3.4 INTERACTIVE COMPUTER-AIDED DESIGN

As of mid 1980’s computer programs have not been used extensively for design of structures. A number of reasons were cited by Adeli and Paek (1986) for the lack of interest in conventional programs for design of structures:

1. In practical design cases there are a large number of alternatives whose selection needs the judgment of the experienced human designer.
2. Design specifications usually cover the general situations and leave the less frequent cases to the judgment of the human designer. In other words, they contain discontinuities and gaps to be filled by the human designer.
3. Human designers use their previously gained experience in design of new structures.
4. A human designer usually visualizes and sketches different structural forms and configurations before making the preliminary design, stress analysis, and the final design.
5. Design specifications change frequently – for example, every three to four years – even though not significantly.
6. Design specifications are based on years of experience gained by researchers and practicing engineers and contain rules of thumb and heuristics which may nor readily implemented in traditional computer languages.
7. Parts of design specifications and standards need interpretation by an experienced designer.
8. Design is an ill-defined and ill-structured problem, lacking a clearly defined goal, and not quite amenable to algorithmic procedures.
9. Design is a creative process.

Adeli (1987, 1988) presented the approach of interactive computer-aided design of steel structures. An interactive program should ideally perform the following:

1. Carry all the numerical calculations.
2. Check for the consistency of design according to the specified design specification.
3. Perform error checks.
4. Present possible alternatives to the user.
5. Prevent the user from entering the data in violation of the design specification.
6. Inform the user about the ranges of practical values.
7. Provide practical values for the final design.