SEMINAR
ON
BEHAVIOUR AND FAILURE
MECHANISM OF INFILL WALLS
Introduction
Masonry infilled walls are provided within the reinforced
concrete structures without being analyzed as a combination of
concrete and brick elements, though in reality they act as a
single unit during earthquakes. The performance of such
structures during earthquakes has proved to be superior in
comparison to the bare frames in terms of stiffness, strength and
energy dissipation. There are plenty of researches done so far for
infilled frames, however partially infilled frames are still the topic
of interest. Though it has been understood that the infills play
significant role in enhancing the lateral stiffness of complete
structure, the past experience in various earthquakes have
proved that the partially infilled framed structures somehow are
affected adversely.
Types Of Infill Provisions
Influence Of Infill Walls
Infill walls provide durable and economical
partitions.
The presence of infill wall changes the behavior
of frame action into truss action.
The structural response is quite complex as it
involves an interaction of infill behavior,
reinforced concrete frames behavior and length
of contact between infill and frame.
Properties of infill walls
If the infills are very light and flexible, or
completely isolated from the RC frame,
presence of infills does not affect the
structural response of the system.
Infills are expected to remain in the
elastic range.
Infills are expected to suffer significant
damage during the seismic event.
Advantages of Infill Walls
Higher stiffness and lower displacement
Higher strength.
Lower ductility requirements.
Frame design for small lateral loads.
Reduce contribution of frame in lateral
resisting.
Design practice of Infill walls
Infills are adequately separated from the RC
frame such that they do not interfere with
the frame under lateral deformations.
Infills are built integral with the RC frame,
but considered as non-structural elements.
Infills are built integral with the RC frame,
and considered as structural elements.
Difficulties in Consideration Of Infill Walls In Structural Design
Computational complexity.
Structural uncertainties.
The non-linear behaviour of infilled
frames.
Various cracking patterns and
concentration of forces in structural
components.
Effects Of Infill Walls
Unequal distribution of lateral forces.
Vertical irregularities in strength and
stiffness.
Horizontal irregularities.
Inducing the effect of short column or
captive column in infilled frame.
Cause of casualities.
Behaviour Of Infill Walls
The structural load transfer mechanism is
changed from frame action to predominant
truss action.
Infills interfere with the lateral deformations
of the RC frame; separation of frame and
infill takes place along one diagonal and a
compression strut forms along the other.
Change In Lateral Load Transfer Mechanism Owing To Inclusion Of
Masonry Infill Walls
(a) Frame action in bare frame
(b) Predominant truss action in infilled frame
Behaviour Of Infill Walls
The state of stress in the infill gives rise
to a principal compressive stress along
the diagonal and a principal tensile stress
in the perpendicular direction.
When infills are strong, strength
contributed by the infills may be
comparable to the strength of the bare
frame itself.
Separation of frame and infill takes place along one diagonal and a compression strut forms along the other
In-plane Behavior
The in-plane capacity of the wall depend
on the relative strength of the masonry
and the mortar.
The level of the axial load significantly
controls the type of failure.
The crack propagation either follows the
mortar joints or passes through the
masonry units, or both.
Out-of-plane Behaviour
Crushing along the edges for low height
to thickness ratio.
Snap-through (small effect of arching)
for high height to thickness ratio i.e.
approximately between 20 and 30.
Behaviour of Partially Infilled Frames
In majority of hospitals, academic institutions
and commercial complexes, partial infills are
provided to attain light within the rooms.
It is observed that such walls on one hand
contribute in enhancing the lateral stiffness of
the structure while on the other hand they
play ironic role with an adverse effect called
"short column effect".
Behaviour of Partially Infilled Frames
Lateral deformation in bare frame Lateral deformation in partially infilled frame
Behaviour Of Infill Frames With Openings
In most cases, door or
window openings are provided in
masonry infill panels because of the
functional and ventilation requirements
of buildings.
Introducing openings in an infill wall
alters its behavior and adds complexity
in behavior.
Behaviour Of Infill Frames With Openings
Right loading Left loading
Soft Storey
One of the main reasons of failure of
structures due to earthquakes is
discontinuity of lateral force resisting
elements like bracing, shear wall or
infill in the first story.
Failure Mechanism Of Infilled Walls
Shear CrackingStepped Cracking Along the Mortar
Joints
Shear Cracking
Horizontal Sliding Along the Mortar Joints
Shear CrackingCracking Due to Diagonal Tension
Compression Failure
Crushing of the Loaded Corner
Flexural Cracking
In those cases where flexure effects are
predominating, such as multistory
infilled frames, and the columns of the
frame are very weak, flexure cracks can
open in the tensile side of the panel due
to the low tensile strength of the
masonry .
Conclusions Many structural engineers ignore such infills when
assessing the seismic vulnerability of these frames.
Consequently, more research is needed to evaluate
the strength and stiffness of masonry-infilled frames
with openings.
Masonry infill wall panels increase strength,
stiffness, overall ductility and energy dissipation of
the building. More importantly, they help in
drastically reducing the deformation and ductility
demand on RC frame members.
Conclusions
The better collapse performance of fully-
infilled frames is associated with the larger
strength and energy dissipation of the
system, associated with the added walls.
The presence of infills leads, in general, to
decreased shear forces on the frame
columns. However, in the case of infilled
frame with a soft ground story, the shear
forces acting on columns are considerably
higher than those obtained from the analysis
of the bare frame.
References I.S. 1893(Part I)-2002, “Criteria for Earthquake Resistant
Design of Structure, General Provisions and Buildings”,
Bureau of Indian Standards, New Delhi.
Asteris, P. G., Kakaletsis, D. J., Chrysostomou, C. Z. &
Smyrou, E. E. (2011).” Failure Modes of In-filled Frames”
Electronic Journal of Structural Engineering 11(1) , 11-20.
Das, D., Murty, C. V. R. (2004). “Brick masonry infills in
seismic design of RC framed buildings: Part 1 –Cost
implications” The Indian Concrete Journal, vol78 No7: 39-
43.
References• Wijanto L. S., (2007). “Seismic Assessment of
Unreinforced Masonry Walls”, A thesis, University of
Canterbury Christchurch, New Zealand.
• Zhang B., (2006). “Parametric Study On The Influence Of
Infills On The Displacement Capacity Of Rc Frames For
Earthquake Loss Estimation” A Dissertation, European
School For Advanced Studies In Reduction Of Seismic Risk.
• Pradhan, P. M., Pradhan, L.P., & Maskey, R.K. (2012). “ A
Review On Partial Infilled Frames Under Lateral Loads”,
Kathmandu University Journal Of Science, Engineering And
Technology, VOL. 8, No. I, 142-152.
Thank you…