to the HOT TOPICin
# 5 !
ELEVATION AS A STRUCTURAL CONTROL
Pyramid-shaped skyscrapers like the recently designed Brazilian Tower,
that could be the tallest and largest building in the world when it is
completed, continue to attract attention of architects and engineers because
such structures promise a better stability against earthquakes and winds.
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:
dissipate the wave energy with the properly engineered damping
absorb the resonant portions of the waves with the help of tuned
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.
|| 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.
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
| Arnold, C. and Reitherman,
R., 1982, “Building Configuration & Seismic Design”, Wiley
1998, "Elevation Configuration as a Structural Control", Proc. 67th Annual
SEAOC Convention, Reno, Nevada.
This page was last updated on
01 March 2000.