Earthquake Engineering PDF

Module 2: Earthquake Effects and Earthquake Resistive Structures Module 2 is about the effects of earthquakes to humans and its surrounding, the safety measures when earthquake is concern and methods to make structures resistive to earthquakes. Objectives: 1. Learn the effec...

Module 2: Earthquake Effects and Earthquake Resistive Structures Module 2 is about the effects of earthquakes to humans and its surrounding, the safety measures when earthquake is concern and methods to make structures resistive to earthquakes. Objectives: 1. Learn the effects of earthquakes and learn lessons from earthquake events. 2. Be able to discuss the different structural/construction methods against earthquakes. 3. Learn some safety rules before, when and after an earthquake occurs. Outline: 1. Earthquake Effects 2. Earthquake Prediction 3. Major Earthquake Zones 4. Earthquake Safety Measure 5. Safety Rules Before, During and After an Earthquake 6. Requirements for Design and Construction of Earthquake Resistive Structures 7. Structural/Construction Methods Against Earthquakes Content: EARTHQUAKE EFFECTS Effects of Earthquakes Response – the effect produced on a structure by an earthquake ground motion. Spectral response – is the maximum response during an earthquake. Ground-motion modification – when soft soils overlying hard bedrock tend to amplify the ground motions which can cause excess damage. Earthquakes have varied effects, including the following: 1. Shaking and ground rupture. Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several metres in the case of major earthquakes. 2. Geomorphological changes or changes in geologic features a. Movements, either vertical or horizontal, along geological fault traces b. The raising, lowering, and tilting of the ground surface with related effects on the flow of groundwater; c. Liquefaction of sandy ground (soil liquefaction – is a state of fluidity occurring in generally granular soils; also describe as a phenomenon in which cohesionless soil losses strength during earthquake and acquires a degree of mobility sufficient to permit large movement); d. Landslides and avalanches – sliding of unstable slopes e. Mudflows 3. Damage to man-made structures. Earthquakes may result in general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings. Earthquake Engineering Page 1  4. Impact on human and animal life. Earthquakes may result in disease, lack of basic necessities, loss of lives, higher insurance premiums. 5. Occurrence of earthquake sounds and lights. The lights are generally low-pitched and have likened to the noise of an underground train passing through a station. The occurrence of such sounds implies the existence of significant short periods in the P waves in the ground. Occasionally luminous flashes, streamers, and balls are seen in the night sky during earthquakes. These lights have been attributed to electric induction in the air along the earthquake source. 6. Tsunami or seismic sea wave – these are ocean waves created by submarine earthquake that travel great distances at a high speed or at an ave. speed of 450 mi./hr and have a high destructive potential; are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. 7. Seiches – these are rhythmic motions of water in nearly landlocked bays or lakes that are sometimes induced by earthquakes and by tsunamis. Oscillations of this sort may last for hours or even for a few day or two. 8. Fire – secondary effect of earthquake, usually generated by break of the electrical power of gas lines. 9. Floods – maybe a secondary effects of earthquake, if dams are damaged. Aftershocks– earthquakes weaker than the principal tremor that usually follows a severe/major earthquake. Foreshocks – weaker/smaller earthquakes that often precede a major earthquakes by days or in some cases as much as several years. Swarm is a series of earthquakes all of about the same size, in which no one event can be identified as the main shock. Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones. The ‘S” Ways that an Earthquake Can Hurt 1. Slip: the slip may tear not only the ground but also man-made structures on the ground. 2. Sliding: the sliding of rock or land masses may undermine foundations at upslope, block roadways, or hit structures at downslope. 1. Spreading: even the lateral spreading of soil mass on fairly level ground may cause gross rotation of foundations, or large unequal displacements of isolated footings. 2. Sand liquefaction: saturated sand under severe shaking may momentarily lose load- bearing capability and cause heavy foundations to sink or rotate, and cause light underground structures to float. 5. Shaking: those structures that are founded on firm ground may shake so strongly that they break at the base, either by rotation or by shearing (translation). Earthquake Engineering Page 2  EARTHQUAKE PREDICTION An earthquake prediction is a prediction that an earthquake of a specific magnitude will occur in a particular place at a particular time (or ranges thereof). In the effort to predict earthquakes people have tried to associate an impending earthquake with such varied phenomena or so-called earthquake precursors. Earthquake Precursors  Increased emission of radon;  Increased helium emission;  Increased methane gas emission, with possible formation of colored methane clouds - Earthquake clouds;  Increased activity of mud volcanoes;  Occurrence of microseismicity;  Modification of ground electrical conductivity;  Fluctuations in the Earth's magnetic field;  Changes in the density of nearby rocks;  Changes in well-water levels close to a fault;  Anomalies in the behavior of animals, such as mass migration of amphibians;  Increased emission of carbon dioxide in volcanic areas; volcanic paroxism;  Occurrence of small sand volcanoes. Other Prediction Theories/Methods  Precursory seismicity patterns. In 1969 Japanese seismologist Kiyoo Mogi proposed that there exists a precursory seismicity pattern before large earthquakes that has become known as the 'Mogi doughnut hypothesis'. He showed maps that suggested that major earthquakes tend to occur in seismically unusually calm areas surrounded by a ring of unusually high seismic activity.The idea that there sometimes exists a 'calm before the storm' is called the quiescence hypothesis, the idea of precursory increased activity in the ring outside is called the accelerated seismic moment release hypothesis.  The VAN method. VAN is a method of earthquake prediction proposed by Professors Varotsos, Alexopoulos and Nomicos in the 1980s; it was named after the researchers' initials. The method is based on the detection of "seismic electric signals" (SES) via a telemetric network of conductive metal rods inserted in the ground. The method stems from theoretical predictions by P. Varotsos, a solid-state physicist at the National and Capodistrian University of Athens. It is continually refined as to the manner of identifying SES from within the abundant electric noise the VAN sensors are picking up.  Pattern theories - recurrence times of previous earthquakes.  Fractoluminescence.One possible method for predicting earthquakes is fractoluminescence. Studies at the Chugoku National Industrial Research Institute by Yoshizo Kawaguchi have shown that upon fracturing, silica releases red and blue light for a period of about 100 milliseconds. Kawaguchi attributed this to the relaxation of the free bonds and unstable oxygen atoms that are left when the silicon oxygen bonds have broken due to the stresses within the rock  Magnetotellurics(MT) is an electromagnetic geophysical method of imaging the earth's subsurface by measuring natural variations of electrical and magnetic fields at the Earth's surface. Earthquake Engineering Page 3   Seismo-electromagnetics is the study of electromagnetic phenomena associated with seismic activity such as earthquakes and volcanos, and also the use of electromagnetic methods in seismology such as magnetotellurics. Electro-kinetic effect - Electrification due to the flow of water driven through permeable rock by crustal strain or gravity Countries that conducted/conducting Research in Earthquake Prediction  China (1956) 1. 1975 Haicheng earthquake – successful prediction (foreshocks) 2. 1976 M7.8 Tangshan earthquake – not predicted 3. Nov. 29, 1999 The Xiuyan earthquake – a correct prediction (earthquake swarms)  United States (mid 1960’s) 1. Failed Lima prediction (1981) 2. Failed Parkfield earthquake prediction (Prediction: 1985 – 1993) ; Actual event: 2004 3. Loma Prieta prediction (Prediction: 1968 – 1988) ;Actual event Oct. 17, 1989. Jim Berkland claims to have predicted the Loma Prieta quake, but the mainstream scientific community does not endorse his techniques as repeatable, attributing his success with this quake partly to random chance. 4. Failed New Madrid prediction by Iben Browning (Prediction: Dec. 2 or 3, 1990); No earthquake occurred on those days or thereafter. 5. Failed SoCal prediction ( Prediction by Dr. Vladimir Keilis-Borok: Sept. 2004); The predicted time window came and went with no significant earthquake.  Japan (1964 and a subsequent 5-year plan was formulated by Rikitake) - failed to result in a prediction of the Great Hanshin earthquake which devastated the city of Kobe in 1995.  Russia- the new program of development of earthquake prediction in Russia was designed by order of the President of the Russian Federation in 2004. It is targeted at increasing the reliability of long, medium, and short-term forecasting of the earthquake potential, including tsunami prediction.  Italy L'Aquila controversy - Italian technician Giampaolo Giuliani claims to have predicted the 2009 L'Aquila earthquake. Early Warning System An earthquake warning system is a system of accelerometers, communication, computers, and alarms that is devised for regional notification of a substantial earthquake while it is in progress. Japan, Taiwan and Mexico all have earthquake early-warning systems. Earthquake Engineering Page 4  MAJOR EARTHQUAKE ZONES MAJOR EARTHQUAKE ZONES IN THE WORLD  The Ring of Fire  The Mediterranean-Asian Belt  Mid-Atlantic Ridges THE RING OF FIRE The Ring of Fire or Pacific Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes. It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt. About 90% of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire. The Ring of Fire is a direct result of plate tectonics and the movement and collisions of lithosphericplates.The eastern section of the ring is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. The Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate. MEDITTEREAN-ASIAN BELT/ALPIDE BELT The Alpide belt is a mountain range which extends along the southern margin of Eurasia. Stretching from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic, it includes the Alps, the Carpathians, the mountains of Asia Minor and Iran, the Hindu Kush, the Himalayas, and the mountains of Southeast Asia. After the Pacific Ring of Fire, it is the second most seismic region in the world, (about 5–6% of earthquakes with 17% of the world's largest earthquakes. The Alpide belt is being created by ongoingplate tectonics, namely the process of collision between the northward-moving African, Arabian and Indian plates and the Eurasian plate. Indonesia lies between the Pacific Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Earthquake Engineering Page 5 Flores, and Timor. The 2004 Indian Ocean earthquake just off the coast of Sumatra was located within the Alpide belt. THE MID-ATLANTIC RIDGES The Mid-Atlantic Ridge (MAR) is a mid- ocean ridge, a divergenttectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South American Plate in the South Atlantic. The Ridge extends from a junction with the Gakkel Ridge (Mid-Arctic Ridge) northeast of Greenland southward to the Bouvet Triple Junction in the South Atlantic. Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level. The section of the ridge which includes the island of Iceland is also known as the Reykjanes Ridge. The average spreading rate for the ridge is about 2.5 cm per year. The Mid-Atlantic Ridge is the third most prominent earthquake belt. MAJOR EARTHQUAKES One of the most devastating earthquakes in recorded history occurred on 23 January 1556 in the Shaanxi province, China, killing more than 830,000 people (see 1556 Shaanxi earthquake). Most of the population in the area at the time lived in yaodongs, artificial caves in loess cliffs, many of which collapsed during the catastrophe with great loss of life. The 1976 Tangshan earthquake, with a death toll estimated to be between 240,000 to 655,000, is believed to be the largest earthquake of the 20th century by death toll. The 1960 Chilean Earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960.Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday Earthquake, which was centered in Prince William Sound, Alaska.The ten largest recorded earthquakes have all been mega thrust earthquakes; however, of these ten, only the 2004 Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create tsunamis that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes. DEADLIEST EARTHQUAKES ON RECORD Rank Name Date Location Fatalities Magnitude January 23, 820,000–830,000 1 "Shaanxi" Shaanxi, China 8.0 (est.) 1556 (est.) 316,000 (Haitian January 12, sources) 2 "Haiti" Haiti 7.0 2010 50,000–92,000 (non- Haitian sources) December 16, Ningxia–Gansu, 3 "Haiyuan" 273,400 7.8 1920 China 4 "Tangshan" July 28, 1976 Hebei, China 242,769 7.8 Earthquake Engineering Page 6 Rank Name Date Location Fatalities Magnitude Antioch, Turkey 5 "Antioch" May 21, 526 (then Byzantine 240,000 7.0 (est.) Empire) "Indian December 26, Indian Ocean, 6 230,210+ 9.1–9.3 Ocean" 2004 Sumatra, Indonesia October 11, 7 "Aleppo" Aleppo, Syria 230,000 Unknown 1138 December 22, 8 "Damghan" Damghan, Iran 200,000 (est.) 7.9 (est.) 856 9 "Ardabil" March 22, 893 Ardabil, Iran 150,000 (est.) Unknown "Great September 1, 10 Kantō region, Japan 142,800 7.9 Kantō" 1923 LARGEST EARTHQUAKE BY MAGNITUDE Date Location Name Magnitude May 22, 1960 Valdivia, Chile 1960 Valdivia earthquake 9.5 March 27, 1964 Prince William Sound, Alaska, USA 1964 Alaska earthquake 9.2 December 26, 2004 Indian Ocean Indian Ocean, Sumatra, Indonesia 9.1–9.3 2004 earthquake November 4, 1952 Kamchatka Kamchatka, Russia (then USSR) 9.0 1952 earthquakes March 11, 2011 Pacific Ocean, Tōhoku region, Japan 2011 Tōhoku earthquake 9.0 September 16, Arica, Chile (then part of the 1615 Arica earthquake 8.8 (est.) 1615 Spanish Empire) November 25, 8.8–9.2 Sumatra, Indonesia 1833 Sumatra earthquake 1833 (est.) 1906 Ecuador-Colombia January 31, 1906 Ecuador – Colombia 8.8 earthquake February 27, Maule, Chile 2010 Chile earthquake 8.8 2010 8.7–9.2 January 26, 1700 Pacific Ocean, USA and Canada 1700 Cascadia earthquake (est.) July 8, 1730 Valparaiso, Chile 1730 Valparaiso earthquake 8.7 (est.) November 1, Atlantic Ocean, Lisbon, Portugal 1755 Lisbon earthquake 8.7 (est.) 1755 February 4, 1965 Rat Islands, Alaska, USA 1965 Rat Islands earthquake 8.7 8.6-9.0 July 9, 869 Pacific Ocean, Tōhoku region, Japan 869 Sanriku earthquake (est.) September 20, Pacific Ocean, Nankai Trough, 1498 MeiōNankaidō 8.6 (est.) 1498 Japan earthquake October 28, Pacific Ocean, Shikoku region, 1707 Hōei earthquake 8.6 (est.) 1707 Japan 1950 Assam - Tibet August 15, 1950 Assam, India – Tibet, China 8.6 earthquake 1957 Andreanof Islands March 9, 1957 Andreanof Islands, Alaska, USA 8.6 earthquake April 1, 1946 Aleutian Islands, Alaska, USA 1946 Aleutian Islands 8.6 Earthquake Engineering Page 7  Date Location Name Magnitude earthquake March 28, 2005 Sumatra, Indonesia 2005 Sumatra earthquake 8.6 April 11, 2012 Indian Ocean, Sumatra, Indonesia 2012 Aceh earthquake 8.6 December 16, Valdivia, Chile (then part of the 1575 Valdivia earthquake 8.5 (est.) 1575 Spanish Empire) November 24, Arica, Chile (then part of the 1604 Arica earthquake 8.5 (est.) 1604 Spanish Empire) Santiago, Chile (then part of the May 13, 1647 1647 Santiago earthquake 8.5 (est.) Spanish Empire) October 20, Lima, Peru (Viceroyalty of Peru) 1687 Peru earthquake 8.5 (est.) 1687 Concepción, Chile (Kingdom of 1751 Concepción May 24, 1751 8.5 (est.) Chile) earthquake November 19, Valparaíso, Chile 1822 Valparaíso earthquake 8.5 (est.) 1822 February 20, 1835 Concepción Concepción, Chile 8.5 (est.) 1835 earthquake 8.5–9.0 August 13, 1868 Arica, Chile (then Peru) 1868 Arica earthquake (est.) 8.5-9.0 May 9, 1877 Iquique, Chile (then Peru) 1877 Iquique earthquake (est.) November 10, Atacama Region, Chile 1922 Vallenar earthquake 8.5 1922 1923 Kamchatka February 3, 1923 Kamchatka, Russia (USSR) 8.5 earthquakes Banda Sea, Indonesia (Dutch East February 1, 1938 1938 Banda Sea earthquake 8.5 Indies) October 13, 1963 Kuril Islands Kuril Islands, Russia (USSR) 8.5 1963 earthquake September 12, Sumatra, Indonesia 2007 Sumatra earthquakes 8.5 2007 PROPERTY DAMAGES CAUSED BY EARTHQUAKE Rank Name Magnitude Property damages 1 2011 Tōhoku earthquake, Japan 9.0 $235 billion 2 1995 Great Hanshin earthquake, Japan 6.9 $100 billion 3 2008 Sichuan earthquake, China 8.0 $75 billion 4 2010 Chile earthquake, Chile 8.8 $15–30 billion 1994 Northridge earthquake, United 5 6.7 $20 billion States 6 2012 Emilia earthquakes, Italy 6.1 (est.) $13.2 billion 2011 Christchurch earthquake, New 7 6.3 $12 billion Zealand 1989 Loma Prieta earthquake, United 8 ~7.0; 6.9-7.1 reported $11 billion States 9 921 earthquake, Taiwan 7.6 $10 billion 10 1906 San Francisco earthquake, United 7.7 to 7.9 (est.) $9.5 billion ($400 million Earthquake Engineering Page 8 Rank Name Magnitude Property damages States 1906 value) PHILIPPINE PLATES, TRENCHES AND FAULTS The Philippines happened to be a part of the Circum-Pacific and volcanic belt. Since the Philippines is in this “Ring of Fire”, it will be rocked by quakes, and active volcanoes will have intermittent eruptions. The Philippine archipelago lies in the fringes of the Philippine Sea Plate, one of the several smaller plates, which in turn lies between two major plates: Pacific and Eurasian. The Pacific Plate moves northwest at the rate of about 7 cm a year. As it moves, it pushes the Philippine Plate on its eastern side. This pressure created the Philippine Trench, where subduction continues to take place at the same rate of 7 cm a year. On the western side of Luzon and Mindoro, the Eurasian Plate moves southeast at the rate of 3 cm a year. This movement deepens the Manila Trench in the South China Sea. Trenches” are long narrow steep-sided depressions in the ocean floor formed when one plate subducts under the other. The Philippine Plate includes the floor of the Philippine Sea of the Western Pacific Ocean, Marianas, Yap, Palau, Volcano and Bonin Islands. Philippine Trench, a deep thorough extending from eastern Batanes southward to southeast Davao and includes the Philippine Deep of 10.54 kilometers below sea level, northeast of Surigao. In addition to its longest trenches – the Philippine Trench in the east and the Manila Trench in the west – the Philippines has five more trenches in its seas: the East Luzon Trench, the Negros Trench, the Sulu Trench, the Cotabato Trench, and the Davao Trench. ACTIVE FAULTS IN THE PHILIPPINES 1. Philippine Fault – runs from north to south of the country. It extends from Davao Gulf in the south, bisects CARAGA region at the Agusan River basin, crosses to Leyte and Masbate islands, and the traverse Quezon province in eastern Luzon before passing through Nueva Ecija up to the Ilocos region in the northwest Luzon. 2. Valley Fault System – formerly known as the Marikina Valley Fault System – a group of dextral strike-slip fault which extends from San Mateo, Rizal to Taguig City on the south; running through the cities of Makati, Marikina, Parañaque, Pasig and Taguig. It has two segements: West Segment (Western Marikina Fault) and East segment (Eastern Marikina Fault). The fault possesses a threat of a large scale magnitude earthquake with a magnitude of 7 or higher within the Manila Metropolitan Area. 3. Digdig Fault 6. Lubang Fault 4. Tablas Fault 7. Mindanao Fault 5. Casiguran Fault DEADLIEST RECORDED EARTHQUAKES IN THE PHILIPPINES SINCE 1600’S Magnitude Origin Location Date Mortality Missing Injured Damages August 16, 1 7.9 Tectonic Moro Gulf 4791 2288 9928 1976 Earthquake Engineering Page 9  More Luzon 2 7.8 Tectonic July 16, 1990 1666 1000 than 10 billion Island 3000 Luzon Unknow 3 7.5 Tectonic Nov. 30,1645 600 3000 Island n Casiguran, August 2, 4 7.3 Tectonic 271 261 Aurora 1968 5.15 5 7.1 Tectonic Mindoro Nov. 15, 1994 78 430 million Negros February 6, 383 6 6.7 Tectonic 51 62 112 Oriental 2012 million Unknow Unknow 7 Tectonic Manila June 19, 1665 19 n n August 8 6.5 Tectonic Laoag 16 47 17,1983 Mindanao 9 7.5 Tectonic March 5, 2002 15 100 Island Sultan 4.175 10 6.1 Tectonic March 6, 2002 8 41 Kudarat million Earthquake Engineering Page 10 Earthquake Engineering Page 11  EARTHQUAKE SAFETY MEASURES EARTHQUAKE SAFETY MEASURES Hazard Hunt- Identify potential dangers in the home using common sense, fore-sight, and your imagination to reduce risk in the event of an earthquake. Take active security measures, surveying the home for possible hazards. Take steps to correct and secure these hazards, reducing risk. Hazard-risk Reduction  Tall heavy furniture which could fall; fix it to a wall.  Hot water heaters that can fall away from pipes and rupture need to be anchored to a wall. Use flexible gas line connectors.  Appliances that can be moved can break electrical or gas lines and must be anchored to a stable location with flexible connections.  Be sure heavy mirrors or picture frames are placed away from beds and mounted securely to the wall.  Cabinets containing breakable items should have latches and heavy objects should be placed low to the ground.  Flammable liquids must be stored securely away from flame.  Masonry chimneys need bricks checked. Firmly support the roof.  Beds should not be placed near windows.  Glass bottles should not be placed on high shelves. FAMILY EARTHQUAKE DRILLS will help you and your family plan and react; remembering where to seek shelter and how to protect yourselves.  Identify safe spots and places in each room. - Under a doorway, sturdy table , desk, or kitchen counter. - Against an inside corner or wall; cover head with hands. - Know and reinforce these locations by practice.  Beware of danger zones and stay clear of: - Windows that may shatter, including mirrors and picture frames. - Heating units, fireplace, stove, and area around chimneys. - Cabinets, refrigerators, and bookcases that may topple.  Practice safe quake actions: - Conduct drills, check reactions and choices.  Discuss what to expect following a major earthquake and be prepared: - To treat and take care of injuries. - To check for gas leaks and learn where and how to turn off the gas, power, and water at main switches and valves. - For aftershocks and exiting the building. - Remember to stay close and if separated to activate the emergency communication plan. Earthquake Engineering Page 12  EARTHQUAKE SAFETY RULES, DURING AND AFTER AN EARTHQUAKE Suggested safety rules during and after the earthquake are as follows:  During the earthquake: 1. Do not panic, keep calm. 2. Douse all fires. 3. If the earthquake catches you indoors, stay indoors. Take cover under a sturdy piece of furniture. Stay away from glass, or loose hanging objects. 4. If you are outside, move away from buildings, steep slopes and utility wires. 5. If you are in a crowded place, do not rush for cover or to doorways. 6. If you are in a moving vehicle, stop as quickly as safety permits, but stay in the vehicle until the shaking stops. 7. If you are in a lift, get out of the lift as quickly as possible. 8. If you are in a tunnel, move out of the tunnel to the open as quickly as safety permits.  After the earthquake: 1. Check for casualties and seek assistance if needed. 2. If you suspect a gas leak, open windows and shut off the main valve. Leave the building and report the gas leaks. Do not light a fire or use the telephone at the site. 3. Turn off the main valve if water supply is damaged. 4. Do not use the telephone except to report an emergency or to obtain assistance. 5. Stay out of severely damaged buildings as aftershocks may cause them to collapse. Report any building damage to the authorities. 6. As a precaution against tsunamis, stay away from shores, beaches and low-lying coastal areas. If you are there, move inland or to higher grounds. The upper floors of high, multi-storey, reinforced concrete building can provide safe refuge if there is no time to quickly move inland or to higher ground Earthquake Engineering Page 13  EARTHQUAKE RESISTIVE CONSTRUCTION Earthquake engineering is the study of the behavior of buildings and structures subject to seismic loading. It can be defined as the branch of engineering devoted to mitigating earthquake hazards. In this broad sense, earthquake engineering covers the investigation and solution of the problems created by damaging earthquakes, and consequently the work involved in the practical application of these solutions, i.e. in planning, designing, constructing and managing earthquake-resistant structures and facilities. General Goals in Seismic-Resistant Design and Construction The philosophy of earthquake design for structures other than essential facilities has been well established and proposed as follows: a. To prevent non-structural damage in frequent minor ground shaking b. To prevent structural damage and minimize non-structural damage in occasional moderate ground shaking c. To avoid collapse or serious damage in rare major ground shaking EARTHQUAKE RESISTANT TECHNIQUES The technologies in earthquake engineering to protect buildings from damaging earthquake effects are vibration control technologies and, in particular, base isolation. I. SEISMIC VIBRATION CONTROL Seismic vibration control is a set of technical means aimed to mitigate seismic impacts in building and non- building structures. All seismic vibration control devices may be classified as passive, active or hybrid where:  passive control devices have no feedback capability between them, structural elements and the ground;  active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure;  hybrid control devices have combined features of active and passive control systems. When ground seismic waves reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential. After the seismic waves enter a superstructure, there are a number of ways to control them in order to soothe their damaging effect and improve the building's seismic performance, for instance:  to dissipate the wave energy inside a superstructure with properly engineered dampers;  to disperse the wave energy between a wider range of frequencies;  toabsorb the resonant portions of the whole wave frequencies band with the help of so called mass dampers. Devices of the last kind, abbreviated correspondingly as TMD for the tuned (passive), as AMD for the active, and as HMD for the hybrid mass dampers, have been studied and installed in high-rise buildings, predominantly in Japan, for a quarter of a century. Seismic Base Isolation Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure's integrity. It is a passive structural vibration control technology. 14 A base isolated structure is supported by a series of bearing pads, which are placed between the buildings and building foundation. The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply, the building does not experience the earthquake. Now, if the same building is rested on the flexible pads that offer resistance against lateral movements (fig 1b), then some effect of the ground shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that experienced by the building built directly on ground, namely a fixed base building (fig 1c). The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base- isolated buildings. The main feature of the base isolation technology is that it introduces flexibility in the structure. As a result, a robust medium-rise masonry or reinforced concrete building becomes extremely flexible. The isolators are often designed, to absorb energy and thus add damping to the system. This helps in further reducing the seismic response of the building. Many of the base isolators look like large rubber pads, although there are other types that are based on sliding of one part of the building relative to other. Also, base isolation is not suitable for all buildings. Mostly low to medium rise buildings rested on hard soil underneath; high-rise buildings or buildings rested on soft soil are not suitable for base isolation. The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, a city in ancient Persia, now Iran: it goes back to 6th century BCE. Mausoleum of Cyrus, the oldest base-isolated structure in the world 15 SEISMIC VIBRATION CONTROL TECHNOLOGIES a. Dry-stone walls control Dry-stone walls of Machu Picchu Temple of the Sun, Peru People of Inca civilization were masters of the polished 'dry-stone walls', called ashlars, where blocks of stone were cut to fit together tightly without any mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications. b. Lead rubber bearing LRB being tested at the UCSD Caltrans-SRMD facility Lead Rubber Bearing or LRB is a type of base isolation employing a heavy damping. It was invented by Bill Robinson, a New Zealander. Heavy damping mechanism incorporated in vibration control technologies and, particularly, in base isolation devices, is often considered a valuable source of suppressing vibrations thus enhancing a building's seismic performance. The bearing is made of rubber with a lead core. It was a uniaxial test in which the bearing was also under a full structure load. Lead-rubber bearings are the frequently-used types of base isolation bearings. A lead rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle of the solid lead “plug”. On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction. c. Spherical sliding base isolation Spherical sliding isolation systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction. During an earthquake the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally and vertically. The forces needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also by adjusting the radius of the bearings curved surface, this property can be used to design bearings that also lengthen the buildings period of vibration. 16  d. Tuned mass damper Tuned mass damper in Taipei 101, the world's third tallest skyscraper Typically, the tuned mass dampers are huge concrete blocks mounted in skyscrapers or other structures and moved in opposition to the resonance frequency oscillations of the structures by means of some sort of spring mechanism. e. Friction pendulum bearing FPB shake-table testing Friction Pendulum Bearing (FPB) is another name of Friction Pendulum System (FPS). It is based on three pillars:  articulated friction slider;  spherical concave sliding surface;  Enclosing cylinder for lateral displacement restraint. f. Building elevation control Building elevation control is a valuable source of vibration control of seismic loading. Pyramid-shaped skyscrapers continue to attract the attention of architects and engineers because such structures promise a better stability against earthquakes and winds. The elevation configuration can prevent buildings' resonant amplifications because a properly configured building disperses the shear wave energy between a wide range of frequencies. Transamerica Pyramid Bldg. A tapered profile of a building is not a compulsory feature of this method of structural control. A similar resonance preventing effect can be also obtained by a proper tapering of other characteristics of a building structure, namely, its mass and stiffness. 17  g. Simple roller bearing Simple roller bearing is a base isolation device which is intended for protection of various building and non- building structures against potentially damaging lateral impacts of strong earthquakes. This metallic bearing support may be adapted, with certain precautions, as a seismic isolator to skyscrapers and buildings on soft ground. Recently, it has been employed under the name of Metallic Roller Bearing for a housing complex (17 stories) in Tokyo, Japan. h. Springs-with-damper base isolator Springs-with-damper base isolator installed under a three-story town- house, Santa Monica, California is shown on the photo taken prior to the 1994 Northridge earthquake exposure. It is a base isolation device conceptually similar to Lead Rubber Bearing. One of two three-story town-houses like this, which was well instrumented for recording of both vertical and horizontal accelerations on its floors and the ground, has survived a severe shaking during the Northridge earthquake and left valuable recorded information for further study. Springs-with-damper i. Hysteretic damper Hysteretic damper is intended to provide better and more reliable seismic performance than that of a conventional structure at the expense of the seismic input energy dissipation There are four major groups of hysteretic dampers used for the purpose, namely:  Fluid viscous dampers (FVDs) – energy is absorbed by silicone-based fluid passing between piston cylinder arrangement.  Metallic yielding dampers (MYDs) – energy is absorbed by metallic components that yield  Viscoelastic dampers (VEDs) – energy is absorbed by utilizing the controlled shearing of solids.  Friction dampers (FDs) – energy is absorbed by surfaces with friction between them rubbing against each other. Thus by equipping a building with additional devices which have high damping capacity, we can greatly decrease the seismic energy entering the building. How Dampers Work The construction of a fluid damper is shown in (fig). It consists of a stainless steel piston with bronze orifice head. It is filled with silicone oil. The piston head utilizes specially shaped passages which alter the flow of the damper fluid and thus alter the resistance characteristics of the damper. Fluid dampers may be designed to behave as a pure energy dissipater or a spring or as a combination of the two. A fluid viscous damper resembles the common shock absorber such as those found in automobiles. The piston transmits energy entering the system to the fluid in the damper, causing it to move within the damper. The movement of the fluid within the damper fluid absorbs this kinetic energy by converting it into 18 heat. In automobiles, this means that a shock received at the wheel is damped before it reaches the passengers compartment. In buildings this can mean that the building columns protected by dampers will undergo considerably less horizontal movement and damage during an earthquake. Fluid Viscous Dampers Active Control Devices for Earthquake Resistance After development of passive devices such as base isolation and TMD. The next logical steps is to control the action of these devices in an optimal manner by an external energy source the resulting system is known as active control device system. Active control has been very widely used in aerospace structures. In recent years significant progress has been made on the analytical side of active control for civil engineering structures. Also a few models explains as shown that there is great promise in the technology and that one may expect to see in the foreseeable future several dynamic “Dynamic Intelligent Buildings” the term itself seems to have been joined by the Kajima Corporation in Japan. In one of their pamphlet the concept of Active control had been explained in every simple manner and it is worth quoting here. People standing in swaying train or bus try to maintain balance by unintentionally bracing their legs or by relaying on the mussels of their spine and stomach. By providing a similar function to a building it can dampen immensely the vibrations when confronted with an earthquake. This is the concept of Dynamic Intelligent Building (DIB). 19  Active mass driver system The philosophy of the past conventional a seismic structure is to respond passively to an earthquake. In contrast in the DIB which we propose the building itself functions actively against earthquakes and attempts to control the vibrations. The sensor distributed inside and outside of the building transmits information to the computer installed in the building which can make analyses and judgment, and as if the buildings possess intelligence pertaining to the earthquake amends its own structural characteristics minutes by minute. The basic configuration of an active control system is schematically shown in figure. The system consists of three basic elements: 1. Sensors to measure external excitation and/or structural response. 2. Computer hardware and software to compute control forces on the basis of observed excitation and/or structural response. 3. Actuators to provide the necessary control forces. Thus in active system has to necessarily have an external energy input to drive the actuators. On the other hand passive systems do not required external energy and their efficiency depends on tunings of system to expected excitation and structural behavior. As a result, the passive systems are effective only for the modes of the vibrations for which these are tuned. Thus the advantage of an active system lies in its much wider range of applicability since the control forces are worked out on the basis of actual excitation and structural behavior. In the active system when only external excitation is measured system is said to be in open- looped. However when the structural response is used as input, the system is in closed loop control. In certain instances the excitation and response both are used and it is termed as open-closed loop control. II. SEISMIC RETROFITTING is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Prior to the introduction of modern seismic codes in the late 1960s for developed countries (US, Japan etc.) and late 1970s for many other parts of the world (Turkey, China etc.), many structures were designed without adequate detailing and reinforcement for seismic protection. The retrofit techniques outlined here are also applicable for other natural hazards such as tropical cyclones, tornadoes, and severe winds from thunderstorms. Even as current practice of seismic retrofitting is predominantly concerned with structural improvements to reduce the seismic hazard of using the structures, it is similarly essential to reduce the hazards and losses from non-structural elements. It is also important to keep in mind that there is no such thing as an earthquake-proof structure, although seismic performance can be greatly enhanced through proper initial design or subsequent modifications. 20 Strategies  Increasing the global capacity (strengthening). This is typically done by the addition of cross braces or new structural walls.  Reduction of the seismic demand by means of supplementary damping and/or use of base isolation systems.  Increasing the local capacity of structural elements. This strategy recognizes the inherent capacity within the existing structures, and therefore adopts a more cost-effective approach to selectively upgrade local capacity (deformation/ductility, strength or stiffness) of individual structural components.  Selective weakening retrofit. This is a counter intuitive strategy to change the inelastic mechanism of the structure, whilst recognizing the inherent capacity of the structure.  Allowing sliding connections such as passageway bridges to accommodate additional movement between seismically independent structures. Performance objectives  Public safety only. The goal is to protect human life, ensuring that the structure will not collapse upon its occupants or passersby, and that the structure can be safely exited. Under severe seismic conditions the structure may be a total economic write-off, requiring tear-down and replacement.  Structure survivability. The goal is that the structure, while remaining safe for exit, may require extensive repair (but not replacement) before it is generally useful or considered safe for occupation. This is typically the lowest level of retrofit applied to bridges.  Structure functionality. Primary structure undamaged and the structure is undiminished in utility for its primary application. A high level of retrofit, this ensures that any required repairs are only "cosmetic" - for example, minor cracks in plaster, drywall and stucco. This is the minimum acceptable level of retrofit for hospitals.  Structure unaffected. This level of retrofit is preferred for historic structures of high cultural significance. Techniques Common seismic retrofitting techniques fall into several categories: One of many "earthquake bolts" found throughout period houses in the city of Charleston subsequent to the Charleston earthquake of 1886. They could be tightened and loosened to support the house without having to otherwise demolish the house due to instability. The bolts were directly loosely connected to the supporting frame of the house. a. External post-tensioning The use of external post-tensioning for new structural systems has been developed in the past decade. Under the PRESS (Precast Seismic Structural Systems) a large-scale U.S./Japan joint research program, unbounded post-tensioning high strength steel tendons have been used to achieve a moment-resisting system that has self-centering capacity. An extension of the same idea for seismic retrofitting has been experimentally tested for seismic retrofit of California bridges under a Caltrans research project and for seismic retrofit of non-ductile reinforced concrete frames. Pre-stressing can increase the capacity of structural elements such as beam, column and beam-column joints. It should be noted that external pre-stressing has been used for structural upgrade for gravity/live loading since 1970s. b. Supplementary dampers 21  Supplementary dampers absorb the energy of motion and convert it to heat, thus "damping" resonant effects in structures that are rigidly attached to the ground. In addition to adding energy dissipation capacity to the structure, supplementary damping can reduce the displacement and acceleration demand within the structures. In some cases, the threat of damage does not come from the initial shock itself, but rather from the periodic resonant motion of the structure that repeated ground motion induces. In the practical sense, supplementary dampers act similarly to Shock absorbers used in automotive suspensions. c. Slosh tank A slosh tank is a large tank of fluid placed on an upper floor. During a seismic event, the fluid in this tank will slosh back and forth, but is directed by baffles - partitions that prevent the tank itself becoming resonant; through its mass the water may change or counter the resonant period of the building. Additional kinetic energy can be converted to heat by the baffles and is dissipated through the water - any temperature rise will be insignificant. d. Active control system Very tall buildings ("skyscrapers"), when built using modern lightweight materials, might sway uncomfortably (but not dangerously) in certain wind conditions. A solution to this problem is to include at some upper story a large mass, constrained, but free to move within a limited range, and moving on some sort of bearing system such as an air cushion or hydraulic film. Hydraulic pistons, powered by electric pumps and accumulators, are actively driven to counter the wind forces and natural resonances. These may also, if properly designed, be effective in controlling excessive motion - with or without applied power - in an earthquake. In general, though, modern steel frame high rise buildings are not as subject to dangerous motion as are medium rise (eight to ten story) buildings, as the resonant period of a tall and massive building is longer than the approximately one second shocks applied by an earthquake. e. Ad hoc-addition of structural support/reinforcement The most common form of seismic retrofit to lower buildings is adding strength to the existing structure to resist seismic forces. The strengthening may be limited to connections between existing building elements or it may involve adding primary resisting elements such as walls or frames, particularly in the lower stories. e.1. Connections between buildings and their expansion additions Frequently, building additions will not be strongly connected to the existing structure, but simply placed adjacent to it, with only minor continuity in flooring, siding, and roofing. As a result, the addition may have a different resonant period than the original structure, and they may easily detach from one another. The relative motion will then cause the two parts to collide, causing severe structural damage. Proper construction will tie the two building components rigidly together so that they behave as a single mass or employ dampers to expend the energy from relative motion, with appropriate allowance for this motion. e.2.Exterior reinforcement of building e.3.Exterior concrete columns Historic buildings, made of unreinforced masonry, may have culturally important interior detailing or murals that should not be disturbed. In this 22 case, the solution may be to add a number of steel, reinforced concrete, or post stressed concrete columns to the exterior. Careful attention must be paid to the connections with other members such as footings, top plates, and roof trusses. e.4. Infill shear trusses Infill shear trusses — University of California dormitory, Berkeley, California Shown here is an exterior shear reinforcement of a conventional reinforced concrete dormitory building. In this case, there was sufficient vertical strength in the building columns and sufficient shear strength in the lower stories that only limited shear reinforcement was required to make it earthquake resistant for this location near the Hayward fault. e.5. Massive exterior structure In other circumstances, far greater reinforcement is required. In the structure shown at right — a parking garage over shops — the placement, detailing, and painting of the reinforcement becomes itself an architectural embellishment. External bracing of an existing reinforced concrete parking garage (Berkeley) References: 1. Encyc. Brit. – Encyclopedia Britannica 2. World Almanac 2015, 2020 3. Phivolcs - Dost 4. National Structural Code of the Philippines 2015 23