WHAT TYPE OF WALLS WERE TESTED?
One wall specimen for each of five types of exterior residential wall systems was tested, each 8 feet high and 4 feet wide. Three of the wall specimens were built with ICFs, creating one flat concrete wall, a waffle grid concrete wall, and a screen grid concrete wall. The walls were reinforced with grade 60 steel rebars. Additional steel extended from the top of the footing into each wall. The nominal compressive strength of the concrete used in the wall panels was 2500 psi. Loads were applied to a concrete beam secured to the top of the wall panels with high strength anchor bolts to transfer the lateral forces to the top of the specimens.
The two frame walls consisted of: a 2x4 wood stud specimen, and a 20-gauge steel stud specimen. The framing was covered with 7/16-inch oriented strand board (OSB) on one side and gypsum wallboard on the other. The frame walls were secured to concrete footings with steel hold-downs anchoring the ends, and with embedded anchor bolts at two intermediate locations. A 6-inch deep timber beam was firmly attached to the top of the frame wall specimens to transfer the lateral forces to the top of the panels.
HOW WAS IN-PLACE SHEAR RESISTANCE MEASURED?
The structural details for the test specimens were based on design recommendations and guidelines for typical exterior wall panels in earthquake zones 1 or 2, and for minimum wind speed of up to 70 miles per hour. The test setup and procedure followed general guidelines of ASTM E564-95 “Standard Practice for Static Load Test for Shear Resistance of Framed Walls for Buildings.” A hydraulic ram was used to transfer lateral load to the beam at the top of each wall. A calibrated instrument measured the increasing magnitude of this load.
HOW DOES THE SHEAR RESISTANCE COMPARE?
The frame walls showed initial damage at relatively light loading and had a much lower maximum lateral resistance. The ICF walls resisted a maximum lateral load six to eight times the maximum loads resisted by the frame wall panels. Under lateral loads of about twice as much as the maximum resistance of the frame walls, the ICF panels were still very stiff, with extremely small deformation, and showed no damage. The table below summarizes the actual results for each tested wall panel.
WHAT DOES THIS DIFFERENCE MEAN?
These results suggest that when subjected to lateral in-plane loading from sources such as wind or earthquake, the ICF wall panels are not only considerably stronger but also much stiffer than the framed wall panels.
The following publications and the full version of this Tech Brief are available from the Portland Cement Assocation.
In-Plane Lateral Load Resistance of Wall Panels in Residential Buildings, Armin B. Mehrabi, Construction Technology Laboratories for Portland Cement Association, 2000, Serial No. 2403
EB118 Prescriptive Method for ICFs in Residential Construction (2nd Edition) $25.00
LT282 Insulating Concrete Forms Construction: Demand, Evaluation, and Technical Practice, VanderWerf, $49.95