Influence of railings stiffness on wheel load distribution in two-span multilane concrete slab bridges

Highway bridge specifications do not account for the presence of railings or parapets in the analysis and design of concrete slab bridges. This paper presents a parametric investigation of the influence of railing or parapet stiffness on the wheel load distribution and bending moments in simply supported, two-equal-span, one- to four-lane concrete slab bridges using the finite-element analysis (FEA). A total of 224 bridge cases were modeled and bridge parameters such as span length and slab width were varied within practical ranges. Various railing stiffnesses were investigated by assuming that the railings were built integrally with the bridge deck and placed on both edges of the bridge. The FEA wheel load distribution and longitudinal bending moments, edge beam moments, as well as live-load deflections were compared to reference bridges without railings, and to the AASHTO design procedures. The FEA results showed that the presence of railings reduced the maximum negative bending moment in slab bridges by a range of 15%–70%, and the positive moment by a range of 10%–60%. This reduction in bending moments due to the presence of railings can be considered an increase in the load-carrying capacity of concrete slab bridges by a significant amount, especially in the cases of lesser number of lanes. The results of this parametric investigation will assist bridge engineers in either designing or evaluating concrete slab bridges by using refined FEA analysis to quantify the contribution of railings in resisting highway loading. This approach of using FEA modeling may serve as an effective alternative for strengthening existing concrete slab bridges.