2. 1. Goals
Construct a micro-simulation finite element model
on Abaqus/CAE that closely represents a
standard test prism
Conduct a parametric analysis to investigate the
effect of mortar joint thickness as well as stiffness
strength on the behaviour of masonry prisms
Briefly compare results with those published in
literature
3. 2. Background
Masonry compressive strength permeates all
design equations
Prism testing is regarded as the standard
method to determine the compressive strength
The results of prism testing are highly
susceptible to such factors as:
Mortar joint thickness
Mortar properties
Block strength
Prism geometry (h/t ratio)
4. 3. Analytical Program
Prism
5 mm
Joint
Eb/Em =
0.5
Eb/Em =
1.0
Eb/Em =
2.0
10 mm
Joint
Eb/Em =
0.5
Eb/Em =
1.0
Eb/Em =
2.0
15 mm
Joint
Eb/Em =
0.5
Eb/Em =
1.0
Eb/Em =
2.0
Note: Eb/Em is the modular ratio of block to
mortar
5. 4. Finite Element Model -
Assumptions
Geometry assumptions taken:
fillets at web to face shell connections were given a radius
of 8mm for lack of a better reference in the literature
joint interfaces between the blocks and mortar are assumed
to be rigid since frictional forces created by compression
prevent slipping
tapering of face shells and webs were eliminated
Material is assumed linear elastic with loading at
less than 50% of failure
Material is taken as homogeneous and isotropic
6. 5. Finite Element Model -
Creation
Total of 8828
elements
Block and mortar are
a 3D deformable
solid extrusion
Block is
190x390x190
Mortar is 32mm wide
times various
Blocks: linear 8 node
brick elements –
meshed at 20 mm with
10 mm surface mesh
top&bottom
Mortar joint: quadratic
20 node 3D brick with
10 mm mesh
Geometry Mesh
Creation 1 Creation 2 Creation 3
8. 5. Finite Element Model -
Creation
Creation 1 Creation 2 Creation 3
All materials are
homo-geneous and
isotropic
Block:
E = 21660 MPa
ν = 0.2
Mortar:
E = Varies as 0.5 to 2 of
block’s modulus
ν = 0.18
Material Assembly
Prior to assembly 6
surfaces were
assigned
2 for each mortar
layer
1 for each interface
block layer
4 instances total
were imported
2 blocks
2 mortar joint layers
10. 5. Finite Element Model -
Creation
Tied all 6 surfaces
together Mortar
joint “binds” the
interface and the
compressive forces
create additional
frictional resistance
One step was
required
Boundary conditions
taken as fixed
(encastre) at the
bottom
Loading is top surface
pressure of 8 MPa
(approx. 50% of failure)
Surface Interaction Steps
Creation 1 Creation 2 Creation 3
12. 6. Results – General Trends
Minimum Principal Stresses
[10M2E]
Maximum Principal Stresses
[10M2E]
General Trends 1 General Trends 2 Parameter Variation 1 Parameter Variation 2
High compressive
stresses
Almost zero
compression
High tensile stress
concentrations
13. 6. Results – General Trends
Minimum Principal Stresses
[10M2E]
Maximum Principal Stresses
[10M2E]
Block face shell
in compression
High compression concentrations in
mortar
No tension in face
shells
Tension in mortar
at intersections
General Trends 1 General Trends 2 Parameter Variation 1 Parameter Variation 2
14. 6. Results – Parameter
Variation
-12
-11
-10
-9
-8
-7
-6
0 0.5 1 1.5 2 2.5
MinimumPrincipalStress[MPa]
Eb/Em Ratio
Minimum Principal Stresses in Hollow Concrete Prisms
5 mm Joint - Block Stress
5 mm Joint - Mortar Stress
10 mm Joint - Block Stress
10 mm Joint - Mortar Stress
15 mm Joint - Block Stress
15 mm Joint - Mortar Stress
Compressive stresses increased in
mortar with THICKER joints and
No distinction in block compressive
stresses with variation of joint thickness or
properties
General Trends 1 General Trends 2 Parameter Variation 1 Parameter Variation 2
15. 6. Results – Parameter
Variation
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 0.5 1 1.5 2 2.5
MaximumPrincipalStress[MPa]
Eb/Em Ratio
Maximum Principal Stresses in Hollow Concrete Prisms
5 mm Joint - Block Stress
5 mm Joint - Mortar Stress
10 mm Joint - Block Stress
10 mm Joint - Mortar Stress
15 mm Joint - Block Stress
15 mm Joint - Mortar Stress
For an Eb/Em ratio less than 1 mortar is in
compression but in tension for a ratio greater
than 1!
Higher stresses in general for THINNER joints
Block: less tensile stress with a
decrease in joint thickness and
softer mortar ( increasing Eb/Em
ratio)
General Trends 1 General Trends 2 Parameter Variation 1 Parameter Variation 2
16. 7. Future Work
Study the nonlinear behaviour of prisms at a
load close to failure
Determine whether or not the parameter
variation in this study will actually influence the
ultimate compressive strength of the prism
Study the influence of prism geometry on the
compressive strength – vary h/t ratio
Elaborate on the cause of
tension/compression variation of mortar as a
function of Eb/Em ratio
Simulate an entire wall wythe and compare
results with those obtained from prisms
17. 8. Conclusion
Finite element modeling is a very useful,
practical, and economical method to study the
cause and effect of parameter variation for
physical problems
The model simulated is in good agreement with
prism tests found in the literature
Varying mortar joint thickness and properties
has minimal effect on block stress propagation
Less compressive stresses are observed in
mortar with thinner joints and higher Eb/Em
ratios
Very interesting results observed for maximum
Note: the code 10M2E stands for a 10mm mortar joint and an Eb/Em ratio of 2
Less confinement with thicker mortar joints causes higher compressive stresses
Very strange! Thinner mortar joints causes higher compressive stresses for Eb/Em less than 1 AND higher tensile stresses for a ratio greater than 1?? I can’t explain this....