mechanical properties of masonry samples · pdf file15th international brick and block masonry...

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

MECHANICAL PROPERTIES OF MASONRY SAMPLES FOR

THEORETICAL MODELING

Sayari Arash

PhD, Assistant Professor, Islamic Azad University, Sanandaj Branch, Iran, [email protected]

ABSTRACT Due to different geometries and material properties, masonry is considered as an anisotropic

composite material. Mechanical properties of the masonry walls are very important

parameters that affect the behaviour of masonry walls under loading.

The mechanical properties of masonry are more complicated than mechanical properties of

other construction materials. Elastic modulus (or Young’s modulus) is one of the most

important parameters in determination of the stiffness of structural elements prior to cracking

and is calculated according to the linear part of stress-strain curves. In addition, in order to

develop the theoretical modelling, mechanical properties including elastic modulus (Young’s

modulus) and compressive strength must be taken into account.

In this research, different experiments are designed to measure the elastic modulus and

compressive strength of masonry and mortar samples. The results are compared with the

published results in this subject area.

Keywords: Masonry, Mechanical properties, Elastic modulus, compressive strength

INTRODUCTION

Masonry is considered as an anisotropic composite material because of different geometries

and material properties of masonry, including: shape of units (bricks/blocks), dimensions of

units, perforations, slenderness ratio, strengths of materials, modulus of elasticity of materials,

water absorption, etc. (Zilch et al., 2001).

The mechanical properties of masonry are more complicated than mechanical properties of

other construction materials (Velazquez-Diams et al., 2000 and 1998). Elastic modulus (or

Young’s modulus) is one of the most important parameters in determination of the stiffness of

structural elements prior to cracking and is calculated according to the linear part of stress-

strain curves. According to Wolde-Tinsae et al. (1993), elastic modulus of masonry walls is

not related to properties of brick units, mortar joints, grout or h/t ratio (of samples)

individually; but is a function of all of mentioned parameters. Woulde-Tinsae concluded that

it is the best option to calculate the value of elastic modulus according to the compressive

strength of masonry samples, because compressive strength is also influenced by mentioned

parameters.

According to EC6, the compressive strength and elastic modulus of masonry samples should

be determined from either results of or in the absence of tests in terms of equations 1 and 2 as

below:

= K. .

(1)


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Where:

is characteristic compressive strength of masonry [N/mm²];

K: is a constant, which is a function of the type of masonry units and mortar

is normalised average compressive strength of units [N/mm²];

is average compressive strength of mortar [N/mm²];

and : are constants, for general purpose mortar =0.7 and =0.3

and

E= . (2)

Where:

E: is modulus of elasticity of masonry [N/mm²];

: is a constant equal to 1000 according to UK National Annex to EC 6;

is characteristic compressive strength of masonry [N/mm²];

For the linear and elastic behaviour of masonry walls, equivalent modulus of elasticity is a

function of physical and mechanical characteristics of brick and mortar (Francis et al., 1971)

given in equation 3:

=

+

+ 2

(

+

) (3)

=

, =

(4)

Where is the elastic modulus of masonry; and are the thicknesses of mortar and

brick, respectively; and are elastic modulus of mortar and brick respectively; and

are the Poisson’s ratio of mortar and brick, respectively

According to Farshchi (2008) for the lateral loading on masonry walls, elastic modulus can be

calculated from equation 5.

=

(5)

Where:

: Elastic modulus of mortar = 30× compressive strength of mortar;

Elastic modulus of brick = 125× compressive strength of brick;

: Elastic modulus of masonry sample;

: Thickness of brick units;

: Thickness of mortar joints;

ICBO (1991) recommended the equation 6 for calculation of the elastic modulus of masonry

walls.

= 750 (6)


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Where:

: Elastic modulus of masonry;

: Compressive strength of masonry walls;

According to the above discussion, different researchers suggested different amount for

mechanical properties of the masonry samples. In this research, different experiments are

designed to measure the elastic modulus of masonry and mortar samples. In addition,

according to direct relation between compressive strength and the elastic modulus,

compressive strength of these samples is also measured.

TEST SET UP FOR MEASUREMENTS OF ELASTIC MODULUS AND COMRESSIVE

STRENGTH

Three different categories of samples were constructed for measurement of the elastic

modulus and compressive strength as below (Photo 1):

۰ Masonry cubes of 215mm×215mm×215mm dimensions.

۰ Mortar cubes of 100mm×100mm×100mm dimensions.

۰ Mortar cylinders with diameter equal to 150mm and height equal to 300mm.

Masonry cubes Mortar cubes Mortar cylinders

Photo 1: Samples used for experimental study

According to UK National Annex (NA to BS EN 1996-1-1:2005) three types of mortar M2,

M4 and M6 were used for production of the masonry and mortar samples (Table 1). The

cement type was Portland cement and the type of lime was Hydraulic lime.

Table 1. Different types of mortars (Table 2 of UK National Annex to EC6)

a) MASONRY CUBES The frog type of London brick (Hanson, 2010) and Ibstock brick were used for construction

of the masonry cubes. Nine masonry cubes were constructed in the material laboratory with

three different types of mortars (M2, M4 and M6) and two different types of bricks (Table 2).

The thickness of the mortar layers between bricks rows was nominal 10mm.


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To check possible variation of compressive strength, the masonry samples constructed from

London bricks are tested at two different ages (40 days and 4 months). For Ibstock it was

decided to use 4 months period of curing.

Table 2. Detail of the masonry samples No. Of

Sample

Brick type Mortar Ratio (Sand;

Cement; Lime)

Mortar type

according to EU6

Curing period

(Day)

1 London Brick 6,1,1 M4 40



4 Ibstock 8,1,0 M2 115

5 Ibstock 4,1,0 M6 115

6 Ibstock 6,1,1 M4 115




All samples were checked to have a horizontal surface using a bubble level. After the

construction of each sample, it was left for more than 28 days to allow for curing and to

achieve its maximum design capacity.

Two different tests were performed for each masonry sample: direct measurement of elastic

modulus and measurement of uni-directional compressive strength.

In order to directly measure the elastic modulus of masonry samples, three pairs of bases for

DEMEC gauges with 150 mm distance were attached to each sample using a special glue

(Photo 2). Before attaching the bases to the samples, exact position of bases on the samples

were indicated and using a steel brush loose and uneven areas were removed from the location

of the DEMEC bases, and all dust was removed using a vacuum cleaner.

Photo 2. Attaching DEMEC bases to a sample

After curing of the glue joining DEMEC bases to the sample, axial compressive load with the

rate of 1kN/sec was applied to each sample. The load was applied in the steps of 10 kN,

distributed on the surface of the sample. After each step of loading, the displacements were

measured using a DEMEC gauge.

53 mm 54 mm

150 mm


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For all cubic masonry samples in Table 2, compressive strength was measured using a

compression-testing machine. The load was applied at the same rate as before to the

horizontal surfaces of the samples.

b) MORTAR CYLINDERS

Due to the required information for calculation of the elastic modulus of masonry according

to equation 3 and equation 5 it has been decided to conduct additional testing of cylinder

mortar samples.

Three mortar cylinders were constructed with type M4 of mortar (sand 6; lime 1; cement 1).

All samples were checked to have a horizontal surface using a bubble level. After

construction of each sample, it was left for more than 28 days for curing and developing its

design capacity.

Two different tests were performed on each sample: direct measurement of elastic modulus

and measurement of uni-directional compressive strength.

In order to directly measure the elastic modulus of mortar samples, axial compressive load

with the rate of 1kN/sec was applied to each sample. The load was applied in the steps of 10

kN, distributed on the surface of the sample. After each step of loading, the deformation was

measured using a mechanical strain gauge attached to the sample.

For all samples, the compressive strength was measured using a compression-testing machine.

The load was applied at the same rate as before to the horizontal surface of the samples.

c) MORTAR CUBES

Twelve mortar cubes (100mm×100mm×100mm) were constructed with three different types

of mortars. Six samples were of type M4, three of M6 and three of M2 (Table 3).

To check possible variation of compressive strength, the cubic samples constructed from type

M4 of mortar are tested at two different ages (40 days and 4 months). For types M2 and M6

of mortar, it was decided to use 4 months period of curing.

Table 3. Detail of the mortar cubes

No. of

Samples

Mortar Rate (Sand,

Cement, Lime)

Mortar type

according to EU6

Curing period

(Day)

1 6,1,1 M4 40

2 6,1,1 M4 40

3 6,1,1 M4 40

4 6,1,1 M4 115

5 6,1,1 M4 115

6 6,1,1 M4 115

7 4,1,0 M6 115

8 4,1,0 M6 115

9 4,1,0 M6 115

10 8,1,0 M2 115

11 8,1,0 M2 115

12 8,1,0 M2 115


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For all samples in Table 3, the compressive strength was measured using a computerised

compressive testing machine. The load was applied at the rate of 1 kN/sec on the horizontal

surface of the samples. ANALYSIS OF THE RESULTS OF MASONRY SAMPLES For the samples that were constructed from London bricks and mortar type M4, the average

elastic modulus is 3750 N/mm² (Figure 1). In addition, the average value for compressive

strength for these samples is 3.7 N/mm² (Figure 2). Masonry sample with 4 months curing

had 6% higher strength in comparison to the average strength of the samples with 40 days

curing.

Figure 1. Elastic modulus of masonry samples (London Brick, Mortar M4)

Figure 2. Compressive strength of masonry samples (London Brick, Mortar M4)

Average value of elastic modulus and compressive strength of different masonry samples

obtained from the experimental study are presented in Table 4.

The results show that elastic modulus and compressive strength of masonry samples

constructed with London bricks and mortar type M6, are larger than those of other masonry

3765.2 3722.2 3675.4 3842.3

0

1000

2000

3000

4000

Sample 1 Sample 2 Sample 3 Sample 4

Elas

tic

mo

du

lus

(N/m

m²)

London Brick, Mortar M4

3.7 3.5

3.7 3.8

0

1

2

3

4

Sample 1 Sample 2 Sample 3 Sample 4

Co

mre

ssiv

e s

tre

ngt

h(N

/mm

²) London Brick, Mortar M4

Average=3751.3 N/mm²

Average=3.7 N/mm²

N/mm²


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samples. In addition, the masonry samples constructed with London bricks and mortar type

M2, showed the lowest elastic modulus and compressive strength compared to the other

masonry samples.

Table 4. Elastic modulus and compressive strength for masonry samples (Test)

Bricks Mortar Elastic modulus (N/mm²) Compressive strength (N/mm²)

London brick M4 3750 3.7

Ibstock M2 3148 3.0

Ibstock M6 4977 5.1

Ibstock M4 3780 3.6



ANALYSIS OF THE RESULTS OF CYLINDER MORTAR SAMPLES

The average value for elastic modulus and compressive strength of cylinder mortar samples

(M4) are 2870 N/mm² and 3.6 N/mm², respectively (Figures 3, 4).

Figure 3. Elastic modulus of mortar cylinders (Mortar M4)

Figure 4. Compressive strength of mortar cylinders (Mortar M4)

ANALYSIS OF THE RESULTS FOR CUBIC MORTAR SAMPLES

For three different types of mortars M2, M4 and M6; the average uni-directional compressive

strengths for cubic samples are presented in Figures 5 to 7 and Table 5.

2906.6 2878 2827.9

0

1000

2000

3000

4000

Sample 1 Sample 2 Sample 3

Elas

tic

mo

du

lus

(N/m

m²)

Cylinder, Mortar M4

3.6 3.6 3.6

0

1

2

3

4


Co

mp

ress

ive

str

en

gth

(N

/mm

²)

Cylinder, Mortar M4

Average=2870.8 N/mm²

Average=3.6 N/mm²


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Figure 5. Compressive strength of cubic mortar samples (Mortar M4)



Table 5. Compressive strength of cubic mortar samples (Test)

Mortar Compressive strength, N/mm²

M6 5.0

M4 3.65

M2 2.6

3.6 3.6 3.6 3.7 3.7 3.7

0

1

2

3

4

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6

Co

mp

ress

ive

stre

ngt

h (

N/m

m²)

Cubic samples, Mortar M4

4.9 5 5

0

1

2

3

4

5


Co

mp

ress

ive

stre

ngt

h

(N/m

m²)


2.6 2.7 2.6

0

1

2

3


Co

mp

ress

ive

stre

ngt

h (

N/m

m²)


Average=3.65 N/mm²

Average=5.0 N/mm²

Average=2.6

N/mm²


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Comparision of the above results show that mortar cubes M6 have higher value of

compressive strength than other cubic samples.

APPLIED ELASTIC MODULUS For calculation of the elastic modulus of masonry according to Francis (1971) in the equation

3 and Farshchi (2008) in the equation 5, the value of elastic modulus for mortar is assumed to

be 2870.8 N/mm² which is the estimated value from our experiments. In addition, value of

elastic modulus for the brick according to Farshchi is assumed to be 125 times of the

compressive strength of the brick. As the compressive strength of London brick is 25 N/mm²

(Hanson, 2010), thus elastic modulus of this type of brick is equal to 3125 N/mm².

The elastic modulus for masonry walls (constructed from London bricks and mortar type M4)

achieved from different sources is presented in Table 6.

Table 23. Elastic modulus of masonry from different sources

Source Elastic Modulus of masonry, E (N/mm²) Equation

Direct measurement

(Figure 1)

3750 -

EC6 E= 1000. = 1000×3. 7= 3700 2

ICBO (1991) = 750 750×3.7= 2775 6

Francis

(1971)

=

+

+2

(

+

)

E= 6960

3

Farshchi

(2008)

=

E= 3605

5

The elastic modulus measured in this research is closest to the one calculated by equation

suggested by EC6 (Figure 8).

Figure 8. Comparison of the elastic modulus from different sources for masonry samples

3750 3670

2722

6960

3605

0

1000

2000

3000

4000

5000

6000

7000

8000

Direct measurment

EC 6 ICBO (1991) Francies (1971)

Farshchi (2008)

Elas

tic

mo

du

lus

(N/m

m²)

Source


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CONCLUSION

The main results of this study are summarised as follows:

1. Estimation of elastic modulus for masonry samples and mortar is confirmed to be

close to the suggested values from EC6.

2. The results for ultimate compressive strength of the mortar M4 via cylinders and via

cubes are almost identical which is different from testing of corresponding concrete

samples.

REFERENCE

۰ EC6, EN 1996-1-1:2005 Eurocode 6, (2005). Design of masonry structures-Part 1-1:

General rules for reinforced and unreinforced masonry structures. CEN.

۰ Farshchi, D.M., Motavali, M., and Marefat, M.R., (2008). A theoretical investigation

on the seismic retrofitting of historical masonry buildings using FRP post-tensioned

systems. PhD thesis, Tehran university.

۰ Francis, A.J., Horman, C.B., and Jerrems, L.E., (1971). The effect of joint thickness

and other factors on the compressive strength of brickwork, proceeding of the 2ed

international brick masonry conference, H.W.H. west, ed, British Ceramic Association,

Stoke on Trent, 31-37, UK.

۰ Hanson, (2010). “Guide to London Brick.”, Available at

<http://www.ribaproductselector.com/Docs/9/04729/external/COL604729.pdf?ac=>

[Accessed on 10, September 2010], Hanson building products.

۰ ICBO Evaluation Services, Inc., (1997). Acceptance criteria for concrete and

reinforced and unreinforced masonry strengthening using fibre reinforced composite

system. ACI 25-R2-0497 (BCG/BNH), International conference of building officials,

Whittier, California.

۰ UK National Annex to Eurocode 6, (2005). Design of masonry structures – Part 1-1:

General rules for reinforced and unreinforced masonry structures. (NA to BS EN 1996-

1-1:2005).

۰ Velazquez-Dimas, J.I., Ehsani, M. R., and Fellow, (2000). Modelling out-of-plane

behaviour of URM walls retrofitted with fibre composites. Journal of composites for

construction, November 173.

۰ Velazquez-Dimas, J.I., (1998). Out-of-plane behaviour of URM walls retrofitted with

fibre composites. PhD Thesis, Faculty of civil engineering and engineering mechanics,

The University of Arizona, USA.

۰ Wolde-Tinsae, A.M.R., Atkinson H., and Hamid A. A., (1993). State-of-the-Art

Modulus of Elasticity of Masonry. In Proceedings of Sixth North American Masonry

Conference. The Masonry Society. Boulder, Colorado. USA.

۰ Zilch, K., Schatz, M., (2001). Masonry construction manual. Published by institute fur

international architektur documentation GmbH, Munich, pages 92-95.

mechanical properties of masonry samples · pdf file15th international brick and block masonry...

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