Automotive engineers, as well as mechanical engineers in nearly every other industry, spend a tremendous amount of time solving equations found in design manuals. Recently, computerized versions of these manuals have reduced the large amount of time that most engineers spend on these tasks. One of the most prominent examples is the Computerized Application and Reference Systems (AISI/CARS) which is a computerized version of the Automotive Steel Design Manual. AISI/CARS was developed by Desktop Engineering Int'l Inc., Woodcliff Lake, New Jersey in cooperation with the Auto/Steel Partnership, a consortium of 10 North American steel companies and Ford, Chrysler and General Motors. AISI/CARS automates the process of designing steel body components by determining correct design procedures and performing necessary calculations.

An important module of AISI/CARS called GAS stands for Geometric Analysis of Sections. This module is fully integrated into AISI/CARS and allows the design engineer to calculate geometric section properties for arbitrary thin-walled sections and it can interface with the AISI/CARS application mode to determine member capacities. GAS facilitates: 1) analysis of thin walled open cell, closed cell, single cell and multiple cell cross sections 2) nominal section property calculations 3) effective section property calculations based on yield, actual or user-specified stress levels 4) prediction of local buckling effects 5) trend analyses that permit parametric studies 6) geometry data input using a keyboard, mouse or digitizing tablet 7) geometric databases that can be created, edited and searched.

The use of AISI/CARS can best be illustrated by a design example -- the design of the lower end of the B-pillar of a four-door automobile. AISI/CARS demonstrated the ability to save a considerable amount of time during several stages of the design and facilitated a weight-saving design improvement that might have been overlooked without this tool because it would have taken so long to validate.

A design change required that a rectangular hole be placed on the inside flange of the B-pillar to accommodate a seat belt retractor system. Structural stiffness requirements and material properties are shown in the illustration. The critical loading condition is a positive moment, which caused compression on the inside flange. GAS was used to compute the nominal section properties of the B-pillar. The results are shown in the accompanying illustrations. Next, the effective section properties were computed, automatically taking into account the local buckling of the compression flange, which may occur under the prescribed loading. The resulting equivalent section properties were less than the nominal properties because of the influence of local buckling of the wide, thin compression flange. However, the results suggested that it might be possible, without any serious consequences, to remove part of the inner compression flange, which is not fully effective. Accordingly, a portion of the inner flange was removed to accommodate the seat belt retractor and the structure was re-analyzed. The results indicated that the computed effective moment of inertia was then less than the required value. As a possible solution, edge stiffeners were added around the hole in the inner flange. Re-analysis established that all stiffness requirements were then met and the section was then optimized for local buckling. Finally, using the section modulus just determined and returning effective properties to the application mode, the moment capacity of the revised section was found to substantially exceed the maximum applied moment completing this step of the B-pillar analysis.