L-Spandrels: Can Torsional Distress Be Induced by Eccentric Vertical Loading?

Abstract

Current code-required design procedures for eccentrically loaded L-spandrels assume that torsional distress is the mode of failure at ultimate shear-torsion capacity and prescribe appropriate reinforcement to accommodate such distress. The more commonly accepted design procedures vary in complexity, but all result in the need for heavy reinforcement and complex detailing that are expensive with regard to both material and fabrication labor costs. Based on observation of the failure mode of an L-beam in a full-scale torsion test conducted by the author in 1961, and particularly on his diagnosis of the failure modes of L-spandrels in tests conducted in the mid-1980s by Wiss, Janney, Elstner Associates Inc., the author concludes that the face shell spalling and severe spiral cracking associated with torsional distress is not induced in L-spandrels at ultimate failure by eccentric vertical loading. Thus, the current complex design procedures and the complexity and expense of reinforcement resulting from these procedures are not justified. Instead, the ultimate capacity in the end region of L-spandrels is satisfied by the reinforcement required in their inside face to resist out-of-plane bending. Concrete shear capacity is checked by the V CW equation and seldom requires additional reinforcement in deep L-spandrels.