United States Department of Transportation
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Abstract:This report describes the architecture, design and implementation of ALADDIN, a new high-level scripting language and tool kit for interactive matrix and finite element analyses of structures. In ALADDIN, finite element computations are viewed as a specialized form of matrix computation, matrices are viewed as rectangular arrays of physical quantities, and numbers are viewed as dimensionless physical constants. ALADDIN's programming language is similar to "C" in the sense that it uses only a small number of keywords, supports a variety of familiar looping and branching constructs, and links to libraries of matrix and finite element functions. It has been designed so that files are humanly readable and consist of a friendly, intuitive syntax rather than a table of numbers. Engineers are provided with the flexibility of modifying problem parameters and problem-solving algorithms without recompiling source codes. The capabilities of ALADDIN are demonstrated by performing linear static and dynamic analyses for simple structural systems and highway bridges, the principal application area for this research. With appropriate structural response quantities in hand (e.g., distributions of stress, displacement, and hysteretic energy dissipation), ALADDIN can evaluate selected design rules from the AASHTO bridge design code. This report presents the formulation of a special flexibility-based fiber beam-column element that includes both flexural and shear effects. Shear effects are an important displacement component in base-isolated highway structures. By using the fiber elements to model the lead-rubber isolators, it is possible to study the behavior of base-isolated bridges. The bi-linear force-displacement hysteresis loops for lead-rubber isolators are obtained by ALADDIN and can be compared with experimental data to show the accuracy of modeling. The essential benefits of base isolation are illustrated by computing the dynamic mode shapes for isolated and un-isolated versions of an example highway bridge. Finally, an energy-balance equation is performed for a full nonlinear time-history analysis of a three-dimensional base-isolated bridge. The important contribution of this work is that now all of the energy balance computations can be specified from the ALADDIN input file (and not be hard-coded into the program source code), thereby enabling energy-based calculations to be directly linked with the checking of design rules or code requirements.
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