11-IJAEST-Volume-No-2-Issue-No-1-SEISMIC-STRENGTHENING-OF-LOW-RISE-BUILDINGS-USING-BRICK-INSERTS-(RE

SEISMIC STRENGTHENING OF LOW RISE

BUILDINGS USING BRICK INSERTS

(RETROFIT) – EXPERIMENTAL

INVESTIGATION ON 2D & 3D RC FRAMED

STRUCTURES

Mr.R.Suresh Babu

Research scholar – Anna University, Coimbatore

Partner – PTK Architects, Chennai

Chennai, India

[email protected]

Dr.R.Venkatasubramani

HOD, VLBJCET, Coimbatore

Coimbatore, India

[email protected]

Abstract— Several literature and research papers

were published in the topic of seismic retrofit of

existing buildings. Attention has been focused on

the existing building (designed without seismic

loads) to prevent damages during future

earthquake. A purpose of the study is to investigate

seismic retrofit using brick inserts to upgrade the

capacity of reinforce concrete frame with brick

masonry infill wall and to addresses the buildings

without following the details as stated in BIS

13920. The overall aim of study is by adding a

small brick insert in the partial infilled RC

structures, the structure could double its strength.

An experimental investigation is conducted to study

the effect of lateral behaviour of RC frames with

partial-infill masonry panels (2D & 3D) viz. one

with opening(frame 1) and other with masonry

insert in the opening(frame 2). One-third scale, two-

bay two-storey RC frame (2D & 3D) designed for

gravity loading is tested under in-plane lateral

loading for 2D RC frames and push & pull load for

3D RC frame structures. A non-linear finite element

analysis has been carried out using Ansys – 10. The

results of experiment and analytical analysis were

only marginal variations. In both 2D & 3D analysis

of both frames, the columns in the bottom storey

sustained critical shear damage with hinges in the

column portions adjacent to the gap. The

experimental results clearly indicated that the partial

infill in RC frame leads to critical damages, which

could be reinforced with the added strength of

masonry inserts. Finally it was suggested that, the

existing columns with short-column mechanism

could be strengthened with masonry inserts. By

improving building strength with the above

methods, the damage can be limited to within

repairable limits and complete collapse of the

building/loss of life can be avoided during an

earthquake. The cost effectiveness of providing

brick insert is very much cheaper than retrofit

normally adopted to strengthen the structural

elements and require simple construction method.

Keywords - Masonry Infill; Masonry Inserts;

Captive Column effect; Retrofit;

I INTRODUCTION

Everyone is aware that earthquake occurred in Gujarat (Bhuj) - India in the year 2001 had several incidents of failure or complete collapse. Majority of the failure in the buildings are predominantly due to Captive column failure or soft storeyed building. After the revision in IS codes for seismic forces, we are able to take care of the proposed new buildings. But even many old buildings of similar nature still exists (built as per IS 456 detailed with SP 34) in highly earthquake prone areas throughout the country. Energy dissipation of these buildings are very poor for lateral loads mainly due to Captive column failure. By providing necessary masonry inserts in the partial infill opening shall increase the

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HOD, VLBJCET, Coimbatore

IJAESTHOD, VLBJCET, Coimbatore

Coimbatore, India

IJAESTCoimbatore, India

[email protected]

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bay two-storey RC frame (2D & 3D) designed for IJAEST

bay two-storey RC frame (2D & 3D) designed for

gravity loading is tested under in-plane lateral IJAEST

gravity loading is tested under in-plane lateral

loading for 2D RC frames and push & pull load for IJAEST

loading for 2D RC frames and push & pull load for

3D RC frame structures. A non-linear finite element IJAEST

3D RC frame structures. A non-linear finite element

analysis has been carried out using Ansys – 10. The IJAEST

analysis has been carried out using Ansys – 10. The

results of experiment and analytical analysis were IJAEST

results of experiment and analytical analysis were

only marginal variations. In both 2D & 3D analysis IJAEST

only marginal variations. In both 2D & 3D analysis

could be reinforced with the added strength of

IJAESTcould be reinforced with the added strength of

masonry inserts. Finally it was suggested that, the

IJAESTmasonry inserts. Finally it was suggested that, the

existing columns with short-column mechanism

IJAESTexisting columns with short-column mechanism

could be strengthened with masonry inserts. By

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Keywords -

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Mr.R.Suresh Babu et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 1, 072 - 085

ISSN: 2230-7818 @ 2011 http://www.ijaest.iserp.org. All rights Reserved. Page 72

stiffness of the building and increase in energy dissipation. Due to this the collapse of the building will delay and the structure became more safer. This remedy is evaluated without major alteration to structural elements and without affecting major existing functioning of the buildings.

II MATERIALS AND METHODS

A LITERATURE REVIEW

Previous experimental research on the behaviour

of brick infilled RC frames(Achintya et.al.

1991:Yaw-jeng Ciou et.al.1999: Diptesh Das et.al.

2004: Ismail et.al 2004: Marina et.al:2006 have

shown that the strudtural behaviour of the framed

masonry wall subject to in – plane monotonic

loading on partial fill masonry wall induce a short

column effect aleads to severe failures of the

column. Further experimental research of Mehmat

Emin Kara et.al:2006 have shown that patially

infilled non-ductile RC Frames exhibited

significantly higher ultimate strength and higher

initial stiffness than the bare frame. Prabavathy

et.al(2006) have shown that infill panels can

significantly improve the performance of RC

Frames. Alidad Hashemi et.al(2006) have shown

that infill wall changes the load path and the

distribution of forces Kasim Armagan Korkmaz

et.al(2007) shown that presence of nonstructural

masonry infill walls can modify the global seismic

behaviour of framed building to a larger extent.

Umarani (2008) examined the behaviour of infilled

frames (5 storey) for lateral loading. Test focused

on the increase of energy dissipation over and above

the base frames. Santiago pujol et.al(2008) shown

that masonry infill walls were effective in increase

the strength(by 100%) and stiffness (by 500%) of

the original reinforced concrete structures. Salah El

– Din Fahmy Taher et.al(2008) lower location of

infill frames yields the higher strength, stiffness and

frequency of the system

III EXPERIMENTAL & ANALYTICAL

INVESTIGATION ON 2D RC FRAME STRUCTURE

1) EXPERIMENTAL INVESTIGATION

A) Modelling of Frames:

A structure representing a multi-storeyed frame

system is analysed and designed. The structure is

modeled for experimental investigation by scaling

down the geometric properties of the prototype

using the laws of Geometric similitude.

B) Details of Test Frame Test models was fabricated to 1:3 reduced scale

following the laws of similitude by scaling down

the geometric and material properties of the

prototype for Frame (1) and Frame (2)(Ref. Fig.1).

Figure.1 Geometry of the frame model

C) Testing Procedure : Lumped mass distribution was

calculated and lateral loads were distributed as 80% for top storey & 20% for bottom storey. All applied lateral loads were divided accordingly. Frame (1) was tested of first increments of 10 kN base shear for each cycle and released to zero after each cycle. The deflections at all storey levels were measured at each increment and decrement of the load. The formation and propagation of cracks, hinge formation and failure pattern were recorded. This procedure was repeated for frame (2) with masonry insert.

D) Results:

The results of various parameters like load Vs.

deflection, stiffness degradation and ductility factor

were considered for study of the captive column

behaviour of the frame

i) Loading And Load-Deflection Behaviour

(P-∆):

The frame was subjected to unidirectional

lateral loading. The load was applied in increment

of 10 kN base shear for each cycle and released to

zero after each cycle. The deflections at all storey

levels were measured using LVDT at each

increment or decrement of load. The ultimate base

shear of 73 KN was reached in the Eighth cycle of

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the strength(by 100%) and stiffness (by 500%) of IJAEST

the strength(by 100%) and stiffness (by 500%) of

the original reinforced concrete structures. Salah El IJAEST

the original reinforced concrete structures. Salah El

– Din Fahmy Taher et.al(2008) lower location of IJAEST

– Din Fahmy Taher et.al(2008) lower location of

infill frames yields the higher strength, stiffness and IJAEST

infill frames yields the higher strength, stiffness and

frequency of the system IJAEST

frequency of the system

XPERIMENTAL IJAEST

XPERIMENTAL & ANALYTICAL IJAEST

& ANALYTICAL

INVESTIGATION ON IJAEST

INVESTIGATION ON 2D RC FIJAEST

2D RC F

Figure.1 Geometry of the frame model

IJAESTFigure.1 Geometry of the frame model

C) Testing Procedure :

IJAESTC) Testing Procedure : Lumped mass distribution was

IJAEST Lumped mass distribution was

calculated and lateral loads were distributed as 80%

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calculated and lateral loads were distributed as 80% for top storey & 20% for bottom storey. All applied

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for top storey & 20% for bottom storey. All applied lateral loads were divided accordingly. Frame (1)

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lateral loads were divided accordingly. Frame (1) was tested of first increments of 10 kN base shear

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was tested of first increments of 10 kN base shear for each cycle and released to zero after each cycle.

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for each cycle and released to zero after each cycle. The deflections at all storey levels were measured at

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The deflections at all storey levels were measured at each increment and decrement of the load. The

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each increment and decrement of the load. The formation and propagation of cracks, hinge

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formation and propagation of cracks, hinge formation and failure pattern were recorded. This

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formation and failure pattern were recorded. This procedure was repeated for frame (2) with masonry

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procedure was repeated for frame (2) with masonry insert.

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insert.

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loading and ultimate base shear of 140KN was

reached in fourteenth cycle for frame 1 & 2

respectively.

Top storey deflection versus base shear is shown in

Fig.2. Load and top storey deflection is presented in

Table 1. At the ultimate base shear the top storey

deflection was found to be 47mm for frame (1) and

56mm for frame (2).

Table.1: Load and Deflection for Frame 1 & 2

Frame (1) Frame (2)

Load

(KN)

Deflectio

n (mm)

Load

(KN)

Deflect

ion

(mm)

0 0 0 0

10 2 10 0.45

20 3.89 20 1

30 6 30 1.55

40 8.12 40 2.9

50 13.69 50 4.25

60 21.23 60 6.95

70 34.33 70 9.08

80 47 80 11.79

90 15.66

100 19.33

110 29

120 37

130 47

140 56

Figure. 2 Base shear Vs Top storey deflection for

both frames

ii) Ductility: The ductility factor (µ) was calculated. For

frame (1), the first yield deflection (∆y) for the

assumed bi-linear load-deflection behaviour of the

frame was found to be 6 mm for 30 KN base shear,

while for frame (2), the same is found to be

11.79mm for 80 KN base shear. The ductility

factor value µ = (∆1/∆y) for various load cycles of

the frames was worked out and the variation of

ductility factor for both frames with load cycles are

shown in Fig.3.

The ductility factor is found to be increasing more

from 1.00 at third cycle to 7.833 at eighth cycle for

frame (1). While for frame (2), the ductility factory

is 1 at eighth cycle of loading and only 4.75 at

fourteenth cycle of loading. This behaviour shows

the reduction of ductility of frame due to the

provision of masonry insert and is shown in Fig.4

Figure. 3 Ductility factor for both frames

iii) Stiffness Degradation: The stiffness of the partially-infilled frames

for various load cycles is calculated and presented.

The variation of stiffness with respect to load cycles

is shown in Fig.4. For frame (1), it may be noted

that stiffness decreases from 5 kN/mm in first cycle

to 1.7 kN/mm in eighth cycle. A sudden reduction

in stiffness takes place after the first crack

occurrence in 30 kN load.

For frame (2), the initial stiffness of frame is 20

kN/mm against 5 kN/mm for the first frame and

stiffness is sustained for a longer duration until the

development of first crack and is reduced to 2.5

kN/mm in fourteenth cycle.

This behaviour shows that the initial stiffness of

frame (1) is comparatively very low and flexural

hinges and shear cracks are developed at an early

stage of loading. For frame(2) with masonry insert,

initial stiffness is increased and occurrence of

flexural hinges and shear cracks in concrete and

masonry takes place only after the eighth cycle.

Also, it could be noted that the initial stiffness is

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90 15.66

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90 15.66

100 19.33

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100 19.33

110 29

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110 29

120 37

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120 37

130 47

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130 47

140 56

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140 56

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hear Vs Top storey deflection for IJAEST

hear Vs Top storey deflection for

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both frames


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iii) Stiffness Degradation:

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iii) Stiffness Degradation: The stiffness of the partially-infilled frames

IJAEST The stiffness of the partially-infilled frames


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increased by 4.5 times due to the introduction of

masonry insert and the stiffness is sustained for a

longer duration of loading. The behaviour of frame

for stiffness values is shown in Fig.4

Figure:4:Stiffness degradation curve for both

frames

iv) Behaviour and Mode of Failure:

a) Frame-1 without masonry insert:

First crack was observed (horizontal hairline) at

30kN at the junction of loaded side of the beam and

column at the bottom storey, where moment and

shear forces are maximum while loading further,

similar cracks were developed in the other bay

columns and flexural cracks were developed from

the junction of the loaded areas. Separation of infill

occurred at the tension corners. At the ultimate

failure load of 70 KN, crushing of loaded corner,

widening of diagonal cracks in columns and infill,

layer separation of brick infill were also observed.

Width of the cracks was ranging from 3mm to

15mm in concrete and masonry. The crack pattern

indicated a combined effect of flexure and shear

failure. Also plastic hinges formation was observed

first at loaded point and later to the middle column

and finally at the leeward column. Captive column

phenomenon was identified with the failure pattern

of loaded column. It was also noticed that flow of

diagonal crack from the loaded column adjacent to

the opening was discontinuous, due to incomplete

strut action (Fig.5).

b) Frame-2 with masonry insert:

First crack observed (inclined downwards and

forwards) at only 80 kN, (against 30 kN for the

frame without insert) at loaded side of the beam and

column junction of the bottom storey where

moment and shear forces were maximum While

loading further, similar cracks were found to

propagate in middle column beam junctions and

diagonal crack were initiated in the first (loaded)

bay. Further, diagonal cracks were seen to flow

through the brick infill. Separation of infill

occurred at the tension corners. Due to the presence

of insert, diagonal cracks were observed to flow

from the loaded beam – column junction to the

diagonally opposite corner, clearly depicting the

expected strut action (Fig.6). At ultimate load of

140 KN, plastic hinge formation and failure of

frame at all bottom storey junctions were noticed.

The width of the cracks was ranging from 2mm –



failure and the direction of flown crack showed the

developed strut action through the brick infill, due

to the presence of masonry insert

Figure.5.Test frame 1 with failure in the bottom and

drift of the top storey (Constructed atVLBJCET,

Coimbatore)


drift of the top storey(Constructed atVLBJCET,

Coimbatore)

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IJAESTfailure and the direction of flown crack showed the

IJAESTfailure and the direction of flown crack showed the


IJAESTdeveloped strut action through the brick infill, due


IJAESTto the presence of masonry insert

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of loaded column. It was also noticed that flow of IJAEST


diagonal crack from the loaded column adjacent to IJAEST

diagonal crack from the loaded column adjacent to IJAEST

the opening was discontinuous, due to incomplete IJAEST


strut action (Fig.5). IJAEST


Frame-2 with masonry insert: IJAEST

Frame-2 with masonry insert:

First crack observed (inclined downwards and IJAEST


forwards) at only 80 kN, (against 30 kN for the IJAEST



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A crack in leeward column of the bottom storey at the base was also observed (Fig.7). Separation of infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends led to early crushing of the loaded corners (Fig.8).No crack was developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to short column effect.

It is also evident from the propagation of cracks at

bottom storey level of the eighth cycle (80 kN Base

shear). Cracks in tension face of leeward column

were developed after tenth cycle of loading. Also

separation of infill from columns at highly stressed

tension faces of column were seen at tenth cycle of

loading. Further, shear flow was observed in frame

2 from the columns through the insert and brick

infill, creating a largely visible crack (about 12mm

wide), which is extended to the adjacent columns.

This phenomenon is clearly exhibits the

development of strut action through masonry insert.

Figure. 7.crack in leeward Figure:8 Crushing of the

column loaded Corners

2) FINITE ELEMENT ANALYSIS – ANSYS –

10:

A comparative study was made between

experimental and analytical values. Non-linear

finite element analysis has been carried out using

ANSYS-10 software for Frame (1) & (2). The

deformed shape of the software model for ultimate

load for Frame (1) and (2) is shown in Fig.9 &10

Load – 80 KN , Deflection – 47.453

Figure.9 Ultimate Deformed Shape of the software Model For Frame 1


Fig.10 Ultimate Deformed Shape of the software Model For Frame 2

The results obtained from analytical by ANSYS-

10 for Frame (1) & (2) are compared with

experimental results and the variation is mariginal.

The experiments conducted on the two frames

(with and without masonry insert) the following

observations are drawn.

1) It is observed in frame with masonry insert

that at a base shear of 80 kN, cracks are

initiated at the junction of the loaded and

middle end of the beam and column of the

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A comparative study was made between IJAEST


experimental and analytical values. Non-linear IJAEST


finite element analysis has been carried out using IJAEST


ANSYS-10 software for Frame (1) & (2). The IJAEST


deformed shape of the software model for ultimate IJAEST


load for Frame (1) and (2) is shown in Fig.9 &10 IJAEST



IJAESTLoad – 80 KN , Deflection – 47.453

Figure.9 Ultimate Deformed Shape of the

IJAESTFigure.9 Ultimate Deformed Shape of the

software Model For Frame 1

IJAESTsoftware Model For Frame 1

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bottom storey where the moment and shear

forces are maximum whereas in frame

without insert, the first crack developed at

30 KN itself. The crack pattern indicated a

combined effect of flexure and shear

failure. However, it could be evidently

seen that the shear carrying capacity of the

frame is increased due to the presence of

masonry inserts

2) Separation of infill occurred at the tension

corners and the high stress concentration at

the loaded diagonal ends lead to early

crushing of the loaded corners.

3) Diagonal cracks flown through the brick

work where masonry inserts are provided

showing clear strut action. While further

loading of frames, further cracks are

initiated and noticed are much dissimilar

between a RC frame with partial infill and

with masonry insert.

4) The stiffness of the partially-infilled frame

with and without insert for various load

cycles is calculated and the variation of

stiffness with respect to load cycles is

plotted. The stiffness of the brick infilled

RC frame with masonry insert is observed

to be very high when compared to frame

without insert. This shows greater

increase of stiffness while introducing

masonry insert.

5) The ductility factor value µ = (∆1/∆y) for

various load cycles of the frame is worked

out for frames with and without insert and

the variation of ductility factors and

cumulative ductility factors for both

frames with reference to load cycles is

plotted. From the values, it may be noted

that ductility factor for frame with

masonry insert is reduced whereas

cumulative ductility factor for both frames

is more or less same.

6) Cracks were developed in the leeward

column (opposite to the loaded end) of the

bottom storey at the base because of

diagonal strut compression of the infill in

the frame with masonry insert.

7) The partial-infilled RC frame failed with

hinges at the portion of columns adjacent

to the gap in the bottom storey indicating a

distinct “captive column effect” whereas

frame with masonry insert strut action took

place and diagonal crack flow clearly.

Also after the localised separation of the

infilled panel from the frame in the bottom

storey, the stress flow is mostly along the

line connecting the load point to the

diagonal opposite corner support

indicating the “diagonal strut” concept.

Therefore, it could be evidently proven

that the lateral strength of the RC frame is

considerably increased due to the presence

of masonry inserts.

8) The partial masonry infill failed with a

diagonal crack by shear along the mortar

and/or bricks joints.

9) In frame without masonry insert no crack

is developed in the columns, beams and in

the infill of top storey clearly depicting

that the frame has failed only by hinges in

columns due to captive column effect.

But, it was noticed that the development of

crack is postponed when the frame is

provided with masonry inserts.

10) The partial infill reduces the stiffness of

the frame leading to critical damages.

However, this could be improved to some

extent by the provision of masonry inserts.

11) In analytical study, it is noticed that a

sudden increase in deflection after the base

shear of 40 kN (nearly equal to

experimental value of 40 kN) for Frame

(1) and affect the base shear of 80 kN

(nearly equal to experiemtnal value of 80

kN) for Frame (2). This proves the

initiation of captive column behaviour

adjacent to gap region.

12) Analytical results by ANSYS-10

variations is very mariginal when

compared to Experimental results

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of masonry inserts.

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IJAEST8) The partial masonry infill failed with a


IJAESTdiagonal crack by shear along the mortar


IJAESTand/or bricks joints.

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5) The ductility factor value µ = (

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5) The ductility factor value µ = (∆

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∆1/

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1/∆

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∆y) for

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frames with reference to load cycles is IJAEST


plotted. From the values, it may be noted IJAEST


that ductility factor for frame with IJAEST


masonry insert is reduced whereas IJAEST


cumulative ductility factor for both frames IJAEST


is more or less same.IJAEST


6) Cracks were developed in the leeward IJAEST


column (opposite to the loaded end) of the IJAEST



IJAEST9) In frame without masonry insert no crack


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IJAESTthe infill of top storey clearly depicting


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IJAEST10) The partial infill reduces the stiffness of


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IJAEST11) In analytical study, it is noticed that a



IV EXPERIMENTAL AND ANALYTICAL

INVESTIGATION ON 3D RC FRAME

STRUCTURE

1) EXPERIMENTAL INVESTIGATION

A) Modelling of Frames: A structure representing a multi-storeyed frame

system is analysed and designed. The structure is

modeled for experimental investigation by scaling

down the geometric properties of the prototype

using the laws of Geometric similitude.

Figure.11 Geometry of the 3D frame model 1&2

B) DETAILS OF TEST FRAME

Test models was fabricated to 1:3 reduced scale





Lumped mass distribution was


for top storey & 25% for bottom storey. All applied

lateral loads were divided accordingly and applied

as push and pull method. Frame (1) was tested of

first incremental Push load of 5 KN and released to

zero and a pull load of 5 KN and released to zero.

The deflections at top storey levels were recorded.

Further an incremental load of 5 KN(Push and Pull)

were applied and top storey deflections were

measured at each increment and decrement of the

load Using LVDT. Additional LVDT also placed at

other levels to find the frame behavior. The

formation and propagation of cracks, hinge

formation and failure pattern were recorded. This

procedure was repeated for frame (2) with masonry

insert.

D) Results:






(P-∆):

The frame was subjected to push and pull

loading. The push and pull load was applied in

increment of 5 kN base shear for each cycle and

released to zero after each cycle. The deflections at

top storey levels were measured using LVDT at

each increment or decrement of load. The ultimate

base shear of 105 KN was reached in the twenty

first cycle of loading and ultimate base shear of

195KN was reached in thirty nine cycle for frame 1

& 2 respectively.

The push pull curve for top storey displacement

versus base shear for both frames is represented in

Fig.12 & 13. Load and top storey deflection is

presented in Table 2. At the ultimate base shear the

top storey deflection was found to be 58.24mm for

frame (1) and 71.15mm for frame (2).

Table.2: Load and Deflection for Frame 1 & 2

Frame (1) Frame (2)

Load

(KN)

Deflectio

n (mm)

Load

(KN)

Deflecti

on (mm)

0 0.00 0 0.00

5 0.75 5 0.27

0 0.08 0 0.02

-5 -0.66 -5 -0.19

0 -0.02 0 -0.01

10 1.60 10 0.54

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C) Testing Procedure :IJAEST


Lumped mass distribution was IJAEST

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calculated and lateral loads were distributed as 75% IJAEST


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for top storey & 25% for bottom storey. All applied

lateral loads were divided accordingly and applied IJAEST

lateral loads were divided accordingly and applied

as push and pull method. Frame (1) was tested of IJAEST

as push and pull method. Frame (1) was tested of


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IJAESTbehaviour of the frame


IJAESTi) Loading And Load-Deflection Behaviour

(P-

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The frame was subjected to push and pull

IJAEST The frame was subjected to push and pull

loading. The push and pull load was applied in

IJAESTloading. The push and pull load was applied in

increment of 5 kN base shear for each cycle and

IJAESTincrement of 5 kN base shear for each cycle and

released to zero after each cycle. The deflections at

IJAESTreleased to zero after each cycle. The deflections at


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& 2 respectively.

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& 2 respectively.


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ISSN: 2230-7818 @ 2011 http://www.ijaest.iserp.org. All rights Reserved. 8

Frame (1) Frame (2)

Load

(KN)

Deflectio

n (mm)

Load

(KN)

Deflecti

on (mm)

0 0.22 0 0.08

-10 -1.67 -10 -0.40

0 -0.39 0 -0.04

15 2.74 15 0.82

0 0.92 0 0.12

-15 -2.51 -15 -0.67

0 -0.44 0 -0.07

20 3.91 20 1.16

0 1.04 0 0.36

-20 -3.17 -20 -0.98

0 -0.72 0 -0.12

25 5.06 25 1.55

0 0.22 0 0.36

-25 -4.84 -25 -1.30

0 -0.48 0 -0.19

30 6.17 30 1.91

0 0.13 0 0.45

-30 -5.67 -30 -1.38

0 -0.59 0 -0.24

35 7.24 35 2.34

0 0.71 0 0.42

-35 -6.69 -35 -2.15

0 -0.71 0 -0.28

40 8.48 40 3.02

0 0.75 0 0.41

-40 -6.81 -40 -2.78

0 -0.74 0 -0.36

45 9.61 45 3.59

0 1.04 0 0.47

-45 -8.68 -45 -3.69

0 -0.84 0 -0.36

50 10.97 50 4.35

0 1.05 0 0.54

-50 -9.64 -50 -3.56

0 -0.89 0 -0.41

55 12.23 55 6.53

0 1.24 0 0.58

-55 -10.44 -55 -5.78

0 -0.92 0 -0.38

60 13.85 60 8.21

0 1.35 0 0.57

-60 -12.80 -60 -7.33

0 -1.16 0 -0.38

65 14.84

65

10.049

Frame (1) Frame (2)

Load

(KN)

Deflectio

n (mm)

Load

(KN)

Deflecti

on (mm)

0 1.35 0 0.67

-65 -13.62 -65 -10.32

0 -1.15 0 -0.47

70 16.17 70 12.31

0 1.43 0 0.69

-70 -16.31 -70 -12.49

0 -1.25 0 -0.50

75 17.34 75 14.07

0 1.47 0 0.77

-75 -17.13 -75 -14.66

0 -1.26 0 -0.53

80 22.81 80 17.40

0 1.89 0 0.70

-80 -21.12 -80 -15.87

0 -1.50 0 -0.52

85 24.05 85 19.02

0 1.77 0 0.68

-85 -23.30 -85 -20.27

0 -1.55 0 -0.62

90 29.79 90 21.76

0 1.93 0 0.79

-90 -24.71 -90 -23.19

0 -1.55 0 -0.62

95 33.88 95 25.02

0 1.83 0 0.83

-95 -35.29 -95 -21.64

0 -1.88 0 -0.68

100 44.42 100 27.20

0 1.98 0 0.86

-100 -40.26 -100 -24.73

0 -1.84 0 -0.64

105 58.24 105 30.49

0 0.83

-105 -25.12

0 -0.62

110 32.15

0 0.98

-110 -30.62

0 -0.73

115 33.82

0 0.97

-115 -33.66

0 -0.76

120

35.53

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-2.15

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-2.15

-0.28

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-0.28

3.02

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3.02

0.41

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0.41

-40

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-40 -2.78

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-2.78

0

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0 -0.36

IJAEST

-0.36

45

IJAEST

45 3.59

IJAEST

3.59

0

IJAEST

0 0.47

IJAEST

0.47

-45

IJAEST

-45 -3.69

IJAEST

-3.69

-0.84

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-0.84 0

IJAEST

0 -0.36

IJAEST

-0.36

10.97

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10.97 50

IJAEST

50 4.35

IJAEST

4.35

1.05IJAEST

1.05 0IJAEST

0 0.54IJAEST

0.54

-9.64IJAEST

-9.64 -50IJAEST

-50 -3.56IJAEST

-3.56

0 IJAEST

0 -0.89IJAEST

-0.89 0IJAEST

0

12.23IJAEST

12.23 55IJAEST

55

1.24IJAEST

1.24 0IJAEST

0

-10.44IJAEST

-10.44

-0.92IJAEST

-0.92

-75

IJAEST

-75

-1.26

IJAEST-1.26 0

IJAEST0

22.81

IJAEST22.81 80

IJAEST80 17.40

IJAEST17.40

1.89

IJAEST1.89 0

IJAEST0 0.70

IJAEST0.70

-21.12

IJAEST-21.12 -80

IJAEST-80 -15.87

IJAEST-15.87

0

IJAEST0 -1.50

IJAEST-1.50 0

IJAEST0

85

IJAEST85 24.05

IJAEST24.05 85

IJAEST85

0

IJAEST0 1.77

IJAEST1.77 0

IJAEST0

-85

IJAEST-85 -23.30

IJAEST-23.30 -85

IJAEST-85

0

IJAEST

0 -1.55

IJAEST

-1.55

90

IJAEST

90 29.79

IJAEST

29.79

0

IJAEST

0 1.93

IJAEST

1.93

-90

IJAEST

-90 -24.71

IJAEST

-24.71

0

IJAEST

0 -1.55

IJAEST

-1.55

95

IJAEST

95

0

IJAEST

0

-95

IJAEST

-95



Frame (2)

Load

(KN)

Deflecti

on (mm)

0 1.05

-120 -36.92

0 -0.83

125 36.92

0 0.99

-125 -35.63

0 -0.80

130 37.95

0 1.08

-130 -41.47

0 -1.00

135 40.00

0 1.30

-135 -44.96

0 -0.96

140 41.20

0 1.40

-140 -37.90

0 -1.08

145 43.66

0 1.53

-145 -41.76

0 -1.07

150 45.22

0 1.48

-150 -42.94

0 -1.14

155 47.72

0 1.93

-155 -49.08

0 -1.38

160 51.78

0 1.96

-160 -51.04

0 -1.55

165 54.42

0 2.12

-165 -52.99

0 -1.71

170 57.65

0 2.08

-170 -52.01

0 -1.69

Frame (2)

Load

(KN)

Deflecti

on (mm)

175 60.97

0 2.13

-175 -60.81

0 -2.12

180 63.09

0 2.70

-180 -65.89

0 -2.20

185 65.72

0 2.93

-185 -55.88

0 -2.56

190 67.63

0 3.04

-190 -61.93

0 -2.47

195 71.15

Figure. 12 Push and Pull curve for Frame 1

Figure. 12 Push and Pull curve for Frame 1

Figure. 12 Push and Pull Curve for Frame 1

Figure. 13 Push and Pull Curve for Frame 2

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-41.76

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-41.76

-1.07

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-1.07

45.22

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45.22

1.48

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1.48

-150

IJAEST

-150 -42.94

IJAEST

-42.94

0

IJAEST

0 -1.14

IJAEST

-1.14

155

IJAEST

155 47.72

IJAEST

47.72

IJAEST

0

IJAEST

0 1.93

IJAEST

1.93

IJAEST

-155

IJAEST

-155 -49.08

IJAEST

-49.08

IJAEST

0

IJAEST

0 -1.38

IJAEST

-1.38

IJAEST

160

IJAEST

160 51.78

IJAEST

51.78

IJAEST

0IJAEST

0 1.96IJAEST

1.96

IJAEST

-160IJAEST

-160 -51.04IJAEST

-51.04

IJAEST

0IJAEST

0

IJAEST

165IJAEST

165

IJAEST

0IJAEST

0

IJAEST

-165IJAEST

-165

IJAEST

IJAEST

185

IJAEST

185

IJAEST

0

IJAEST

0

IJAEST -185

IJAEST-185

IJAEST 0

IJAEST0

IJAEST 190

IJAEST190 67.63

IJAEST67.63

IJAEST 0

IJAEST 0 3.04

IJAEST3.04

IJAEST -190

IJAEST-190 -61.93

IJAEST-61.93

IJAEST 0

IJAEST0

IJAEST 195

IJAEST195

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ii) Ductility: The ductility factor (µ) was calculated. For frame

(1), the first yield deflection (∆y) for the assumed

bi-linear load-deflection behaviour of the frame was

found to be 8.48 mm for 40 KN base shear, while

for frame (2), the same is found to be 14.06mm for

75 KN base shear. The ductility factor value µ =

(∆1/∆y) for various load cycles of the frames was

worked out and the variation of ductility factor for

both frames with load cycles are shown in Fig.14.

The ductility factor is found to be increasing more

from 1 at eighth cycle to 6.86 at twenty first cycle

for frame (1). While for frame (2), the ductility

factory is 1 at fifteenth cycle of loading and only

5.05 at thirty nine cycle of loading. This behaviour

shows the reduction of ductility of frame due to the



iii) Stiffness Degradation: The stiffness of the partially-infilled frames for

various load cycles is calculated and presented. The

variation of stiffness with respect to load cycles is

shown in Fig.15. For frame (1), it may be noted

that stiffness decreases from 6.7KN/mm in first

cycle to 1.8 KN/mm in twenty first cycle. A sudden

reduction in stiffness takes place after the first crack


For frame (2), the initial stiffness of frame is

18.69 KN/mm against 6.7 kN/mm for the first frame

and stiffness is sustained for a longer duration until

the development of first crack and is reduced to

2.74 KN/mm in Thirty nine cycle.

This behaviour shows that the initial stiffness of

frame (1) is comparatively very low and flexural

hinges and shear cracks are developed at an early

stage of loading. For frame(2) with masonry insert,

initial stiffness is increased and occurrence of

flexural hinges and shear cracks in concrete and

masonry takes place only after the Fifteenth cycle.

Also, it could be noted that the initial stiffness is

increased by 2.8 times due to the introduction of

masonry insert and the stiffness is sustained for a

longer duration of loading. The behaviour of frame

for stiffness values is shown in Fig.15


frames






















diagonal crack from the loaded column adjacent to



IJAEST


IJAEST


iii) Stiffness Degradation:

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iii) Stiffness Degradation: The stiffness of the partially-infilled frames for

IJAEST

The stiffness of the partially-infilled frames for


IJAEST



IJAEST



IJAEST


that stiffness decreases from 6.7KN/mm in first IJAEST

that stiffness decreases from 6.7KN/mm in first

cycle to 1.8 KN/mm in twenty first cycle. A sudden IJAEST

cycle to 1.8 KN/mm in twenty first cycle. A sudden

reduction in stiffness takes place after the first crack IJAEST

reduction in stiffness takes place after the first crack

occurrence in 40 kN load. IJAEST


For frame (2), the initial stiffness of frame is IJAEST

For frame (2), the initial stiffness of frame is

18.69 KN/mm against 6.7 kN/mm for the first frame IJAEST

18.69 KN/mm against 6.7 kN/mm for the first frame

and stiffness is sustained for a longer duration until IJAEST

and stiffness is sustained for a longer duration until

the development of first crack and is reduced to IJAEST

the development of first crack and is reduced to


IJAESTFigure:15:Stiffness degradation curve for both

frames

IJAEST

frames


IJAEST



IJAEST



IJAESTFirst crack was observed (horizontal hairline) at


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Figure.16.Test frame 1 with failure in the bottom

and drift of the top storey (Constructed

atVLBJCET, Coimbatore)

b) Frame-2 with masonry insert:





















failure and the direction of flown crack showed the



Figure.17.Test frame 2 with failure in the bottom and drift of the top storey(Constructed atVLBJCET,

Coimbatore)

A crack in leeward column of the bottom storey at the base was also observed (Fig.18). Separation of infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends led to early crushing of the loaded corners (Fig.19).No crack was developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to short column effect.


bottom storey level of the Fifteenth cycle (75 kN

Base shear). Cracks in tension face of leeward

column were developed after twenty first cycle of

loading. Also separation of infill from columns at

highly stressed tension faces of column were seen at

tenth cycle of loading. Further, shear flow was

observed in frame 2 from the columns through the

insert and brick infill, creating a largely visible

crack (about 12mm wide), which is extended to the

adjacent columns. This phenomenon is clearly

exhibits the development of strut action through

masonry insert.

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from the loaded beam – column junction to the IJAEST


diagonally opposite corner, clearly depicting the IJAEST


expected strut action (Fig.17). At ultimate load of IJAEST


195 KN, plastic hinge formation and failure of IJAEST


frame at all bottom storey junctions were noticed. IJAEST


The width of the cracks was ranging from 2mm – IJAEST


10mm in concrete and masonry. The crack pattern IJAEST


indicated a combined effect of flexure and shear IJA

EST


Figure.17.Test frame 2 with failure in the bottom

IJAESTFigure.17.Test frame 2 with failure in the bottom

and drift of the top storey(Constructed atVLBJCET,

IJAESTand drift of the top storey(Constructed atVLBJCET,

Coimbatore)

IJAESTCoimbatore)

A crack in leeward column of the bottom storey at

IJAEST

A crack in leeward column of the bottom storey at the base was also observed (Fig.18). Separation of

IJAEST

the base was also observed (Fig.18). Separation of infill occurred at the tension corners and the high

IJAEST

infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends led

IJAEST

stress concentration at the loaded diagonal ends led to early crushing of the loaded corners (Fig.19).No

IJAEST

to early crushing of the loaded corners (Fig.19).No crack was developed in the columns, beams and in

IJAEST

crack was developed in the columns, beams and in the infill of top storey clearly depicting that the

IJAEST

the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to

IJAEST

frame has failed only by hinges in columns due to short column effect.

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short column effect.


IJAEST


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Figure 18.crack in leeward Figure.19 Crushing of the



10:








Figure.20 Ultimate Deformed Shape of the software Model For Frame 1








observations are drawn.

1) It is observed in frame with masonry insert

that at a base shear of 75 kN, cracks are

initiated at the junction of the loaded and

middle end of the beam and column of the

bottom storey where the moment and shear

forces are maximum whereas in frame

without insert, the first crack developed at

40 KN itself. The crack pattern indicated a

combined effect of flexure and shear

failure. However, it could be evidently

seen that the shear carrying capacity of the

frame is increased due to the presence of

masonry inserts

2) Separation of infill occurred at the tension

corners and the high stress concentration at

IJAEST

IJAEST

Load – 105 KN , DefleIJAEST

Load – 105 KN , Defle

Figure.20 Ultimate Deformed Shape of the IJAEST

Figure.20 Ultimate Deformed Shape of the software Model For Frame 1IJA

EST



IJAEST


Fig.21 Ultimate Deformed Shape of the

IJAEST


IJAEST



IJAESTThe results obtained from analytical by ANSYS-


IJAEST



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IJAESTThe experiments conducted on the two frames


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the loaded diagonal ends lead to early

crushing of the loaded corners.

3) Diagonal cracks flown through the brick

work where masonry inserts are provided

showing clear strut action. While further

loading of frames, further cracks are

initiated and noticed are much dissimilar

between a RC frame with partial infill and

with masonry insert.

4) The stiffness of the partially-infilled frame

with and without insert for various load








masonry insert.

5) The ductility factor value µ = (∆1/∆y) for
























storey, the stress flow is mostly along the

line connecting the load point to the

diagonal opposite corner support

indicating the “diagonal strut” concept.




of masonry inserts.


























variations is very mariginal when

compared to Experimental results

V CONCLUSION

For existing buildings with short column in

earthquake prone areas needs this easy method of

providing masonry insert to improve the base shear

capacity. Many of the existing captive columns

have poor seismic detailing. Due to short dowels

and little transverse reinforcement, risk of brittle

shear failure in such members is very high.

Therefore, it is important to develop efficient

techniques to strengthen shear critical columns and

increase their energy dissipation capacity. Wrapping

concrete columns with a proper strengthening

material can be an effective solution. . The various

method of improve the strengthening of existing

building and the costs are prescribed.

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IJAEST



IJAEST


7) The partial-infilled RC frame failed with IJAEST


hinges at the portion of columns adjacent IJAEST


to the gap in the bottom storey indicating a IJAEST


distinct “captive column effect” whereas IJAEST


frame with masonry insert strut action took IJAEST


place and diagonal crack flow clearly. IJAEST


Also after the localised separation of the IJAEST


infilled panel from the frame in the bottom IJAEST



IJAEST



IJAEST



IJAEST



IJAESTprovided with masonry inserts.


IJAEST10) The partial infill reduces the stiffness of


IJAESTthe frame leading to critical damages.


IJAESTHowever, this could be improved to some


IJAESTextent by the provision of masonry inserts.


IJAEST11) In analytical study, it is noticed that a


IJAESTsudden increase in deflection after the base


IJAESTshear of 40 kN (nearly equal to


IJAEST



IJAEST



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IJAEST12) Analytical results by ANSYS-10



Cost/Sqm

Si.No Technique

External Internal

1 Introducing

masonry insert

in the opening

Rs.750/- Rs.1500/-

2 Beam column

joint

strengthening

using carbon

fibres

Rs.10000/- Rs.12000/-

3 Beam column

joint

strengthening

using GFRP

Rs.7500/- Rs.8750/-

4 Introducing

longitudinal and

shear

reinforcement

and micro

concrete pack up

Rs.17000/- Rs.19700/-

Therefore, cheaper and affable solutions involving

easily available materials and simple construction

techniques such as masonry inserts must be given

much consideration during construction.

From the studies, the width of diagonal strut

transferring the shear is approximately found to be

0.10 times the length of the diagonal of infill.

Therefore, a minimum width of insert based on the

above criteria may be provided as described.

References:

1) Yaw-Jeng Chiou, Jyh-Cherng Tzeng, and Yuh-Wehn Liou, (1999), “Experimental and Analytical

Study of Masonry Infilled Frames”, Journal of

Structural Engineering, Vol. 125, No. 10, October

1999, pp. 1109-1117

2) Murtthy , C.V.R., and Das, Diptesh., (2000),

“Beneficial Effects of Brick Masonry In Fills In

Seismic Design of RC Frame buildings" Engineering

Structures Journal, Vol. 21, No 4, pp. 617-627

3) R. Morshed and M.T. Kazemi, (2005), "Seismic

shear strengthening of R/C beams & columns with

expanded steel meshes", Structural Engineering and

Mechanics, Vol. 21, No.3, pp. 333-50 (2005).

4) Galal, K.E., Arafa, A., and Ghobarah, A., (2005),

“Retrofit of RC square short columns" Engineering

Structures Journal, Vol. 27, No 5, pp. 801-813

5) Melhmet Mehmet Emin Kara, Altin Sinan, (2006),

“Behavior of reinforced concrete frames with

reinforced concrete partial infills”, ACI structural

journal, 2006, vol. 103, no5, pp. 701-709

6) FEMA 306, “Evaluation of earthquake damaged

concrete and masonry wall buildings”, Applied

Technology Council, USA

7) “NEHRP guidelines for the seismic rehabilitation of

buildings. FEMA Publication 273”, Multidisciplinary

Center for Earthquake Engineering Research

(MCEER), USA

8) Dr.C.V.R. Murthy (2005) on Key notes on seismic

resistance buildings.

IJAEST

guidelines for the seismic rehabilitation of

IJAEST

guidelines for the seismic rehabilitation of


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IJAEST

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IJAEST

IJAEST


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ilable materials and simple construction

IJAEST

ilable materials and simple construction


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IJAEST


IJAEST


IJAEST



IJAEST



IJAEST



IJAEST



IJAEST


References: IJAEST

References:

Yaw-Jeng Chiou, Jyh-Cherng Tzeng, and Yuh-IJAEST

Yaw-Jeng Chiou, Jyh-Cherng Tzeng, and Yuh-IJAEST

Wehn Liou, IJAEST

Wehn Liou, (1999)IJAEST

(1999), IJAEST

, “Experimental and Analytical IJAEST

“Experimental and Analytical

Study of Masonry Infilled Frames”, Journal of IJAEST

Study of Masonry Infilled Frames”, Journal of

Structural Engineering, Vol. 125, No. 10, October IJAEST

Structural Engineering, Vol. 125, No. 10, October

1999, pp. 1109-1117 IJAEST

1999, pp. 1109-1117

Murtthy , C.V.R., and Das, Diptesh.,IJAEST

Murtthy , C.V.R., and Das, Diptesh.,

“Beneficial Effects of Brick Masonry In Fills In IJA

EST

“Beneficial Effects of Brick Masonry In Fills In

(MCEER), USA

IJAEST

(MCEER), USA

.C.V.R. Murthy (2005) on Key notes on seismic

IJAEST.C.V.R. Murthy (2005) on Key notes on seismic

resistance buildings.

IJAESTresistance buildings.



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Transcript of 11-IJAEST-Volume-No-2-Issue-No-1-SEISMIC-STRENGTHENING-OF-LOW-RISE-BUILDINGS-USING-BRICK-INSERTS-(RE