Exposed column base plate connections in moment frames — Simulations and behavioral insights

• Base plate design methods use stress distributions not independently verified.
• Paper outlines FEM and simulation of exposed column base connections.
• New insights regarding stress distributions and behavioral modes.
• Current design methods misrepresent stress distributions for thick base plates.
• Refinements suggested for current approaches.

The response of exposed column base connections under axial and flexural loadings is controlled by complex interactions of various components within them, i.e. the column, base plate, anchor rods, and footing. Current approaches for strength characterization of these connections show good overall agreement with test data from specimens that are smaller relative to the prototype scale. However, internal stress distributions that underpin these approaches have not been independently verified, presenting challenges for the generalization of these approaches to full scale connections. A finite element (FE) simulation study is presented to offer insights into connection response with a focus on internal stress distributions. The 3-d FE simulations incorporate important aspects of behavior including contact, gapping and nonlinear multiaxial constitutive response of the various components. The simulations are rigorously validated based on multiple data streams obtained from a series of six experiments on exposed base plate connections. The results of the simulations indicate that current strength characterization and design approaches (that assume a rectangular bearing stress block) may grossly misrepresent the stress distribution under the plate. Thicker base plates tend to concentrate the stresses at the compression toe of the base plate. This significantly amplifies the bending moment in the base plate on the compression side of the connection, indicating that current approaches that do not consider this effect may be non-conservative. A simplified approach to address this issue is discussed. Similar issues are not observed for axial force estimates in anchor rods. Limitations of the work are outlined.