Finite Element Prism Presentation_Print Slides

“COMPRESSIVE BEHAVIOUR OF

MASONRY PRISMS”

Prepared by: Mina GayedApril 19th, 2010

CIVIL ENGINEERING: AN INTRODUCTION TO FINITE ELEMENT ANALYSIS

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

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)

3. Analytical ProgramPrism

5 mm JointEb/Em =

0.5Eb/Em =

1.0Eb/Em =

2.0

10 mm JointEb/Em =

0.5Eb/Em =

1.0Eb/Em =

2.0

15 mm JointEb/Em =

0.5Eb/Em =

1.0Eb/Em =

2.0Note: Eb/Em is the modular ratio of block to mortar

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

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 thickness

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

Meshing Details



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

Assembly Detail


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


B.C.’s and Loading Detail

6. Results – General TrendsMinimum 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

6. Results – General TrendsMinimum 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


6. Results – Parameter Variation

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

-12

-11

-10

-9

-8

-7

-6

Minimum Principal Stresses in Hollow Concrete Prisms

5 mm Joint - Block Stress5 mm Joint - Mortar Stress10 mm Joint - Block Stress10 mm Joint - Mortar Stress15 mm Joint - Block Stress15 mm Joint - Mortar Stress

Eb/Em Ratio

Min

imum

Pri

ncip

al S

tres

s [M

Pa]

Compressive stresses increased in mortar with THICKER joints and STIFFER mortar

No distinction in block compressive stresses with variation of joint thickness or properties


6. Results – Parameter Variation

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Maximum Principal Stresses in Hollow Concrete Prisms

5 mm Joint - Block Stress5 mm Joint - Mortar Stress10 mm Joint - Block Stress10 mm Joint - Mortar Stress15 mm Joint - Block Stress15 mm Joint - Mortar Stress

Eb/Em Ratio

Max

imum

Pri

ncip

al S

tres

s [M

Pa]

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)


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

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 principal stresses in the mortar material with the variation of Eb/Em ratios

QUESTIONS ?

Compressive Behaviour of Masonry Prisms

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Finite Element Prism Presentation_Print Slides