Prediction of Hollow concrete block masonry

Journal of Civil Engineering Technology and Research
Volume 2, Number 1 (2014), pp.351-362
© Delton Books
http://www.deltonbooks.com
Prediction of Hollow Concrete Block Masonry
Compressive Strength Using Fe Model
Mr Shivaraj kumar H Y & Dr M V Renuka Devi
R.V. College of Engineering
Abstract:
The strength of hollow concrete block masonry depends on various factors like
strength of unit blocks, mortar and their bond strength. An analytical non-linear
investigation to predict the compressive strength, failure and crack pattern of
hollow concrete block masonry prisms has been done by adopting 3-Dimentional
Micro-modeling in ANSYS R14.5. The required non-linear parameters like the
multi-linear stress-strain has been obtained by laboratory experiments for units
and mortar. Willam–Warnke’s five parameter failure theory has been adopted to
model the failure of masonry materials.
Key words: Masonry, Prisms, Micro-modeling, Compressive strength, Nonlinear
Introduction:
The compressive strength of masonry is the most important characteristic of masonry
for using in the design. Compressive strength of masonry depends on strength of individual
blocks, mortar used and their bond strength. From literature it found that correlation between
the compressive strength of interlocking masonry and prism and the wall panels has been
established as fcp = 0.47fcb, fcw = 0.83fcp and fcw = 0.39fcb[1]. In standard codes of practice of
masonry design the strength of unit type and mortar is related to arrive at the compressive
strength of masonry.
Micro modeling is preferred because of the facts that in macro modeling there is no
distinction between individual units and joints and further more the masonry is considered as
homogeneous, isotropic or anisotropic continuum. The well known reason for failure because
of plane of weakness in mortar joints cannot be addressed as required for arriving at accurate
required results. Non-linear analysis is adopted as the masonry material can be stressed
exceeding the elastic limit to predict the ultimate compressive stress and crack pattern
accurately.
Finite element (FE) tools were utilised in developing models to predict masonry
behavior in the late 1980s[2]. Initially linear FE models were attempted and later non-liner
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
FE models were developed. Some of the FE models were effective in predicting the global
behavior of masonry such as crack pattern and strength of masonry in compression etc[2].
Development of suitable FE model is a complex due to the involvement of large number of
isoparametric elements to account for the large variation of stress in the block and around
mortar joints. To accommodate the material non-linearities in failure process a 3D model is
necessary to simulate the appropriate behavior. In the present investigation an attempt has
been made in 3D micro-modeling of masonry prisms subjected to concentric compressive
loading to predict the compressive strength and crack pattern by making use of Willam–
Warnke’s five parameter failure theory to model the failure of masonry materials. The FE
model is validated by comparing the predicted results with the experimental results.
Objectives:
(i) To obtain the Compressive strength and stress-strain characteristics of hollow concrete
block, mortar and grout.
(ii) To obtain the Compressive strength and stress-strain characteristics of Unreinforced
Masonry (URM) and Reinforced Masonry (RM ) prisms
(iii) Developing of non-linear micro-model of unreinforced and reinforced masonry prism
and Validation of FE model results by comparing with the experimental results.
Review of related literature:
2008- F. L. De oliveira [3], j. B. De hanai -Axial compression behavior of concrete masonry
wallettes strengthened with cement mortar overlays:
steel mesh reinforced overlays showed the best efficiency, possible explanation is that the
steel meshes could mitigate the effects of damages in the block and sudden loss of rigidity
was avoided and the composite element could attain a higher load capacity
2010- Ch. V. Uday Vyas , B. V. Venkatarama Reddy [2]- Prediction of solid block masonry
prism compressive strength using FE model
The crack pattern predicted by the FE model shows vertical splitting cracks in the prism.
Such vertical splitting cracks across the prism height were seen in the masonry prisms tested
for compressive strength.
Research methodology:
— In this study both experimental and analytical studies was carried out to investigate
the behavior of hollow concrete block masonry prism of five block high with and
without reinforcement under axial compression.
— In the experimental program preliminary tests were carried out on 200mm hollow
concrete block, mortar, and grout to obtain its basic properties. A total four numbers
of reinforced and unreinforced five block height stack bonded masonry prisms were
casted and after 28 days of curing period, tested under compression following IS:
1905-1987.
— Compressive strength and failure pattern for both reinforced and unreinforced
masonry prism was studied.
Prediction of Hollow Concrete Block Masonry Compressive Strength Using Fe Model
353
— In the numerical program, three dimensional non-linear FE model based on the micromodeling approach was developed for both unreinforced and reinforced masonry
prisms using ANSYS (14.5)
— The FE model was validated by comparing the predicted results with the experimental
results.
Experimental Data:
Compression and modulus of hollow concrete blocks
Compression test was carried out on the hollow concrete blocks adopting gypsum
capping[4] of 1:1/4:2 as per IS: 2185 part1 [5], whose 3 day 50x50 mm cube average
compressive strength was found to be 6MPa.
Compressive strength and modulus of elasticity were found to be 6.57 MPa and 7830 MPa
respectively.
Compression and modulus of 1:6 cement-sand mortar as per IS 2250:1981 [6]
Table 1. Compressive strength and modulus of 1:6 cement-sand mortar cubes
Particulars
7day compressive strength
MPa
28day compressive strength
MPa
Initial tangent modulus MPa
No of specimen
tested
Value
C.O.V
6
2.57
9.5
6
6.3
19.7
6
10558
-
Compressive strength and modulus of elasticity of 1:6 cement mortar were found to be 6.3
MPa and 10558 MPa respectively.
Compression and modulus of grout concrete as per IS 516:1959 [7]
M20 Grade of concrete was adopted with a proportion of 1:1.5:3. Grout concrete
consisted of 12.5 down size aggregates with water-cement ratio 0.75 to get a flowable
concrete of 220 mm slump.
Compressive strength and modulus of elasticity of M20 grout concrete were
found to be 23 MPa and 26314 MPa respectively.
Table 2. Compressive strength and modulus of 1:6 cement-sand mortar cubes
Particular
7day compressive strength
MPa
28day compressive strength
MPa
No of specimen
tested
Value
C.O.V
6
14.91
7.7
6
23
9.4
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
Initial tangent modulus MPa
6
26314
-
Compression and modulus of Unreinforced Masonry Prisms (URM) and Reinforced
Masonry Prisms (RM) as per ASTM C1314 [8].
Table 3. Compressive strength of URM and RM Prisms
Particulars
No. of samples
Mean compressive
strength, MPa
Coefficient of
variation, %
URM
4
4.21
18.6
RM
4
8.02
22.3
Compressive strength and modulus of elasticity of URM and RM prisms [8] were found to be
4545 MPa and 10199 MPa respectively.
Analytical Programme:
Finite element analysis of masonry prisms are carried out using ANSYS R14.5. 3-D
dimensional non-linear FE micro-modeling is adopted for deveploing both URM and RM
prism. This FE analysis requires multi-linear stress-strain relationships to model the nonlinear behavior of hollow concrete block, mortar, and grout. A Willam-Warnke’s five
parameter failure theory has been adopted to model the failure of masonry materials.
Finite element modeling of Unreinforced masonry prism (URM)
Unreinforced masonry prism of dimension 400x200x990 mm adopting a mortar joint
thickness of 10mm was considered for modeling. The hollow unit blocks and mortar joints
were modeled using solid 65 element, which is a eight noded element with three degrees of
freedom at each node i.e translations in the nodal x, y and z directions. Solid 65 element is
capable of developing cracks and crushing in the masonry elements.
The model of URM is finely meshed to predict accurate results as shown in Fig1.
Micro-modeling of individual elements allows to address the connectivity of the elements in
the continuum. Loading is applied to the net area of the top block in terms of pressure and the
bottom net area is constrained in Y direction to simulate exact experimental condition as
shown in Fig1.
Prediction of Hollow Concrete Block Masonry Compressive Strength Using Fe Model
355
Fig 1. Meshed model of URM
Finite element modeling of Reinforced masonry prism (RM)
Reinforced masonry prism of dimension 400x200x990 mm adopting a mortar joint
thickness of 10mm was considered for modeling. The hollow unit blocks and mortar joints
were modeled using solid 65 element, the reinforcements are modeled using link180 3-D
3 spar
element which is a two noded line element having three degrees of freedom for each node,
translations in the nodal x, y and z directions as shown in Fig2.
Fig 2. Components of reinforced masonry
Fig2. shows the components of RM prism with the grout in fill and the reinforcements in
longitudinal direction of #12 and transverse direction of #8. The model is finely meshed and
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
the loading in terms of pressure is applied to the top gross area of the prism and bottom gross
area of the prism is constrained in Y direction.
Material Properties
Table 4. Linear material properties for Solid 65
Linear Isotropic
Masonry
unit
Material property
Young's Modulus, E (Mpa)
Poisson's ratio, ν
Mortar
joint
Grout
14,393.50 10428.63 26367.47
0.18
0.16
0.18
Table 5. Multi-linear material properties for Solid 65
Hollow concrete
Cement-sand
block
mortar(1:6)
Grout (M20 concrete)
SL No.
Strain
Stress
Mpa
Strain
Stress
Mpa
Strain
Stress Mpa
1
0.0002
2.87
0.00012
1.251435
0.00001
0.263675
2
0.0004
4.97
0.00024
2.291335
0.00002
0.525712
3
0.0006
6.70
0.00036
2.910289
0.00003
0.786112
4
0.0008
8.05
0.00048
3.323839
0.00004
1.044874
5
0.001
9.22
0.0006
3.79269
0.00005
1.301998
6
0.0012
9.55
0.00072
4.153252
0.00006
1.557485
7
0.0014
10.41
0.00084
4.41542
0.00007
1.811335
8
0.0016
10.92
0.00096
4.899172
0.00008
2.063547
9
0.0018
11.20
0.00108
4.961844
0.00009
2.314121
10
0.002
11.48
0.0012
5.024515
0.0001
2.563058
Prediction of Hollow Concrete Block Masonry Compressive Strength Using Fe Model
357
11
0.0022
12.44
0.00132
5.087186
0.0002
4.962361
12
0.0024
12.69
0.00144
5.149858
0.0003
7.19791
0.00156
5.212529
0.0004
9.269704
14
0.0005
11.17774
15
0.0006
12.92203
16
0.0007
14.50256
17
0.0008
15.91934
13
Table 6. Concrete constants for Solid 65
Material property
Masonry
Mortar
unit
joint
Grout
Shear transfer coefficient for open crack,
[2]
0.3
0.3
0.3
Shear transfer coefficient for close crack,
[2]
0.6
0.6
0.6
Uniaxial cracking stress
(MPa)
1.2
0.6
2.3
Uniaxial crushing stress
(MPa)
12
6
23
Table 7. Material properties for Link 180
Linear Isotropic
Young's Modulus, (Mpa)
Poisson's ratio, ν
Bilinear Isotropic
Yield stress, (Mpa)
Tangent modulus, ′ (Mpa)
2.00E+05
0.3
415
0
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
Non Linear Finite Element Solution
Unreinforced masonry prism (URM)
Fig3. Displacement plot
Fig4. Stress plot
Prediction of Hollow Concrete Block Masonry Compressive Strength Using Fe Model
Reinforced masonry prism (RM)
Fig5. Displacement plot
Fig6. Stress plot
359
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
Fig7. Stress plot of Reinforcement
Crack plot of Unreinforced and Reinforced Masonry Prism
Fig8. Crack plot of URM FE model and Experimental
Prediction of Hollow Concrete Block Masonry Compressive Strength Using Fe Model
361
Fig9. Crack plot of RM FE model and Experimental
Table 8. Masonry compressive strength
Mean compressive strength, MPa
SL No.
1
2
Masonry Type
Unreinforced
masonry prism
Reinforced
masonry prism
Experimental
FE model
4.21
3.7
8.02
7.8
Discussion:
The finely meshed FE models of URM and RM is appropriately constrained and pressure is
applied at the top of prism in substeps in order to carry out non-linear analysis until the
solution was converged.
The FE model results shown in fig 3 and 4 shows the displacement and stress distribution
respectively, clearly the predicted results showed stress concentration at the corners, web of
block and mortar joints as it was seen in experimental investigation.
The FE model results shown in Fig 5,6,7 show the displacement plot, stress plot of RM prism
and stress plot of reinforcement of RM prism respectively. It could be seen that the predicted
result showed that there was stress concentration at the top two blocks as it was seen in some
cases of the experimental investigation.
Fig8 and Fig 9 shows the predicted FE model crack pattern and the experimental crack
pattern
of URM and RM prism. It was observed that the Predicted crack pattern could be appreciably
compared with the crack pattern read from the experimental investigation.
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Mr Shivaraj kumar H Y & Dr M V Renuka Devi
Conclusions :
Ø Percentage increase in compressive strength for 0.56% steel adopted in RM prisms,
was found to be 90.5%.
Ø Also Modulus of elasticity of Reinforced prism increases to 2.24 times of
unreinforced prism.
Ø The experimental and ANSYS model results is seen to be matching around 90%.
Ø Crack pattern predicted could show the vertical splitting of the blocks.
Recommendations:
Ø Masonry behavior being complex involving several variation factors, it is
recommended that more investigation involving 3,4,5 block height masonry prisms is
needed to be carried out to arrive at a fair conclusion.
Ø The results encourages for Experimental work and numerical analysis to be carried
out for wallets and full scale wall.
References:
Mohd Saleh Jaafar et al.(2006), " Strength correlation between individual block, prism and
basic wall panel for load bearing interlocking mortarless hollow block masonry" ,
Construction and Building Materials, vol 20, 492–498
Ch. V. Uday Vyas B. V. Venkatarama Reddy (2010)," Prediction of solid block masonry
prism compressive strength using FE model", Materials and Structures, 43:719–735
F. L. De Oliveira and J. B. De Hanai (2008), "Axial compression behavior of concrete
masonry wallettes strengthened with cement mortar overlays", IBRACON Structures
and Materials Journal, vol. 1, p. 158 - 170.
Robert G. Drysdale and Ahmad A. Hamid (2008), “Masonry structures behavior and design”
Third edition, McMaster University, Hamilton, Ontario.
IS: 2185 (part 1) “Specification for concrete masonry units”, BIS Publication, New
Delhi.1979.
IS:2250, "Code of practice for preparation and use of masonry mortars", BIS Publication,
New Delhi.1981
IS:516, "Method of tests for strength of concrete", BIS Publication, New
Delhi.1959,reaffirmed 2004.
ASTM C 1314, “Standard Test Method for Compressive Strength of Masonry Prisms”,
2003.

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