Archetype Dynamically Equivalent 3-DOF Model to Evaluate Seismic Performances of Intermediate Discontinuity in Frame Structures

Abstract

This paper investigated an intermediate discontinuity in a frame structure and its capability to mitigate the effects of seismic ground motions. The discontinuity represents a sudden change in the stiffness of the frame. The behavior of a structure after the introduction of discontinuity was studied by means of an archetype dynamically equivalent three-degree-of-freedom model. Two auxiliary systems were introduced to evaluate the effectiveness of the discontinuity. The first auxiliary system represented the structure without discontinuity. The second represented a system in which the part of the structure below the discontinuity is rigid. These two auxiliary systems allowed us to evaluate whether discontinuity is able to reduce the displacements of frame structure. The results were summarized using three gain coefficients that portray the ratio of displacements and drifts with and without the discontinuity. When the gain coefficients are less than unity, the discontinuity improves the dynamic behavior of the frame. To check the effectiveness of the proposed archetype model, results provided by an archetype and by spatial shear-type frames were compared. Then the archetype three-degrees-of-freedom system was used to conduct an extensive parametric analysis by varying geometrical and mechanical parameters. The results were organized in gain maps that represent the contour plot of the gain coefficients. Some maps were built using the spectrum compatibility criterion so that the results depend only on the seismic design spectrum. The gain maps show several ranges of the parameters’ region in which discontinuity is effective.