to the HOT TOPICin Earthquake Engineering
# 9 !
EARTHQUAKE / WIND QUIETING BUILDING SYSTEM
Seismic isolators, if properly used, can partially
cut off the earthquake energy transmission to a structure (Topic
4). Further, after the earthquake waves which penetrated
through a shield of base isolators enter the structure, there are three
ways to soothe their damaging effect, namely:
a) to dissipate the seismic
waves energy with the properly engineered damping devices;
disperse the seismic waves energy between a much wider range
of natural frequencies by adequately configuring the building elevation
thus preventing the resonant amplifications (Topic
absorb the resonant portions of the whole seismic waves band
with the help of mass dampers.
Devices of the last kind have been installed in high-rise
buildings for a quarter of a century. They are, usually, located at one
of the upper stories or distributed along the building height. Those devices
have the following major deficiencies:
1. They are
targeting only one, fundamental frequency and cannot control the higher
modes of vibration.
2. They require
special space inside the building for their accommodation.
3. They are
often very intricate and need a permanent maintenance that makes them a
To increase the shielded range of forcing
frequencies while keeping the construction costs as low as possible, the
concept of Multi-Frequency Quieting Building
System (MFQBS) was developed.
Each MFQBS includes horizontal
rigid floor or roof diaphragms enclosed
by an assembly of extended cantilevers of varying natural periods, connected
in parallel and running perpendicular to the diaphragm boundaries along
its perimeter. The cantilevers connected to each side of the diaphragm
are pliant to vibrations in the directions of those sides (see Figure above).
is a kind of a distributed system. However, in contrast with the
system described, for instance, in Kitada
and Park, 1994, it represents a more
sophisticated structural control technique in which each individual mass
damper is substituted with a mass damping floor diaphragm substructure
consisting of a multitude of differently tuned mass dampers.
Being tuned, with the help of their
geometry and material properties, to the main natural frequencies of the
building, the MFQBS cantilevers act as partial
tuned mass dampers that increase the earthquake/wind mitigation
of the system and permit an architectural design both attractive and functional.
The MFQBS cantilevers
should not be necessarily some sorts of solid beams. They can be constructed
as 3D frames like, e.g. the roof diaphragm cantilevers in Figure to the
| Normally, the
cantilever beams are staying still in a waiting mode. When swaying of a
building begins, one or several beams gets involved in a vigorous resonant
vibration which absorbs the propagating energy of the major resonant waves
in the building structure thus preventing lateral displacement amplifications
in the building structure during an earthquake or wind.
Y. and Park,
K.C., 1994, "A Comparative Study of Distributed
vs.Concentrated Hybrid Mass Damper Systems in High-Rise Buildings",
Proc.1st World Conf. on Structural Conrtrol, FA2-23, Vol.3,
This page was last updated on
14 April 2000.