Abstract
During the past decade the need to perform nonlinear static and dynamic analyses on bridge structures has increased significantly. Nonlinear dynamic analysis has become the approach that is used when protective systems such as base isolators and isolation systems are present in the bridge structure. The commercial computer programs available that are used for these types of analyses and that can be understood and used by structural bridge engineers have been far from adequate. Recently, the research community has produced a number of useful computer programs. Among these are the IDARC-Bridge and 3D-BASIS family of programs from the State University of New York at Buffalo. Bridge engineers are not usually familiar with the available computer codes primarily used by researchers, and it is generally known that these programs are not user friendly. Prediction of the nonlinear dynamic responses of bridge structures has presented other challenges. These range from the volume of input and output to the computational effort needed to obtain solutions. The increase in computer speed and the use of faster-solution algorithms have drastically reduced the time needed to perform iterative nonlinear dynamic analysis. Use of the Microsoft Windows-based standardized graphical user interface with the ability for the seamless exchange of data between programs makes the volume of input and output manageable. The implementation of 3D-BASIS-ME—type nonlinear base isolators and isolation systems and the analysis methods used in the family of Microsoft Windows-based software LARSA, with which bridge engineers have become familiar over the years using a wide range of applications for bridges and buildings, are presented.
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