Lecture 02 Chapter1.ppt - kashanu.ac.ir · Microsoft PowerPoint - Lecture_02_Chapter1.ppt...
Transcript of Lecture 02 Chapter1.ppt - kashanu.ac.ir · Microsoft PowerPoint - Lecture_02_Chapter1.ppt...
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Chapter 1Chapter 1
Objectives D i ( ib ti ) l i
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Dynamic (vibration) analysis and control
1.1 IMPORTANCE OF VIBRATION ANALYSIS
Vibrations may cause:
I Large displacements and severe stresses in a structureI. Large displacements and severe stresses in a structure.
II. Material failure through fatigue.
III. severe discomfort to people who stay in the vibrating structure.
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Therefore, the dynamic response of the structure has to be predictedand the analytical solution has to be applied for proper design ofstructure.
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1.2 STRUCTURES AND THEIR VIBRATIONS
Al ll bj d i f i i- Almost all structures are subjected to various types of excitations(wind, earthquake, impact, explosion, etc.) So, dynamic analysis isneeded in all engineering projects.
- Some selected and important examples of vibrating structures are as
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- Some selected and important examples of vibrating structures are asfollows.
Typical wind-sensitive bridges
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5Cable-stayed bridge (Tokyo, Japan)
6Suspension bridge (Tokyo, Japan)
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Local vibrationGlobal vibration
8High-rise building
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9High-rise building & Elevated railway (Tokyo, Japan)
1.3 DEFINITION OF VIBRATION
-The term dynamic may be defined as time varying and dynamic loadis any load of which the magnitude, direction or position varies withtimetime.
-Vibration is a type of dynamic behavior in which system oscillatesabout a certain equilibrium positionabout a certain equilibrium position.
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1.4 TYPES OF VIBRATION
I. Time dependent external forces such as
- earthquake or underground explosion- wind or water waves- machine- vehicle motion- human
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In fluid dynamics:
II. Motion dependent force
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1.5 CONTROL OF VIBRATION
The modern structures tends to be higher, larger, more flexible andcomplex, so they are prone to vibrate.
Various disturbance due to vibrations:- Collapse- human discomfort- noise- non-serviceability
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The need for passive or active control systems to suppress vibration ofstructure is required.
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Some techniques of vibration reduction:
I. Passive control- base isolation- damper/ dynamic absorber- TMD, TLD- etc.
II. Active control- active mass control
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- active tendon control- etc.
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The first building to be seismically isolated
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Conventional structure Base-isolated structure
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Tuned Liquid Damper (TLD) system
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Tuned Mass Damper (TMD) system
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Visco-elastic Damper
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Active Tuned Mass Damper
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Actuated Mass Damper
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Active Tendon
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1.6 USE OF VIBRATIONVibrations usually have negative impact on a structure, and they cancause damage through large stress, displacements and fatigue.
In several cases, vibration can be used as a mean. For example:p1. Measurement or test
- identification of dynamic parameters of structure (by imposingcertain dynamic excitation and analyzing a response)- checking cable tension- mechanical vibration meters
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2. Vibration suppression- vibration absorbers / dampers
3. Construction or demolition- drills- explosions