Yield line analysis of an AASHTO New Jersey concrete parapet wall

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Virginia Tech


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 Ft (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 Rw (kips), the total transverse resistance of a rail (which must be greater than or equal to Ft), and Lc (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 Rw and Lc 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 Rw for variable thickness concrete walls where Mc, 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 Mc, taken over the height of the wall, be used in the Hirsch equations when this situation arises.