Fundamental mechanisms of earthquake response reduction in building structures with inertial mass dampers are investigated. The inertial mass damper is effective with respect to relative acceleration between two nodes. The influence of inertial mass dampers on the ground‐motion input can be expressed by the influence coefficient vector to be multiplied on the ground‐motion acceleration in the right‐hand side of the equations of motion. It is shown that, when an inertial mass damper is taken out from one story, the component of the influence coefficient vector above that story becomes 1. This means that, if an inertial mass damper is taken out from one story, the inertial mass dampers above that story do not influence the input acceleration above that story. This observation is supported by the closed‐form expression of the influence coefficient vector. The mechanism of earthquake response reduction is also discussed from the viewpoint of earthquake input energy. It is shown that the earthquake input energy under an acceleration input with a constant Fourier spectrum depends on the influence coefficient vector. Finally, the characteristics of earthquake response reduction via inertial mass dampers are presented for three recorded ground motions. Copyright © 2011 John Wiley & Sons, Ltd.

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