Title: Behavior of compact L-shaped spandrel beams with alternative web reinforcement
Date Published: March - April 2019
Volume: 64
Issue: 2
Page Numbers: 39 - 54
Authors: Vivek Hariharan, Gregory Lucier, Sami Rizkalla, Paul Zia, Gary Klein, and Harry Gleich

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Open web reinforcement has been shown to be an effective alternative to closed stirrups in the webs of slender precast concrete L-shaped spandrel beams subjected to combined shear and torsion.1–6 For slender beams, an open reinforcement scheme is a better alternative to the traditional closed stirrups mandated by the American Concrete Institute’s (ACI’s) Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14)7 because the beams are easier to produce with open reinforcement. Although the behavior of slender L-shaped beams (having aspect ratios of 4.5 or greater) with open web reinforcement has been well documented, the use of alternatives to closed stirrup reinforcement for compact L-shaped cross sections having aspect ratios much less than 4.5 has not been investigated previously.

This paper presents an experimental study in which four full-scale, 46 ft (14 m) long, precast concrete, compact L-shaped beams were tested to failure. One of the test specimens served as a control and was designed with traditional closed stirrups. The remaining three beams were designed with alternative open and segmented reinforcement configurations.

The results of the study demonstrate the viability of replacing closed stirrups with alternative open and segmented web reinforcement in compact L-shaped spandrel beams. All four beams behaved satisfactorily at all loading stages and failed at loads much greater than the factored design loads. When failure occurred in the end region of the compact L-shaped beams with open reinforcement, no spiral cracking or face-shell spalling were observed, which is contrary to the failure mode associated with the torsion design concept of ACI 318- 14.7 Rather, the observed failure planes in the compact L-shaped beams were similar to those observed in slender L-shaped beams, with skewed bending along a diagonal crack extending upward from the support. The results confirm the potential to simplify the design and detailing of compact L-shaped beams by using alternative transverse reinforcement details proportioned with a design approach based on failure in combined shear and torsion.