Modeling the buckling behavior of bridge braces: the example of San Francisco-Oakland Bay Bridge Featured

The California Toll Bridge Seismic Retrofit Program was initiated by the California Department of Transportation (Caltrans). The Program aims to assess the vulnerability of major toll bridges in California to damage caused by powerful earthquakes and to design retrofits for improved seismic safety. In order to facilitate this program, Caltrans and contractors chose ADINA as their main tool.

A crucial aspect of the bridge analysis involves modeling the braces in the bridge structures. These braces, made of laced built-up members with rivets, underwent laboratory testing. Due to the large number of braces found in each bridge structure, the development of a straightforward yet efficient finite element model for a standard brace became essential.

In the following lines, we provide a brief account, courtesy of SC Solutions, California, on how the ADINA moment-curvature beam elements were employed to model and validate the behavior of these braces. This capability of ADINA has been important in conducting nonlinear analyses of bridges.

Learn more about ADINA nonlinear analysis

For the validation study, braces subjected to axial and flexural stresses were initially modeled with detailed shell elements, and then a simplified representation was achieved using the moment-curvature beam elements in ADINA. This approach significantly reduced the number of degrees of freedom required (from approximately 15,000 dofs to about 50 dofs) to represent a brace, without compromising the practical accuracy of the results. Consequently, the utilization of the simplified beam model for braces considerably reduced the modeling and computation time while maintaining sufficient accuracy.

Furthermore, the axial force-displacement hysteresis loops obtained from physical testing were compared with the numerical results derived from the moment-curvature beam elements. The moment-curvature beam elements exhibited a close correlation with the experimental data.

These findings were consistent across various brace slenderness ratios, indicating that the moment-curvature beam elements are a highly valuable tool in ADINA for effectively modeling braces in large bridge structures.

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