Description:

Shear in Discontinuity Regions: Planned Changes for the Structural Concrete Building Code

Abstract
Since its introduction into the ACI 318 code in 2002, the strut-and-tie method has been based on the premise that strength is sufficient if the idealized truss model is in equilibrium with the applied load without exceeding the capacity of struts, ties, and nodes. However, in spite of low strut efficiency factors for so-called bottle-shaped struts, the strut-and-tie method can be unconservative. Struts are not weaker because they are bottle-shaped; rather, the apparent weakness is due to shear failure where struts cross a diagonal tension field. Unless minimum distributed reinforcement is provided, discontinuity regions designed using the strut-and-tie method should be separately checked for shear strength, considering both strut angle and size effect. Furthermore, minimum distributed reinforcement should be provided unless struts are laterally confined. This presentation describes the development of new ACI 318 code requirements for shear design of discontinuity regions using the strut-and-tie method.

Bio
Gary Klein, is Executive Vice President and Senior Principal at Wiss, Janney, Elstner Associates, in Northbrook, Illinois. Mr. Klein is a licensed structural engineer with more than 40 years of experience in failure investigation and structural research. He a long-time member of ACI Committee 318, Structural Concrete Building Code and 445, Shear and Torsion. Research interests include behavior and design of precast concrete elements and discontinuity regions in structural concrete. Honors include ACI’s Wason and Charles S. Whitney medals as well as election to the National Academy of Engineering.