Influence of Parapets and Aspect Ratio on Live-Load Distribution

Abstract

Significant discrepancies in girder distribution factors have been observed between actual bridge field-testing results and AASHTO code predictions. One of the reasons for the discrepancies is that code methods fail to account for the existence of secondary members such as parapets in bridges. This research investigates the effects of parapets and bridge aspect ratio on live-load moment distribution for bridge girders. The influence on distribution factors of parapets with varying overhang lengths and of aspect ratio with varying roadway width is investigated. To study the effects of parapets and aspect ratios, 34 two-span continuous bridges with a 0° or a 45° skew angle and with varied structure parameters are analyzed using the finite element method. The distribution factors obtained from these analyses are compared with those from the AASHTO methods. The presence of parapets is shown to reduce distribution factors by as much as 36 and 13% for exterior and interior girders, respectively. The effect of parapets is slightly less for skewed bridges. Aspect ratio is shown to have very little effect on distribution factors until the ratio exceeds 1.8.