Analysis and Design of Large-Scale Civil Works Structures Using LS-DYNA

The Folsom Joint Federal Project (JFP) Auxiliary Spillway is a high profile addition to the Folsom Dam, located approximately thirty miles upstream of Sacramento, California. Total concrete placements on the project will exceed 140,000 cubic yards at a projected cost of nearly $1 billion. The main component of the JFP is a large concrete control structure with steel bulkhead gates, submerged tainter gates, and post-tensioned anchorage. As a critical piece of the flood control system in a densely populated, active seismic region, the JFP demanded a rigorous analysis of a scale never before used by the U.S. Army Corps of Engineers to design a civil works structure. The Sacramento District of the Corps developed a three-dimensional LS-DYNA model of the control structure, foundation, and reservoir in order to capture the fluid-structure and soil-structure interaction during a seismic event, something not possible with standard dam analysis procedures. The model incorporated anomalies within the foundation; their effects were significant and could not have been established and properly accounted for without the LS-DYNA model. The analysis examined seven suites of ground motions and two pool elevations that envelope the expected demand on the structure. Results from the model were used for both evaluation and design purposes. This paper presents suggestions on the modeling of large scale civil works structures such as the JFP. Included is an overview of lessons learned regarding contact definitions and troubleshooting, the application and scaling of seismic input, and methods for accurately modeling the behavior and load paths. Extensive verification of the LS- DYNA results was conducted using another widely used finite element analysis program; the procedures and results are discussed. Additionally, the paper advises on items to be considered during model development, with a focus on generating output suitable for design.