RELIABILITY ANALYSIS OF REINFORCED CONCRETE SLAB BRIDGES

Abstract

Empirical expressions for estimating the wheel load distribution and live-load bending
moment are typically specified in highway bridge codes such as the AASHTO procedures. The objective of
this paper is to assess the reliability levels that are inherent in concrete slab bridges that are designed based
on the simplified empirical live load equations in the AASHTO LRFD procedures. To achieve this objective,
typical one and two-lane straight bridges with different span lengths were modeled using finite-element
analysis (FEA) subjected to HS20 truck loading, tandem loading, and standard lane loading per AASHTO
LRFD procedures. The FEA results were compared with the AASHTO LRFD moments in order to quantify
the biases that might result from the simplifying assumptions adopted in AASHTO. A reliability analysis was
conducted to quantify the reliability index for bridges designed using AASHTO procedures. To reach a
consistent level of safety for one lane and two lane bridges, the live load factor in the design equation
proposed by AASHTO LRFD needs to be revised by increasing the live load factor to 2.07 for one lane and
1.8 for two lanes. The results will provide structural engineers with more consistent provisions to design
concrete slab bridges or evaluate the load-carrying capacity of existing bridges.