combined system of scaffolds with wooden shores of different lengths should be installed in the out-of-plane direction of the scaffold unit. This system can also be used when the ceiling slab is inclined and the ground has a difference in elevation (e.g., stairs) in a building. By using the second -order elastic analysis with semirigid joints, the load-bearing capacity and failure model are found to be very close to those obtained in the loading tests using various scaffold configurations. In the loading tests for reused scaffolds, the lower bound of the load -bearing capacity of the scaffolding systems can be obtained by applying a subsequent load on the scaffolding systems, which are commonly adopted on the construction sites. The strength reduction factor () of these scaffolding systems installed by reused scaffolds can be obtained by calculating the mean value and standard deviation, which can serve as a reference for the strength design of scaffolding systems with different safety requirements.