Calibration of Temperature Gradient Load Factor for Service Limit State Design of Concrete Slab-on-Girder Bridges

Abstract

Design factors in load and resistance factor design (LRFD) codes are determined using structural reliability theory to account for the uncertainties in loads and resistance. The calibration of load factors for strength limit states has been investigated during the development of AASHTO LRFD bridge design specifications (BDS). In comparison, sparse efforts can be found for calibrating service limit state load factors. Temperature variations affect all types of bridges and cause additional stresses, deformations, and moments in different bridge components. Calibration of load factors for vertical temperature gradients appear to be lacking for both strength and service limit states. This paper focuses on calibrating positive vertical temperature gradient load factors for the Service III limit state. A design space consisting of 70 two-span continuous bridges with different bridge configurations is established and designed for severe corrosive exposure conditions. Design stresses for various load cases are first calculated. Using the first-order reliability method (FORM) and considering the sources of uncertainties due to materials, fabrication, and load effects, temperature gradient load factors were then calibrated for different risk levels. The results show that vertical temperature gradient load factors between 1.00 and 1.40 should be used for the Service III limit state.