One of the challenges of analyzing high-rise buildings is the typical use of architectural symmetry. This causes closely spaced modes, i.e. modes have different mode shapes but natural frequencies of more or less same values.

Drift Analysis of a 54 storey building in Los Angeles during the 1994 Northridge Earthquake. The critical relative drift ratio has been set to 0.1%, which has triggered four out of the nine drift definitions. The selected definition has triggered one time shortly after the most intense shaking.

Drift Analysis is a powerful tool for the study of growing damage in structural elements. Here the relative drift of two structural elements is observed. It has been calculated using 22 measurements on a structure exhibiting an increasing damage. The two curves in the top diagram depict the development of the relative drift of each of the two structural elements. The damage affects the structural element corresponding to the blue curve most. In the diagram at the bottom, a damage indicator of the overall structural integrity is also shown for the same 22 measurements (available using the damage detection module). It is clear to see that damage starts at the ninth measurement, where damage indicators turn red, and the relative drift ratios start increasing significantly.