Abstract

The rotational fixity of column base connections in Steel Moment Resisting Frames (SMRFs) strongly influences their seismic response. However, approaches for estimating base fixity have been validated only against laboratory test data. These approaches are examined based on strong motion recordings from four instrumented SMRF buildings in California to informbest practices for seismic response simulation. These buildings represent a range of structural properties, including height, layout, as well as different types of base connections and foundations. Three-dimensional simulationmodels are constructed for these buildings, including the gravity framing and nonstructural stiffness. For each building, base fixities are parametrically varied. These include pinned and fixed bases, aswell as intermediate fixities determined frompreviously developedmodels that are appropriate for simulating the specific types of base connections used in the buildings. The simulated response of these buildings is comparedwith strong motion recordings to informoptimal approaches for simulating column bases. The results indicate that: (1) for frames with exposed base plate connections, model-based estimates of base fixity result in the least error with respect to the recordings, compared to both pinned and fixed estimates, (2) for frames with embedded base connections, model-based estimates, as well as the fixed base assumption are equivalent, resulting in the least error, whereas the pinned base estimate results in large error, and (3) if simulated with the appropriate estimate of fixity as inferred fromthese observations, the simulations predict peak displacements and accelerations with good accuracy.

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Authors (3)