Behaviour of reinforced concrete frame with in fill walls under seismic loads using etabs

1. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
181
BEHAVIOUR OF REINFORCED CONCRETE FRAME
WITH IN-FILL WALLS UNDER SEISMIC LOADS USING
ETABS
Shaharban P.S1
, Manju P.M2
1
(M.Tech Computer Aided Structural Engineering, Sree Narayana Gurukulam College of Engineering, Kadayiruppu,
Eranakulam, Kerala, India
2
(Asst. Prof, Dept of Civil Engineering, Sree Narayana Gurukulam College of Engineering, Kadayiruppu, Eranakulam,
Kerala, India
ABSTRACT
Reinforced concrete framed buildings with in-fills are usually analyzed as bare frame, without considering the
strength and stiffness contributions of the in-fills. However during wind and earthquake these infill walls contribute some
response of the structure. Masonry Brick infill walls have been used in Reinforced concrete Frame structures as interior
and exterior partition walls. Since they are usually considered as nonstructural elements their interaction with the
bonding frame is ignored in the design. Infill substantially alters the behavior of the building subjected to lateral loads
such as wind and earth quake forces. However when subjected to a strong lateral loads, infill panels tends to interact with
bonding frame and may induce a load resistance mechanism that is not accounted for the design. To study the
performance of masonry- in filled R.C frames under Brick infill wall condition, analytical investigations have been
conducted. The objective of this study is to investigate the behavior of Brick masonry in-fill R.C Frames under cyclic
lateral loading. The Analysis has been done using Etabs software. In this project report five different type of models has
been analyzed. A 10 storey building with and without Brick infill was tested under siesmic load for case one. A 10 storey
building with 4 different infill conditions are analysed.
Keywords: Displacement, Etabs, Infill walls, Siesmic, Stiffness.
1. INTRODUCTION
Reinforced concrete (RC) frame buildings with masonry infill walls have been widely constructed for
commercial, industrial and multi storey residential uses in seismic regions. Masonry infill typically consists of bricks or
concrete blocks constructed between beams and columns of a reinforced concrete frame. The masonry infill panels are
generally not considered in the design process and treated as architectural (non-structural) components. Nevertheless, the
presence of masonry infill walls has a significant impact on the seismic response of a reinforced concrete frame building,
increasing structural strength and stiffness (relative to a bare frame). Properly designed infill 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. Hence, accounting for the infill in the analysis and design leads to slender frame members,
reducing the overall cost of the structural system. The total base shear experienced by a building during an earthquake is
dependent on its time period. The seismic force distribution is dependent on the stiffness and mass of the building along
the height. The structural contribution of infill wall results into stiffer structure thereby reducing the storey drifts (lateral
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2. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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displacement at floor level). This improved performance makes the structural design more realistic to consider infill
walls as a structural element in the earthquake resistant design of structures.
A panel constructed from masonry, usually built in between the columns and beams of the structural frame of a
building. Infill walls are used in framed building construction to create the building facade or envelope (external infill
walls) and to sub-divide the internal space of the building (internal infill walls).
Traditionally external infill walls have been of masonry construction and internal infill walls have been of either
masonry or timber stud with plasterboard. More recently light steel sections have also been used to form both internal
and external infill walls. Infill walls do not need to use the same structural material as the primary building frame. For
example, light steel infill walls may be used in a concrete framed building. Using lighter weight infill walls has the
obvious advantage of reducing the load on the structure.
Masonry is the building of structures from which individual units laid in and bound together by mortar; the term
masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone, marble,
granite, travertine, limestone, cast stone, concrete block, glass block, stucco, and tile. Masonry is generally a highly
durable form of construction. Various advantages have been acquired on analyzing the structures with infill, they are,
1. The use of materials such as bricks and stones can increase the thermal mass of a building.
2. Most types of masonry typically will not require painting and so can provide a structure with reduced life-cycle
costs.
3. Masonry is very heat resistant and thus provides good fire protection.
4. Masonry walls are more resistant to projectiles, such as debris from hurricanes or tornados.
Here also arise some of the disadvantages like,
1. Extreme weather causes degradation of masonry wall surfaces due to frost damage. This type of damage is
common with certain types of brick, though rare with concrete blocks.
2. Masonry tends to be heavy and must be built upon a strong foundation, such as reinforced concrete, to avoid
setting and cracking.
3. Save for concrete, masonry construction does not lend itself well to mechanization, and requires more skilled
labour than stick-framing.
In Euro code 6, six types of masonry units are defined: clay units, calcium silicate units, aggregate concrete
units, autoclaved aerated concrete units, manufactured stone units and dimensioned natural stone units complied with the
relevant European standards EN 771-1 to 6. However, brickwork can be combined from many of the following
components: adobe, ashlars, blocks, bricks, bitumen, chalk, cement, lime and mortar. Depending on which materials are
used, and how they are located, reinforced masonry (RM) walls can be divided into the following classes: confined
masonry, reinforced cavity masonry, reinforced solid masonry, reinforced hollow unit masonry, reinforced grouted
masonry and reinforced pocket type walls.
Effect of Infill
1. The stresses, in the infill wall, however, were found to increase with the increase in Young’s Modulus of
elasticity due to the increase in stiffness of the system, attracting more forces to the infill.
2. The infill wall enhances the lateral stiffness of the framed structures; however, the presence of openings within
the infill wall would reduce the lateral stiffness.
3. The fundamental period only slightly increases as the infill wall thickness increases, since the increase in
thickness only increases the mass of the structure rather than its stiffness.
4. The infill was assumed to crack once the stress in the infill exceeded the ultimate compressive stress of the infill
material.
5. The strength if infill in terms of its Young’s modulus (Ei) has a significant influence on the global performance
of the structure. The structural responses such as roof displacements, inter-storey drift ratios and the stresses in
the infill wall decrease with increase in (Ei) values due to increase in stiffness of the model.
6. The opening size of the infill has a significant influence on the fundamental period, inter-storey drift ratios, infill
stresses and the structural member forces. Generally, they increase as the opening size increases, indicating that
the decrease in stiffness is more significant than the decrease in mass.
7. The specific weight of reinforced masonry is smaller, the thermal and somniferous conductivity of the masonry
is worse and it also has better resistance against fire and chemicals.
8. The wall can be loaded right after finishing the construction.

3. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
183
Fig 1: ‘Equivalent Diagonal Strut’ model for infill panel
Fig 2: Masonry infill panels in framed structures
To study the performance of masonry- in filled R.C frames under Brick infill wall condition, analytical
investigations have been conducted. The aim of this study is to investigate the behavior of Brick masonry in-fill R.C
Frames under lateral loading. The Analysis has been done using ETABS software. In this project report five different
type of modals has been analyzed.
2. ANALYSIS
Following data is used in the analysis of the RC frame building models
1. Type of frame: Special RC moment resisting frame fixed at the base
2. Seismic zone: III
3. Number of storey: G+9
4. Floor height: 3.5 m
5. Depth of Slab: 150 mm
6. Size of beam: (230 × 450) mm

4. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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7. Size of column: (230 × 600) mm
8. Spacing between frames: 5 m along both directions
9. Live load on floor: 3 KN/m2
10. Floor finish: 0.6 KN/m2
11. Materials: M 20 concrete, Fe 415 steel and Brick infill
12. Thickness of infill wall: 230 mm
13. Density of concrete: 25 KN/m3
14. Density of infill: 20 KN/m3
15. Type of soil: Medium
16. Response spectra: As per IS 1893(Part-1):2002
17. Damping of structure: 5 percent
Model Specifications
Grade of concrete : M20
Grade of Steel : Fe415
Beam Size : 0.23 x 0.45 m (for 3D modal)
Column Size : 0.230 x 0.60 m
Beam c/c Distance : 5 m (for all 3D modal)
Column c/c Distance : 5 m (for all 3D modal)
In-fill wall Material : Brick
Material Properties
Steel Reinforcement
Type of Material - Isotropic
Mass per Volume (ρ) - 7850kg/m3
Weight per Volume (W) - 78.50kN/m3
Modulus of Elasticity (E) - 2x105
N/mm2
Poisson’s ratio (µ) - 0.30
Co-efficient of Thermal Expansion-1.1x10-5
Yield Strength- 415N/mm2
Brick Masonry Infill
Type of Material - Isotropic
Mass per Volume (ρ) - 1800kg/m3
Weight per Volume (W) - 18kN/m3
Modulus of Elasticity (E) - 13500N/mm2
Poisson’s ratio (µ) - 0.16
Compressive strength of clay brick - 3.5N/mm2
Co-efficient of Thermal Expansion-5.5x10-6
Concrete
Type of Material - Isotropic
Mass per Volume (ρ) - 2500kg/m3
Weight per Volume (W) - 25kN/m3
Modulus of Elasticity (E) - 22000 N/mm2
Poisson’s ratio (µ) - 0.17
Co-efficient of Thermal Expansion-9.90x10-6
Characteristic compressive strength -25N/mm2
Models
Case 1 - 3D 10 storey with in-fill wall.
Case 2 - 3D 10 storey without in-fill wall.
Case 3 - 3D 10 storey with brick in-fill cross walls
Case 4 - 3D 10 storey with infill walls at lift portions
Case 5 – 3D 10 storey with soft storey.
3. RESULTS AND DISCUSSIONS
In this study, five different models of an eight storey building symmetrical in the plan are considered. Usually in
a building 40% to 60% presence of Masonry infill (MI) are effective as the remaining portion of the Masonry Infill (MI)
are meant for functional purpose such as doors and windows openings (Pauley and Priestley, 1992). In this study the
buildings are modeled using 40 % Masonry Infill (MI) but arranging them in different manner as shown in the Figure 1
Following five different models are investigated in the study.

5. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
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1. Model I : Bare frame
2. Model II : Masonry infill are arranged in outer periphery
3. Model III: Masonry infill are arranged in outer periphery with soft storey
4. Model IV: Masonry infill are arranged as inner core
5. Model V : Masonry infill are arranged as lift core
TABLE 1: Parameters From ETAB And SAP Analysis
PARAMETERS ETABS
MODEL
SAP MODEL
Tx(Sec) 2.728 2.641
Ty(Sec) 2.0068 1.965
Wx(Hz) 2.303 2.379
Wy(Hz) 3.130 3.197
VBX(KN) 2108.31 2156.2
VBY(KN) 2650.44 2706.01
Fig 3: Graph showing displacements of Fig 4: Graph showing displacements of
various stories(case 1) various stories(case 2)
Fig 5: Graph showing displacements of Fig 6: Graph showing displacements of
various stories(case 3) various stories(case 4)

6. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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Fig 7: Graph showing displacements of various stories(case 5)
4. DISCUSSIONS
In this paper ten storey RC frame building models are studied that includes bare frame, infill frame and open
first storey frame. The parameters which are studied are time period, natural frequency, base shear and storey drift.
Fig 8: Graph showing comparison of displacement for all the cases in X direction
5. CONCLUSIONS
In this paper seismic analysis of RC frame models has been studied that includes bare frame, infill frame, open
first storey frame, cross shaped infill frame and infill at lift core frame. From the seismic analysis of RC frames
following conclusions are drawn,
1) The seismic analysis of RC frames was conducted by considering the infill walls in the analysis.
2) Infill frames should be preferred in seismic regions than the open first storey frame, because the storey drift of
first storey of open first storey frame is very large than the upper storey, this may probably cause the collapse of
structure.
3) The presence of infill wall can affect the seismic behavior of frame structure to large extent, and the infill wall
increases the strength and stiffness of the structure.
4) The seismic analysis of RC (Bare frame) structure leads to under estimation of base shear. Therefore other
response quantities such as time period, natural frequency, and storey drift are not significant. The
underestimation of base shear may lead to the collapse of structure during earthquake shaking. Therefore it is
important to consider the infill walls in the seismic analysis of structure.
5) In case of an open first storey frame structure, the storey drift is very large than the upper storey, which may
cause the collapse of structure during strong earthquake shaking. Therefore the infill frame structures will be the
better option to prefer in the seismic regions.
6) While comparing periphery infill frame with cross shaped infill frame, both having same base shear but time
period, natural frequency, displacements are varying. That means position of infill frames also having
significance. If we are taking infill also in design account we can effectively use infill walls.
7) In case of cross shaped infill frames with infill at lift core frame, cross shape gives better result, that means it is
having less displacement.

7. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
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