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TOPIC in Earthquake Engineering # 6
CHARTING FOR DYNAMIC STRUCTURAL CONTROL PROJECTS
By Valentin Shustov
Structural control for the purpose of earthquake protection
has been, mostly, associated with
landmark projects or those with practically unlimited budgets.
irony of the situation lies in
fact that engineers are under no pressure to make the control effective:
regulations require neither performance
based design nor
performance testing. Due
the inadequate regulations permit indiscriminate implementation
of this technology.
No wonder: neither optimization study of dynamic structural control in
general nor with respect to controlling devices parameters K (lateral
stiffness) and C (damping) were performed until recently (Shustov,
1997) when the Charts of Seismic Performance
(CSP) technique was introduced. A CSP
resembles the isoseismic maps of seismic zonation. However, the contours
here connect the points of equal Mitigation
Factor in the domain of K and C coordinates.
| Mitigation Factor
(MiF) equals a ratio of the maximum story
drift without structural control to that with the control (Shustov,
1994). If isolation is effective, MiF
holds. Otherwise, MiF<1, which should not
be tolerated even for any limited range of ground frequencies.
| The CSP
will reduce often lengthy and costly computations at a conceptual / preliminary
design stage and will considerably simplify the decision making process.
Charts of Seismic Performance
for a given building's structural type is a system consisting of a number
of individual charts like one shown on the right. The data from the previous
research (Shustov, 1993), having been
transformed into terms of MiF, reveal its
dependency on a story number N and earthquake intensity. Therefore,
a system of CSPs constitutes a matrix where
the horizontal rows account for different numbers of stories while the
vertical ones represent different seismic intensities .
|| Each element of the system
matrix, an individual CSP, relates to
a certain structural type and height of a building and to a certain magnitude
of earth shaking. The rectangles on the plane K-C should account
for possible deviations in the control device's stiffness and damping characteristics
and may be called the Control Devices Footprints.
Having been projected on the corresponding chart levels, they screen the
areas of the anticipated mitigation.
In order to start, the user needs to specify a particular
chart to deal with. Then make projections of the targeted footprints, say
and C, on the chosen chart (on the left).
It is obvious that the device A has the best
| The global optimization technique with the help of Charts
of Seismic Performance represents an expansion of the response
spectra approach to the MDOF building systems. It provides a user-friendly
graphical environment that may prevent unwarranted extrapolation of favorable
and overoptimistic judgments onto the range of parameters where those judgments
do not not belong.
| Shustov, V.,
Isolation: Fresh Insight", Technical Report to NSF BCS-9214754,
SRE, Los Angeles, CA.
Shustov, V., 1994, "Energy
Absorbing Technique: Challenge of Proportioning", Proc. 3rd Int'l
Conf. on Structures under Shock and Impact, Madrid, Spain.
Shustov, V., 1997,
"Future Seismic Codes and Earthquake Insurance", Proc. 66th Annual
SEAOC Convention, San Diego, CA.