Load Resistance: ICFs vs. Steel & Wood-Frame
Research was conducted to compare the ability
of insulating concrete form (ICF) walls, and conventionally
framed walls, to resist structural stresses that can occur
during earthquakes. All of the walls were tested by applying
a sideward or lateral force along the top edge of each wall,
in line with the plane of the wall, while restraining the
bottom. This "racking" of the specimens creates
internal tearing or shear forces as the top of the wall tries
to move while the bottom of the wall remains stationary. The
concrete walls demonstrated significantly higher structural
capacity and stiffness to resist the in-plane shear forces
than wood or steel frame walls.
Grid ICF Wall
Grid ICF Wall
of walls were tested?
One wall specimen
for each of five types of exterior residential wall systems
were 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, all shown below. 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. No finishes
were applied to the surfaces of the wall specimens. 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 foam plastic formwork
was removed from one side of each panel to permit the performance
of the concrete to be observed.
The two frame walls
consisted of: a 2 x 4 wood stud specimen, and a 20-gauge steel
stud specimen. The framing was covered with 7/16-in. OSB (Oriented
Strand Board) 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-plane
shear resistance measured?
The structural details
for the test specimens were adopted 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. Additional devices were used
to measure any movement of the panels or footing. The amount
of load was gradually increased while any major distress,
cracking, or damage was observed and recorded. The loading was
typically continued beyond the peak loading capacity of each
wall and testing terminated when the strength of each wall was
significantly reduced due to excessive damage to the wall specimens.
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 6 to 8 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.
Shear Wall Testing and Loading Results:
Lateral Stiffness (lbs/in)1
at First Major Damage (lbs)
at First Major Damage (in)
Lateral Resistance (lbs)
at Maximum Lateral Resistance (in)
1 Global Lateral Stiffness
at 1/3 the maximum lateral force resistance for the wood and
steel frame, at a lateral load of 5,000 lbs. for the ICF walls.
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 higher strength of ICF walls enable concrete
homes to resist winds and earthquakes of much higher magnitudes.
The higher stiffness demonstrated by the ICF wall panels at
the loading limits of the frame wall systems, would result in
smaller lateral deformation and prevention of potential damage
to non-structural elements of a home such as finishes and trim.
In the case of moderate earthquakes, the repair cost of the
damaged non-structural components is usually the major, and
sometimes the only part of the restoration costs. ICFs offer
great potential for reduced property loss from strong wind and
The following publication is available from the Portland
Cement Association. To order, call PCA Publications at (800)
"In-Plane Lateral Load Resistance of Wall Panels in
Residential Buildings", by Armin B. Mehrabi, Construction
Technology Laboratories for Portland Cement Association, 2000,
Serial No. 2403
This report documents the results of comparative in-plane
shear wall testing conducted on wood and metal frame, and
insulating concrete form wall specimens. The panels represented
some of the typical wall systems being used for current construction
of residential buildings. Full results of the testing is reported.
The test setup and procedure followed the general guidelines
of the ASTM E564-95, Standard Practice for Static Load Test
for Shear Resistance of Framed Walls for Buildings.