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Performance of Screen Grid Insulating Concrete Form Walls under Combined
In-Plane Vertical and Lateral Loads
Article in Advanced Materials Research · December 2010
DOI: 10.4028/www.scientific.net/AMR.163-167.1803
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Advanced Materials Research Vols. 163-167 (2011) pp 1803-1810
Online available since 2010/Dec/06 at www.scientific.net
© (2011) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.163-167.1803
Performance of Screen Grid Insulating Concrete Form Walls under
Combined In-Plane Vertical and Lateral Loads
M. Abdel-Mooty1, a, M. Haroun2, b , Y. El-Maghraby1,c, E. Fahmy1, d, and
M. Abou-Zeid1, e
1
Department of Construction and Architectural Engineering, The American University in Cairo,
AUC Avenue, PO Box 74, New Cairo 11835, Egypt
2
Dean and AGIP Professor, School of Sciences and Engineering, The American University in Cairo,
AUC Avenue, PO Box 74, New Cairo 11835, Egypt
a
b
c
mamooty@aucegypt.edu, maharoun@aucegypt.edu, yosra78@aucegypt.edu,
d
ezzat@aucegypt.edu, emnagiba@aucegypt.edu
Keywords: Insulated Concrete Forms; Screen Grid Walls; Experimental Tests; Lateral Loads
Abstract. Insulating Concrete Forms (ICF) walls generally comprise two layers of Expanded
Polystyrene (EPS), steel reinforcement is placed in the center between the two layers and concrete is
poured to fill the gap between those two layers. ICF’s have many advantages over traditional methods
of wall construction such as reduced construction time, noise reduction, strength enhancement,
energy efficiency, and compatibility with any inside or outside surface finish. The focus of this study
is the Screen Grid ICF wall system consisting of a number of beams and columns forming a concrete
mesh. The performance of ICF wall systems under lateral loads simulating seismic effect is
experimentally evaluated in this paper. This work addresses the effect of the different design
parameters on the wall behavior under seismic simulated loads. This includes different steel
reinforcement ratio, various reinforcement distribution, wall aspect ratios, different openings sizes for
windows and doors, as well as different spacing of the grid elements of the screen grid wall. Ten full
scale wall specimens were tested where the effects of the various parameters on wall behavior in
terms of lateral load capacity, lateral displacement, and modes of failure are presented. The test
results are stored to be used for further analysis and calibration of numerical models developed for
this study.
Introduction
Insulating Concrete Forms (ICFs) is a fast growing technology in the construction industry. ICFs are
hollow blocks or panels made of Expanded Polystyrene (EPS) where the construction crew assembles
them like Legos to create a wall formwork with cavities to be filled with concrete. Steel reinforcement
is fixed inside these blocks or panels, and then concrete is poured to fill the gap or cavities between
the two layers of foam [1-4]. ICF systems are categorized based on two characteristics that have broad
implications: the shape of the foam and the shape of the concrete after being poured. The foam comes
in a variety of forms: blocks, planks or panels. The cavities inside the foam and consequently the
concrete also have various shapes: flat solid concrete, grid waffle wall and screen grid wall of post and
beam. The screen grid ICF wall system is considered in this study as lateral load resisting wall system.
ICFs are light in weight which reduces labor and makes its assembly and installation fast and easy
[5]. Forms are fixed to the footings or slab either by foam adhesive or are set to the wet concrete of the
footings or slab. ICF forms are cut to fit to any shape and size of openings. Horizontal and vertical
steel reinforcement is fixed inside the forms according to the structural design. After steel
reinforcement is placed, concrete is then pumped into the wall. Interior and exterior finishing: any
kind of finishing could be easily secured to the forms.
The use of ICF wall system to provide the needed thermal insulation for desert environment is
considered in this research. The permanent EPS outer layer provide thermal insulation to keep heat
outside during day time and inside during the night time. The use of screen wall grid system reduces
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Advances in Structures
the amount of concrete and increases the volume of EPS thus increasing the heat insulation property
of the wall system and reduces the concrete cost. Furthermore the ICF wall construction system
reduce or eliminate the need for curing water or curing compound thus minimize the use of water
during construction and save the environment. Furthermore, the use of permanent EPS form
eliminates the use of wooden and metal formworks thus reduce the construction solid waste and
preserve natural resources.
Previous research in ICF concrete wall system focused on investigating in-plane shear resistance of
various wall systems in relation to other wood and steel wall system commonly used in residential
construction in North America [6-8]. The wall panel specimens were subjected to monotonically
increasing static lateral in-plane loads. The loading was continued beyond the maximum resistance
level. In most cases, the test was terminated after the residual strength had been considerably reduced
from the peak value, due to excessive damage in the specimens. The flat ICF specimen experienced
initial cracking along the leading edge at the wall panel to footing interface. As the displacement
increased, the initial cracking extended to the toe and vertical cracks formed at the bottom of the wall
at the leading edge due to bond failure between the concrete and reinforcing dowel. Crushing of the
toe was also evident on the compression side. Pullout of the dowel bar from the wall specimen led to
gradual decrease in load that was deemed failure of the specimen even though it was restrained
against rotation. It should be pointed out that the connections between wall panels and footings, and
more importantly, between panels and roofs/floors can strongly influence the behavior of wall panels.
In this paper the performance of screen grid ICF wall system in resisting combined in-plane
vertical and lateral loads simulating seismic action is considered. The effect of the different design
parameters on the wall performance is considered. This includes the amount and distribution of the
reinforcement, the grid spacing, and the window and door opening. As pointed out in previous work
the dowel connection to the base plays an important role in the wall resistance to lateral load.
Therefore different dowels arrangements are used in this research. Figure 1 shows the full-scale ICF
screen grid wall specimens used in this study.
a) ICF wall with EPS forms
b) EPS forms removed
Fig. 1, ICF screen grid wall specimens
c) ICF wall testing
Advanced Materials Research Vols. 163-167
1805
Table 1: Test Program
Wall Code
Wall Dimensions
(m)
Grid Spacing
CL to CL
(m)
SG1, SG2
& SG4
1.00x2.00
0.25
SG3
1.00x2.00
0.25
SG5
1.00x2.00
0.25
SG6
1.00x2.00
0.25
SG7
2.00x2.00
0.25
SG8
1.00x2.00
0.40
SG9
1.00x2.00
0.25
SG10
2.00x2.00
0.25
Parameter
Control specimen, 150 mm grid member size
(diam.), 12 mm rebar in each grid member.
Different reinforcement distribution with
12 mm rebar in every other grid member
8 mm rebar for grid members and two 12 mm
double dowels bars to the base
8 mm rebar and 12 mm double dowels.
Steel fibers added to concrete mix
Window opening 1.0 x 1.0 m
8 mm rebar and 12 mm double dowels
Different grid spacing
8 mm rebar and 12 mm double dowel.
12 mm rebar for grid members and two 12 mm
double dowels bars to the base
Door opening 1.0 x 1.425 m
8 mm rebar and 12 mm double dowels
Fig. 2, Test set-up.
Test Program and Set-up
Ten full scale ICF screed grid walls are considered in this study. The wall dimensions are 1.0x2.0
meter in elevation with 0.15 m thickness. They are made of a grid of circular columns and beams of
diameter 0.15 m and spacing 0.25 m center-line to centerline. The control wall is reinforced with one
8 mm steel bar in each grid member. The wall specimens are provided with RC base beam of
dimension 0.4x0.4x2.40 m and top RC beam of dimension 0.15x0.20x1.00 m. The base beam is
anchored to the test floor to prevent horizontal sliding or uplift during testing. The top beam is used to
evenly distribute the vertical load and horizontal load applied to the wall top on the wall cross-section.
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Advances in Structures
Table 1 displays the tested wall specimens and the different parameters considered in the test
program.
The wall specimen is first loaded vertically to an initial vertical compressive load. The vertical
load is applied to a rigid steel beam that rest on the wall top through five steel rollers rods to distribute
the load evenly on the wall through the wall top beam and to allow for the horizontal displacement of
the wall top under lateral load. Then the lateral load is applied horizontally to the wall top through the
horizontal actuator fixed to the rigid reaction wall as shown in Fig. 2.
The wall response during testing is measured by a variety of instrumentation devices as shown in
Fig. 3. Both vertical and lateral loading were measured through load cells attached to the actuators.
The in-plane lateral displacement of the wall is measured using LVDT attached to the wall top. Two
other LVDT’s are attached vertically at the wall top to measure the wall tilting at the top under
loading. Twelve strain gages are attached to the steel reinforcement bars at selected locations as
shown in Fig. 3 to record strain distribution during testing to be used for further numerical analysis. A
high speed data acquisition system with sampling rate 1000 sample per second is used to record the
response during testing and save it on a dedicated PC for further analysis.
Fig. 3, Instrumentation layout
Crushing of the compression bottom corner
Tensile cracking at the tension bottom corner
Fig. 4, Failure of SG1 ICF screen grid wall specimen
Advanced Materials Research Vols. 163-167
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Experimental test results
Walls SG1 and SG2 were the first two walls to be prepared. They had small water/cement ratio with
low workability that resulted in honeycombing. This was avoided in the subsequent walls through
using superplasticizer. The honeycombing in wall SG1 left unrepaired and the wall was tested and
failed at 8.6 tons lateral load. The wall failure was mainly due to concrete crushing of the compression
bottom corner due to the reduced section due to honeycombing. Wall SG2 (control) was the same as
Wall SG1 but the honeycombing was repaired using cement mortar. The wall failed at 16 tons lateral
load where cracks developed along the main diagonal. Figure 4-6 shows the variation of the lateral
displacement and strain with the applied lateral loads and the wall cracking at failure.
The first two walls SG1 and SG2 were subjected to initial compressive vertical load of 24 and 25
tons which is approximately 20% of the vertical load carrying capacity of the wall. However, it was
observed that during lateral loading the wall top tilted and the wall started to separate at the base thus
pushing on the top vertical actuator. This resulted in significant increase in the vertical load to high
values of approximately 60 tons. To avoid this increase the vertical initial loading was kept to a
minimum value less than 4 tons. The vertical load continued to increase with increasing lateral load
but to a reasonable value of approximately 25 tons. The vertical load values influenced the lateral load
capacity and the mode of failure.
Wall SG3 with different steel distribution where 12 mm rebar was used in every other grid
member. The wall failed at 16.4 tons lateral load. Failure was due to tension dowel failure and
separation from the base at the tension corner thus wall overturning about the compression corner.
Consequently concrete crushed at the compression corner at the bottom of the wall. No cracks were
observed in the grid members as shown in Fig 7.
Wall SG4 is a control wall similar to SG1 and SG2 but without honeycombing. The wall was
reinforced with 12 mm rebar in each grid member. The wall failed at 14.4 tons lateral load due to wall
overturning about the compression corner. No cracks were observed in the grid member while the
tension dowels failure resulted in wall separation from the base at the tension corner. No ductility was
observed as the wall undergoes rigid body tilting with limited cracking.
Wall SG5 was reinforced with 8 mm rebar in each grid member instead of 12 mm bars. In order to
avoid dowels failure, two bars 12 mm were used as dowels in the tension side. The wall failed at 8.88
tons lateral load where overturning and separation at the base were completely avoided. Tension
cracks developed horizontally above the dowels and propagated diagonally to the compression corner
as shown in Fig. 8.
Steel fiber concrete was used in Wall SG6 and 8 mm rebar reinforcement was provided in each grid
member and 12 mm double dowels were used. The wall failed at 11.24 tons lateral load where neither
overturning nor separation at the base was observed. Tension cracks developed horizontally above the
dowels and propagate diagonally to the compression corner (Fig. 9).
Wall SG7 was provided with 1.00x1.00 m central window opening. The wall failed at 8.9 tons
lateral load where cracks developed along the main diagonal at the corners of the opening. As the
lateral loading increased secondary diagonal cracks developed at the other corners of the opening as
shown in Fig. 10.
In Wall SG8 different grid spacing where used where the distance between the grid centerlined
were 400 mm instead of 250 mm. The wall failed at 9.96 tons lateral load. Failure was mainly due to
shear where diagonal tension cracks developed in the vertical and horizontal grid members along the
main diagonal (Fig. 11). Tension (bending) cracks perpendicular to the grids were also developed in
the grid members at the end of the spacing.
Wall SG9 control with 12 mm double dowels and 12 mm rebar reinforcement failed at 20 tons
lateral load due to failure of the base beam. Diagonal cracks developed along the main diagonal.
Subsequent tension (bending) cracks developed perpendicular to the grids (Fig. 12). No separation at
the base was observed however the base beam failed and test stopped.
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Advances in Structures
Fig. 4: Lateral load-displacement relationship in SG2
Fig. 5: Strain variation with loading in SG2 wall
Fig. 7, Failue of wall SG3
Fig. 6, Diagonal shear cracks failure of SG2
Fig. 8, Failure of wall SG5
Fig. 10, Failure of wall SG7 with window opening
Fig. 9, Failure of wall SG6
Fig. 11, Failure of wall SG8
Advanced Materials Research Vols. 163-167
Fig. 12, Failure of wall SG9
1809
Fig. 13, Failure of wall SG10 with door opeing
Wall SG10 was provided with 1.00x1.425 central door opening. The wall failed at 9 tons lateral
load due to diagonal cracks initiated at the opening corner and developed mainly in the wall strips
next to the opening. Tension (bending) cracks were developed perpendicular to the grids as shown in
Fig. 13.
The results of the test program are summarized in Table 2 and Figure 14. The strain and
displacement measured at the different location were recorded for further analysis and comparison
with the numerical modeling reported elsewhere.
Table 2: Summary of Test Results
Wall
SG1
SG2
SG3
SG4
SG5
SG6
SG7
SG8
SG9
SG10
Brief Description
Initial Lateral
Fcu
Vertical Load at
(kg/cm2)
Load
Failure
(ton)
(ton)
Displ. at
Maximum
Lateral
Load (mm)
Control with
honeycombing
Control repaired
honeycombing
different distribution
of steel rebars
405
25
8.65
14.14
405
24
16.23
45.25
360
4
16.40
137.77
Control
360
4
14.44
58.58
345
3
8.88
28.28
380
3.5
11.24
49.70
345
4
8.90
26.66
375
1
9.96
53.73
375
1
20.12
137.00
375
0.25
9.04
35.15
8 mm rebars & double
dowel
8 mm rebars, double
dowel & Steel fibers
Window opening
Wide grid spacing &
double dowel
Control with double
dowel
Door opening
Remarks
Vertical load
increased with
lateral load
Wall tilting
Failure of base
beam
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Fig. 14, Comparison of maximum lateral load at failure for the tested specimens.
Summary
Ten full scale ICF screen grid walls were tested under combined vertical and lateral loads. Different
parameters are considered in this study including: reinforcement ratio and distribution; grid spacing;
dowels connection to the base; small window opening; large door opening, and the use of steel fiber
concrete. The performance of the wall was measured in terms of lateral load capacity, lateral
displacement, as well as strain distribution. The measured response is recorded to be used for the
calibration of numerical models being developed. The dowel connection to the base plays an
important role in the stability of the wall. The use of 2 bars 12 mm as dowels prevented the wall tilting
and separation from the base. Wall strength increased more than twice by increasing the
reinforcement from 8 mm to 12 mm if wall tilting is avoided. The use of steel fibers (2 kg/m3 of
concrete) increased the lateral load capacity by 25%.
Acknowledgement
This publication is based on work supported by Award No. UK-C0015, made by King Abdullah
University of Science and Technology (KAUST).
References
[1] P.A. VanderWerf, S.J. Feige, P. Chammas, L.A. Lemay: Insulating Concrete Forms for
Residential Design and Construction, McGraw-Hill (1997)
[2] Benson, D.. The advantages of insulated concrete forms. New Hampshire Business Review,
29(4), 4, (2007).
[3] P.A. VanderWerf, and D. Drodge: Specifying ICFs. The Construction Specifier, 59(7), 70-78,
(2006).
[4] Lyman, J. (2003). ICF 101: An introduction to insulating concrete forms. Environmental Design
and Construction, 6(5), 21-23.
[5] T. Sutherland: ICFs: simpler, faster home-building. New Hampshire business review, 27(4), 19,
(2005).
[6] A. Merhabi “In-plane Lateral Load Resistance of Wall Panels in Residential Buildings” Portland
Cement Association PCA R&D Serial No. 2403 (2001)
[7] PD & R and PCA “In-Plane Shear Resistance of Insulating Concrete Form Walls” U.S.
Department of Housing and Urban Development, Office of Policy Development and Research
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[8] PD & R and PCA “Lintel Testing for Reduced Shear Reinforcement in Insulating Concrete Form
Systems” U.S. Department of Housing and Urban Development, Office of Policy Development
and Research PD & Rand Portland Cement Association contract H-21065CA (1998)
Advances in Structures
10.4028/www.scientific.net/AMR.163-167
Performance of Screen Grid Insulating Concrete Form Walls under Combined InPlane Vertical and Lateral Loads
10.4028/www.scientific.net/AMR.163-167.1803
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