Development of a Rational Design Methodology for Precast Slender Spandrel Beams

Abstract

The use of open web reinforcement for torsion and shear reinforcement in slender spandrel beams has been suggested by the precast concrete industry as an alternative to the traditional closed stirrups mandated by ACI 318-08. Investigations of slender precast spandrel beams by Raths (1984), Klein (1986), Logan (2007), and others have indicated that such closed stirrups may not be necessary for these slender, non-compact sections. The proposal of eliminating closed stirrups is very appealing to the precast industry because closed stirrups tend to significantly increase production costs. This report documents an extensive experimental and analytical research program sponsored by the Precast Prestressed Concrete Institute and conducted at North Carolina State University. The objective of the research was to develop a rational design procedure for precast slender spandrel beams. Specifically, the research aimed to simplify the detailing requirements for the end regions of precast slender spandrel beams. Such regions are often congested with heavy reinforcing cages when designed with current procedures.

Evolution of the L-shaped spandrel beam

“…The PCI-funded research had a profound impact on the evolution of design procedures for such beams. [1][2][3] L beams are typically placed at the perimeter of a precast concrete structure and support double-tee-beam floor components. As used in parking structures, the web of the L often extends above the floor surface to function also as a barrier wall.…”

“…PCI funded further research at North Carolina State University (NCSU) and Wiss, Janney, Elstner Associates Inc. (WJE). 2 Alternative torsion design procedures were developed for slender spandrels based on separate consideration of the plate bending and twist components of torsion across an inclined failure plane. As a result, closed transverse reinforcement was no longer required, and reinforcement congestion at L-beam ends was greatly reduced.…”