Note for Earthquake Resistant Design of Structure - ERDS By Ayush Agrawal
- Earthquake Resistant Design of Structure - ERDS
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06CV834: Earthquake Resistant Design of Structures INTRODUCTION TO SEISMOLOGY Dr. S. K. Prasad Professor of Civil Engineering S. J. College of Engineering, Mysore 570 006 prasad_s_k@hotmail.com Syllabus of VTU 06CV834 covered (Chapters 1 and 2) Earthquake ground Motion, Engineering Seismology, Theory of plate tectonics, seismic waves, Magnitude and intensity of earthquakes, local site effects, seismic zoning map of India, Seismic Design Parameters, Types of Earthquakes, earthquake ground motion characteristics. Topics covered Definition of Earthquake and Terminologies Importance of Earthquake Engineering Continental Drift Elastic Rebound Theory Plate Tectonic Theory Tectonic Plate Boundaries Faults Surface and Body Waves Seismic Waves and their propagation Causes for Earthquake Types of Earthquakes Magnitude and Intensity Strong Motion Characteristics of earthquake Typical earthquake ground motion Characteristics of ground motion necessary for design Seismic Instrumentation Seismic Zoning map of India – Background, Basis and Zone factor Design Basis Earthquake and Maximum Credible Earthquake Concept of different levels of design Importance of Local site effect Microzonation Base Isolation Liquefaction 1.1 EARTHQUAKE is the disturbance that happens at some depth below the ground level which causes vibrations at the ground surface. These vibrations happen in all the directions and are totally uncertain. The location, time, duration, magnitude and frequency of earthquake are totally unknown. Also, these vibrations are momentary, happening for a short while. It should be noted that earthquakes are totally unpredictable. Earthquake is the shaking or trembling caused by the sudden release of energy below the ground. It is usually associated with faulting or breaking of rocks. Continuing adjustment of position results in aftershocks. Fig. 1 explains some terminologies in the field of earthquake engineering. 1
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06CV834 : Earthquake Resistant Design of Structures Introduction to Seismology, Prof. S. K. Prasad 1.1.1 Focus or Hypocenter: It is the location from where earthquake originates. The point within Earth where faulting begins is the focus, or hypocenter. It may be a point, line or a plane. It will be deep below the earth surface. 1.1.2 Epicenter: It is the projection of focus on the surface of earth. It is a point which is closest to point of release of energy. The point directly above the focus on the surface is the epicenter. 1.1.3 Focal Depth: Distance between focus and epicenter is the focal depth. The closer the focal depth, more damaging is the earthquake. 1.1.4 Epicentral Distance: Distance between point of interest and epicenter is called Epicentral Disatnce. Fig. 1 : Terminologies in Earthquake Geotechnical Engineering Table 1 : Comparison of damaging effects of earthquakes in different countries HAITI INDIA JAPAN Haiti Earthquake Bhuj Earthquake Ryukyu Island Earthquake Port Au Prince Bhuj, Gujarat 26 Feb 2010 12 Jan 2010 26 Jan 2001 Mw 7.0, 1 Death Mw 7.0 Mw 7.3 Izu Island Earthquake MM X MM X 9th Aug 2009 Focal Depth 13 km Focal Depth 15 km Mw 7.1, 0 Death 2.5 Lakh Deaths 20,000 Deaths Iwate Miyagi Nairiku Earthquake 3 Lakh Injured 1.67 Lakh Injured 14 June 2008 1.3 Lakh Displaced - Mw 6.9, 12 Deaths 1.0 Lakh Houses Destroyed 2.0 Lakh Houses Destroyed Noto Peninsula Earthquake 2.0 Lakh Houses Damaged 4.0 Lakh Houses Damaged 25 March 2007 Mw 6.9, 1 Death Kuril Island Earthquake 15 Nov 2006 Mw 7.9, 0 Death 2
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06CV834 : Earthquake Resistant Design of Structures Introduction to Seismology, Prof. S. K. Prasad Table 1 presents a list of big earthquakes that hit different parts of the globe in recent times. The list is prepared considering only a few earthquakes that had similar magnitude and focal depths. It means that the energy released was similar and from similar depths. Hence, the effects of these earthquakes at the ground level were also similar. What is shocking to note is the comparison of number of deaths. In Haiti, one out of twelve from capital city Port Au Prince perished leading to 2.5 Lakh casualities, while in India the total death was about 20000. In contrast, the number of deaths in Japan due to earthquake was insignificant. An inference can be made that the knowledge about earthquake engineering among engineers and awareness about importance of earthquake engineering among policy makers and general public is essential. However, the recent earthquake in Japan on 11th March 2011 had different effect killing more than 25000 people. Some details about this great earthquake are furnished below. 1.1.5 Some vital statistics about Great Japan earthquake of March 2011 Magnitude : 9.0 Intensity : > X Date : Friday, the 11th March 2011 Time : 11.30 am in Japan (8.00 am IST) Focal Depth : 24.4 km Region : Near east coast of Honshu Island, Japan, 130 km east of Sendai, 178 kn east of Yamagata, 178 km east north east of Fukushima, 373 km North east of Tokyo Death Toll : More than 25000 Evacuated : About 5 Lakh People Infrastructure : Entire towns were wiped off the map, Houses, cars, ships, buildings were washed away, roads buckled, highway collapsed, power line tangled, railway track damaged (1.2 Lakh houses damaged, 15000 houses completely destroyed) Insured loss : USD 35 Billion (175000 Crore Rupees) Overall loss : USD 350 Billion (1750000 Crore Rupees) Honshu Island moved by 2.4 m Duration of shaking 3 to 5 minutes Number of after shocks > 400 and some with magnitudes of 7.2 Change in length of day caused by redistribution of earth mass : 1.8 microsecond shorter It can therefore be inferred that we are still in the process of understanding the nature. Nature this time was furious on Japan and resulted in a very large earthquake, fourth biggest. Top five earthquakes ever recorded on earth were 1. Mw9.5 Chile, 5th May 1960, 1600 Killed, 20 Lakh Homeless 2. Mw 9.2 Prince William Sound, Alaska, 27th March 1964, 128 Killed, Tsunami 3. Mw 9.1 Sumatra, 26th Dec 2004, 2.2 Lakh Killed 4. Mw 9.0 Kamchatka Peninsula, Russia, 4th Nov 1952 5. Mw 9.0 Tohoku earthquake, Japan, 11th March 2011 1986 Chernobyl disaster ranked 7, which is the highest in terms of severity in Nuclear Radiation. Fukushima Power Plant disaster was also ranked more than 6 for Nuclear radiation indicating that the severity of radiation in Japan was close to the worst. Table 2 presents some of the popular earthquakes that were eye openers to researchers, policy makers and general public. Each of these earthquakes had some special features that helped 3
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06CV834 : Earthquake Resistant Design of Structures Introduction to Seismology, Prof. S. K. Prasad in enhancing the knowledge. Always, it is possible to learn from failures and the below detailed earthquakes caused many failures. Table 2: Summary of specialties of different earthquakes Name Date Location Specialty Sl No 1 Kanto earthquake 1 Sep 1923 7.9 Mw 2 Hyogo Ken Nambu earthquake Great Hanshin earthquake Kobe earthquake 17 Jan 1995 6.8 Mw 3 Bhuj earthquake Gujarath earthquake 26 Jan 2001 7.2 Mw 4 Sumatra earthquake 26 Dec 2004 9.1 Mw 5 Haiti earthquake 13 Jan 2010 7.0 Mw 6 Christchurch earthquake Canterbury earthquake Super earthquake Great East Japan Earthquake 22 Feb 2011 4 Sept 2010 11 Mar 2011 6.3 Mw 7 One of the first recorded earthquakes with huge number of deaths. Most deaths were due to fire Earthquake happened exactly one year after Northridge earthquake in the US. Japanese experts then had felt that earthquake management in Japan is better Japanese experts were shamed due to more than 5000 deaths Most deaths were due to fire accident An eye opener to politicians & administrators All the earth dams near epicenter (50 km radius) were severely damaged Several newly constructed apartment buildings in Ahmedabad (200 km away from epicenter collapsed) 4th largest earthquake magnitude-wise Caused Tsunami that took away more than 2 lakh lives After shocks as big as 8 Mw recorded for years Clear indication of lack of knowledge in earthquake engineering. More than 2.5 lakh people in the capital city Port Au Prince were killed (out of 30 Lakhs). Even after two years the country has not come to normalcy Focal depth among the smallest (5 km) Widespread liquefaction and Liquefaction of already liquefied ground 5th largest earthquake ever recorded Nuclear radiation due to damage to Fukushima nuclear reactor. Tsunami waves as high as 20 m Many permanent structures performed very well 9.0 Mw Fig. 2 presents the map of India with the epicenters of most recent earthquakes that hit India. Sumatra earthquake of 2004, Kashmir earthquake of 2005 and the most recent Sikkim 4
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