Recent Approaches to Shear Design of Structural Concrete
|Publication Date:||1 January 1999|
Scope and objectives
Design procedures proposed for regulatory standards should be safe, correct in concept, simple to understand, and should not necessarily add to either design or construction costs. These procedures are most effective if they are based on relatively simple conceptual models rather than on complex empirical equations. This report introduces design engineers to some approaches for the shear design of oneway structural concrete members. Although the approaches explained in the subsequent chapters of this report are relatively new, some of them have reached a sufficiently mature state that they have been implemented in codes of practice. This report builds upon the landmark state-of-the-art report by the ASCE-ACI Committee 426 (1973), The Shear Strength of Reinforced Concrete Members, which reviewed the large body of experimental work on shear and gave the background to many of the current American Concrete Institute (ACI) shear design provisions. After reviewing the many different empirical equations for shear design, Committee 426 expressed in 1973 the hope that "the design regulations for shear strength can be integrated, simplified, and given a physical significance so that designers can approach unusual design problems in a rational manner."
The purpose of this report is to answer that challenge and review some of the new design approaches that have evolved since 1973 (CEB 1978, 1982; Walraven 1987; IABSE 1991a,b; Regan 1993). Truss model approaches and related theories are discussed and the common basis for these new approaches are highlighted. These new procedures provide a unified, rational, and safe design framework for structural concrete under combined actions, including the effects of axial load, bending, torsion, and prestressing.
Chapter 1 presents a brief historical background of the development of the shear design provisions and a summary of the current ACI design equations for beams. Chapter 2 discusses a sectional design procedure for structuralconcrete one-way members using a compression field approach. Chapter 3 addresses several approaches incorporating the "concrete contribution." It includes brief reviews of European Code EC2, Part 1 and the Comité Euro-International du Béton-Fédération International de la Précontrainte (CEB-FIP) Model Code, both based on strut-and-tie models. The behavior of members without or with low amounts of shear reinforcement is discussed in Chapter 4. An explanation of the concept of shear friction is presented in Chapter 5. Chapter 6 presents a design procedure using strut-and-tie models (STM), which can be used to design regions having a complex flow of stresses and may also be used to design entire members. Chapter 7 contains a summary of the report and suggestions for future work.