To reduce the likelihood of impact damage from over-height vehicles and meet AASHTO minimum vertical clearance requirements, some bridges in Georgia have been rehabilitated using steel pedestals as a cost-effective means to increase the vertical clearance height of bridges. Steel pedestals perform a similar function as bearings, which are not designed to resist lateral loads but rather transfer loads from the bridge deck to the substructure. As a result, steel pedestals may exhibit structural instability under horizontal inertial loads similar to how bearings were proven to be extremely vulnerable components in past earthquakes. These vulnerabilities include instability, lack of appropriate connection details, and limited deformation capacity.

To address these concerns, the performance of steel pedestals under low seismic loads is evaluated both experimentally and analytically. Large-scale quasi-static tests for low-to-moderate and ultimate loads are conducted on a 40'-0" bridge rehabilitated with "short" pedestals of 1'-7" in height, and "tall" pedestals of 2'-9½" in height at the Structures Laboratory on the campus of the Georgia Institute of Technology. Installation of the steel pedestals is based on field conditions from a candidate bridge in Georgia . One of the major testing goals is to determine the structural properties and vulnerability of the steel pedestals including any structural instability due to horizontal inertial loads. Experimental test results complement detailed analytical studies, where bearing stiffness properties of the steel pedestals are defined to determine the displacement demands of the bridge system. Findings and recommendations for the best practices of steel pedestals subjected to low-to-moderate seismic loads will be presented to the Georgia Department of Transportation, for which this comprehensive study was motivated. Additionally, the methodology used for this experimental and analytical study can be used for other states that may be considering the use of steel pedestals for elevating bridges in regions of higher seismic risk than Georgia.