Dependence of Sensitivity Factors on Ratio of Traffic Load to Dead Load

Abstract

According to modern structural codes, a design is considered to be adequate if the limit states are not exceeded. For the ultimate limit state, the design value of action effect Ed is required to be less or equal than the design value of ultimate resistance Rd. This ensures, according to the Eurocode, a sufficiently low probability of failure expressed as the target reliability index β. Consequently, the distributions of action effect and of resistance need to satisfy the following conditions: PE>Ed≤Φ+αEβ and PR≤Rd≤Φ−αRβ, where αE and αR, with |α| ≤ 1, are the values of the FORM sensitivity factors. The values of the sensitivity factors αE and αR are suggested, according to EN1990, as −0.7 and 0.8, respectively; for the accompanying actions, the sensitivity factor is recommended as 0.28. In this paper, the dependence of the sensitivity factors for traffic live load, dead load, and resistance on the ratio of traffic load to dead load is studied (which is directly proportional to the maximum span of the bridge). Significantly different sensitivity factors for resistance, dead load, and traffic load, other than proposed by the Eurocode, has been calculated for typical ratio of traffic to dead load. It further showed that, if it is assumed that Ed = Rd and the Eurocode partial safety factors are used, a different design point than the starting point, i.e., Ed = Rd, is obtained.