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Keywords: time history, accelograms, earthquake, Fourier amplitude spectrum.

Summary

This paper summarizes the importance of input data (accelograms) used to perform time history. Focus of article is analysis how distance from epicentre reflects on seismic forces in structure. This paper is based on work and results obtained by Nizic [1].

Almost all earthquake victims are caused by failures of buildings. Earthquakes are one of the greatest threats to bridges, and rpesent significant design challenges for structural engineers because of many yet unknown and unidentified parameters.

The bridge at Zeceva Draga was built in Croatia several months ago. Its total length is 940.8m. It lies on a horizontal curve. The columns are very tall; the tallest of them is 53m high. The span structure is a box girder 12.5m wide and 4m high. The area of cross section above the support is 10.2m², and in the span it is 9.4m².

The bridge was calculated using eight accelograms with magnitudes of 5.5, 6, 6.5 and 7, with epicenter distances of 0 and 15 km. The accelograms were created based on two earthquakes that took place in 1979 in the Adriatic region [2]; they were in Petrovac, with the magnitude M=6.8, and in Ulcinj, with the magnitude M=5.3.

Time history analysis was preformed for the past period of 1000 years. Calculation was made for a synthetic time sequence of accelerations which, on the average, corresponds to earthquakes with magnitudes 5.5, 6.5 and 7.0 with epicenter distances of 0 and 15km.

The greatest values of sectional forces from the time-history analysis are obtained for the magnitude of 7.0 (as expected), but for a distance of 15km from the epicenter to the bridge. To fully understand why forces for the epicenter distance e=15km are greater then ones with e=0km (peak ground acceleration for e=0km is more then 40% greater then one for e=15km), from the given accelograms, the acceleration spectrum curves (acceleration vs. frequency) are obtained and analyzed (as in Reference [3]). Based on acceleration spectrum curves for e=0km and e=15km and natural frequencies of the bridge the conclusion is made. It is shown that bridge has a very narrow frequency range and the accelogram with epicenter of 15km is more dangerous.

To take a more "in depth" view of frequency characteristics of accelograms the Fourier amplitude spectrum (Reference [4]) is calculated. Using this we are able to determine frequency content of accelograms. The whole frequency range was analyzed. In the low frequency range Fourier amplitude is greater, effectively meaning that the structure that has dominant frequencies is this range, and will have greater seismic forces (as bridge Zeceve Drage)

In this article two earthquakes with different epicenter distance are compared and analyzed. It is evident that earthquake occurring 15km from bridge Zeceva Draga is more dangerous then one at 0km. The seismic forces depend not only on peak acceleration but also on frequency content of a particular accelogram.

References

1: A. Nizic, "Seismic devices in bearing structures", M. Sc. Degree Thesis, University of Zagreb, Faculty of Civil Engineering, 2004.
2: E. Prelogovic, B. Aljinovich, and S. Bahun, "New data on structural relationship in the north Dalmatian Dinaride area": Geologia Croatica, v. 48, no. 2, 1985.
3: S.R.A.C. inc., "COSMOS/M 2.6 Electronic Documentation", ASTAR - Advanced Dynamics, p. 166-175, Los Angeles, 2000.
4: SeismoSoft [2004] "SeismoSignal - A computer program for signal processing of strong-motion data" [online]. Available from URL: http://www.seismosoft.com.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 81 PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping Paper 233 Earthquake Engineering of the Zeceva Draga Bridge A. Nizic, D. Mestrovic and J. Radic Department of Structures, Faculty of Civil Engineering, University of Zagreb, Croatia doi:10.4203/ccp.81.233 purchase the full-text of this paper Full Bibliographic Reference for this paper A. Nizic, D. Mestrovic, J. Radic, "Earthquake Engineering of the Zeceva Draga Bridge", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 233, 2005. doi:10.4203/ccp.81.233 Keywords: time history, accelograms, earthquake, Fourier amplitude spectrum. Summary This paper summarizes the importance of input data (accelograms) used to perform time history. Focus of article is analysis how distance from epicentre reflects on seismic forces in structure. This paper is based on work and results obtained by Nizic [1]. Almost all earthquake victims are caused by failures of buildings. Earthquakes are one of the greatest threats to bridges, and rpesent significant design challenges for structural engineers because of many yet unknown and unidentified parameters. The bridge at Zeceva Draga was built in Croatia several months ago. Its total length is 940.8m. It lies on a horizontal curve. The columns are very tall; the tallest of them is 53m high. The span structure is a box girder 12.5m wide and 4m high. The area of cross section above the support is 10.2m², and in the span it is 9.4m². The bridge was calculated using eight accelograms with magnitudes of 5.5, 6, 6.5 and 7, with epicenter distances of 0 and 15 km. The accelograms were created based on two earthquakes that took place in 1979 in the Adriatic region [2]; they were in Petrovac, with the magnitude M=6.8, and in Ulcinj, with the magnitude M=5.3. Time history analysis was preformed for the past period of 1000 years. Calculation was made for a synthetic time sequence of accelerations which, on the average, corresponds to earthquakes with magnitudes 5.5, 6.5 and 7.0 with epicenter distances of 0 and 15km. The greatest values of sectional forces from the time-history analysis are obtained for the magnitude of 7.0 (as expected), but for a distance of 15km from the epicenter to the bridge. To fully understand why forces for the epicenter distance e=15km are greater then ones with e=0km (peak ground acceleration for e=0km is more then 40% greater then one for e=15km), from the given accelograms, the acceleration spectrum curves (acceleration vs. frequency) are obtained and analyzed (as in Reference [3]). Based on acceleration spectrum curves for e=0km and e=15km and natural frequencies of the bridge the conclusion is made. It is shown that bridge has a very narrow frequency range and the accelogram with epicenter of 15km is more dangerous. To take a more "in depth" view of frequency characteristics of accelograms the Fourier amplitude spectrum (Reference [4]) is calculated. Using this we are able to determine frequency content of accelograms. The whole frequency range was analyzed. In the low frequency range Fourier amplitude is greater, effectively meaning that the structure that has dominant frequencies is this range, and will have greater seismic forces (as bridge Zeceve Drage) In this article two earthquakes with different epicenter distance are compared and analyzed. It is evident that earthquake occurring 15km from bridge Zeceva Draga is more dangerous then one at 0km. The seismic forces depend not only on peak acceleration but also on frequency content of a particular accelogram. References 1 A. Nizic, "Seismic devices in bearing structures", M. Sc. Degree Thesis, University of Zagreb, Faculty of Civil Engineering, 2004. 2 E. Prelogovic, B. Aljinovich, and S. Bahun, "New data on structural relationship in the north Dalmatian Dinaride area": Geologia Croatica, v. 48, no. 2, 1985. 3 S.R.A.C. inc., "COSMOS/M 2.6 Electronic Documentation", ASTAR - Advanced Dynamics, p. 166-175, Los Angeles, 2000. 4 SeismoSoft [2004] "SeismoSignal - A computer program for signal processing of strong-motion data" [online]. Available from URL: http://www.seismosoft.com. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £135 +P&P)
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