Structural Dynamics Lecture 4 Response to harmonic and periodic excitations: Application 目 同榜大学 上水工程学院 COLLEGE OF CIVIL ENGINEERING
Structural Dynamics Lecture 4 Response to harmonic and periodic excitations: Application
Contents Response of SDOF to harmonic excitation: application Identify the natural frequency and damping ratio Vibration measurements Earthquake Isolation ·Vibration Isolation Response of SDOF to periodic excitation 闺 土本2程学院
Contents Response of SDOF to harmonic excitation: application • Identify the natural frequency and damping ratio • Vibration measurements • Earthquake Isolation • Vibration Isolation Response of SDOF to periodic excitation
Field test of full-scale structures:Vibration shaker Rotating machine with eccentric mass p(1)=(meo)sin(ot) m。:maSS e:eccentricity @rotating frequency 35 kg vibration shaker Max.Force generated1500T 闺 土本程李悦
35 kg vibration shaker Max. Force generated1500T Field test of full-scale structures: Vibration shaker • Rotating machine with eccentric mass 2 sin e p t m e t : : : m mass e e eccentricity rotating frequency
Measurement of Natural Frequency and Damping Free Vibration test(logarithmic decrement method) Forced vibration test: ambient vibration(vibration due to environmental excitation) Forced vibration Forced vibration:resonance test Nature frequency Damping ratio 180 g=0.01 0.1 002 90 5=1 Frequency ratio/n —0.1-02…0.5 目 二水二程季院
Measurement of Natural Frequency and Damping • Free Vibration test (logarithmic decrement method) • Forced vibration test: ambient vibration (vibration due to environmental excitation) Forced vibration Forced vibration: resonance test • Nature frequency • Damping ratio
Forced vibration:frequency sweep method Selected frequencies---amplitude of S-S response Frequency-acceleration curve Frequency-displacement curve(Frequency -response curve) Identify natural frequency by the Peak of the curve Identify the damping ratio by half power-bandwidth method 5-0。-0 5=0-02 20n 0b+0a es/W② 6=f上5-人- 2f f6+f。 fa 6 Forcing frequencyf 闺 土亦工鞋季悦
Forced vibration: frequency sweep method • Selected frequencies --- amplitude of S-S response • Frequency – acceleration curve • Frequency-displacement curve (Frequency –response curve) • Identify natural frequency by the Peak of the curve • Identify the damping ratio by half power-bandwidth method 2 b a n b a b a 2 b a n f f f b a b a f f f f