Use of computers in structural analysis

Computer based methods use matrix formulation of the force or displacement method (matrix stiffness method, finite element method) so that large structures can be analysed quickly by software such as SAP2000, ETABS, STAAD.Pro and ANSYS.

Steps in computer analysis

1. Model the structure: joints (nodes), members (elements), supports, material and section properties.
2. Apply loads and load combinations.
3. The program forms member stiffness matrices, assembles the global matrix $[K]$, and solves $[K]\{\Delta\} = \{F\}$ for joint displacements.
4. Member forces, reactions and stresses are back-calculated and presented as diagrams and tables.

Uses and advantages

• Handles highly indeterminate structures (multi-storey frames, 3D frames, shells, plates) that are impractical by hand.
• Very fast and accurate; many load combinations (dead, live, wind, earthquake) can be run quickly.
• Allows non-linear, dynamic, buckling and soil-structure interaction analysis.
• Easy to repeat the analysis after changing member sizes in design iterations.
• Gives graphical output (deformed shape, bending moment diagrams).

Cautions

• Results depend on the correctness of the model, so the engineer must check them, e.g. equilibrium of reactions and approximate hand calculations.
• "Garbage in, garbage out": wrong supports or loads give wrong results.