# COMPUTATIONAL MECHANICS OF STRUCTURES cod. 1009199

1° year of course - Second semester
Professor
Roberto BRIGHENTI
Scienza delle costruzioni (ICAR/08)
Field
Ingegneria civile
Type of training activity
Characterising
48 hours
of face-to-face activities
6 credits
hub: PARMA
course unit
in ITALIAN

## Learning objectives

Knowledge and understanding:
The course aims to present concepts and tools for computational mechanics applied to generic solid structures.
Furthermore the course intends to provide to the students the basis to perform numerical linear static or dynamic analyses of structures and enables them to read and understand computational mechanics books and to study autonomously the subject.

Applying knowledge and under standing:
At the end of course the student should be able to correctly develop a numerical model of structural elements or generic structures through the finite element technique; in particular the student should be able to choose the most suitable finite element kind to represent the structural problem under study, and to correctly introduce the boundary conditions and the mechanical properties of the materials.

Making judgments:
At the end of course the student should be able to correctly interpret the structural behavior of generic structures and to propose a proper numerical modeling.

Communication skills:
At the end of course the student should have a proper use of the terminology of the computational mechanics applied to structures and will be able to properly use it.

## Prerequisites

It is necessary to have at least attended to the following courses: Structural Mechanics and Mechanics of Structures.

## Course unit content

The topics treated in the course are listed below:

Basic concepts in computational mechanics.
Modeling of structures.
Variational methods.
Residual methods.
Basic concepts of the finite element method.
Isoparametric formulation.
Structural discretisation with finite elements.
Use of finite elements in non linear problems.

## Full programme

1. Basic concepts of computational mechanics.
Introduction to the finite element method: displacement method for plane beam structures. Variational methods. Weak and strong form of a physical problem. Natural and essential boundary conditions.

2. Variational principles. Virtual work theorem. Approximate polynomial solution. Bubnov-Galerkin method. General formulation of a problem by using finite elements: differential and integral forms. Minimum potential energy principle. Displacement field approximation. Rayleigh-Ritz method applied to beams and plates. The finite element method as a subclass of the variational methods.

3. Residual methods. Weighted residual method: subdomain method, collocation method, least square method, Galerkin method. The finite element method as a particular case of the Weighted residual method.

4. Basic concepts of the finite element method Algebraic static and dynamic equilibrium equations of a structure discretized by finite elements. Stiffness matrix and nodal force vector . Stiffness matrix assembling. Treatment of boundary conditions and their classification: linear and non linear, single freedom constraints, multi freedoms constraints. Master-slave method, penalty method, Lagrange's multipliers method.

5. Structural discretisation with finite elements. Choice of the finite element and of the shape functions. Shape functions in the local reference system and their derivatives. Examples of linear shape functions. Isoparametric elements: convergence requirements. Lagrangian and Serendipidy elements.
Shape functions completeness.

6. Isoparametric elements in one, two and three dimensions.
Truss elements, beam bending elements (Bernoulli and Timoshenko formulation). Finite elements for 2-D problems under plane stress, plane strain and axisymmetric conditions (shells); 2-D bending plates elements(Kirchhoff and Mindlin formulations). Finite elements for 3-D problems with isotropic or orthotropic materials.
Numerical integration methods. Variable transformation in 1D, 2D, 3D. Gauss rule. Accuracy of the numerical integration.

7. Convergence problems. Numerical errors and ill conditioning of a matrix. Causes of ill conditioning. Matrix scaling. Scaling of a matrix. Convergence requirements: completeness, compatibility, stability. The patch test. The Babuška-Brezzi condition. Stiffness overestimation, accuracy of the solution, reduced integration, hourglass

8. Some more aspects about the finite element method. Flow-chart of a simple program for finite element analysis. Substructuring. Post-processing of the results. Basic concepts on FORTRAN programming; development of simple FE programs for structural analyses.

9. Applications: numerical modeling of generic structures. Use of FE software for the analysis of structures or generic structural elements.
Convergence tests. Analysis and interpretation of the results, assessment of the solution accuracy.

## Bibliography

- R. Brighenti, Analisi numerica dei solidi e delle strutture: fondamenti del metodo degli elementi finiti. (in Italian), Esculapio Publisher (Bologna), III Ed. (ISBN: 978-88-9385-111-4), 2019.
- Cook, R.D., Malkus D.S., Plesha, M.E.: “Concept and application of finite element analysis”, 4th edition, John Wiley & Sons, 2002.
-Zienkiewicz, O.C.: “The finite element method”, Mc Graw-Hill, 2000.
- Corradi dell’Acqua, L.: "Meccanica delle strutture", Vol. 1,2 e 3, Mc Graw-Hill, 1995.

Teaching stuff:
- Stuff provided by the teacher (see the teacher’s website: http://www2.unipr.it/~brigh/index.htm) or from the Elly website of the Univ. of Parma.

All the suggested textbooks are available in the library of the Engineering school.

## Teaching methods

The course is organized in theoretical and practical lessons (by making use of electronic presentations); the exercises are either developed by the teacher and autonomously in class also by making use of the computer and at home by the students.

For every topic, the practical activities are properly scheduled in order to provide the students the ability to solve the proposed problems on the basis of the previously explained theoretical concepts.

## Assessment methods and criteria

The final exam consists in an oral test.
On a voluntary basis, the students can decide to develop individually a project (or in groups of max. 2 or 3 students, on a topic agreed with the teacher) concerning the coding of a simple finite element program and of its verification.

The evaluation of the final exam will be as follows:
- Project development (Applying knowledge, 30%).
- Oral test (theoretical questions 30%, exercises 30%) (knowledge).
- Clarity of presentation (Communication skills, 10%).

- - -