Concrete Industries Structural Division recently completed the first phase of testing on the new 16” hollowcore section. The load testing was completed at the Peter Kiewit Institute located at University of Nebraska-Omaha under the direction of Dr. George Morcous.
The 16” hollowcore forms were purchased primarily for use on podium structures where the owners/architects of these mixed use buildings are requiring longer spans with increased load requirements. A podium structure is built with a concrete deck comprised of hollowcore, inverted tee beams and columns which in turn support three or four floors and a roof of light frame construction (wood or metal stud). The lower level has primarily been utilized as a parking garage and storm shelter.
Since there are two different uses, the structural grids do not align requiring the bearing walls from the light famed structure above to be placed on the center span of hollowcore. The center span of hollowcore and IT beams are the primary load carrying element in the building. Once hollowcore exceeds 12 ½” in depth, the building code permits only half of the shear capacity at the ends of the section, which can be a significant design hurdle in these heavily loaded members.
In order to provide an economical design solution for our clients, CI Structural decided to perform load testing to prove this reduction in capacity was not required, therefore removing the hurdle. Additionally, the first phase of load testing indicated the section has significant ductility along with stable post cracking behavior. The 4’-0” wide section supported 85,000 lbs while deflecting 10 inches without failure. The testing was stopped because the testing equipment had reached the maximum deflection.
The second phase will further define the shear capacity of the section but the first phase demonstrated 65% capacity without deformation. The testing and final report will be completed at the beginning of March.