A series of PCI-sponsored torsion tests on precast spandrel beams has netted alternatives to current design procedures that economize production through lower material costs (approximately 30 percent less web steel) and significantly decreased labor (about 50 percent less time to tie the steel cage)
Source: Precast/Prestressed Concrete Institute, Chicago
A series of PCI-sponsored torsion tests on precast spandrel beams has netted alternatives to current design procedures that economize production through lower material costs (approximately 30 percent less web steel) and significantly decreased labor (about 50 percent less time to tie the steel cage). Investigators at North Carolina State University (NCSU), Raleigh, recently concluded the tests on 12 full-size, L-shaped specimens and will prepare a final report and new design procedures by mid-2009.
Investigators observed the behavior of end regions of beams subjected to eccentric loading, according to PCI Research and Development Director Paul Johal, P.E. The appropriateness of the existing design procedure has been questioned, he notes, because it is based on data collected from tests of conventionally reinforced and prestressed concrete members having compact cross sections. Applied to slender cross sections of typical L-shaped spandrel beams, the method results in the use of closed reinforcement, which is usually tightly congested and difficult to place.
Precast specimens, software, engineering support and testing labor were donated by PCI members Metromont Corp., Tindall Corp., Finfrock Industries, High Concrete Group, Stresscon Corp., JVI Inc., and Leap Software (now Bentley), Wiss, Janney, Elstner Associates, and NCSU. A final report containing the new spandrel design procedures should be completed by June. The new design guidelines, which PCI assures will maintain high levels of safety while reducing internal steel requirements, will also be included in the next edition of the PCI Design Handbook.