• Review Points

Computer-based Structural Analysis

Background

• It's easy to think
  • Structures involves a lot of calculating, which we do by hand.
  • Computers are good at calculating.
  • Let's have the computer do the calculating that we are doing by hand. It will save us work.

• Early work with computers in the 1950s did that.

• It was marginally successful.

• The use of computers didn't make real progress until methods were developed that took advantage of the computer's special characteristics.
  • Methods completely impractical by hand, but very well suited to a computer.

• These methods involved creating a very abstract mathematical model and simulating the effects of load.
  • Like electronic tinker toys.

• Today we will learn the basic vocabulary, concepts, and limitations of this modelling method.

Overview

• Modelling: Creating an idealized mathematical model of a real or conceived structure and the loads on it. The modelled structure will typically be a portion of a larger structure.

• Analysis: Determining the reactions, internal forces, and displacements of the model in response to the loads; this is a form of simulation.

• Interpretation: Determining the meaning of the analysis results to assess the performance of the structure and make design decisions.

Here is an example:

1: A real structure

2: Modelling creates a computer-based representation, as shown below. The model includes only a portion of the complete bridge, and leaves out many details.

3: Analysis produces graphic displays and numeric data describing the state of the model under a specified load.

Member Axial Forces.

Member Bending Moments

Deflected shape

4: Interpretation involves deriving meaning from the results, including checking for anomalies and errors, checking performance criteria, and developing ideas for improvements in the concept or its execution.

There's good news and other news.

The good news: The computer does the analysis automatically, in a matter of minutes or seconds.

The other news: The computer is no help whatsoever with modelling or interpretation. These tasks require a skilled human. In today's world, we learn calculation methods not in order to do analysis, the computer does that, but to help with conception of an initial design, and in the modelling and interpretation required to refine and critique the computer-based analysis.

Key Terms

• Node
• Element
• Boundary Condition
• Element End Force
• Nodal Load
• Element Load