Simulation of Buckling of Bridge Braces —
the San FranciscoOakland Bay Bridge
About a decade ago, the California Department of Transportation (Caltrans) initiated the California Toll Bridge Seismic Retrofit
Program. The objectives are to determine the vulnerability of
California's major toll bridges to damage associated with strong
earthquakes and to design retrofits to improve seismic safety.
ADINA is used abundantly by Caltrans and contractors in this
Retrofit Program.
A very important part in the bridge analyses is the
modeling of the braces in the bridge structures (a photograph of the San
FranciscoOakland Bay Bridge is shown below). Typical braces, which
are laced built up members with rivets, were tested in the
laboratory. Since there are many such braces in bridge structures, it
was necessary to establish a simple and effective finite element model of
a typical brace.
In the following we briefly describe, courtesy of SC Solutions,
California, the modeling and verification of the behavior of these
braces using the ADINA momentcurvature beam elements. This ADINA
capability has proven to be of major importance for the nonlinear
analyses of bridges.
For the verification study, braces subjected to axial and
flexural stresses were modeled in detail with shell elements and, simplified, with the momentcurvature beam elements in ADINA. The following figures show that a drastic reduction in degrees of freedom (from about 15,000 dofs to about 50 dofs) to represent a brace is possible by employing the momentcurvature beam element models, without losing
any practical accuracy in the results. Therefore, the computation
time is drastically reduced by the use of the simplified beam
model for a brace while maintaining sufficient accuracy.
Also, axial forcedisplacement hysteresis loops that were
obtained from the experiment were compared with the numerical
results obtained using the momentcurvature beam elements, as shown in the following figure. The momentcurvature beam elements provided a good correlation with experiment.
These conclusions were reached for various brace slenderness ratios and
thus the momentcurvature beam elements were qualified to be a
very important capability in ADINA for modeling braces in large bridge
structures.
