prepared by: Engr.Mustafeez Ur Rahman, Engr.Abd ur rahim supervised by: Dr.Muhammad Yaqoub Institute: UET Taxila

2. TOPIC
INFILLED FRAMES
Abd-Ur-Rahim 38
Mustafeez-Ur-Rahman 19
M.Haseeb 42

3. CONTENTS
• STRUCTURAL FORMS OF TALL BUILDINGS
• INFILLED FRAME
– INTRODUCTION
– DESIGN CONSIDERATIONS
– IN-FILLED FRAME COMPONENTS
– FAILURE MODES
– EFFECTS OF INFILL
– MODELING OF INFILL
– COMPARISON OF BARE FRAME AND INFILL FRAME
– ENHANCEMENT IN CAPACITY
– CONCLUSION

4. STRUCTURAL FORMS OF TALL
BUILDINGS
• The term structural form systems in structural engineering refers to
lateral load resisting system of a structure.
• The commonly used structural forms can be classified into different
categories.
• Sometimes two or more of the basic structural forms may be
combined in a single structural form system to form a hybrid system
in order to meet the structures operational requirements.

5. STRUCTURAL FORMS OF TALL
BUILDINGS
• The structural system of a tall building is designed to deal with
vertical gravity loads and mainly the lateral loads caused by wind and
seismic activity.
• The structural system consists of only the members designed to carry
the loads.
• All other members which does not participate in carrying loads are
referred as non-structural members.

6. STRUCTURAL FORMS OF TALL
BUILDINGS
• Following are the different structural forms systems which are
adopted in tall building structures of different height.
1. Rigid frames,
2. Braced frames,
3. In-filled frames,
4. Shear walls,
5. Wall frame,
6. Framed tube,
7. Outrigger braced,
8. Suspended,
9. Core structures,
10. Space structures, and
11. Hybrid structures.

7. HERE WE WILL STUDY ONLY
INFILLED FRAME

8. INTRODUCTION
• Infill frame structure comprises of the reinforced beam and
column frame in which the vertical space is infilled with brick
masonry or concrete block work
• Infill frames are commonly used for low and medium-height
buildings all over the world.
• Used for buildings up to 30 stories.
• Common in many countries.
• Infilled frame construction has been in use for more than 200
years.

9. Fig 1: frame structures with brick masonry infill

10. DESIGN CONSIDERATIONS
• Infill walls are generally considered as nonstructural elements. i.e.
most structure analyses still use open frame method that does not
consider the effect of stiffness of masonry panel to the stiffness
and strength of the whole structure.
• Not including the effect of panel in the design process can greatly
affect behavior of a building in responding to an earthquake, and it
can even cause a building to collapse as has been reported after
great earthquakes worldwide.

11. DESIGN CONSIDERATIONS
• But in some studies, specially in earthquake prone area, it is treated
as structural element which is equivalent to the bracing of the
frame against lateral loadings.
• Designing a structure that considers masonry panel can be done by
modeling that masonry panel as compression brace/strut or shell
element as shown in fig.

12. Fig 2: infill panel modeling

13. DESIGN CONSIDERATIONS
• In terms of designing masonry panel as compression brace, there are
number of methods popular to be used by structure Every method
has a different equation and parameters to use.
• Properly designed infills can increase the overall strength, lateral
resistance and energy dissipation of the structure. An infill wall
reduces the lateral deflections and bending moments in the frame,
thereby decreasing the probability of collapse.
• Infill behaves as a strut in compression.
• Tension contribution is ignored.

14. DESIGN CONSIDERATIONS
• During an earthquake, diagonal compression struts form in the infills
so the structure behaves more like a Braced Frame rather than a
Moment Frame. When subjected to lateral loads, the infill acts as a
strut along the compression diagonal to brace the frame.
• Due to random nature of masonry infill, it is difficult to predict the
stiffness and strength of this system.
• Up to now, no method of analyzing infilled frames has gained general
acceptance.

15. IN-FILLED FRAME COMPONENTS
• Infilled frame elements are made up of
(A). infilled-panel
(B). frame components
Component type Description/Examples Material/Detail
Solid infill panel Space within frame components
completely filled
Concrete Reinforced Unreinforced
Masonry (clay brick, hollow clay
tile, concrete block) Reinforced
Unreinforced
Infill panel with openings Doors and windows Horizontal or
vertical gaps Partial-height infill
Partial-width infill
Same as solid infill panel
Frame column Vertical, gravity-load-carrying Concrete /
Steel
Frame Beam Horizontal, gravity-load-carrying Concrete /
Steel
Frame joint Connection between column and
beam components Rigid moment-
resisting Partially-rigid Simple
shear
Monolithic concrete Precast
concrete Bolted steel Riveted steel
Welded steel

16. IN-FILLED FRAME COMPONENTS
A. Infilled Panels
Infilled panels are primarily according to material and geometric
configuration.
According to Materials
• Clay brick masonry is perhaps the most commonly encountered type of
infill material. Most often, brick masonry is unreinforced. In more
modern buildings, reinforced, grouted-cavity wall construction may be
found.
• Concrete masonry unit (CMU) construction is a form of infill using
hollow concrete blocks laid up with mortar. CMU may be left hollow or
filled with grout, either partially or completely. If grouted, steel
reinforcement may or may not be present. The strength and ductility of
the infill is highly dependent on the degree of grouting and
reinforecement.

17. IN-FILLED FRAME COMPONENTS
According to Geometry
• Infill may have a wide variety of geometric configurations. Aspect ratios
(length/height of the planar space defined by the surrounding frame
components) for infilled panels varies from approximately 1:1 to 3:1
with most ranging from 1.5:1 to 2.5:1
• There are two categories for infilled panel components based on
geometric configuration as shown in table above.
• Solid infill panel : Solid infilled panel components are those that
completely fill the planar space tightly within the surrounding frame
components.
• Infill panel with openings: Doors and windows are the two most
prevalent opening types. Perforations within the infill panels are the
most significant parameter affecting seismic behavior of infilled
systems.

18. IN-FILLED FRAME COMPONENTS
(a) solid panel (b) panel with window opening (c) panel with door opening
Fig 3: infill panel
(a) (b) (c)

19. IN-FILLED FRAME COMPONENTS
B. Frames
The frame components of infilled-frame seismic elements are categorized
primarily by material.
i. Steel
• Steel frames are common, especially for older structures. Steel frames are
also popular for modern high-rise buildings and low-rise, light-weight,
commercial, building construction.
ii. Concrete
• Reinforced concrete frames may be classified as either ductile or nonductile
for seismic performance, based primarily on the details of reinforcement.
• Contemporary structural design requires ductile detailing of the members.
Ductile detailing requires closely-spaced transverse hoops in the beams,
columns, and connections. If such members surround weak infill panels,
they will suffer relatively less serious damage under lateral loads. Fully-
ductile frames are relatively rare.

20. IN-FILLED FRAME COMPONENTS
ii. Concrete:
• Non-ductile frames are very common, particularly in regions of low-to-
medium seismic risk. These frames are not detailed for ductility and may
have one or more deficiencies: columns weaker than beams, lap splices in
column hinge zones, and insufficient transverse reinforcement for
confinement, for shear strength, and for longitudinal reinforcement
stability. The beam/ column joints in concrete frames need to transmit
high shear forces. When infills are present, shear force demands are
considerably higher, leaving the beam or column vulnerable to shear
failure.
• Precast, prestressed, concrete frames are also commonly encountered
with infilled panels.

21. FAILURE MODES OF INFILL PANEL
Based on both experimental and analytical results during the last five decades
different failure modes of masonry in-filled frames were proposed, that can be
classified into five distinct modes.
1. The Corner Crushing (CC) mode
which represents crushing of the infill in at least one of its loaded corners, as shown in
Fig. (a). This mode is usually associated with in-filled frames consisting of a weak
masonry infill panel surrounded by a frame with weak joints and strong members.
2. The Sliding Shear (SS) mode
which represents horizontal sliding shear failure through bed joints of a masonry infill,
as shown in Fig. (b). This mode is associated with infill of weak mortar joints and a
strong frame.

22. FAILURE MODES OF INFILL PANEL
Fig 4: different failure modes of infill

23. FAILURE MODES OF INFILL PANEL
3. The Diagonal Compression (DC) mode
which represents crushing of the infill within its central region, as shown in
Fig. (c). This mode is associated with a relatively slender infill, where failure
results from out-of-plane buckling of the infill.
4. The Diagonal Cracking (DK) mode
which is seen in the form of a crack across the compressed diagonal of the
infill panel and often takes place with simultaneous initiation of the SS
mode, as shown in Fig. (d). This mode is associated with a weak frame or a
frame with weak joints and strong members in-filled with a rather strong
infill.
5. The Frame Failure (FF) mode
which is seen in the form of plastic hinges developing in the columns or the
beam-column connections, as shown in Fig. (e). This mode is associated with
a weak frame or a frame with weak joints and strong members in-filled with
a rather strong infill.

24. ADVERSE EFFECTS OF INFILL
As the infill has some advantages ( increasing overall strength, increasing
lateral resistance, reducing lateral deflection and bending moments) but it has
also some adverse effects on the structure.
Some of the adverse effects will be discussed here.
1.Soft Story Effect
when a story has no or relatively lesser infills than the adjacent storys
• 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.
• Similarly fig 5. shows that the first story act as soft story, in which the infills
are not provided due to parking or some other purpose, in this case
columns are imposed to large deformation and plastic hinges are formed at
top and bottom of the element. This phenomena is so-called story
mechanism (severe drift of the story). The upper stories have infills and
consequently their stiffness is much more than the first story.

25. ADVERSE EFFECTS OF INFILL
(a). Schematic view of soft story mechanism
(b).soft story failure in a building during EQ ,Italy 1976
Fig (5)
(a) (b)

26. ADVERSE EFFECTS OF INFILL
2. Torsion
when infills are unsymmetrically located in plan
• The stiffness of masonry infill is a considerable value relating to
that of the structure.
• Because of architectural and structural considerations,
sometimes there is an eccentricity between center of mass and
center of rigidity and the structure is irregular in plan called
asymmetric building.
• The structure is also might be asymmetric as an irregular
arrangement of infills in plan, which leads to unbalance
distribution of stiffness. Produced torsion from eccentricity
because of infill stiffness leads to extra forces and
deformations in structural members and diaphragms.
• An appropriate alternative to solve this problem especially in
existing buildings is using dampers.

27. ADVERSE EFFECTS OF INFILL
Fig 6: torsional effects

28. ADVERSE EFFECTS OF INFILL
3. Short column effect
when infills are raised only up to a partial height of the columns.
• Sometimes the infill are not provided up to whole height of columns,
leaving a short space for clerestory window (A high windows above
eye level to bring outside light, fresh air, or both in to the inner space)
which leads to short column effect.
• Shear failure is a critical kind of concrete column failure that occurs in
short columns as repeatedly demonstrated during recent
earthquake.

29. ADVERSE EFFECTS OF INFILL
Fig 7: (a) Partial floor-height panel infill (b) failure of short column, Italy 1976

30. MODELING OF INFILL
• As Infill walls are generally considered as nonstructural elements. But
in some cases, such as earthquake prone area, we need to properly
design the infill.
• Designing a structure that considers masonry panel can be done by
modeling that masonry panel as compression brace or shell element.
• To simulate the structural behavior of infilled frames, two methods
have been developed such as Micro and Macro model.

31. MODELING OF INFILL
1.Micro Modeling
• The micro model method is a finite element method (FEM)where the
frame elements, masonry wok, contact surface, slipping and
separation are modeled to achieve the results.
• This method has seems to be generating the better results but it has
not gained popularity due to its cumbersome nature of analysis and
computation cost.

32. MODELING OF INFILL
2. Macro Modeling:
• The macro models which is also called a simplified model or
equivalent diagonal strut method was developed to study the global
response of the infilled frames.
• The concept of equivalent diagonal strut method was initially
introduced by Polyakov (1960) while investigating a three storeys
infilled structure. He found that the stress from peripheral frame
members to the infill was transferred only through the compression
corners of the frame-infill interface.

33. MODELING OF INFILL
• The Basic principle of the method is that an infill frame can be assumed as
brace frame and it functions equivalent to the compression brace
(equivalent diagonal strut). An equivalent diagonal strut can only handle
compression force, therefore the effect of continuous lateral load due to an
earthquake can be overcome by formation of two-ways diagonal strut as
shown in fig 8(a)
• In terms of designing masonry panel as compression brace, there are
number of methods popular to be used by structure designers (almost 14
methods). Every method has a different equation and parameters to use.
• The thickness of the strut will be equal to the thickness of the wall. Length
will be equal to diagonal length of the panel.
• The effective width of equivalent strut in the infill wall proposed by
different researchers has severe variation from 10 to 35%.

34. MODELING OF INFILL
(a) (b)
Fig 8: Modeling of infill

35. MODELING OF INFILL
Effective Width Of Compression Strut
As there are number of methods to find the effective width of equivalent
compression strut. But here we will present three of them.
1. Mainstone and Weeks
• based on experimental data, proposed an empirical equation for the calculation
of the width of an equivalent strut.

36. MODELING OF INFILL
• H=column height between centerlines of beams, in.
• dinf=diagonal length of infill panel, in.
• 𝝀h=lateral stifness of panel
• Einf =expected modulus of elasticity of infill material, psi.
• tinf=thickness of infill panel and equivalent strut, in.
• Ec=expected modulus of elasticity of frame material, psi.
• Ic=moment of inertial of column, in4
• Hinf=height of infill panel, in.
• 𝜃=angle whose tangent is the infill height-to-length aspect ratio,
radians
• Linf=length of infill panel, in.

37. MODELING OF INFILL
2. Stafford Smith and Carter Method
• Stafford Smith and Carter proposed a theory on the width of a
diagonal strut based on the relative stiffness of infill and frame:
• The parameters are defined above

38. MODELING OF INFILL
3. Holmes Method
Holmes states that the width of an equivalent strut should be one third of the
diagonal of an infill frame, which results in the infill strength being independent of
the frame stiffness.
Where:
w = width of equivalent strut
dinf = diagonal of infill

39. COMPARISON OF BARE AND INFILL
FRAME
• Mehrabi performed experiments on two frames. One was bare
frame (i.e. without infill) and the other was with infill as shown in fig.
• The column base is fixed on plate to the floor of the laboratory.
• To simulate gravitation load of a floor above, both columns were
loaded with vertical constant load (Pv).
• Horizontally, it was also given a monotonic force until it collapsed.

40. COMPARISON OF BARE AND INFILL
FRAME
(a) Open Frame and (b) Frame with Solid Masonry Infill Panel
Fig 9: Experimental Test by Mehrabi for Comparison

41. COMPARISON OF BARE AND INFILL
FRAME
• The fig shows force - deflection diagram of experimental test by
Mehrabi.
• As we can see in the graph, the frame with infill remains in a steady
line until it reaches 180.000 N of horizontal loading force, and the
open frame stays similarly until it crosses 60.000 N.
• Frame with infill has bigger value of stiffness, thus needing a bigger
force to make horizontal deflection as compared to an open frame.

42. COMPARISON OF BARE AND INFILL
FRAME
Fig 10: Force-Deflection Diagram of Experimental Test by Mehrab

43. COMPARISON OF EQUIVALENT
DIAGONAL STRUT MODELS
• This experimental work was also compared with the methods of
equivalent diagonal strut.
• The width of the strut was different for every proposed method.
• The force-displacement curve of the experimental work and the
proposed diagonal strut methods are shown in fig..

44. COMPARISON OF EQUIVALENT
DIAGONAL STRUT MODELS
Fig 11: Force Deflection Diagram of Various Models

45. ENHANCEMENT IN CAPACITY
The capacity of infilled frames can be enhanced by taking certain measures.
1. Tapered beam-column joint
• The use of tapered beam-columns joints with diagonal reinforcement
contributes to a reduction of the distortion of the masonry panel by
limiting the opening of the joints (see Fig. 12).
• This improves the transfer of the lateral forces from the frame to the panel
and increases the width of the compressive strut.
• For practical reasons, tapered beam-column joints are easy to build in
framed masonry structures, that is when the reinforced concrete frame is
cast after the construction of the masonry wall.

46. ENHANCEMENT IN CAPACITY
Fig 12: (a) reinforcement detail of tapered beam-column joint (b) recommended design of infill frame
(a) (b)

47. ENHANCEMENT IN CAPACITY
2. Provision of RC bands
• The capacity of the infill can also be enhance by providing small RC
bands across the infill panel at small distances.
• These bands will divide the panel into small sub-panels. So in each
sub-panel a compression strut will develop.
• This will prevent the out of plane expulsion.

48. ENHANCEMENT IN CAPACITY
Fig 13: small RC bands in panels

49. CONCLUSION
• Infill frames are commonly used for low and medium-height
buildings all over the world. Normally up to 30 storeys.
• The introduction of MI in RC frames changes the lateral-load
transfer mechanism of the structure from predominant frame action
to predominant truss action, which is responsible for reduction in
bending moments and increase in axial forces in the frame
members.
• The infill have good effects, like increasing the lateral stiffness and
strength of frame, and also adverse effects like creation of short
column, soft storey, and torsion effects.

50. CONCLUSION
• There is no proper guidance in codes for the design of infill.
However modeling it as a compression strut can give approximate
results.
• The capacity of infill can be enhanced by limiting the size of panel,
which can be done by providing small RC bands at appropriate
distance.

51. REFERENCES
• Comparative Study on Diagonal Equivalent Methods of Masonry Infill Panel by
Aniendhita Rizki Amalia, and Data Iranata
• CAPACITY DESIGN OF INFILLED FRAME STRUCTURES by Francisco J CRISAFULLI, Athol J
CARR And Robert PARK.
• Code Approaches to Seismic Design of Masonry-Infilled Reinforced Concrete
Frames: A State-of-the-Art Review by Hemant B. Kaushik, Durgesh C. Rai,
• FEMA 306 EVALUATION OF EARTHQUAKE DAMAGED CONCRETE AND MASONRY WALL
BUILDINGS Basic Procedures Manual
• Structural Forms Systems for Tall Building Structures by Er. Nishant Rana, SiddhantRana
• Seismic Analysis of RC Frame Structure with and without Masonry Infill Walls. By Haroon
Rasheed Tamboli* and Umesh.N.Karadi

52. INFILLED FRAME52