Department of Civil EngineeringINDIAN INSTITUTE OF SCIENCE

BANGALORE

STRUCTURAL MASONRY:PROPERTIES AND BEHAVIOUR

K S Nanjunda Rao

Research Team Publications

1.K S Jagadish

2.B V Venkatarama Reddy

3.G Sarangapani

4.S Raghunath

5.K S Gumaste

6.S M Manjunath

7.K S Nanjunda Rao

1.Materials & Structures (Rilem)

2.Masonry International3.Jl of Materials in Civil

Engg. (ASCE)4.Jl of Structural Engg.5.National & International

conferences

ConcreteGood in compression &

weak in tension,Brittle, Uni-modulus

Coarse and fine aggregates

and binder

Random, Isotropic

MasonryGood in compression

& weak in tension,Brittle, Bi-modulus

Masonry units and mortar

Orderly, Orthotropic

Behaviour

Composition

Distribution ofthe component

materials

Comparison of concrete and masonry

English bond Flemish bond Header bond

Stretcher bond Quetta bond Rat-trap bond

Different kinds of bonds adopted in practice

Different ways of reinforcing masonry

Prestressed masonry

Distribution of external load within masonry

In-plane loading Out-of-plane loading

Masonry is a composite construction consisting of:

• Masonry units

• Adobe (Sun dried mud blocks)

• Stone, Laterite blocks

• Burnt clay bricks

• Concrete blocks (solid or hollow)

• Calcium silicate bricks

• Stabilized mud blocks (SMB)

• Fly-ash gypsum blocks

• Mortar

•Mud mortar•Lime sand mortar•Cement, lime, sand mortar•Cement sand mortar•Composite mortars( cement,lime,soil,sand and additives)

• Reinforcement •Metallic•Non-metallic

Based on method employed in production, three varieties of burnt clay bricks are available in India viz.

• Country brick

• Table moulded brick

• Wire-cut brick

Properties of burnt clay bricks

1.Compressive strength

2.Water absorption

3.Initial rate of absorption (IRA)

4.Porosity and pore size

5.Stress-strain characteristics

Compressive strength& modulus of elasticity of

bricks

Properties of Bricks(Table moulded bricks of Southern Peninsular India)

Location No. of samples

Dry density(kN/m3)

Water absorption

(%)

IRAkg/m2/min

.

Soaking duration(minutes)

Compressive strength (MPa)

Bangalore (TMB1) 06 18.40 10.1 1.52 12 5.7

Bangalore (TMB2) 06 18.40 11.7 2.22 08 5.6

Bangalore (TMB3) 06 19.50 11.1 1.17 15 3.5

Bangalore (TMB4) 06 19.00 12.2 1.73 07 5.5

Bangalore (TMB5) 06 18.30 11.7 2.05 15 8.3

Harihar (TMH6) 02 17.50 12.5 2.10 15 -

Thrissur (TMK7) 02 18.70 15.4 1.90 20 -

Vijaywada (TMA8) 04 17.40 11.8 3.37 03 3.3

Vizag (TMA9) 04 16.90 10.1 3.35 03 6.8

Maharashtra (TMM10) 04 13.30 26.0 9.33 03 2.5

Maharashtra (TMM11) 04 16.10 22.0 6.97 05 5.2

Properties of Bricks (Contd.)Table moulded bricks of North India

Location No. of samples

Dry density(kN/m3)

Water absorption

(%)

IRA

kg/m2/min

Soaking duration

(minutes)

Compressive strength (MPa)

Ahmedabad(TMG12) 02 16.00 13.6 1.75 20 -

Jaipur (TMR13) 03 16.30 12.5 5.66 03 9.4

Patna (TMP14) 02 16.00 12.0 2.58 30 -

Jammu (TMJ15) 06 18.60 16.0 3.03 04 14.4

WIRE-CUT BRICKS OF SOUTH INDIA

Bangalore (WCB1) 06 17.30 17.3 1.39 45 23.0

Bangalore (WCB2) 06 18.80 14.4 1.52 45 15.7

Cannanore (WCK3) 06 18.40 17.0 1.25 60 18.5

Type 1 brick (TB1)Type 2 brick (TB2)

Porosity and pore size of burnt clay bricks

MortarsMortar is a homogeneous mixture of cementitious material/s, inert material/s and water that is produced at site for joining the masonry units. Mortar influences the strength, durability and resistance to rain penetration of masonry.

Some of the desirable properties of mortar for masonry construction

1. It should gain enough strength and harden in a reasonable time so that further courses of masonry can be laid without excessive racking movements of courses below.

2. The fresh mortar should have sufficient workability so that the mason can easily fill the joints.

3. It should have ability to retain water preventing its escape into masonry units.

Depending on the type of cementitious material used mortars can be broadly classified as;1. Lime mortar2. Cement mortar3. Composite mortar4. Lime- pozzolana mortar5. Soil-cement mortar

The word pozzolana generally means a mixture of amorphous silica and alumina, which can combine with calcium hydroxide at ambient temperatures in presence of moisture.

Typical sizes of prisms for compressive strength test

Stack bonded prism English bonded prism

Front view Side view Front view Side view

230 mm

460 mm

105 mm

12 mmmortar joint

230 mm

460 mm

230 mm

12 mm thick mortar joints

Typical sizes of wallettes for compressive strength tests

Stretcher bond wallette

English bond wallette

Mortar is stiffer than masonry unit(Indian condition)

mb EE ⟨mb EE ⟩

Masonry unit stiffer than mortar(Western condition)

Stresses in masonry under compression

td

bm σσ =

Masonry efficiency = η = Corrected prism strength brick strength

Compressive strength of brick masonry prisms

÷

Prism types (no. of prisms tested = 4)

Einitial tangent (MPa)

Esecant at 25 % σult (MPa)

σult(MPa)

Strain at σult

Masonry efficiency

Stack bonded, load normal-to-bed-joints 417.17 406.15 2.67 0.01088 0.43

½ brick thick wallettes, load normal-to-bed-joints 467.42 456.5 2.74 0.01123 0.44

½ brick thick wallettes, load parallel-to-bed-joints 1652.56 1486.36 1.308 0.00157 0.21

1-brick thick prisms, load normal-to-bed-joints 502.67 451.58 2.05 0.008 0.33

1-brick thick prisms, load parallel-to-bed-joints 1788.75 1615.40 1.62 0.002 0.26

Strength and elastic properties of masonry prisms and wallettes under compression(Wet strength of brick =6.25MPa, CM 1:6)

Strength and elastic properties of masonry prisms and wallettes under tension(Wet strength of brick =6.25MPa, CM 1:6)

Prism types (no. of prisms tested = 4)

Einitial tangent (MPa)

Esecant at 25 % σult (MPa)

σult (MPa) Masonry efficiency

Stack bonded, load normal-to-bed-joints

758.88 713.79 0.0414 0.32

½-brick wallette, load parallel-to-bed-joints

2496.32 2285.71 0.166 1.29

Specimens for tension testof brick masonry

Equivalent modulus of elasticity for brick masonry

(i) Perpendicular bed joints Prism type: (CM 1:6, type-1 bricks)

Normal-to-bed-joints

Stack bonded prisms

½ brick thick wallettes

417.17

467.42

758.88

758.88

1.82

1.62

-

597.22

550.27

586.83

Parallel-to-bed-joints

1652.6 2496.3 1.51 1944.92010.06

tEcEc

t

EE

VibflexE . eqE

(ii) Parallel to bed joints

2

1

4

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=

c

t

teq

EE

EE

Schematic diagram offlexural vibration test set-up

Data acquisition system

A/D converter

PC

Accelerometer

Wallette

1/2-brick thick wallette, stresses normal-to-bed-joints

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0 0.2 0.4 0.6 0.8 1

Time (s)

Dis

plac

emen

t (m

m)

response at top

response atmid-height

4nn mLEIC=ω

f2n πω =

C=3.516 for cantileverm is mass/unit length(kg/m)L is length in meterE is modulus of elasticityf is frequency in HzI is moment of inertia

Brick-mortar bond strength

Modified bond-wrench test setup

Shear-bond test setup

Bond enhancement techniquesType A: Cement slurry coatingType B: Epoxy coatingType C: Additional frogType D: Additional frog

Type C Type D

Concrete base

3.058.25

2.902.46

Type of brick

Compressive strength (MPa)

Secant modulus@ 25% Ult.Stress(MPa)

B1 10.67 509

B2 4.29 467

B3 3.17 485

Bond enhancing technique Shear bond strength (MPa)

Nil 0.054

Type A 0.138

Type B 0.265

Type D 0.131

Flexure bond strength of stack bonded prisms using wire-cut bricks

Mean compressive strength of brick = 23 MPa

Flexural bond strength(MPa)

Mortar

C:L:So:Sa

Mortar strength(MPa)

No. of joints tested

Range Average

Compressive strength(MPa)

Mode of failure

M1:1/2:0:4 12.21 10 0.22-0.52 0.414 10.0 Brick-mortar interface

M1:0:1:6 5.93 08 0.16-0.27 0.210 7.4 Brick-mortar interface

M1:0:2:5 7.60 06 0.10-0.22 0.149 6.9 Brick-mortar interface

M1:0:0:6 7.30 06 0.02-0.19 0.100 6.7 Brick-mortar interface

Relation between masonry compressive strength & Brick-mortar bond strength

Factors that influence masonry compressive strength

bonding

234.0778.0 )()(334.0 mb fff =

Hendry and Malek’s relationship

208.0531.0 )()(242.1 mb fff = for stretcher bonded walls

for English bonded walls

146.085.0 )()(225.0 mb fff =

134.086.0 )()(317.0 mb fff = for stack bonded prisms

for English bonded prisms

Stretcher bonded wall is stronger than English bonded wall

Relation between masonry compressive strength & Brick & mortar compressive strength

Crushing of table moulded bricks in English bonded wallettes :cement-soil mortar

Splitting and crushing of table moulded bricks inEnglish bonded wallettes : cement mortar

Bond failure in stack bonded Splitting failure in Englishprisms: cement-soil mortar bonded prisms: cement-lime

mortar

Splitting and diagonal shear failure in wallettes

Failure patterns in brick masonry prisms & wallettes

Modes of failure in 230mm thick English bonded wall:

table moulded bricks (Wall No.2).

Splitting, crushing of bricks and

Diagonal shear failure of wall

Hourglass type failure of bricks

Separation of the two leaves of the

wall

Back Face of the wall

Testing of storey height wire cut brick masonry wall

Designation Type* and strength of

brick

Mortar ProportionC:So:Sa#

Size of wall (mm)b x t x h

Wall strength(MPa)

Wallettestrength (MPa)

Wall strength

Wallettestrength

Wall No.1 TMB1 (5.7MPa) 1:0:6 (6.2MPa)

720 x 105 x 2770Stretcher bond 1.08 1.18 0.91

Wall No. 2 TMB1 (5.7MPa) 1:0:6 (6.4MPa)

970 x 230 x 2770English bond 1.32 1.35 0.98

Wall No. 3 WCB1 (23MPa) 1:1:6 (6.2MPa)

750 x 115 x 2770Stretcher bond 6.64 8.0 0.83

*TMB- Table moulded brick, WCB- Wire-cut brick. #C:cement, So:soil, Sa:sand. Values in parenthesis indicate average compressive strength.

÷

storey height masonry wall test results

Basic compressive stress (MPa)

Stress reduction factor

Area reduction factor

Permissible compressive

stress (MPa)

As per IS: 1905 - 1987

Safety Factor

Wall1 19.8 0.57 0.54 0.81 0.25 4.32

Wall 2 9.0 0.57 0.92 1.0 0.52 2.54

Wall 3 18.0 1.39 0.67 0.83 0.77 8.62

Designation Slendernessratio

Influence of axial stress on flexural bond strength of masonry

Collapse analysis of unreinforced masonry vault

Dimensions of vaultLength= 3m; Span=1.5mRise=0.52m; R=0.796mSemi-central angle=70 degreeThickness=0.075mCement:soil:sand mortar (1:10:8)

Experimental (N/m2)

FEM (N/m2)

14651 13734

Comparison of collapse load

Performance of Masonry Buildings during Earthquakes&

Earthquake Resistant Design Concepts for Masonry Buildings

Unreinforced masonry (URM) structures are the most vulnerable during an earthquake due to the following reasons:

•Brittle nature of URM•Large mass of masonry structures•Large initial stiffness•Large variability in masonry material properties

The breakdown of earthquake fatalities by cause for each half of the last century indicates that 75% of the fatalities are due to collapse of buildings.

(Coburn and Spence, 2002)

From the above it is clear that collapse of masonry buildings is the primary cause for loss of life during an earthquake

BIS CODAL PROVISIONS: IS: 4326-1993

• HORIZONTAL RC BANDS AT LINTEL AND ROOF LEVELS

• VERTICAL STEEL AT CORNERS, JUNCTIONS AND DOOR & WINDOW JAMBS

Details of providing vertical steel bars in brick masonry as per IS 4326:1993

It is always useful to study the behaviour of masonry buildings after an earthquake as it gives an insight into the performance of various kinds of masonry materials used and earthquake resistant features adopted in the buildings. Following slides shows photographs of failure patterns of masonry buildings observed after Latur and Kachchhearthquakes of 1993 and 2001 respectively

Plate 1: Out-of plane collapse of wall of a school building (Sastur)

Plate 2: Timber post supported wall of a shop building intact after earthquake (Sastur)

Out-of-plane collapse of sandstone in lime mortar masonry wall (MORBI)

House with lintel band and columns (SAMAKHYALI)

Separation of corner column

from the neighbouring

masonry (SAMAKHYALI)

Out-of-plane failure of wall leading to collapse of lintel band (BHUJ)

Corner failure in presence of corner reinforcement

(BHUJ)

Rigid box like behaviour above lintel band (BHACHAU)

Collapse of walls between openings (KHAVDA)

Wall flexure – RC roof on stone-in-CM

(Lodhrani)

Following typical types of damage can be identified from the earthquake survey

•Cracks between walls and floor•Cracks at corners and at wall intersections•Out-of –plane collapse of perimetral walls•Cracks in spandrel beams•Diagonal cracks in structural walls•Partial disintegration or collapse of walls•Partial or complete collapse of building

Figure below shows the deformation and typical damages suffered by a simple masonry building subjected earthquake ground motion.

Fundamental mode shape of building without roof, with openings

Fundamental mode shape of building with roof and openings

STRESSES IN MASONRY WALLS DURING EARTHQUAKE GROUND MOTIONS

Figure 1: Buildings without roof (a) without bands (b) with RC lintel and roof bands

(a) (b)

Figure 2: Building with RC roof and lintel band

Cross wall

Shear wallB1B2

B3

Table 1: Details of finite element analysis

Parameter Property

Size of cross-wall (height x length)

Size of shear-wall (height x length)

3.0m x 6.0m; one cross-wall with a door and a window opening, other cross-wall with two window openings3.0m x 3.0m; no openings in shear-walls

Masonry 0.23m (1 – brick thick); table moulded burnt bricks of Bangalore; mortar: CM 1:6

Reinforced concrete RC lintel and roof bands: 0.15m thick; 0.23m wide; RC slab: 0.15m thick

Boundary conditions Base clamped

Masonry properties [5]Modulus of elasticity normal-to-bed-joints (Ey)Modulus of elasticity parallel-to-bed-joints (Ex)Modulus of rigidity (Gxy assumed)Poisson’s ratio (ν, assumed)Flexural strength normal-to-bed-jointsFlexural strength parallel-to-bed-jointsShear strength [9]Density

600.0 MPa1800.0 MPa800.0 MPa0.20.137 MPa0.36 MPa0.06 MPaMasonry: 2000.0 kg/m3

Dynamic analysis Linear transient dynamic analysis (base acceleration input); no. of modes chosen: 10

Element adopted Masonry:4 noded orthotropic shell element, each node having 6 d-o-fRC lintel and roof band:2 noded 3d beam element, each node having 6 d-o-fRC roof:4 noded orthotropic shell element, each node having 6 d-o-f

Table 3: Details of earthquakes used as input

Earthquake Details

EQ-1 Kangra earthquake, Himachal Pradesh, India; date: 26th April 1986; 3.05 IST; total duration: 20.08s; PGA: 0.248g at 3.04s; median frequency: 5.86Hz

EQ-2 Koyna earthquake, Maharashtra, India; date: 10th December 1967, longitudinal component; total duration: 10.33s; PGA: 0.613g at 3.85s; median frequency: 11.86Hz

EQ-3 Koyna earthquake, Maharashtra, India; date: 10th December 1967, transverse component; total duration: 10.33s; PGA: 0.473g at 3.13s; median frequency: 12.43Hz

Table 2: Natural frequencies (Hz) of buildings

Mode no.

Buildings without roof Building with roof

B-1 B-2 B-3

1 6.43 8.17 14.87

2 6.88 9.05 17.11

3 14.01 18.61 18.95

4 15.92 20.12 20.03

Table 4: Results of stress analysis

Building type*

Maximum flexural stress (MPa) σx at top edge of

cross-wall (parallel-to-bed-joints)

Maximum flexural stress (MPa) σy at base of

cross-wall (normal-to-bed-joints)

Maximum shear stress (MPa) τyz at the base of

shear-wall

EQ-1 EQ-2 EQ-3 EQ-1 EQ-2 EQ-3 EQ-1 EQ-2 EQ-3

B-1 0.42 0.368 0.302 0.113 0.12 0.092 0.09 0.09 0.078

B-2 0.14 0.163 0.158 0.156 0.192 0.18 0.095 0.132 0.121

B-3 0.032 0.062 0.055 0.12 0.242 0.186 0.14 0.208 0.172

* B-1, B-2 : Buildings without roof; B-3: Building with roof

Regions of maximum flexural stress for buildings without roof (a) σx (b) σy

Regions of maximum flexural stress for buildings with roof (a) σx (b) σy

Regions of maximum shear stress in shear-walls (τ)

Behaviour of URM wall subjected to vertical and out-of-plane lateral load

CONTAINMENT REINFORCEMENT AS AN EARTHQUAKE RESISTANT FEATURE

• Should always be accompanied by horizontal RC bands

• ‘Containment reinforcement’ is a vertical reinforcement provided on both faces in a parallel manner. It may be either on the surface or hidden in 3.0 cm grooves beneath the surface

• It is generally provided every 1.0m in the horizontal direction and also next to door and window jambs

(a) Un-reinforced (b) core-reinforced (c)Containment reinforcement

Containment reinforcement in grooved blocks

• Reinforcement on both faces to be held by ties going through the wall in alternate courses or once in 3 courses

• Following materials are possibleGI wire – 3.0 to 4.0 mmCorrosion resistant steel ~ 6.0mmStainless steel – 3.0 to 4.0 mmBambooTimber

• Function is to prevent growth of flexural cracks

• Experiments show good flexural ductility

Masonry building with horizontal bands and ‘Containment reinforcement’

Testing of masonry beams with containment reinforcement

0

200

400

600

800

1000

1200

1400

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

curv ature (/m)

mom

ent (

Nm

)

RB-11

RB-12RB-13

RB-14

1st crack

Specimen details Curvature ductility(/m)

1-brick thick2 x 6mm MS

22.512.6112.0

1-brick thick2 x 3.16mm GI

12.2111.2313.0716.4

17.0923.2411.4224.6017.3412.8810.69

½-brick thick2 x 3.4mm GI

½-brick thick2 x 3.7mm GI

Shock table testing

• Quick evaluation of earthquake resistant features using simple impacts

• Developed in 1956 at Roorkee, used at Omerga/Latur for model testing

• Pendulum impact method also developed at I.I.Sc

• Tests at I.I.Sc, Bhuj, BMS College of Engg.

Construction of one fourth scale masonry building models

Acceleration response: Impact number 4SHOCK TABLE RESPONSE

-2

-1

0

1

2

3

4

5

0 1 2 3 4

TIME (Sec)

AC

CE

LER

ATI

ON

(m/S

ec2 )

RESPONSE OF CONTAINMENT REINFORCEMENT MODEL AT TOP

-3-2-1012345

0 1 2 3 4

TIME (Sec)

ACC

ELER

ATI

ON

(m/S

ec2 )

RESPONSE OF BIS MODEL AT TOP

-1.5-1

-0.50

0.51

1.52

2.53

0 1 2 3 4

TIME (Sec)

AC

CEL

ER

ATIO

N (m

/Sec

2 )

RESPONSE OF CONTAINMENT REINFORCEMENT MODEL AT MIDDLE

-3

-2

-1

0

1

2

3

0 1 2 3 4

TIME (Sec)

AC

CE

LER

ATI

ON

(m/S

ec2 )

(873 cm/sec2)

Near-fault ground motion record of an earthquake

FREQUENCY REDUCTION AFTER SUCCESSIVE IMPACT

Impact no.

BIS modelpeak frequency in Hz

Containment reinforcement model peak frequency in Hz

1 40.039 64.822 30.273 52.0023 19.531 36.6214 11.475 27.4665 8.545 20.2646 7.08 12.5737 - 10.018 - 7.5689 - 6.10410 - 5.12711 - 5.12712 - 2.9313 - 3.05214 - 2.808

CONTACT DURATIONWith mass Without mass

Pendulum side Rebound side Pendulum side Rebound side

Contact duration in

milli-secondsAvg.

Contact duration in

milli-secondsAvg.

Contact duration in milli-seconds

Avg.

Contact duration in milli-seconds

Avg.

10 45 173 44 132

10 44 144 38 119

10 42 133 41 116

20 25 87 32 99

20 23 85 30 83

20 24 88 30 78

30 21 77 _ _ _ _

30 21 80 _ _ _ _

30 21 80 _ _ _ _

79.021.0

86.6730.6786.6724.0

122.3341150.043.67

Angle of release of pendulum

Model

BeforeTest

Containment reinforcement

After Test

Shock table test results

Model Energy input Final state

Un-reinforced 135.0 Nm Collapse

Model with horizontal bands

671.0 Nm Partial collapse

Model with horizontal bands and ‘Containment reinforcement’

1967.0 Nm Not collapsed, but with a number of cracks

Our sincere thanks to

1.Shanthakumar2.Arogiaswamy3.Vasudevan4.Sagairaju5.Raghavendra6.Muniraju

and all others who have directly or indirectly helped us in conducting the experimental

investigations

THANK YOU