Basic Theory of Plates and Elastic Stability - Part 5

Tài liệu tham khảo giáo trình cơ học kết cấu trong ngành xây dựng bằng Tiếng Anh - Yamaguchi, E. “Basic Theory of Plates and Elastic Stability” Structural Engineering Handbook Ed. Chen Wai-Fah Boca Raton: CRC Press LLC, 1999 - Earthquake Engineering
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Basic Theory of Plates and Elastic Stability - Part 5Scawthorn, C. “Earthquake Engineering”Structural Engineering HandbookEd. Chen Wai-FahBoca Raton: CRC Press LLC, 1999 Earthquake Engineering 5.1 Introduction 5.2 Earthquakes Causes of Earthquakes and Faulting • Distribution of Seis- micity • Measurement of Earthquakes • Strong Motion At- tenuation and Duration • Seismic Hazard and Design Earth- quake • Effect of Soils on Ground Motion • Liquefaction and Liquefaction-Related Permanent Ground Displacement 5.3 Seismic Design Codes Purpose of Codes • Historical Development of Seismic Codes • Selected Seismic Codes 5.4 Earthquake Effects and Design of Structures Buildings • Non-Building Structures 5.5 Defining TermsCharles Scawthorn ReferencesEQE International, San Francisco, Further ReadingCalifornia and Tokyo, Japan5.1 IntroductionEarthquakes are naturally occurring broad-banded vibratory ground motions, caused by a numberof phenomena including tectonic ground motions, volcanism, landslides, rockbursts, and human-made explosions. Of these various causes, tectonic-related earthquakes are the largest and mostimportant. These are caused by the fracture and sliding of rock along faults within the Earth’scrust. A fault is a zone of the earth’s crust within which the two sides have moved — faults maybe hundreds of miles long, from 1 to over 100 miles deep, and not readily apparent on the groundsurface. Earthquakes initiate a number of phenomena or agents, termed seismic hazards, which cancause significant damage to the built environment — these include fault rupture, vibratory groundmotion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanentground failure (e.g., liquefaction), fire or hazardous materials release. For a given earthquake, anyparticular hazard can dominate, and historically each has caused major damage and great loss oflife in specific earthquakes. The expected damage given a specified value of a hazard parameter istermed vulnerability, and the product of the hazard and the vulnerability (i.e., the expected damage)is termed the seismic risk. This is often formulated as E(D) = E(D | H )p(H )dH ψ (5.1) Hwhere = hazardHψp(·)ψ = refers to probability = damageDψ 1999 by CRC Press LLCcE (D |H ) = vulnerabilityE(·) = the expected value operator Note that damage can refer to various parameters of interest, such as casualties, economic loss,or temporal duration of disruption. It is the goal of the earthquake specialist to reduce seismic risk.The probability of having a specific level of damage (i.e., p(D) = d ) is termed the fragility. For most earthquakes, shaking is the dominant and most widespread agent of damage. Shakingnear the actual earthquake rupture lasts only during the time when the fault ruptures, a processthat takes seconds or at most a few minutes. The seismic waves generated by the rupture propagatelong after the movement on the fault has stopped, however, spanning the globe in about 20 minutes.Typically earthquake ground motions are powerful enough to cause damage only in the near field (i.e.,within a few tens of kilometers from the causative fault). However, in a few instances, long periodmotions have caused significant damage at great distances to selected lightly damped structures. Aprime example of this was the 1985 Mexico City earthquake, where numerous collapses of mid- andhigh-rise buildings were due to a Magnitude 8.1 earthquake occurring at a distance of approximately400 km from Mexico City. Ground motions due to an earthquake will vibrate the base of a structure such as a building.These motions are, in general, three-dimensional, both lateral and vertical. The structure’s mass hasinertia which tends to remain at rest as the structure’s base is vibrated, resulting in deformation ofthe structure. The structure’s load carrying members will try to restore the structure to its initial,undeformed, configuration. As the structure rapidly deforms, energy is absorbed in the process ofmaterial deformation ...