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By Valentin Shustov It has long been accepted by profession that the shape of the building elevation and its effect on the building behavior are well understood. Thus, the vertical setback configurations are usually considered as common irregularities in a building geometry. Been intended, primarily, for some non-structural reasons, they are often recognized as a potential source of structural problems (Arnold and Reitherman, 1982). However, the elevation configuration can and should be used to prevent buildings' resonant amplifications. |
| There are two well known ways
to decrease damaging effects of earthquake / wind initiated shear waves,
which may propagate in a building structures, namely:
a) to dissipate the wave energy with the properly engineered damping devices; b) to absorb the resonant portions of the waves with the help of tuned mass dampers. Both energy dissipation and absorption assume installation of special structural control devices, often requiring a permanent maintenance, which makes such types of control rather expensive. |
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There is, yet, a better choice:
to disperse the shear wave
energy between a wide range of frequencies of oscillation by configuring the building elevation adequately thus preventing the structural system from possible resonances (for a demo, click on the picture. In case of success, this new design approach may yield up 2 to 3- fold mitigation effect. |
| To increase a building's ability to curb horizontal excursions at winds or earthquakes, while keeping the costs as low as possible, the Earthquake and Wind Protective Building Structure or EWPBS was developed (Shustov, 1998) that includes, in its simplest embodiment, a multistory building tower tapered upward. The taper is smooth or with superficial notches, and the angle of taper required for the targeted dispersion of shear waves energy is determined by the general building size and a nature, size and location of structural and nonstructural elements. In general, the term elevation configuration may refer both to a building's shape and to a distribution of masses and stiffness along its height. |
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Earthquake or wind quieting ability of EWPBS
is provided by a specific pattern of multiple reflections and transmissions
of vertically propagating shear waves, which are generated by breakdowns
into homogeneity of story layers, and a taper. Any abrupt changes
of the propagating waves velocity result in a considerable dispersion of
the wave energy between a wide ranges of frequencies thus preventing
the resonant displacement amplifications in the building.
It should be understood that a tapered profile of a building is not a compulsory feature of the new method of structural control. A similar resonance preventing effect can be also obtained by a proper “tapering" of other characteristics of a structure, namely, the mass and stiffness. As a result, the EWPBS techniques permit an architectural design that may be both attractive and functional. |
| Arnold, C. and Reitherman,
R., 1982, “Building Configuration & Seismic Design”, Wiley
Public., NY.
Shustov, V., 1998, "Elevation Configuration as a Structural Control", Proc. 67th Annual SEAOC Convention, Reno, Nevada. |
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