Tests on precast L-spandrel beams focus on improved design procedure

CHICAGO—North Carolina State University in Raleigh, N.C., conducted a series of full-scale torsion tests intended to improve the design procedure for L-spandrel beams. In total, 12 full-size spandrel beams were tested by the end of January.

Sponsored by the Precast/Prestressed Concrete Institute (PCI), the tests were conducted to investigate the behavior of end regions of slender spandrel beams subjected to eccentric loading, according to Paul Johal, P.E., director of PCI Research and Development.

The main objective of the research project was to develop appropriate design procedures that simplify reinforcement detailing requirements for precast, L-shaped spandrel beams subjected to eccentric ledge loading. The appropriateness of the current design procedure has been questioned, said Johal, because it is based on data collected from tests of conventionally reinforced and prestressed concrete members having compact cross sections. Using this method for slender cross sections of typical L-shaped spandrel beams results in the use of closed reinforcement, which is usually tightly congested.

The experimental results have been used to calibrate an analytical model. Analytical and experimental results will be used together to develop a refined and improved design procedure. According to the PCI Advisory Group, the tests on the more compact L-spandrels were quite valuable since they showed that the basic failure mode doesn’t change significantly as the slender spandrel (aspect ratio 7.5) becomes more compact (4.6).

A final report containing the new design procedures should be completed by the end of June. PCI will then move to get these procedures into common practice. The new design guidelines will also be included in the next edition of the PCI Design Handbook. The new design procedures will maintain the required high levels of safety while reducing internal steel.

As a result of the new design procedures, the cost to produce slender spandrel beams will be significantly reduced. This reduction comes from decreased material cost (approximately 30 percent less web steel is required) and an estimated 50-percent decrease in labor cost required to tie the steel cage.

TrusSteel acquires Dynatruss

TrusSteel, a division of ITW Building Components Group, Inc., acquired the assets of Dynatruss, a supplier of cold-formed steel truss products. TrusSteel will maintain the Dynatruss brand name and operate it as a subsidiary of TrusSteel. The Dynatruss system will continue to be manufactured at the facilities of Allied Tube & Conduit, Inc., located in Phoenix and Harvey, Ill.


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