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Structural Damping Applications in Seismic Response Modification
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The Authors of Structural Damping eBook
There are three editors of Structural Damping Applications in Seismic Response Modification:
George C. Lee,
Gary F. Dargush
and Jianwei Tune.
Preface to Structural Damping Applications in Seismic Response Modification eBook
In the present day, earthquake engineering analysis is devoting a serious effort towards establishing seismic efficiency necessities related to giant inelastic deformations of the construction. On the similar time, structural response modification techniques (definitely, passive power dissipation and seismic isolation techniques) have been extensively used.
It’s cheap to count on that the subsequent analysis emphasis in performance-based engineering is to combine each frontiers for extra optimum seismic efficiency of constructions.
On this Structural Damping Applications in Seismic Response Modification e book, latest advances in structural damping are introduced and their functions to the design of passive structural response modification gadgets are given to enrich the present supplemental damping design apply for high-level damping.
So far as security, efficiency, and value for each elements of inelastic deformation and structural response management are involved, structural damping is a core data space.
Integration with seismic efficiency requirement just isn’t addressed in this Structural Damping Applications in Seismic Response Modification e book. Aseismic design utilizing supplemental dampers has steadily gained recognition in the earthquake engineering career over the previous a number of many years.
Many sensible functions of assorted dampers will be discovered worldwide and, in america, damper design has been included in constructing codes.
To this point, damping design is based totally on the ideas of the power equation, efficient proportional damping, and simplified linear single-degree-of-freedom (SDOF) response spectrum.
These ideas, together with their related underlying assumptions, help the concept that putting in supplemental dampers in constructions will dissipate power.
Nonlinear damping is introduced by an efficient damping ratio by linearization schemes, and the damping coefficients of constructions are assumed to be traditional damping matrices in order to ascertain a process for damping design.
As well as, it’s assumed that statistical procedures that use earthquake data will be carried out by proportional scaling of their amplitudes.
These assumptions have enabled us to develop a design process for supplemental dampers. Nevertheless, it’s not effectively understood that a few of these assumptions work effectively solely when the quantity of damping in constructions is inside a selected low stage.
The primary foremost goal of this Structural Damping Applications in Seismic Response Modification e book is to supply a theoretical basis on the position of damping in the dynamic response of constructions, particularly when the extent of damping is excessive or when nonlinearities turn into necessary design points.
The second foremost goal is to supply response spectra–based mostly design ideas and tips for sensible functions of damping gadgets to cut back earthquake-induced structural vibration.
Typically talking, structural responses underneath seismic excitations are dynamic processes. There are three resisting power elements to counter the earthquake load, one in every of which is the damping power.
Whereas damping expertise has been developed and superior in a spread of mechanical and aerospace engineering functions over a few years, it has turn into a well-liked strategy in structural engineering solely in the later a part of the 20th century.
Whereas the event and utility of power dissipation gadgets in structural engineering proceed to broaden, there are a selection of basic points associated to the dynamic conduct of constructions with supplemental damping as a system that require additional research.
Limitations and impacts of utilizing power dissipation gadgets have to be clarified and established. This Structural Damping Applications in Seismic Response Modification e book intends to fill the data hole by serving to earthquake engineers to raised perceive the dynamic conduct of constructions and to extra successfully use the design codes for dampers.
The important thing parts in this Structural Damping Applications in Seismic Response Modification e book are summarized as follows. An easy idea usually advocated in damping design is that “extra power dissipated by the added dampers will end result in much less vibration power remaining in the construction, and thus the structural response is lowered.
” This isn’t all the time true. A better stage of damping might not successfully scale back the responses of a given construction. In some circumstances, high-level damping might even amplify the responses, as a result of the extent of structural response relies upon not solely on native power dissipation, but in addition on power enter and its redistribution.
Thus, minimizing the conservative power of the vibrating system in constructions with supplemental damping is a extra acceptable normal guideline.
A number of different fundamental points in structural damping are rigorously reviewed. These embrace the utmost power dissipation precept underneath preset damping power and allowed structural displacement; the damping adaptability of gadgets that may function in a big dynamic vary of earthquake hundreds;
the viscoelastic conduct of any damping parts that take the supporting stiffness in addition to set up apply into consideration; nonproportional damping that must be minimized as a lot as potential in design apply;
the limitation of utilizing damping power that gives a sensible engineering restrict past which including extra damping offers diminishing beneficial properties; and the issue of damping and stiffness nonlinearity that can not be precisely approximated by immediately’s design approaches.
As well as, a design precept based mostly on power distribution is mentioned, which can be helpful for typically damped multi-degree-of-freedom (MDOF) techniques. The traits of nonlinear damping and nonlinear constructions are advanced points to handle in damping design.
On this Structural Damping Applications in Seismic Response Modification e book, nonlinearity is taken into account in three circumstances. The primary case includes a linear construction with small nonlinear damping, the second case is for a linear construction with bigger nonlinear damping, and the third case applies when each the construction and the damping are nonlinear.
Within the first case, as a result of the damping power is reasonably small, virtually any kind of linearization can be utilized with out inflicting any vital design discrepancies. Within the second case, care should be taken to decide on correct linearization; using nonlinear design spectra can usually be an inexpensive strategy.
Within the third case, linearization strategies, although adopted by many constructing codes, can present extremely inaccurate outcomes. Strategies such because the equal displacement strategy (utilizing R-factors), equal power strategy, and pushover strategy all have their limitations.
Because the nonlinear design spectra strategy requires too many response spectra, not just for particular damping and stiffness, but in addition for particular ranges of floor excitations, it’s not helpful in apply. Thus, nonlinear time historical past evaluation should be used.
This latter methodology, although all the time workable for the primary two circumstances, can yield an unacceptable computation burden, making it unattractive to be used in day-to-day sensible damping design. For that reason, time historical past evaluation just isn’t emphasised in all discussions.
Two varieties of design approaches are supplied in this Structural Damping Applications in Seismic Response Modification e book. The primary is the design response spectra strategy. Particularly, the design is modified by a simplified issue, the damping ratios of the primary a number of vibration modes of the construction.
For readers accustomed to the design response spectra methodology for an SDOF linear system, this strategy offers design when damping is small and for structural responses in elastic ranges.
The modified strategy addresses circumstances the place damping is giant and nonlinear. Examples of how you can modify the response spectra design are additionally supplied. The second kind of damper design is predicated on time historical past evaluation, for which a number of points are necessary.
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