BY

HEMANTH KUMAR M.N

UNDER GUIDANCE OFUNDER GUIDANCE OF

Smt MANGALA KESHAVASmt MANGALA KESHAVA

Asst. Professor, Dept of civil Engineering, BMSCEAsst. Professor, Dept of civil Engineering, BMSCE

FLEXURAL AND SHEAR STRENGTH OF HOLLOW CONCRETE BLOCK MASONRY PRISMS UNDER

NORMAL STRESS

INTRODUCTION

• Masonry may be defined as an assemblage of masonry units along

with mortar laid in a predetermined orientatation..

• Concrete block masonry is the versatile material of today’s construction industry because Concrete blocks having good

• thermal properties

• compressive strength

• resistance to chemical attack

• Earthquake resistance

• durability

• Concrete masonry units are used for load-bearing and Non-load bearing walls.

IMPORTANT FEATURES OF BLOCK MASONRY CONSTRUCTION

It ensures rapid construction

Fewer joints are constructed and hence saves mortar

The true plane surface does not require plastering

It can be used for both load bearing and non load bearing walls

Classification of concrete blocks as per IS-2185-part-

I(1979)Mainly 2 classifications.

Hollow ( Open or Closed Cavity Concrete Blocks) have core area greater than 25%, but not greater than

40%. Sub classification of Hollow blocks

Grade A- min. block density-1500 kg/m3 , compr .strength of 3.5,4.5,5.5,7.0 N/mm2 @ 28 D

Grade B- block density- 1000-1500 kg/m3 , compr .strength of 2.0,3.0,5.0 N/mm2 @ 28 D

Grade C- block density- 1000-1500 kg/m3 , compr .strength of 1.5 N/mm2 @ 28 D.

Grade D- block density not less than 1800 kg/m3 compr .strength of 4.0,5.0 N/mm2 @ 28 D.

APPLICATIONS

Masonry is commonly used for the walls of buildings,

retaining wallsGarden wallsChimney Piers

TYPES OF MASONRYSTONE MASONRY

BRICK MASONRY

BLOCK MASONRY

REINFORCED MASONRY

STONE AND BRICK MASONRY STRUCTURES

CONCRETE BLOCK MASONRY STRUCTURES

HOLLOW CONCRETE BLOCK MASONRY CONSTRUCTION

EARLIER STUDIES ON MASONRYRaghunath etal (2003) reported the flexural

strength of TMB was in the range of 0.36 MPa to 0.53 MPa .Also the flexural bond strength of TMB prisms with cement mortar 1:6 was 0.088Mpa

Atul kumar(2009) conducted the flexure tests on SCB prisms under normal stress

It was concluded that with increase in normal stress the flexural strength also increased

The shear test was conducted on SCB triplet specimens under normal stress

It was concluded that their was increase an shear strength with increase in normal stress

OBJECTIVE OF PRESENT INVESTIGATION

TO EVALUATE COMPRESSIVE STRENGTH OF HOLLOW BLOCK MASONRY PRISMS

TO EVALUATE THE FLEXURAL STRENGTH AND SHEAR STRENGTH OF HOLLOW BLOCK MASONRY UNDER VARYING NORMAL STRESS.

Dimensionality test Dry density test Water absorption test Initial rate of absorption test Compressive strength Modulus of Elasticity

Compressive strength of mortar

PRELIMINARY TESTS Hollow concrete blocks

Mortar

DIMENSIONALITY TEST

Sl. No Total measurein mm

Average measurein mm

1. 8050 402.500

2. 3000 150.000

3. 3980 199.000

Twenty hollow concrete blocks were selected at random from the samples as per IS: 2185-(part-I) 1979 . The overall length, breadth, height of blocks were measured with steel tape

.

The avg dimensions of block were 402*150*199mm.

DIMENSIONALITY TEST

COMPRESSIVE STRENGTH OF BLOCK

IS: 2185-(part-I) 1979 gives the compressive strength of concrete blocks both to be used for load bearing and non-load bearing walls.

As per IS:2185-(part-I)1979 value of compressive strength of hollow blocks ranges from 2-7 Mpa.

Compressive = Failure Load . Strength Area of Sample

The Average compressive strength of block is 6.10N/mm2.

DRY DENSITY

The test was carried out as per IS:2185-1979(part-I).

Formula= Dry Weight

Volume of Block

The average dry density of hollow concrete block is

1.155 g/cc.

WATER ABSORPTION

Water absorption test was conducted on the concrete block samples as per the IS: 2185 (part I) - 1979, appendix D. the water absorption of any unit shall not be more than 10 percent by mass

Water Absorption = Wet Weight – Oven Dry Weight . X 100

Oven Dry Weight

The average water absorption of block is 5.33%.

INITIAL RATE OF ABSORPTION

In a plastic tray, distilled water was filled up to a depth of 2.5cm from the bottom of tray.

IRA = Wet Weight – Dry Weight X 1min.

Area of Sample

The average IR of block is1.75 kg/m2/min

MODULUS OF ELASTICITY

Modulus of elasticity of any material is the ratio of linear stress to linear strain within elastic limit. It is also known as “Young’s modulus” and represented by “E” and its unit is N/mm2

MOE=5898Mpa

NORMALIZED STRESS V/S STRAIN CURVE FOR HOLLOW CONCRETE BLOCK

MASONRY

FLEXURAL STRENGTH OF HOLLOW BLOCK

The flexural strength of the concrete block was computed as given by “Dayarathnam P. in ‘Brick and Brick Masonry Structures’ (1987)”. This test gives the strength of the hollow concrete block against the bending load.

[ Flexural strength= (3PL) / (2bd2) ]

The average flexural strength of block is 1.87N/mm2

COMPRESSIVE STRENGTH OF MORTAR

28 days compression strength of 70.6X70.6X70.6mm size mortar cubes of 1:6 cement sand ratio with a W/C ratio of 1.2.

The average compressive strength

of mortar was obtained after testing

6 cubes (IS:2250-1980)

The average compressive strength of

Mortar is 10.13MPa

EXPERIMENT PROGRAMME

COMPRESSION TEST ON HOLLOW CONCRETE BLOCK PRISMS

•

Compressive strength Elastic modulus Stress- Strain relation ship Masonry efficiency

The main objective was to evaluate the basic properties like :

CASTING OF PRISMS

PRESENT EXPERIMENTAL DETAILS

From this experiment the compression strength was obtained.

The specimen was cast with a CM of 1:6 & W/C ratio 1.2

Four hollow concrete block prisms of dimension (400*150*673)mm

The loads were applied using hydraulic jack

Digital dial gauge was fixed on the prisms for taking strain measurements

LOADING FRAME DETAILS

The prism specimens were constructed on the loading platform of the loading frame of 2000KN capacity having a clear dimension of 3.0Mts x1.75 Mts. As shown in figure.

Accessories for loading

•Hydraulic jack

•Hydraulic pump

•Proving ring 50T Capacity (LC=0.9206kN)

•Digital dial gauge with stand(LC=0.001mm)

OBSERVATIONS OF THE PRISMS DURING TEST

observed Failure pattern (vertical cracks front side)

Vertical cracks propogated from top to

bottom course ,Bond failure.

Observed Failure pattern (vertical cracks- side side)

OBSERVATION AND TABULATION• Wet Compressive Strength =Failure load(P) / (Area of specimen in mm2)

• Corrected compressive strength= wet compressive strength x correction factor(from IS-1905-1987-TABLE-12)

• Stress= Load(P) / (Area of specimen in mm2)

• Strain= Difference in length (mm) / original length (mm).

•Masonry efficiency (%) = Compressive strength of prism/compressive strength of unit

Compressive strength of prisms

specimen Dimension in mm

Maximum failure load in

kN

Wet compressive strength in

MPa

h/t ratio Correction factor

Corrected compressive strength in

MPa

1 400x150x673 240 4.00 4.48 1.33 5.32

2 400x150x673 230 3.83 4.48 1.33 5.10

3 400x150x673 230 3.83 4.48 1.33 5.10

4 400x150x673 220 3.67 4.48 1.33 4.88

Average compressive strength = 5.1MPa

(REF IS:1905-1987)

Results of Modulus elasticity and Masonry efficiency of prisms

Specimen Corrected compressive strength(MP

a)

Modulus of Elasticity

(MPa)

Masonry Efficiency

(%)

1 5.32 6868 87

2 5.10 6855 83

3 5.10 6515 83

4 4.88 6047 80

Mean compressive

strength = 5.1

Normalized value= 6535

Overall efficiency =83.25

NORMALIZED STRESS V/S STRAIN CURVE OF HCB MASONRY

TEST ON HOLLOW CONCRETE BLOCK PRISMS FOR FLEXURE AND SHEAR UNDER NORMAL STRESS

TEST DETAILS FOR FLEXURE Flexural strength of a masonry is its capacity to restrain the

transverse/lateral loads.

Nine hollow concrete block prism specimens of dimension

400mm*150mm*673mm were cast for the experiment

End condition - hinged

loading arrangement – 2 point loading

The loads were applied using screw jacks

The normal stress applied on prisms were 0.125, 0.20, 0.40, (MPa).

EQUIPMENTS USED

Fabricated hinge (2 no’s)

Props (1 no’s)

Screw jack (2 no’s)

Proving ring of 10T & 50T capacity

Two-point loading arrangement

Steel plate and wooden supports

TEST SET UP

PR1

JACK1

JACK2 , PR2

Hinge Two point loading

Arrangement for normal loading Arrangement for lateral loading

Prism failure normal to bed joint Prism failure normal bed to joint

Prism failure normal to bed joint Prism failure normal to bed joint

The maximum B.M for beam-column, at mid span is

Beam-column equation

Where, W = Lateral load in N

K =

P = Normal load in N

a =

L = effective length(c/c of hinge) in mm

Sl No.Normal Stress

(N/mm2)

Proving Ring

Normal Load (P)

N

Lateral Load (w)

NK=√P/EI

Moment (M) N-mm

Flexure

Strength

(N/mm2)

1 0.125 155 7500 3801.371.010x10

-4

929472.08 0.619

2 0.125 150 7500 3678.751.010x10

-4

899492.30 0.600

3 0.125 140 7500 3433.501.010x10

-4

839521.76 0.550

4 0.200 230 12000 5640.751.278x10

-4

1380697.73 0.920

5 0.200 210 12000 5150.251.278x10

-4

1260639.28 0.840

6 0.200 200 12000 4905.001.278x10

-4

1200605.06 0.800

7 0.400 280 24000 6867.001.807x10

-4

1681072.40 1.120

8 0.400 275 24000 6744.371.807x10

-4

1651056.33 1.100

9 0.400 270 24000 6621.75

1.807x10-4

1621030.27 1.080

Ultimate flexure strength

Normal stress(MPa

)

Applied

Flexure strength of half brick thick

prisms(MPa)(Chandrasekhar2009)

Flexure strength of one brick

thick prisms(MPa)(Vidya sagar

2009)

Flexure strength of

thick SCB prisms(MPa)( Atul Kumar

2009)

Flexure strength of

thick HCB prisms(MPa)

(Present study)

0.025 0.14 - - -

0.125 0.210 0.40 0.505 0.589

0.2 0.281 0.481 0.613 0.853

0.4 0.45 0.88 1.013 1.10

0.5 0.53 1.16 1.321 -

An attempt was made to compare the test results of hollow concrete block masonry with brick masonry & solid concrete block masonry studied by earlier investigations.

Comparison of Flexural strength v/s Normal stress of prisms

GRAPH OF FLEXURAL STRENGTH V/S NORMAL STRESS

TEST ON HOLLOW CONCRETE BLOCK MASONRY TRIPLET UNDER SHEAR

Shear strength of a masonry is its capacity to restrain the shear

loads.

The dimension of triplet specimens of height 412mm, width

624mm and thickness 150mm were constructed and cured

for 15 days

loading arrangement,the loads were applied using screw jacks

The normal stress applied on The triplet specimens were 0.125

(Mpa).

TEST DETAILS FOR SHEAR SPECIMENS

Setup for testing

Schematic diagram showing details of Test setup for Shear

Capacity of jack used for normal loading(J1) = 12 tons

Capacity of proving ring used for normal loading (PR1) = 50 tons

Capacity of jack used for shear loading (J2) = 30 tons

Capacity of proving ring used for lateral loading (PR2) = 05 tons

TABULATION AND CALCULATIONS

OBSERVATIONS OF THE TRIPLETS TESTED UNDER SHEAR

Triplet failure pattern

ULTIMATE SHEAR STRENGTH

Sl No.

Normal Stress

(N/mm2)

No of Divisions in

Proving Ring

Shear Load (N)

Shearing Area

(mm2)

Shear Strength (N/mm2)

1 0.125 460 22563.00 120000 0.188

2 0.125 475 23298.75 120000 0.194

3 0.125 585 28694.25 120000 0.240

4 0.125 470 23053.50 120000 0.192

SHEAR STRENGTH(MPa)

Normal stress(MPa)

Applied

Shear strength half brick thick

Triplets(Karthik 2009)

Shear strength of SCB Triplets(Atul kumar

2009)

Shear strength of HBM Triplets

(Present study )

0.025 0.06255 _ _

0.125 0.09037 0.2825 0.2035

0.2 0.1548 0.665 _

0.4 0.286 0.98 _

0.5 0.391 1.192 _

Comparison of Shear strength v/s Normal stress of Triplets

CONCLUSION

It can be concluded that there is an increase in flexural strength for hollow concrete block prisms, when compared to solid concrete block masonry & brick masonry

It can be concluded that there is a decrease in shear strength for hollow concrete block triplet, when compared to solid concrete block but a higher value when compared to brick triplets.(needs further investigation)

FURTHER SCOPE OF RESEAECH

Evaluation of compressive strength and modulus of elasticity of reinforced masonry prisms with large number of samples is required to completely understand the behavior of hollow block masonry

A comparison can be made between strength of unreinforced &reinforced hollow concrete block masonry

Further study can be carried out with varying values of normal stress

REFERENCES•IS: 1905-1987, ‘‘Code of practice for structural use of unreinforced masonry”. ( 3rd Revision) Bureau of Indian standards, New Delhi.•IS: 2185(part-I)-1979, ‘‘Code of specification for concrete masonry units-Hollow and solid concrete blocks”. Bureau of Indian standards, New Delhi.•Dayaratham.p (1987). ‘‘Brick and Reinforced Brick masonry structures” Oxford IBH Publishing Co.Pvt Ltd.New Delhi.•Sp-20(1991) ‘‘Handbook on masonry design and construction”, Bureau of Indian standards, New Delhi.•Atul Kumar (2009) ‘‘A study on behavior of solid concrete block masonry under flexure and shear loading conditions”. M-Tech Thesis Submitted to Department of Civil Engineering, BMSCE, and Bangalore.•Avinash.A.C (2006) ‘‘A Comprehensive study on masonry Units” M-Tech thesis submitted to Department of Civil Engineering, BMSCE, and Bangalore.•Siddangouda.patil (2007) ‘‘Compressive strength and Modulus of Elasticity of a Full Scale Concrete Block Masonry Wall Subjected to Axial Loading”. M-Tech Thesis Submitted to Department of Civil Engineering, BMSCE, and Bangalore.•Chandrasekhar (2009) ‘‘Effect of normal stress on Flexural strength of brick masonry”. M-Tech Thesis Submitted to Department of Civil Engineering, BMSCE, and Bangalore.•Karthik.M (2009) ‘‘Effect of normal stress on Shear strength of Brick masonry”. M-Tech Thesis Submitted to Department of Civil Engineering, BMSCE, and Banglore.