Synopses of Master Papers

Bulletin of IISEE, 47, 85-90, 2013

EXPERIMENTAL STUDY OF EFFECTIVE FLANGEWIDTH ON SYMMETRICAL CROSS-SECTION WALLS
Tedi Achmad Bahtiar *MEE11615

Supervisor: Koichi KUSUNOKI **ABSTRACTIn the February 27, 2010 Chile Earthquake many medium height buildings with structural wall
elements collapsed. According to damage surveys one of the factors associated with this structural
failure was high flexural compression stress in flange walls. The objectives of this study are toevaluate the provision in the current standard for effective flange width in tension and compression, toclarify high compression stress in flange walls, and clarify the effect of porous sub-standard concreteon effective width. The effective flange width is the width of the flange that influences the lateralforces acting in the plane of the web wall. It is related to stress and strain distribution. As stress andstrain distribution is nonlinear, to avoid nonlinearity used uniform distribution of stress and strain.
This study is based on experimental testing of three specimens of symmetricalcross-sections walls (H-shaped). The Specimens are designed in accordance with Japanese standard at
1/3 scale acting monotonic or cyclic lateral and axial force. The output the tests is strain distribution inflange walls from each side of each specimen. Data was obtained by installing reinforcement strain
gauges in all three specimens, as well as concrete strain gauges in specimen H2 to observe
compression. Mechanical properties also analyzed in this study to determine stress-strain relationshipmodels. Bilinear model for steel and trilinear model for concrete used to obtain stress. Effective flange
width is calculated by divided the area of stress distribution with the maximum stress.
From these tests it is concluded that effective width should be greater than standard
provisions for both tension and compression. In cyclic tests, effective flange width for compression isgreater than for tension, before compression is neglected. In general, it is indicated that the use of
sub-standard concrete does not significant effect to effective flange width.
Keywords: experimental, flange, wall, cross-section, stress-strain
1. INTRODUCTION
Construction in many countries prone to earthquakes use walls as a structural element sometimes withan additional frame. This structural element have excellent seismic performance good fire resistance,
due to the use of reinforced concrete, and they are also economical, as load-bearing walls are as thickas wall girders but allow for greater internal space, as columns and beams are not necessary.
In the February 27, 2010 The Maule earthquake in Chile caused many medium heightbuildings to collapse or suffer sufficiently heavy damage to merit being demolished, while otherbuildings suffered only non-structural, or reparable structural damage. Most of the medium heightbuildings in Chile are constructed using structural walls. One of the factors commonly associated withthe structural failure of this type of element is compression failure, apparently related to high flexural
compression stress in flange walls [Moehle, 2010] 1 . The question research background is why
compression has caused damage to the flange wall.

*

Research Institute for Human Settlements, Ministry of Public Works, Indonesia
Associate Professor, Yokohama National University, Japan**1

Moehle, Wallace, et. al., February 27, 2010 Chile Earthquake Reconnaissance Team Investigations, EERI,2010

Earthquake force assumed as lateral load acting on the in-plane direction of wall willproduce tension force on one side and compression force on the other side. If the wall is flanged wall,
the flanged will contribute to resisting the force. The width of the flange that influences the lateralforces acting in the plane of the web wall is called the effective flange width. The important aspect of
behavior is the shape of the stress and strain distribution, as the distribution of strain andcorresponding stress in flange walls is nonlinear. This highly complicates design and analysis, and to
avoid this, a uniform distribution of stress and strainis used, as effective flange portion contributes tostructure behavior. Some variables that influence effective flange width and dominant parameters are:drift level, geometry of the wall, material and axial load level.
When axial force acts on a wall with a cross-section the flange wall will be subjected tocompression. One side of wall will act in an opposite to tension force and same direction tocompression force; these conditions make compression force become higher than pure flexural force.
The stress distribution produce by tension, compression forces and axial force is nonlinear; to simplify
the representation of nonlinear stress and strain distribution a fictitious geometrical shape like a squarewith a total area of the same proportions of strain or stress distribution. Effective flange width is thearea of stress distribution (A) divided by maximum stress of stress distribution (𝜎𝑚𝑚𝑚 ).
Effective flange width is different in some standards; the US standard for effective flange
width for a single wing (right or left side flange) is the minimum between one-four height of the wall(ℎ) and half of distance between an adjacent walls web (𝐿). In Japan the standard effective flange
width for a single wing depends on minimum of the six time wall thickness (t) and one-four distance
between an adjacent walls web (𝑙′).
The objectives of this study are to evaluate the provision in the current standard for
effective flange width in tension and compression, to clarify high compression stress in flange walls,
and clarify the effect of porous sub-standard concrete on effective width
2. EXPERIMENTAL METHODS
Symmetrical cross-section reinforced concrete walls used in this study are H-shaped. This form factor
has good stability when subjected to tension and compression forces, as the wall has the same flange
on both sides. H-shaped walls are designed according to the Japanese standard. Specimen are threesymmetrical cross-section H-shaped type wall with the same reinforcement steel bar design andgeometry used in this study (H1, H2 and Hx) which have length of web wall 1000 mm, height 1000
mm with a thickness of 80 mm. Connected to both edges are flange walls, both with dimensions oflength 1250 mm, height 1000 mm and thickness 80 mm. Two specimens are of similar concrete quality,
and one specimen is of different concrete quality. Specimen H1 is subjected to static cyclic lateral andaxial load, specimens H2 and Hx are subjected to static monotonic lateral and axial load. The purposeof using different types of load is to facilitate the use of different types of stress-strain relationshipmodel. Hx is porous sub-standard concrete specimen.
The samples of concrete and reinforcement steel bars collect for mechanical properties
test as unconfined concrete compression strength test, concrete shear test and reinforcement steel bars
tension strength test. Mechanical properties test use to develop stress-strain relationship model.
The specimens are 1/3 scale and use a customized 5 mm reinforcing bars diameter aslongitudinal reinforcement and tensile reinforcement. Transverse reinforcement is 4 mm in diameter.
Longitudinal reinforcement put in every 50 mm with a total of 19 rows. Longitudinal reinforcement
spacing in the web and flange walls is the same. Transversal reinforcement is spaced every 100 mm
with a total of 10 columns in the flange wall and 7 columns in the web wall. Tension reinforcement ismounted in both. Tensile reinforcement is installed in each end wall, 2 lines for the web wall and one
for flange wall. The specimen reinforcement steel bars design and location of steel and concrete strain
gauges is shown in Figure 1. The specimens have a slit (clearance) 10 mm between upper stab (beamfor loading) and wall develop concentration force in the tension reinforcement.

Figure 1. The specimen reinforcement steel bars design andlocation of steel and concrete strain gauges

A lateral static cyclic load and lateral monotonic load were applied to the top of the specimen.
Constant axial load acts in the web wall is 0.07AgFc. Two loading protocol models were used. For
specimen H1 a static cyclic lateral load and for specimens H2 and Hx a static monotonic lateral load.

Figure 1 H-shape shear wall testing setup

The loading protocol
consists of the following
drift level:
1/6400,1/3200, 1/1600, 1/800,
1/6400, 1/400, 1/200,
1/100, 1/66, and 1/50.
For Cyclic each drift
level is performed twice
to see the deterioration.
H-shape walls testing
setup shown in Figure 1.

3. RESULT AND ANALYSIS
Figure 2. shown test result for all specimen. Specimen H1 and H2 had good performance and ductility
when subjected to lateral force and Hx specimen lower than ultimate shear design capacity.

Figure 2. Hysteretic curve load vs. displacement, specimen H1and Backbone Curve H2 and Hx
Reinforcement strain distribution is one of the data outputs of the H-shaped wall testing. This data isrequired to obtain the stress distribution area (A) and maximum stress of stress distribution (𝜎𝑚𝑚𝑚 ) andto calculate effective flange width.
The mechanical properties testing materials is a very important part of this study. The
output of this testing is used to making a stress-strain relationship model for stress-strain conversion.
The results of steel reinforcement bars strength test is shown in Table 1.
Table 1. Result of steel tensile strength test
Steel Fracture Maximum Yield strength Yield strain Tensile strength Yield(N/mm2)(%)(N/mm2)
ratiobars strain (%) load (kN)

Young's modulus 2nd Stifness(N/mm2)(N/mm2)

D4

23.11

11.30

354.020.194

514.06

1.45

1827633315.5

D5

17.48

7.00

374.120.216

498.03

1.33

1730052691.6

Table 2 shown unconfined concrete compression strength test result. Analysis of
specimen testing results in order to calculate effective flange width for symmetrical cross-section walls
is based on modeling mechanical properties of the materials. Each material will employ a different
model and each reinforcement diameter will have another model, also model for different types ofloading.
Table 2. Results of unconfined concrete compression strength test
Specimen

Height(mm)

Maximum
Load (kN)

Young'smodulus

Strain whenmaximum (%)

Compressive strength(N/mm2)

H2

201.6

240.6

26886.29

0.184

30.587This study has been divided effective flange width into tension and compression. The
tension effective width is all from steel strain gauge. Total data of tension effective width from thesestudies is ten sides. The maximum effective flange width in H1 specimen A side is 1154.2 mm drift
1/50(1) and load level 211.06 kN, B side is 1136.9 mm drift 1/66(2) and load level 222.77 kN, C sideis 1094.7 mm drift -1/100(2) and load level -271.57 kN, D side is 1105.3 mm drift -1/100(2) and load
level -271.57 kN. The maximum effective flange width in H2 specimen A side is 1201.2 mm drift
1/100 and load level 249.86 kN, B side is 1200.9 mm drift 1/100 and load level 249.86 kN, C side is1201.6 mm drift 1/50 and load level 220.58 kN. The maximum effective flange width in Hx specimen
A side is 1201.1 mm drift 1/400 and load level 220.09 kN, B side is 1200.2 mm drift 1/100 and load
level 237.17 kN, C side is 1201.4 mm drift 1/100 and load level 237.17 kN.

Figure 3. Effective flange width both wings for specimen H2 and Hx(different concrete quality)

Figure 4. Tension and compression Effective flange width both wings
specimen H1

The
compression
effective width isfrom steel
andconcretestraingauge. Total data ofcompression
effective width fromthese studies isseven sides. The
maximum effective
flange width in H1
specimen A side is1120.4 mm drift
1/50(2) and load
level 192.52 kN, B
side is 987.8 mm
drift 1/50(1) andload level 211.06
kN, C side is 1120
mm drift -1/66(2)
and
load
level
-280.60 kN, D sideis 1140.3 mm drift-1/50(2) and load
level -285.48 kN all
data from steel
strain gauges.

The maximum effective flange width in H2 specimen from steel strain gauges in D side is909.1 mm drift 1/400 and load level 220.09 kN, and from concrete strain gauges in C side is 1080.23
mm drift 1/50 and load level 220.58 kN. The maximum effective flange width in Hx specimen fromsteel strain gauges in D side is 912.5 mm drift 1/400 and load level 209.35 kN.
The difference between the widest and narrowest values is very small. This proves thevalidity of the results, as they are derived from many different types of data. The average maximum
tension effective flange width is 1169.75 mm and compression is 1132.6 mm.
Figure 3 shows effective width of both wings is quite similar in specimens H2 and Hx
have same design and type of loading. The difference is specimen Hx made from substandard
concrete; however, it indicated that the concrete quality does not have significant effect on the results.
Figure 4 shows the cyclic load compression is greater than tension. The cyclic loading results aredifferent from monotonic loading. It is possible that this is because, in the cyclic load, walls
experience alternating tension and compression that mean in the flange wall not just acting one type offorce. This is increasing the potential high compression force occurred in the wall. These results haveanswered that in the design earthquake force building compression effective width have dominant
contribution.

Figure 5. Compression effective flange width both wings concrete H2,steel H2 and Hx

Figure 5 shows thecompression stressin reinforcement is
about
half
of
compression stressin concrete. The
difference with thecyclic test is thatcompression stressin the reinforcement
is almost the sameas with monotonic
compression stressin concrete.

So these mean compression stress must observe from concrete and reinforcement with cyclic force.
4. CONCLUSIONSThe conclusion of the study, in terms of verifying the standard provisions suggest that
effective width for tension is larger than that currently proposed by the standard, indicating that thestandard provisions would be inadequate for resisting flexural force. In terms of compression, standard
provisions also need to be more conservative. Effective flange width provision in the Japanesestandard is at slight variance with the test results, which suggest that 7 times wall thickness (7t) would
be adequate. In this study the compression stress was greater than the tension stress. Compression was
greater that tension stress in cyclic lateral load tests and almost similar in concrete. This indicates thatin symmetrical cross-section walls with axial load the compression side must be considered as
significant. The conclusion in terms of clarifying the effect of sub-standard porous concrete is that, ingeneral, the quality of the concrete does not have a significant effect on the effective flange width.
REFERENCES
American Concrete Institute, 2011, “Building Code Requirements for Structural Concrete andCommentary, ACI 318-11
Architectural Institute of Japan, 2005, Guidelines for Performance Evaluation of Earthquake
Resistant Reinforced Concrete Buildings
Architectural Institute of Japan, 2010, AIJ Standard for Structural Calculation of Reinforced
Concrete Structures (in Japanese)
Earthquake Engineering Research Institute, February 27, 2010 Chile Earthquake ReconnaissanceTeam Investigation.
Hassan, M., El-Tawil, S., Tension Flange Effective Width in reinforced Concrete Shear Walls,
Technical Paper, ACI Structural Journal, No. 100-S38, May-Jun 2003, pp. 349-356
Sunley, P. S. A., Experimental Study of Flexural Behavior of Reinforced Concrete Walls, Grips, BRI,IISEE, 2011
Wallace, J. W., Evaluation of UBC-94 Provisions for Seismic Design of RC Structural Walls,
Earthquake Spectra, V. 12, No. 2, May 1996, pp. 327-348