1. FE analysis with beam elements
E. Tarallo, G. Mastinu
POLITECNICO DI MILANO, Dipartimento di Meccanica 1

2. Subjects covered in this tutorial An introduction to beam elements
Summary
Subjects covered in this tutorial
An introduction to beam elements
A guided example to evaluate a simple structure through the use of FEM
Comparison analytical vs numerical solutions
Other few exercises (to include in exercises-book)

3. Beam element – topic
The element library in Abaqus contains several types of beam elements
A “beam” is an element in which assumptions are made so that the problem is reduced to one dimension mathematically: the primary solution variables are functions of position along the beam axis only (as bar element)
A beam must be a continuum in which we can define an axis such that the shortest distance from the axis to any point in the continuum is small compared to typical lengths along the axis
The simplest approach to beam theory is the classical Euler-Bernoulli assumption, that plane cross-sections initially normal to the beam's axis remain plane, normal to the beam axis, and undistorted (called B23, B33)
The beam elements in AbaqusCAE allow “transverse shear strain” (Timoshenko beam theory); the cross-section may not necessarily remain normal to the beam axis. This extension is generally considered useful for thicker beams, whose shear flexibility may be important (called B21, B22, B31, B32 and PIPE)

4. Beam element – shape function
Classic mechanical approach uses 3rd order interpolation function (elastic line theory)
To follow this theory use element B23, B33
Beam defined in Abaqus CAE has linear or quadratic interpolation function (element B21, B22, B31, B32)

5. Beam element – topic (stiffness matrix)
Let us consider an Euler-Bernoulli beam:
where the stiffness matrix is:

6. Exercise 1 – data problem
Geometry: L=1 m;
A=100x100 mm
Material: E=210 GPa; ν=0.3
Load: p=1 N/mm
Write the relation of internal load e solve the analytic problem of the deformed shape of the isostatic beam

7. Exercise 1 – Results (analytic vs numeric)
FEM Results
Exact solution:
v2= mm
θ2= e-5 rad
M1 = 5e5Nmm
F1Y=1000N
Comparison btw analytic solution and FEM results
Note: sensitive variables are
Number of elements
Linear or quadratic order

8. Exercise 1 – Modeling geometry and property2 3 5 4

9. Exercise 2 – data problem
Geometry: L=1 m;
A=100x100 mm
Material: E=210 GPa; ν=0.3
Load: p=1 N/mm
Write the relation of internal load e solve the analytic problem of the deformed shape of the iperstatic beam

10. Exercise 2 – Results (analytic vs numeric)
FEM Results
Exact solution:
θ2= e-5 rad
F1=625N
F2=375N
M1 =1.25e5 Nmm
Comparison btw analytic solution and FEM results
Note: sensitive variables are
Number of elements
Linear or quadratic order

11. Excercise 3 - data Material Property: E=210GPa Forces: F1=-20kN (Z)
F2=30kN(Y)
P=80N/mm(X)
Note:
All the written dimensions are 500mm
Problem:
Solve the system and report max displacement and max stress F1 A2 F2 A1 A4 A3 P A1 A2 A3 A4

12. Exercise 3 - results

13. Geometry: L=1m, H=0.2 m, Section variable
Excercise 4 P L H
Geometry: L=1m, H=0.2 m, Section variable
Material: E= MPa, ν=0.3 (steel)
Load: P=10 kN
Compare max stress and displacement of the structures used in the previous lesson using beam elements