University of Florida/Eml4500/f08.qwiki/Lecture 5

Read: Chapter 4 Chapter 1: Big Picture

• 1.1 Discritization (1.1.1 Plane truss elem)
• 1.2 Assembly of elem. eqs. Ex. 1.4: Five-bar truss
• 1.4 Elem Soln and model validity (1.4.1 Plane truss elem)

Steps to solve simple truss system described on 9/3

1.Global: The displacement dofs are partitioned into: 1)a known part,e.g.(fixed dofs, constraints) 2)an unknown part: solve using FEA

The same for global forces: 1) known part 2) unknown part

2.Element picture:

• Element dofs
• Element forces

3.Global FD relation:

• Element stiffness matrices in global coordinates
• Element force matrices in global coordinates
• Assembly of element stiffness matrix and element force matrix into global FD relation knxndnx1=Fnx1

4.Elimination: The elimination of known dofs to reduce the global FD rel. (stiffness matrix non-singular => invertible)

m = number of unknown displacement dofs

n = number of all displacement dofs

• m < n

d=k-1F

5. Compute Element Forces

6. Compute Reactions

Example:

• L(1)=4 L(2)=2 (Length)
• E(1)=3 E(2)=5 (Young's Modulus)
• A(1)=1 A(2)=2 (Area)