UC San Diego

Baseplate connections, typically consisting of a steel baseplate welded to the terminus of a structural member, concrete anchors, and grout, are common features in buildings and nonbuilding structures. Incorporation of yielding anchors in these critical connections has received increased attention due to good performance observed during recent earthquakes. Such a strategy is attractive as a design approach, as the connections can provide a fuse at the location of seismic input, add to overall system ductility, and may elongate the system period. However, neither a systematic study of connection details that permit robust performance with yielding anchors, nor an investigation of the potential benefits of using such connections to reduce system-level seismic demands has been performed to date.

To these ends, a suite of baseplate component and system-level tests, as well as complimentary high-fidelity numerical simulations, was undertaken to systematically investigate detailing options to help advance the innovative concept of yielding-anchor base connections. First, a program of pseudo-static testing of a typical exposed steel column baseplate connection was executed to understand the details that may influence connection performance, including the anchor type, constituent materials, anchor stretch length, and connection setting arrangement. The impacts of these details on connection strength and rotation capacity are quantified. A novel categorization scheme of connection limit states was developed to track the evolution of damage in the connection. A 3-D, fiber-section numerical model was developed and verified against the results of this test program and several others available in the literature, providing a robust, generalized predictive method for the response of connections with parameters outside the current test program.

Subsequently, dynamic shake table testing of a miniature steel building was undertaken to probe the beneficial system-level effects that ductile, uplifting baseplate connections may have versus traditional "strong anchor" connections and superstructure fuses. These benefits were readily observed in testing and found in numerical analyses including reductions in total base shear of up to 50% and the virtual elimination of residual drift when compared to traditional systems. These results, combined with the ease of post-earthquake repair, demonstrate the usefulness of the ductile-anchor approach in improving overall seismic performance.