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Random Differential Settlement Effects on Reliability of Existing Bridges
Zuo-Cai Wang
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DOI:10.17265/1934-7359/2024.02.002
Department of Civil Engineering, Hefei University of Technology, Hefei 230009, Anhui Province, China
This paper investigates the impact of differential foundation settlement on the reliability of bridge superstructure based on loads and resistances statistical properties in Missouri State. Maximum deterministic differential settlement is often used in current AASHTO LRFD (load and resistance factored design) specification. However, the expected foundation settlement is quite different from the actual settlement due to the soil’s large variability. Therefore, it makes sense to consider settlement as a random variable. In this paper, a lognormal distribution with coefficient of variation of 0.25 of random settlement is considered in reliability analysis based on limited previous studies. Dead and live loads are modeled as random variables with normal and Gumbel Type I distributions, respectively. Considering the regional traffic condition on Missouri roadways, the live load effect on existing bridges based on weight-in-motion data is also investigated. The calibrated resistance statistical properties such as bias and COV (coefficient of variance) are used for reliability analysis. Total 14 existing bridges based on Strength I Limit State are analyzed. Since no differential settlement is considered in the past designed bridges in Missouri, small differential settlement can significantly reduce the reliability indices of the superstructure, depending upon the span length and rigidity of the girder. The analysis results also show that the reliability of existing steel-girder bridges is consistently higher than prestressed concrete and solid slab bridges; the shorter and stiffer the spans, the more significant the settlement’s effect on the reliability of bridge superstructures; As the span length ratio becomes less than 0.75, the girder and solid slab bridges’ reliability drops significantly at small settlements.
Bridges, superstructure, LRFD.
Journal of Civil Engineering and Architecture 18 (2024) 60-68 doi: 10.17265/1934-7359/2024.02.002
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