Title:
Stirrup Effectiveness in Reinforced Concrete Beams under Flexure and Shear
Author(s):
Gaetano Russo and Giovanni Puleri
Publication:
Structural Journal
Volume:
94
Issue:
3
Appears on pages(s):
227-238
Keywords:
beams (supports); building codes; models; reinforced concretes;
shear strength; stirrups; structural design; tests;
DOI:
10.14359/475
Date:
5/1/1997
Abstract:
The socalled shear failure of slender beams is known to be due to combined action of flexure and shear which causes beam failure moment to be lower than ultimate moment in pure flexure, even for beams with stirrups. Current design procedures for shear strength analysis provide simple superposition of stirrup and concrete capacities, hence ignoring any stirrup influence on concrete mechanisms and/or any dependence of stirrup action on the failure mode. By contrast concrete shear resisting mechanisms, made of the beam and arch action contributions, can interact with stirrups in different ways. Latter interaction results in a truss mechanism variable contribution and in some enhancement of beam action contribution. A stirrup effectiveness function is introduced, which provides the ratio of effective mean shear stress increase due to stirrup inclusion and the conventional one drawn from 45 deg truss model. On these bases a mechanical model is proposed to provide mean ultimate shear stress of RC beams with stirrups. By testing the proposed model against available experimental results from different authors, more accurate prediction is obtained than from ACI Code, Eurocode, New Zealand Code, and ZsuttyÆs formula. Thus, a design formula is proposed which is simple and results in a reasonably conservative design.