International Journal of the Physical Sciences Vol. 5(13), pp. 1981-1998, 18 October, 2010
Available online at http://www.academicjournals.org/IJPS
ISSN 1992 - 1950 ©2010 Academic Journals
Full Length Research Paper
Analytical and experimental studies on infilled RC
Mehmet Baran1* and Tugce Sevil2
1Department of Civil Engineering, Kirikkale University, 71450, Yahsihan, Kirikkale, Turkey.
2Department of Civil Engineering, Maltepe University, 34857, Maltepe, Istanbul, Turkey.
Accepted 27 September, 2010
Although hollow brick infills, widely used as partition walls, are considered as non-structural members,
experimental studies revealed that hollow brick infills have favourable effects on strength and stiffness
of structures. In this work, analytical studies were conducted to investigate the hollow brick infill
behaviour, in which infills were modeled by diagonal compression struts. Results were compared with
experimental ones obtained from tests of one-bay, one or two story reinforced concrete (RC) frames,
tested under both vertical and reversed-cyclic lateral loads simulating earthquake. Test frames have
intentionally been constructed poorly to reflect the most common deficiencies encountered in Turkey
such as strong beam-weak column connections, insufficient confinement, low-grade concrete, poor
workmanship and insufficient lap-splice length. Experimental studies shows that hollow brick infills
increased both strength and stiffness of RC frames. Analytical studies conducted, shows that hollow
brick infills could adequately be modeled by diagonal compression struts.
Key words: Reinforced concrete, strength, stiffness, hollow brick infill, diagonal compression strut and reversed-
cyclic lateral load.
Filling reinforced concrete (RC) frames with clay tile
serving as partitions are very common, especially in
Turkey. In structural design process, such infills are
considered as “nonstructural” members. Structure is
assumed to carry horizontal loads only by the frame
elements. However, it is apparent from geometrical
considerations that infills also resist loads and impede
deformations compatible with infilled frame action.
Analytical and experimental studies shows that infilled
frames have greater strength and stiffness compared to
bare frames. Due to changes in stiffness and mass,
dynamic characteristics of the building also change.
Understanding the behaviour of infilled frames and being
capable of making a satisfactory modeling of infills during
structural design process will help engineers to have
more realistic and economical solutions. Behaviour of
infilled frames under seismic loading is complicated.
*Corresponding author. E-mail: email@example.com. Tel:
++ (90) (318) 357 42 42 – 1254. Fax: ++ (90) (318) 357 24 59
This is the most probable reason for hollow brick infills
not being considered as “structural” members during the
structural design process, resulting with inaccurate
solutions. With this approach, natural period of building,
earthquake load transferred to each beam and column,
short column mechanisms that can occur and the failure
mode of building under an earthquake loading can not be
evaluated precisely. Since the behaviour is nonlinear and
closely related to the interaction conditions between
frame and infill, analytical studies should be revised and
supported by experimental data. Earthquake regulations
of many countries (Israel, Costa Rica, France, Algeria,
European Union, Colombia, Phillipines, etc.) recommend
to take the effect of infill walls into account during the
design process (Kaplan, 2008).
In the experimental part of the present study, one and
two-story RC frames were tested. In two-story frames,
lateral load was applied at a greater height resulting in
more turning effect whereas compressive and shear
stresses are more dominant in one-story frames. By this
way, hollow brick infill behaviour can be analyzed under
tensile stresses as well as compressive and shear stresses.
1982 Int. J. Phys. Sci.
Figure 1. Dimensions and reinforcement of the test frames.
In the experimental part of the study, one-third scale,
one-bay, one and two-story RC frames were used as test
units. Taking into account the fact that the building stock
in Turkey and many countries around consists mainly of
deficient RC framed buildings, test frames have
intentionally been designed and constructed with the
most common deficiencies observed in local practice,
such as strong beam-weak column connections,
insufficient confinement, low-grade concrete, insufficient
lap-splice length and poor workmanship. The frames had
their columns fixed to the rigid foundation beams.
Dimensions and reinforcement of both types of test
frames are illustrated in Figure 1.
Low strength concrete was deliberately used in the test frames to
represent the concrete commonly used in majority of existing
buildings in Turkey. Both frame bays were infilled with scaled hollow
Baran and Sevil 1983
Figure 2. Hollow brick used as infill material and infilling method.
bricks (with void ratio of 0.52) covered with a scaled layer of plaster.
Ordinary cement-lime mortar was used for the plaster, reflecting the
usual practice. Hollow brick and infilling method is shown in Figure
2. Ordinary workmanship was intentionally employed in wall
construction and plaster application. For the same reason, mild
steel plain bars were used as longitudinal steel in both test frames.
Typical properties of reinforcing bars used in this study and average
compressive strength values for frame concrete and plaster
determined on testing day are listed in Table 1.
Loading and supporting system
In Figure 3, general views of the test set-up for two and one-story
test frames are given, respectively. As can be seen in Figure 3,
tests were performed in front of a reaction wall. Frames were
subjected to reversed cyclic lateral loading resembling seismic
effects. The quasi-static test loading consisted of reversed cyclic
lateral loading besides constant vertical load applied on both
columns. The axial load on columns was provided by steel cables
post-tensioned by hydraulic jacks.
Reversed cyclic lateral loading was applied by using a double
acting hydraulic jack. The lateral loading system had pin
connections at both ends to eliminate any accidental eccentricity
mainly in vertical direction and tolerating a small rotation in
horizontal direction normal to testing plane. Lateral load was
applied on a spreader beam at one-third of its span to ensure that
the lateral load at second floor level always remains twice as the
lateral load at first floor level. A very rigid external steel ‘guide
frame’ attached to the universal base, was used to prevent any out-
of-plane deformations. During the tests, increasing load cycles were
applied up to the capacity of frame and beyond that, deformation
controlled loading was performed with increasing displacement
cycles. Load histories of all test frames are given in Figure 4.
Deformation measurement system
All deformations were measured by displacement transducers;
using either linear variable differential transformers (LVDTs) or
electronically recordable dial gages (DGs) as shown in Figure 3.
Sway displacements were measured both at first and second floor
levels. Infill wall shear deformations were determined on the basis
of displacement measurements along the diagonals. Displacement
measurements taken at the bottom of both columns were meant for
computation of rotations of the entire frame. They also provided
1996 Int. J. Phys. Sci.
Lateral Load (kN)
1st Storey Level Displacement (mm)
Lateral Load (kN)
-40-30 -20 -100 102030 40
1st Storey Level Displacement (mm)
Lateral Load (kN)
Figure 13. Comparison of analytical and experimental load-displacement curves (one-story).
Table 4. Comparison of experimental response curves with the analytical push-over curves.
Ultimate load (kN)
SP2 50.3 55.4
SP3 66.6 69.0
SP4 76.8 79.0
SP5 74.2 84.2
SP7 86.6 82.3
SP8 62.3 71.4
SP9 65.5 68.7
(1)Ratio of the experimental data to the analytical data.
Initial stiffness (kN/mm)
Two-story and one-story equivalent test frames showed
very similar behaviour, especially lateral load capacities
of equivalent pairs were close. Presence of inadequate
(20 bar diameter) lapped-splices on column longitudinal
steels did not seem to adversely affect the infill
effectiveness significantly, if the column axial load was
not less than 20% of its axial load capacity. Hence, bond
problems due to lapped-splices on column steels would
not be critical in the cases when the axial load level on
the columns are not very low. Independent from the
presence of lapped-splice in steel, lower axial load on
columns created a negative effect on the lateral strength.
Hence, it can be concluded that higher column axial
loads made the infills stronger which provided higher
lateral load capacity to the frame. This phenomenon was
taken into account in calculating the ultimate load
carrying capacity of a compression strut modeling the
plastered hollow brick infill.
The proposed equivalent diagonal compression strut
modeling showed good correlation with the test results. In
the structural design process, equivalent diagonal
compression struts modeling the plastered hollow brick
infills can easily be added to the existing frame model of
the buildings. By this way, considerable amount of time
and work might be saved by the use of this method which
enables the quick determination of the ultimate load
carrying capacities of the frames with plastered hollow
Baran and Sevil 1997
Lıst of symbols
: Reinforcing bar diameter
: Angle whose tangent is infill height to length
: Relative displacement between two successive floors
: A variable due to column axial load effect on the ultimate load carrying capacity of the
: A dimensionless parameter
: Poisson’s ratio defined as the ratio of the strain in the direction normal to the mortar bed
joints to the strain in the direction parallel to the mortar bed joints
: Ultimate strain of the equivalent compression strut
: Effective width of the equivalent diagonal strut
: Thickness of the infill
: Diagonal length of infill panel
: Young’s Modulus of the column
: Young’s modulus of the infill material
: Young’s Modulus of the infill
: Young’s modulus at peak load
: Young’s modulus of the infill in the direction parallel to mortar bed joints
: Young’s modulus of the infill in the direction normal to mortar bed joints
: Young’s modulus of the infill in the θ direction
: Young’s modulus of the plaster
: Ultimate load carrying capacity
: Ultimate strength of the infill material
: Axial strength
: Ultimate strength of the infill in the direction parallel to mortar bed joints
: Ultimate strength of the infill in the direction normal to mortar bed joints
: Ultimate strength of the infill in the θ direction
: Ultimate strength of the plaster
: Yield stress of the longitudinal steel
: Reduced yield stress of the longitudinal steel
: Shear modulus
: Story height
: Column height between centerlines of beams
: Height of the infill
: Moment of inertia of the column
: Column axial load level
: Thickness of the infill material
: Thickness of the plaster
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