Yield line analysis of an AASHTO New Jersey concrete parapet wall

Concrete bridge rails are rated according to three performance levels. For classification at a given performance level, the rail must meet specific strength and geometric requirements. To meet the strength requirement, the rail must be able to satisfactorily withstand a transverse concentrated load applied at the top of the rail. This load is called F_t (kips) and is listed for each performance level in the Draft NCHRP Project 12-33 document entitled Development of a Comprehensive Bridge Specification and Commentary.

Researchers at the Texas Transportation Institute have developed equations to determine R_w (kips), the total transverse resistance of a rail (which must be greater than or equal to F_t), and L_c (ft), the critical length of wall failure (Hirsch 1978). These equations (referred to as Hirsch equations is this study) were developed by yield line analysis for a constant thickness concrete parapet wall.

The purpose of this study is to develop similar equations for R_w and L_c based on yield line analysis of a variable thickness New Jersey concrete parapet wall instead of a constant thickness wall.

The results from this study indicate that the Hirsch equations significantly over estimate R_w for variable thickness concrete walls where M_c, the flexural resistance of the wall about the horizontal axis, varies substantially over the height of the wall. This study recommends that an average value for M_c, taken over the height of the wall, be used in the Hirsch equations when this situation arises.