By how much does the natural frequency of structures decrease during seismic response?

This web page was originally created in August of 2006, just before the 1^st European Conference on Earthquake Engineering and Seismology (1ECEES), to facilitate communication among the participants of one of the debate sessions of this conference with the same title. Due to the interest in this topic, I decided to maintain this page on USC web, and expand its scope by adding references to related publications communicated to me by colleagues who attended the session. If you would like to contribute a citation, URL address or a file of a paper on this topic to be posted on this web page, please send me an email. Finally, I am grateful to Martin G. Koller, the Co-chair of 1ECEES for earthquake engineering, for proposing this session.

Thank you for your interest.

Maria Todorovska, mtodorov@usc.edu

1st European Conference on Earthquake Engineering and Seismology

(a joint event of the 13th ECEE & 30th General Assembly of the ESC)

Geneva, Switzerland, 3-8 September 2006

STS E10: By how much does the natural frequency of structures decrease during seismic response?

Chairs: Maria Todorovska and Pierino Lestuzzi

Session abstract: Most seismic building codes estimate the design forces in structures based on the seismic coefficient C(T), where T is the “fundamental vibration period of the building.” Hence, having realistic estimates of the structural frequencies during strong earthquake shaking is very important for seismic design of new and retrofit of existing structures. Based on laboratory and field experiments, as well as on analysis of earthquake records in structures, it has been generally accepted that the frequency during strong earthquake shaking is smaller than measured during small amplitudes ambient vibration tests, and predicted analytically. However, there is a disagreement as to how large the decrease in frequency is. In this debate session on a contradictory issue, the following opposing views will be presented: (1) the decrease of natural frequency is large, and (2) the decrease of natural frequency is moderate. The emphasis will be on reinforced concrete structures. Michele Calvi from University of Pavia (Italy) will defend the view that the decrease of natural frequency is large, and Philippe Guéguen from University Joseph Fourier in Grenoble (France) will defend the view that the decrease is moderate (for RC buildings the decrease is less than 30% as compared to the values obtained from ambient vibrations tests). Maria Todorovska from University of Southern California (USA) will be the moderator for this session.

Poster Session:

Poster session display time: Thursday and Friday (Sept. 7 – 8^th), Level 1.

Oral Session:

Thursday, Sept. 7, 15:30 – 17:00 (3:30 pm – 5:00 pm)

15:00-16:30 : brief introduction (Todorovska) and two invited presentations (Calvi and Gueguen)

16:30-17:00 : discussion

STS E10: List of accepted abstracts (as of Aug. 20, 2006)

No.	ID	Title	Presenter	Paper
1	1535	State-of-the-knowledge on the period elongation of RC buildings during strong ground shaking	Calvi, Gian Michele	ECEES
2	1021	Comparison of the dynamic parameters extracted from weak, moderate and strong building motion	Gueguen, Philippe	ECEES
3	2062	Comparison of periods of buildings due to strong and weak motion	Celebi, Mehmet	SDTB
4	1918	Changing natural frequencies in structures: the case of Millikan library	Clinton, John	BSSA
5	1122	Simplified equations for estimation of period of vibration of existing buildings	Crowley, Helen	ECEES
6	1002	Dynamic auscultation of buildings and seismic integrity threshold assessment	Hans, Stephane Claude Boutin	ECEES
7	1005	Dynamic characteristics of an 8-storey building estimated from strong motion records	Kashima, Toshihide	ECEES 8NCEE
8	1246	In situ and modeling of RC-structure using ambient vibration and Timoshenko beam	Michel, Clotaire	ECEES
9	1848	Frequency and damping shift due to a damaging earthquake: the case of Molise (2002) Italy	Mucciarelli, Marco	BSSA
10	1207	Monitoring the dynamics of a concrete building enduring earthquake and wind excitation	Snæbjornsson, Jonas Thor	ECEES
11	2067	By how much does the natural frequency of structures decrease during seismic response? - IZIIS experience from shaking table test of reduced scale model	Tashkov, Ljubomir	Slides
12	1547	Variations of apparent building frequencies - lessons from full-scale earthquake observations	Todorovska, Maria	ECEES ISC,VanNuys

Abstracts

Other references:

• Celebi M (1993). Dynamic characteristics of five tall buildings during strong and low-amplitude motions, The Struct. Design of Tall Buildings, 2: 1-15.
• Clinton JF, Bradford SK, Heaton TH, and Favela J (2006). The observed wander of the natural frequencies in a structure. Bull. Seism. Soc. Amer., 96(1), 237-257.
• Fukuwa N, Tobita J, Kojima H (2004). Seismic observation systems in Nagoya University and publication of data, Proc. Third UJNR Workshop on Soil-Structure Interaction, March 29-30, 2004, Menlo Park, California.
• Kashima T, Kitagawa Y (2004). Dynamic characteristics of buildings estimated from strong motion records, Proc. 8^th U.S. National Conference on Earthquake Engineering, April 18-22, 2006, San Francisco, California, USA, Paper No. 1136.
• Motosaka M, Sato T, Yamamoto Y (2004). The amplitude dependent dynamic characteristics of an existing building before and after seismic retrofit, Proc. 13 World Conf. on Earthquake Engineering, Vancouver, B.C., Canada, August 1-6, 2004, Paper No. 1023, pp 14.
• Mucciarelli M, Masi A, Gallipoli MS, Harabaglia P, Vona M, Ponzo F, Dolce (2004). Analysis of RC building dynamic response and soil-building resonance based on data recorded during a damaging earthquake (Molise, Italy, 2002), Bulletin of the Seismological Society of America, 94(5): 1943-1953.
• Todorovska MI, Trifunac MD (2006).  Impulse response analysis of the Van Nuys 7-story hotel during 11 earthquakes and earthquake damage detection, Structural Control and Health Monitoring, in press 2006.
• Todorovska MI, Trifunac MD (2006).  Earthquake damage detection in the Imperial County Services Building III: analysis of wave travel times via impulse response functions, M.I. Todorovska and M.D. Trifunac, Soil Dynamics & Earthquake Engrg, submitted for publication, 2006.
• Todorovska MI, Al Rjoub Y (2006). Effects of rainfall on soil-structure system frequency: examples based on poroelasticity and a comparison with full-scale measurements, Soil Dynamics and Earthquake Engrg, 26(6-7), 708-717, 2006. 
• Zembaty Z, Kowalski M, Pospisil S (2006). Dynamic identification of a reinforced concrete frame in progressive states of damage, Engineering Structures 28: 668–681.

Contact: mtodorov@usc.edu