Study of Yielding Zone on Reinforced Concrete Bridge Parapet Design for Vehicular Impact

Abstract

Reinforced concrete bridge parapets have important safety roles in the highway system. Currently AASHTO and FHWA require all new permanent installation of bridge rails on the National Highway System to be compliant with Manual for Assessing Safety Hardware (MASH) requirements. Therefore, there is an immediate need to update Section 13: Railings of the AASHTO LRFD [Load and Resistance Factor Design] Bridge Design Specifications to incorporate the MASH requirements. However, the current provisions for designing and analyzing concrete parapets in AASHTO using yield-line theory have been found to possess many inherent limitations, including an inaccurate yield-line pattern for computing nominal resistance to transverse load. This paper presents an evaluation of AASHTO’s yield-line pattern using both dynamic finite element analysis (FEA) and an analytical investigation based on theory of plates. In the dynamic FEA, a three-dimensional numerical model of a parapet section was created and analyzed using non-linear material properties. In the analytical approach, MATLAB was used to compute the stresses throughout a plate having properties equivalent to those of a reinforced concrete parapet. Computed stress values on the plate were graphically displayed to locate areas of highest stress concentration or yielding zones, where yielding of rebars has a high chance of occurring during impacts. The outcomes of the two independent analyses were found to be in very good agreement. The goal of this study is to predict reliable boundaries of the yielding zones, which will provide a strong foundation for developing a more precise yield-line pattern.