The standard requires seismic design of specified ceilings under linear response of main frames caused by occasional earthquake motion. But it is preferable to check safety under non-linear response of main frames caused by rare earthquake motion. In this paper, a direct estimation method for non-linear floor response spectrum is proposed. The method is adapted one of linear modal analysis, composed of empirical formulas of non-linear response. By comparing seismic design forces for specified ceilings with those caused by rare earthquake motion, it is shown that specified ceilings with high natural frequency can avoid damage even under severe earthquakes.
