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Report No.: CCEER-07-5

Title: Strut-and-Tie Modeling for Disturbed Regions in Structural Concrete Members with Emphasis on Deep Beams

Authors: Neil Bahen and David Sanders

Date: December 2007

Sponsoring Agency: National Cooperative Highway Research Program (NCHRP)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557

Abstract:

Strut-and-tie modeling (STM) is used for the design of disturbed regions in structural concrete members. The design community has recently showed a great deal of concern regarding the proper application and conservatism of the STM provisions of the AASHTO LRFD Bridge Design Specifications and ACI 318-05. In order to investigate the STM provisions of the AASHTO LRFD Bridge Design Specifications and ACI 318-05, the STM provisions of both specifications were compared to the findings of an extensive literature review and the STM provisions of other design specifications. In addition, the limiting strut stress provisions of the AASHTO LRFD Bridge Design Specifications and ACI 318-05 were closely examined by performing STM analyses on deep beams in a database of 360 deep beams compiled for this research. From comparisons to the findings of the literature review, the STM provisions from other design specifications, and the results of the STM analyses of the deep beams in the database, discrepancies in the STM provisions of the AASHTO LRFD Bridge Design Specifications and ACI 318-05 were identified. The most significant finding was that the limiting strut stress provisions for both specifications were found to be unconservative. Additional research was then performed to determine how to modify the limiting strut stress provisions to make them conservative. Based on the findings of the additional research, revisions to the limiting strut stress provisions of the AASHTO LRFD Bridge Design Specifications and ACI 318-05 were made.

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