The Montana Department of Transportation (MDT) has found concrete-filled steel tube (CFST) piles connected at the top by a concrete pile cap to be a very cost-effective support system for short and medium span bridges. This type of system offers low initial cost, short construction time, low maintenance requirements, and a long service life. While the gravity load performance of these systems is well understood, their strength and ductility under extreme lateral loads (e.g., seismic events) is more difficult to reliably predict using conventional design procedures. The proposed research aims to further develop newly established design and analysis methodologies, and to ultimately ensure the desired bridge performance.

MDT has sponsored previous research at Montana State University (MSU) to investigate the performance of these systems under extreme lateral loads and to develop appropriate analysis/design procedures. The primary objective of the proposed research is to further validate/improve MDT’s CFST to concrete pile cap connection design/analysis methodologies, and to ensure the efficacy of these methodologies for a wide variety of potential design configurations. This research will include physical tests of scaled specimens, which may include specimens with variations in cap dimensions, CFST diameter, or number of embedded piles. This project will consist of two phases. The first phase of research (to be conducted through this project) will be focused on identifying potential gaps in the existing design/modeling strategies, and then designing future tests to help close these gaps. The second phase of research (to be proposed at a later date) will involve the testing of the specimens designed in the first phase of research.

Bridges have been found to be a particularly vulnerable element of critical infrastructure systems during earthquakes. While CFST pile to concrete pile cap bridge support systems designed following the current methodology offer significantly better performance in seismic events than those designed using older methodologies, this design procedure has not been fully validated by physical testing and analytical modeling. The results of this project are expected to provide such validation, and the data necessary to revise this procedure so that the required connection performance during seismic events is realized under various conditions.