The contribution of column deflection, ∆_c is generally small compared to joist and girder deflections for buildings with few (1-5) stories but becomes significant for buildings with many (>6) stories because of the increased length of the column "spring". For a building with very many stories (>15), the natural frequency due to the column springs alone may be in resonance with the second harmonic of the jumping frequency (Alien, 1990).