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Memorandum

TO: All Design Section Staff
FROM: J. Kapur
DATE: August 17, 2001
SUBJECT: Design Policy Memo LRFD Deck Overhang Design

The deck overhang should be designed in accordance to the requirements of the AASHTO-LRFD article A13.4 to provide a flexural resistance MS, acting coincident with the tensile force T.  At the inside face of the barrier the deck overhang design forces per foot not including dead loads may be taken as:

      

      Where:

LC                    critical length of yield line failure, ft

H                     height of traffic barrier, ft

       

The nominal traffic barrier resistance to transverse load, RW, for the design of deck overhang specified in article A13.4 need not exceed 120% of the transverse force, Ft, as specified in LRFD Table A13.2-1 based on the traffic railing test levels. 

 

Background:

The AASHTO LRFD Specifications article A13.4-2 requires that the flexural capacity of the deck overhang, MS, exceed the flexural capacity of concrete barrier at its base, MC.  This means that the deck must have sufficient resistance to force the yield line failure pattern to remain within the barrier.

 

The WSDOT traffic barriers are reinforced based on the FHWA crash testing program oriented toward survival.  This reinforcement requirement produces a traffic barrier system that is overdesigned, leading to the possibility that the deck overhang is also overdesigned.  In order to prevent this unnecessary overdesign of the deck overhang, the nominal traffic barrier resistance to transverse load, RW, transferred from the traffic barrier to deck overhang need not exceed 120% of the design force required for traffic barrier design in table A13.2-1.

 

If you have any questions regarding these issues, please contact Bijan Khaleghi at 705-7181.

 

JK:dsb

BK

 

cc:   J. Weigel, 47340

        F. Higgins, 47340