Column base connections for hollow steel sections: Seismic performance and strength models

The seismic response of exposed hollow steel section columns to base plate connections is examined through a series of eight experiments. The prototype-scale tests investigate a range of variables including base plate size and thickness, column size, and anchor rod layout (four rods in two rows, and eight rods in three rows). The specimens were subjected to cyclic flexural loading and instrumented to provide direct (rather than inferred) measurement of tension forces in the anchor rods. All the specimens showed excellent deformation capacity, with a stable hysteretic response for base rotations as large as 0.057-0.13 rad. Three specimens failed by fracture of the weld between the column and the plate, whereas five did not fracture. Evaluation of the test data against the current design approach prevalent in the United States suggests that (1) the design approach is reasonably conservative but (2) does not address the effect of the third (i.e., central) row of anchor rods; as a result, it cannot be used to design them. A new design method is presented that explicitly incorporates the third row of rods. The new approach is evaluated against the test data and it is determined that the new approach reflects the internal mechanics of the connections in an improved way while providing more accurate estimates of forces in the rods. Recommendations for the design of the connections are outlined, along with ongoing work that leverages the deformation capacity of these connections for displacement-based design. The limitations of the study are summarized, especially in terms of challenges to the generalization of its findings.