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Slides Earthquake Resistant design part1
 

Slides Earthquake Resistant design part1

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Details earthquakes and their effect on Structures

Details earthquakes and their effect on Structures

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    I'm designing a vertical column 11meter High (steel pressure vessel) for Zone 2 Addis Ababa in Ethiopia, I need to use in calculation G Loading, I need to know Longitudinal Acceleration (Gx); Lateral Acceleration (Gz); Vertical Acceleration (Gy), Can you help me? Best Regards.
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    Slides Earthquake Resistant design part1 Slides Earthquake Resistant design part1 Presentation Transcript

    • Earthquakes and Seismic Design By Dr. N. Subramanian 3rd Nov. 2012
    • Cross-section of EarthThough we have explored Space above ground extensively, wecould go only about 7.6 miles below ground! Russiangeologists started drilling into the Kola Peninsula, nearFinland, in 1970 and after 22 years could not proceed further.
    • Plate tectonics- Alfred Wegener , 1912 Dr. N. Subramanian
    • Plate tectonics (PT) Earlier theories assume gradual shrinking (contraction) or gradual expansion of the globe. PT is based on continental drift & developed in early 20th century Lithosphere is broken up into 7-8 major tectonic plates, and numerous smaller plates Tectonic plates move – because lithosphere has a higher strength and lower density than the underlying asthenosphere- Dissipation of heat from the mantle is the source of energy Lateral relative movement of the plates- 0 to 100 mm annually Dr. N. Subramanian
    • Three types of plate boundaries exist Dr. N. Subramanian
    • Global earthquake epicenters, 1963– 1998 Dr. N. Subramanian
    • Aerial view of San Andreas Fault in the Carrizo Plain, northwest of Los Angeles Dr. N. Subramanian
    • Earthquakes• Around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt.• Human activities that produce minor earthquakes: – Storage of large water behind a dam, – Injecting liquid under high pressure into wells (fracking to extract natural gas), – Coal mining – Oil drilling Dr. N. Subramanian
    • Recurrence of Earthquakes• Average recurrence of Earthquakes are: – Earthquake of M3.7–4.6 every year, – Earthquake of M4.7–5.5 every 10 years, – Earthquake of 5.6 or larger every 100 years.• The United States Geological Survey estimates that, since 1900, there have been an average of 18 major earthquakes (M 7.0– 7.9) and one great earthquake (M 8.0 or greater) per year. Dr. N. Subramanian
    • Aftershocks An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. It occurs in the same region of the main shock but always of a smaller magnitude. If it is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Formed as the crust around the displaced fault plane adjusts to the effects of the main shock They are dangerous - usually unpredictable, can be of a large magnitude, and can collapse buildings that are damaged from the main shock Dr. N. Subramanian
    • Earthquakes-EpicenterEpicenter is the point on the Earths surface that is directly above thehypocenter (where the Strain energy stored in the rock is first released) Dr. N. Subramanian
    • EARTHQUAKES Dr.N.Subramanian 12
    • Earthquake Prediction Instrument... from ancient China Dr. N. Subramanian
    • Seismograph is used to measure wave amplitude Dr. N. Subramanian
    • Can we predict earthquakes correctly?• Long ago, Catholic Church in Rome condemned Galileo Galilei and put him under house arrest for teaching ‘Earth revolves around the sun’!• Now, (Oct 22, 2012) an Italian court convicted seven scientists and experts for 6 years in prison for failing to adequately warn citizens before an earthquake struck central Italy in 2009, killing more than 300 people. Dr. N. Subramanian
    • Can we predict earthquakes correctly?• Scientists generally cannot predict the time, location and magnitude of EQ - But they did it once!• On Feb. 4, 1975, seismologists issued a warning to residents of Haicheng in northeastern China, prompting people to seek safety outdoors. – A M7.3- EQ struck that evening, killing more than 2,000 people and destroying more than 90 percent of the city. – Without the warning, about 150,000 people would have died! Dr. N. Subramanian
    • Characteristics of an Earthquake Dr. N. Subramanian
    • As the “quality” of the sediment decreases, the amplitude of the waves increases Dr. N. Subramanian
    • Magnitude: Richter scale- Californian seismologist Charles F. Richter, in 1930s Dr. N. Subramanian
    • P and S waves and Magnitude• P waves are the first to arrive due to their high displacement speed,• Followed by the S waves. Two parameters that determine magnitude:• The time delay between the arrival of the first P waves and S waves(proportional to the distance between the seismograph and the hypocentre of the earthquake), and• Their amplitude. Dr. N. Subramanian
    • P and S waves Dr. N. Subramanian
    • Graphical solution of the mathematical formula fordetermining magnitude on the Richter scale Dr. N. Subramanian
    • Intensity of earthquakes• Modified Mercalli Intensity scale (MMI) and MSK scale (Appendix D of Draft IS 1893)• Initially developed early last century by Giuseppe Mercalli.• Both have twelve levels of intensity – Level I – least perceptive – Level XII – most severe Dr. N. Subramanian
    • Factors Influencing Seismic DamageThe following factors influence theseismic damage:Peak Ground Acceleration (PGA) Amplitude, Duration and frequency of ground vibration, Magnitude, Distance from epicenter Geographical conditions between the epicenter and the site, Soil properties at the site and foundation typeBuilding type and characteristics. Damage to a Steel building in Dr.N.Subramanian Mexico City, 1985 24
    • Lateral Force Resisting Systems Dr.N.Subramanian 25
    • Better Performance in Earthquakes Have simple and regular Plans Dr.N.Subramanian 26
    • Collapse of L-shaped building in Ahmedabad, 2001 Dr. N. Subramanian
    • Avoid Irregular Configurations Dr.N.Subramanian 28
    • Avoid Novel Structural Features(If their EQ behavior is not known) Dr.N.Subramanian 29
    • Geometric vulnerabilities - CCTV Tower, China Dr. N. Subramanian
    • Response Spectra for Different Strong Earthquakes Dr.N.Subramanian 31
    • Response Acceleration coefficient as given in IS 1893 (Part 1)-2002 Smoothened Elastic Design Acceleration Response Spectrum (SEDRS) for 5% damping. For Steel structures use 2% damping Dr.N.Subramanian 32
    • SEISMIC ZONES OF INDIA Dr.N.Subramanian 33
    • Probabilistic Seismic Hazard Map (PSHM) of India• The National Disaster Management Authority, Govt. Of India, New Delhi has also developed a Probabilistic Seismic Hazard Map (PSHM) of India• http://ndma.gov.in/ndma/disaster/earthquak e/India-psha-finalreport.pdf Dr. N. Subramanian
    • Equivalent Lateral Base Shear Force ProcedureEquivalent Lateral Base Shear Force :Where Z= zone factor, I = importance factor, and R= Response reduction Factor I = 1.5 for largely crowded and imp. Buildings, and equal to 1.0 for other buildings. Dr.N.Subramanian 35
    • Approximate Fundamental PeriodThe approximate fundamental natural period of vibration for amoment resisting frame without brick infill panels is :Ta = 0.085 h0.75 in secondswhere h = height of the building in mFor all other buildings, including moment resisting framebuildings with brick in-fill,Ta = 0.09h / √d in secondswhere d = base dimension of the building at the plinthlevel, along the considered direction of the lateral force, inmeters. Dr.N.Subramanian 36
    • Equivalent Static Method (seismic coefficient method)Total design seismic base shear if determined by VB = Ah WAh = Design horizontal acceleration spectrum valueW = Seismic weight of the building Dr.N.Subramanian 37
    • Fundamental natural periods of structures differ over a large rangeAdapted from: Newmark, (1970), Current trends in the Seismic Analysis and Design of HighRise Structures, Chapter 16, in Wiegel, (1970), Earthquake Engineering, Prentice Hall, USA. Dr. N. Subramanian
    • Distribution of Base Shear to Different Levels of the Building After the base shear force VB is determined it should be distributed along the height of the building (to the various floor levels) using the following expression: After the Base shear is distributed, the frames may be analyzed by any standard computer program to get the internal forces! Dr.N.Subramanian 39
    • Dynamic AnalysisThe dynamic analysis methods are grouped into:Response spectrum method (multistory buildings, irregular buildings, overhead water ranks and bridge piers are often designed using this method) Time-history response analysis (most important structures such as nuclear reactors, large span structures or very tall buildings are designed using this method). Dr.N.Subramanian 40
    • EARTHQUAKE DESIGN PHILOSOPHYThe seismic design philosophy as per IS 1893(part 1) is: Minor and frequent earthquakes should not cause any damage to the structure Moderate earthquakes should not cause significant structural damage but could have some non-structural damage Major and infrequent earthquakes should not cause collapseHence design is done for much smaller forces than actual seismic loads.Note that this approach is different than that adopted in the case of wind, dead, live and other loads, where the structure is designed for the actual loads. Dr.N.Subramanian 41
    • Earthquake design philosophy Dr. N. Subramanian
    • Seismic Design PhilosophyThough the structure is designed for reduced earthquake loads, thefollowing contributing factors will prevent the collapse of the structure:Over-strength,Redundancy,Ductility Dr.N.Subramanian 43
    • Ductile and Brittle performance Dr. N. Subramanian
    • CURRENT DESIGN CODESExpected Performance:The design requirements primarily are intendedto safeguard against major failures and loss oflife, NOT to limit damage, maintain functions, orprovide for easy repairs. Dr.N.Subramanian 45
    • Performance Based Design (PBD)Future (PBD) Codes will be based on:Desired performance chosen by owner.Reduced business interruptionReduced damage costsCurrent Performance based design documents: Vision 2000 FEMA 356/273 ATC 40 FEMA 310 Dr.N.Subramanian 46
    • Load CombinationsIn general consider the 8- load combinations:(1) 1.5 (DL + IL) + 1.05(CL or SL)(2) 1.2 (DL + IL) + 1.05(CL or SL) ± 0.6(WL or EL)(3) 1.2 (DL + IL ± WL or EL) + 0.53 (CL or SL)(4) 1.5(DL ± WL or EL)(5) 0.9 DL ± 1.5 (WL or EL)(6) 1.2 (DL + ER)(7) 0.9DL + 1.2 ER(8) DL + 0.35(IL + CL or SL) + ALWhere, DL = Dead load, IL = imposed load (live load), WL = wind load, SL = snow load, CL = crane load (vertical / horizontal), AL = accidental load, ER = erection load and EL = earthquake load. Dr.N.Subramanian 47
    • Loading Combination for Non- orthogonal buildingsEight additional possibilities should also be considered.(1) ELx + 0.3 ELy(2) 0.3ELx + ELy(3) ELx – 0.3ELy(4) 0.3ELx - ELy(5) – (ELx + 0.3ELy(6) (0.3ELx + ELy)(7) – (ELx – 0.3ELy)(8) – (0.3ELx – ELy) Dr.N.Subramanian 48
    • Dr. N. Subramanian
    • Dr. N. Subramanian
    • Seismically Active regions in India Dr. N. Subramanian
    • Past Earthquakes in India Four Great earthquakes (M>8) occurred in a span of 53 years from 1897 to 1950; the January 2001 Bhuj earthquake (M7.7) is almost as large Dr. N. Subramanian
    • Past Earthquakes in India Dr. N. Subramanian
    • Dr. N. Subramanian