Performance Investigation and Design of Pile-to-Pile Cap Connections Subject to Uplift

Abstract

Substructure bridge components are designed to resist gravitational forces such as dead load and vehicular live load, as well as lateral forces including wind, vehicular braking, and centrifugal force effects. Significant lateral forces can create “uplift” conditions on some portions of the foundation. A review of current design techniques regarding uplift in the pile-to-pile cap connection indicates a lack of uniformity in the design process across state agencies stemming from minimal research performed in this area. In addition, approved uplift anchors for use in the field have not been tested. In order to close this gap, twenty-one full-scale steel H-pile specimens were fabricated and tested in Iowa State University’s Structural Engineering Laboratory to test the capacity of the pile-to-pile cap connection under static tensile loading. Specimens were cast both with and without anchorage and with 12” and 24” embedment depths in order to understand the behavior of the connection and to determine a suitable anchorage detail and design approach for uplift cases. Findings revealed that: (i) capacity of bare piles is generally underestimated and could be more frequently considered for uplift design; (ii) concrete cracking leads to a loss of bond in these types of connections; and (iii) positive anchorage or embedment that extends above the lower rebar mat of the footing is necessary to develop a high capacity connection.