11 Ijaest Volume No 2 Issue No 1 Seismic Strengthening of Low Rise Buildings Using Brick Inserts Retrofit) 072 085

8/7/2019 11 Ijaest Volume No 2 Issue No 1 Seismic Strengthening of Low Rise Buildings Using Brick Inserts Retrofit) 072 085

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SEISMIC STRENGTHENING OF LOW RISE

BUILDINGS USING BRICK INSERTS

(RETROFIT) – EXPERIMENTAL

INVESTIGATION ON 2D & 3D RC FRAMEDSTRUCTURES

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 asmall 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 elementanalysis 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 mechanismcould 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 inGujarat (Bhuj) - India in the year 2001 had severalincidents of failure or complete collapse. Majority of the failure in the buildings are predominantly due toCaptive column failure or soft storeyed building.

After the revision in IS codes for seismic forces, weare able to take care of the proposed new buildings.But even many old buildings of similar nature stillexists (built as per IS 456 detailed with SP 34) inhighly earthquake prone areas throughout thecountry. Energy dissipation of these buildings arevery poor for lateral loads mainly due to Captivecolumn failure. By providing necessary masonryinserts in the partial infill opening shall increase the

katasubr

BJCET, CoimBJC

oimbatore, Indiabatore,

[email protected] yahoo.

e

atea

de thede the

th brick ick

e buildings

stated in BIS

is by adding apartial infilled RCal inf

ld double its strength.l ts strengt .

tion is conducted to studyu tudy

ehaviour of RC frames withha h

y panels (2D & 3D) viz. oanels

me 1) and other with maand o

ening(frame 2). One-third sc. One

rey RC frame (2D & 3D) derey & 3D

oading is tested under in-ding in-

2D RC frames and pusRC f

structures. A non-lctures. -lcarried outrried o

nt andand

ns

reinforced with the addedf addery inserts. Finally it was sur u

ting columns with short-cong ns w tould be strengthened withbe strengthened

improving building strenim tr

methods, the damage

repairable limits an

building/loss of liil s l

arthquake. ThT

brick insertbr t

normallynorm

lementmen

Ke

Mr.R.Suresh Babu et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIESVol 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 energydissipation. Due to this the collapse of the buildingwill delay and the structure became more safer. Thisremedy is evaluated without major alteration tostructural elements and without affecting majorexisting 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 MehmatEmin 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 Korkmazet.al(2007) shown that presence of nonstructural

masonry infill walls can modify the global seismicbehaviour 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 scalefollowing 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 appliedlateral loads were divided accordingly. Frame (1)was tested of first increments of 10 kN base shearfor each cycle and released to zero after each cycle.The deflections at all storey levels were measured ateach increment and decrement of the load. Theformation and propagation of cracks, hingeformation and failure pattern were recorded. Thisprocedure was repeated for frame (2) with masonryinsert.

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

an

RCR

shownown

and thee

an Korkmazof nonstructural

the global seismice gg to a larger extent.larger e

the behaviour of infilledinfilled

teral loading. Test focusede f ed

rgy dissipation over and abovrgy d

antiago pujol et.al(2008) shoo pu

fill walls were effective in inere e

y 100%) and stiffness (bytiffnes

al reinforced concrete structurl rein struct

hmy Taher et.al(2008) lowTah w

yields the higher strelds the stre

e systemstem

ENTATA

2

Figure.1 Geometry of the fra

) Testing Procedure : s ting Procedure :Lumped massLu m

alculated and lateral loaa for top storey & 20% f lateral loads were de s rewas tested of firsa efor each cyclef le

he deflectiheach incrach c

formata forp





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) and56mm 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 37130 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 earlystage 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

.33

29

37474

40 5656

ar VV

g.g.

ility of

insert and is shinser

Figure. 3 Du.

iii) Stiffness DiiiThe s

for varior varihe v

is





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) at30kN 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 to15mm 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 theexpected 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 –

10mm in concrete and masonry. The crack pattern


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)

Figure.6.Test frame 2 with failure in the bottom and

drift of the top storey(Constructed atVLBJCET,

Coimbatore)

sonrsonr

effect of e

tion of flown crion o

ction through the bricct throu

of masonry insertf inser

m

nfillnfi

ltimatemate

ed corner,r,

ns and infill,

e also observed.

ng from 3mm tof rry. The crack patterne crack p

ct of flexure and sheard shear

ges formation was observeded

nd later to the middle columnd la

eeward column. Captive colurd co

s identified with the failured with re

umn. It was also noticed thau o noti

rack from the loaded columnrack colu

ing was discontinuous, duewas e

Fig.5)..5).

2 with masonry t h ma

ed (i(i

F





A crack in leeward column of the bottom storey atthe base was also observed (Fig.7). Separation of infill occurred at the tension corners and the highstress concentration at the loaded diagonal ends ledto early crushing of the loaded corners (Fig.8).No

crack was developed in the columns, beams and inthe infill of top storey clearly depicting that theframe has failed only by hinges in columns due toshort 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 thesoftware Model For Frame 1


Fig.10 Ultimate Deformed Shape of thesoftware 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

Figure:8 Crushing of theof the

loaded Corners

ENT ANALYSIS – ANSANA

parative study was madparat s m

ntal and analytical valuesand es

nt analysis has beennalys een

ftware for Fraare fo

f the softwe soft

d (2)2

0 KN , Deflection –, Def

.9 Ultimate Deformed Shapei formesoftware Model For Frameso or Fr





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 theframe 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 dissimilarbetween 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 introducingmasonry 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 theline 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

rengteng

ncreasedn

inserts.insert .

tial masonry infill f i asonr

nal crack by shear along tl she

d/or bricks joints.

f

s iss

nfillednf illed

observeded

red to frame

shows greater

while introducinghile

r value µ = ( 1/ 1/ y) fory) for

cles of the frame is workedl ed

s with and without insert ands wi i

tion of ductility factorsof

tive ductility factors fortility f

es with reference to loade ce to

otted. From the values, it motte . es, it

hat ductility factor forduc or

sonry insert is rery in

lative ductility fave duc

or less samess sam

re ded

n frame without masonry innry iis developed in the column

the infill of top storeyill of

that the frame has faithat the frame h

columns due tot

But, it was notii

crack is pos o

provided

10) The pe p

thee

1





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

following the laws of similitude by scaling down

the geometric and material properties of the

prototype for Frame (1) and Frame (2)(Ref. Fig.11).

C) Testing Procedure :

Lumped mass distribution wascalculated and lateral loads were distributed as 75%

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 masonryinsert.

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 push and pullloading. 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 inFig.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

me model 1&2

ricated to 1:3 reduced scaleri e e

of similitude by scaling dowf sim a

nd material properties of aterial s

rame (1) and Frame (2)(Ref. FFram . F

ing Procedure :Proce

umped mass ded dlateral loads weral loa

% for bof or bo

vide

atioati

udy of t

ee

And Load-Deflection A oad-

):

rame was subjected to pur e to pu. The push and pull loadd

ement of 5 kN base shear f

leased to zero after each cycld to zero after eac

op storey levels were meo le

ach increment or decre

base shear of 105 Ka

first cycle of loadist a

195KN was reac9 re

& 2 respective& v

The pusThe

versussusFig..

p





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

.28

3.02

0.41

-2.78

0 -0.36-0.36

45 3.59.59

0 0.47

-45 -3.69-

. 4 0 -0.36-

0.97 505 4.35.

1.05 00 0.

-9.64- -500

-0.89-0. 0

2.232.23 555

1.2424

.44

-75

0

.81. 80

.89. 0 0.

-21.12 -80-80 -1

-1.50- 00

85 24.05 85

0 .77.77

-8585 -23.30-23.3

0 -1.55

90 29.79

0 .93.

-90 -24..

0

95

0

-9-





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 I

.07

45.22

1.48

-42.94-

0 -1.14-1.14

155 47.72.72

0 1.93

-155 -49.08-

0 -1.38-1

16016 51.78.

00 1.

-1600 -

0

16516

0

-185

0

1901 6 .

00

-19090 0

19





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

provision of masonry insert and is shown in Fig.4

Figure. 14 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.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

occurrence in 40 kN load.

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 flexuralhinges 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 framefor stiffness values is shown in Fig.15

Figure:15: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

40kN at the junction of loaded side of the beam and

column at the bottom storey, where moment andshear 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 100 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



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.16).

both frames

on:artially-infilled frames f orf or

calculated and presented. Thecalcu s

ss with respect to load cycleith res

. For frame (1), it may beme ( e

decreases from 6.7KN/mm6.7

. KN/mm in twenty first cycle. KN rst cy

in stiffness takes place aftertiffne ter

n 40 kN load.kN l

(2), the initial sthe i

ainst .7 kNt .7 k

inedd

r

Figure:15:Stiffness degradigure:15:Stiffness

framera

iv) Behaviour and M n

a) Frame-1 withou a tho

First cracc

0kN at th0kN

olumnlumshear

si





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:

First crack observed (inclined downwards and

forwards) at only 75 kN, (against 40 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 Whileloading 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.17). At ultimate load of

195 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.17.Test frame 2 with failure in the bottomand drift of the top storey(Constructed atVLBJCET,

Coimbatore)

A crack in leeward column of the bottom storey atthe base was also observed (Fig.18). Separation of infill occurred at the tension corners and the highstress concentration at the loaded diagonal ends ledto early crushing of the loaded corners (Fig.19).Nocrack was developed in the columns, beams and in

the infill of top storey clearly depicting that theframe has failed only by hinges in columns due toshort column effect.

It is also evident from the propagation of cracks at

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

adjacent columns. This phenomenon is clearly

exhibits the development of strut action through

masonry insert.

s andan

for thethe

e beam and

storey where

maximum Whilem s were found towere

n beam junctions andnctions a

ated in the first (loaded)oaded)

l cracks were seen to flowc

infill. Separation of inf infill.

sion corners. Due to the presrners. e

onal cracks were observedwere

aded beam – column junctiad umn

y opposite corner, clearlyoppos rly

trut action (Fig.17). Ataction

stic hinge formatihing atitom storey justore

racks ws w

gure.17.Test frame 2 with failg id drift of the top storey(Constrift o the top store

oimbatoim

A crack in leeward coluhe base was also obsa s

infill occurred at thf il tstress concentratir c nto early crushio shrack wasrac

he infille inframee sho





Figure 18.crack in leeward Figure.19 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 usingANSYS-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.20 &21


Figure.20 Ultimate Deformed Shape of thesoftware Model For Frame 1


Fig.21 Ultimate Deformed Shape of thesoftware 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 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 acombined 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

05 KN , DeN ,

atee

Load – 195 KN , Doad – ,

Fig.21 Ultimatesoftwaro a

The results obte lts

10 for Fram1 m

xperimentaxp

TheTh





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 dissimilarbetween 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 introducingmasonry 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 framesis 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 75 kN

(nearly equal to experiemtnal value of 75

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 whencompared 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.

d

otho

cles iscles is

be noteded

frame with

uced whereas

or for both framesr fo

eloped in the leewardleewar

te to the loaded end) of thethe

ey at the base because of y a e

trut compression of the infillcomp h

e with masonry insert.asonry

partial-infilled RC frame faiRC fr

nges at the portion of columnges f col

o the gap in the bottom store gap or

tinct “captive columnt “cap um

with masonry inth mas

nd diagonadiagon

the lol

f

d thad th

poned wh

th masonry inseth ma

ial infill reduces thei fill re

rame leading to criticalm ng to

wever, this could be improvebe i

extent by the provision of masof maIn analytical study, it isis

sudden increase in deflen increa

shear of 40 kNshear of 40

experimental valua

(1) and affect

(nearly equae

kN) for)

initiatiiat

adja j

12)12





Cost/SqmSi.No Technique

External Internal

1 Introducing

masonry insertin 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), "Seismicshear 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”, AppliedTechnology 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.

icatiocatio

quake E

involving

construction

s must be given

ruction.tion.

dth of diagonal strutonal str

pproximately found to beto be

of the diagonal of infill.o l.

m width of insert based on twidth a

y be provided as described.vided .

w-Jeng Chiou, Jyh-Cherngng ChLiou,u, (1999)(19 , “Experimperi

f Masonry Infilledasonry

Engineering, Veering,

-111717

.R.

urthy (2005) on Key nu (200

uildings.uil


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