Earthquake resistance in buildings

A report format presentation of earthquake-resistance construction techniques, stressing upon the relevance of such techniques in the architecture industry.

1. Earthquake resistance in buildings REPORT: BUILDING CONSTRUCTION Submitted by: Pranay Bhavsar Rithika Ravishankar Achal Kalaskar Rama Shirwalkar Vishranti Madne Roshani Tamkhade 1

2. INDEX EARTHQUAKE AND EQ-RESISTANT BUILDINGS CLASSIFICATION OF EARTHQUAKES CONSIDERATIONS AND PLANNING TECHNIQUES / METHODOLOGIES SIESMIC ZONES AN EXAMPLE OF HORRIFIC FAILURE:BHUJ, INDIA AN EXAMPLE OF ASTOUNDING SUCCESS: TAIPEI 101, TAIWAN AN ANCIENT EXAMPLE OF ASTOUNDING SUCCESS:HORYUJI PAGODA, JAPAN 2

3. What is an earthquake? A sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth's crust or volcanic action . What are earthquake resistant buildings ? Earthquake-resistant structures  are structures designed to withstand earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to erect structures that fare better during seismic activity than their conventional counterparts. According to building codes, earthquake-resistant structures are intended to withstand the largest earthquake of a certain probability that is likely to occur at their location. This means the loss of life should be minimized by preventing collapse of the buildings for rare earthquakes while the loss of functionality should be limited for more frequent ones. 3 EARTHQUAKE AND EQ-RESISTANT BUILDINGS

4. 4 Serviceability level Earthquake Frequent and minor earthquakes Building should not be damaged and continue to remain in service Expected ten times during the life of building Damageability level Earthquake Occasional moderate earthquakes No structural damage is expected Non structural damage should not lead to any loss of life Expected once or twice during the life of building Safety level Earthquake Rare major earthquakes Building should not collapse Non structural & structural damage should not lead to any loss of life. Earthquake types CLASSIFICATION OF EARTHQUAKES

5. 5 Considerations: ( i ) Structures should not be brittle or collapse suddenly. Rather, they should be tough, able to deflect or deform a considerable amount . ( ii) Resisting elements, such as bracing or shear walls, must be provided evenly throughout the building, in both directions side-to-side, as well as top to bottom. (iii) All elements, such as walls and the roof, should be tied together so as to act as an integrated unit during earthquake shaking, transferring forces across connections and preventing separation. (iv) The building must be well connected to a good foundation and the earth. Wet, soft soils should be avoided, and the foundation must be well tied together, as well as tied to the wall Planning: • Planning and layout of the building involving consideration of the location of rooms and walls, openings such as doors and windows, the number of storeys, etc. At this stage, site and foundation aspects should also be considered. • Lay out and general design of the structural framing system with special attention to furnishing lateral resistance, and • Consideration of highly loaded and critical sections with provision of reinforcement as required Stress concentration zone Gradual change in lateral stiffness and building floor mass in vertical direction can be provided CONSIDERATIONS IN PLANNING

6. 6 Geometrical Asymmetry – Building Joint Typical problem occurs in the junction areas as two neighbourhood block strikes each other and try to separate out in a periodic motion During earthquake three blocks undergo twist in three different orientations Solution Building blocks can be separated by seismic Gaps. The individual building blocks now vibrate in plan separately. The Stress concentration in block joints can be avoided. Mass Asymmetry Difference in CoM & CoR will invite Torsion Couple, which produce instability Liquefaction Three main prerequisites for liquefaction : A layer of relatively loose sand or silt. A water table high enough to submerge a layer of loose soil. An intensity of ground shaking sufficient to increase the water pressure between soil particles to cause the soil-water mixture to liquefy. SOLUTION FOR Isolated Foundation Individual footings should be interconnected with tie-beams or a structural slab to prevent any relative horizontal movement occurring during earthquake shaking . Raft Foundation As the raft has a common base and it equally and uniformly distribute the super structure load to the sub soil. It spreads concentrated loads onto a larger area and makes the structure tolerant of minor ground subsidence. It mobilizes the entire weight of the building to resist inertia-induced overturning moments.

7. 7 VARIOUS TECHNIQUES / METHODOLOGIES BASE ISOLATION: T his concept relies on separating the substructure of a building from its superstructure. One such system involves floating a building above its foundation on lead-rubber bearings, which contain a solid lead core wrapped in alternating layers of rubber and steel. Steel plates attach the bearings to the building and its foundation and then, when an earthquake hits, allow the foundation to move without moving the structure above it. Now some Japanese engineers have taken base isolation to a new level. Their system actually levitates a building on a cushion of air. Here's how it works: Sensors on the building detect the telltale seismic activity of an earthquake. The network of sensors communicates with an air compressor, which, within a half second of being alerted, forces air between the building and its foundation. The cushion of air lifts the structure up to 1.18 inches (3 centimeters) off the ground, isolating it from the forces that could tear it apart. When the earthquake subsides, the compressor turns off, and the building settles back down to its foundation. SHOCK ABSORBERS: Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of your bouncing suspension into heat energy that can be dissipated through hydraulic fluid. In physics, this is known as damping, which is why some people refer to shock absorbers as dampers. Turns out dampers can be useful when designing earthquake-resistant buildings. Engineers generally place dampers at each level of a building, with one end attached to a column and the other end attached to a beam. Each damper consists of a piston head that moves inside a cylinder filled with silicone oil. When an earthquake strikes, the horizontal motion of the building causes the piston in each damper to push against the oil, transforming the quake's mechanical energy into heat.

8. 8 A   fuse  provides protection by failing if the current in a circuit exceeds a certain level. This breaks the flow of electricity and prevents overheating and fires. Researchers from Stanford University and the University of Illinois call their idea a  controlled rocking system  because the steel frames that make up the structure are elastic and allowed to rock on top of the foundation. In addition to the  steel  frames, the researchers introduced vertical cables that anchor the top of each frame to the foundation and limit the rocking motion. Not only that, the cables have a self-centering ability, which means they can pull the entire structure upright when the shaking stops. The final components are the replaceable steel fuses placed between two frames or at the bases of columns. The metal teeth of the fuses absorb seismic energy as the building rocks. If they "blow" during an earthquake, they can be replaced relatively quickly and cost-effectively to restore the building to its original, ribbon-cutting form. VARIOUS TECHNIQUES / METHODOLOGIES

9. I t is essential that the foundation system move in unison during an earthquake. When supports consist largely of isolated column footings, it is advisable to add ties of the type illustrated in in order to achieve this and to enable the lateral loads to be shared among all the independent footings . When they consist of separate elements building frames of the traditional post and beam system lack lateral force resistance. For a single bay of such a system, stability may be achieved by: Strengthening the connections between the elements of the frame to make them moment-resistant Providing bracing in the shape of the letter (X ) Building rigid infill walls between the columns Factors that influence the building’s response to lateral loading effects of earthquakes are: Building Sites High-risk sites of the types illustrated and locations with low bearing capacity soils such as expansive clay, loose sand, unstable hillsides etc. should be avoided. Weight of the Construction Heavy buildings are a seismic hazard. Buildings, particularly the roof and the floors should be kept as light as structurally possible. Building Form Symmetrical buildings of relatively simple form usually perform better than complex shapes where walls are asymmetrically distributed on the plan. 9 VARIOUS TECHNIQUES / METHODOLOGIES

10. 10 VARIOUS TECHNIQUES / METHODOLOGIES Confined Masonry This is a construction system where masonry structural walls are surrounded on all four sides with reinforced concrete. In order to ensure structural integrity, vertical confining elements should be located at all corners and recesses of the building, and at all joints and wall intersections. In addition, they should be placed at both sides of any wall opening whose area exceeds 2.5 m2 Typical distribution of vertical confining element in the plan of building Stiffness of Non-structural Elements It is recommended to reinforce non-structural partition walls with 4-6 mm diameter bars placed in the bed joints with a vertical spacing of not more than 600 mm. Where weather conditions necessitate the use of reinforced concrete pitched roofs the masonry gable end walls should be anchored to the uppermost tie beams. If the height of the gable wall exceeds 4 m, intermediate tie beams should be added at intervals not exceeding 2 m

11. 11 TECHNIQUES/METHODOLOGIES Floors and Roofs During earthquakes, floors and roofs should act as rigid horizontal diaphragms, which distribute the seismic forces among structural walls in proportion to their stiffness. One of the main reasons for the poor behaviour of existing masonry buildings is a lack of proper horizontal diaphragm action of floor and roof structures and or lack of proper connections between them and the structural walls which carry them. Use of timber floors and roofs in high-risk seismic zones is only recommended where the requisite carpentry skills exist and if specially designed details to ensure the integrity of these elements and their anchorage to the supporting walls . Jack arches in lime mortar spanning between steel joists are adequate, provided the spans do not exceed 900 mm and steel cross bracing welded to corners of the outer joists above on the upper surface of the floor or roof is provided. Use of deformed bars for this is not allowed because they produce brittle welded joints. In the case of reinforced concrete floors and roofs, two-way slabs are to be used in preference to one-way slabs. Connections to walls are to follow the details illustrated.

12. 12 EARTHQUAKE AND EQ-RESISTANT BUILDINGS In many modern high-rise buildings, engineers use core-wall construction to increase seismic performance at lower cost. In this design, a reinforced  concrete  core runs through the heart of the structure, surrounding the elevator banks. For extremely tall buildings, the core wall can be quite substantial -- at least 30 feet in each plan direction and 18 to 30 inches thick. A better solution for structures in earthquake zones calls for a rocking-core wall combined with base isolation. A rocking core-wall rocks at the ground level to prevent the concrete in the wall from being permanently deformed. To accomplish this, engineers reinforce the lower two levels of the building with steel and incorporate post-tensioning along the entire height. In post-tensioning systems, steel tendons are threaded through the core wall. The tendons act like rubber bands, which can be tightly stretched by hydraulic jacks to increase the tensile strength of the core-wall. While core-wall construction helps buildings stand up to earthquakes, it's not a perfect technology. Researchers have found that fixed-base buildings with core-walls can still experience significant inelastic deformations, large shear forces and damaging floor accelerations. One solution, as we've already discussed, involves base isolation -- floating the building on lead- rubber  bearings. This design reduces floor accelerations and shear forces but doesn't prevent deformation at the base of the core-wall. VARIOUS TECHNIQUES / METHODOLOGIES

13. 13 . Another promising solution, much easier to implement, requires a technology known as  fiber-reinforced plastic wrap , or  FRP . Manufacturers produce these wraps by mixing  carbon fibers  with binding polymers, such as epoxy, polyester, vinyl ester or nylon, to create a lightweight, but incredibly strong, composite material. In  retrofitting  applications, engineers simply wrap the material around concrete support columns of bridges or buildings and then pump pressurized epoxy into the gap between the column and the material. Based on the design requirements, engineers may repeat this process six or eight times, creating a mummy-wrapped beam with significantly higher strength and ductility. Amazingly, even earthquake-damaged columns can be repaired with carbon-fiber wraps. In one study, researchers found that weakened highway bridge columns cocooned with the composite material were 24 to 38 percent stronger than unwrapped columns  TECHNIQUES/METHODOLOGIES

14. 14 MAP INDICATING SEISMIC ZONES OF THE WORLD MAP INDICATING SEISMIC ZONES OF INDIA SEISMIZ ZONES

15. 15 Case Study 1: Gujarat Earthquake: 2001 Bhuj Earthquake A Powerful Earthquake of magnitude 6.9 on Richter-Scale rocked the Western Indian State of Gujarat on the 26 th of January, 2001. It caused extensive damage to life & property. This earthquake was so devastating in its scale and suffering that the likes of it had not been experienced in past 50 years. Leaving thousands seriously injured, bruised and handicapped; both physically, psychologically and economically . The epicenter of the quake was located at 23.6 north Latitude and 69.8 east Longitude, about 20 km Northeast of Bhuj Town of the Kutch district in Western Gujarat. At a depth of only 23 kms below surface this quake generated intense shaking which was felt in 70% region of India and far beyond in neighbouring Pakistan and Nepal too. This was followed by intense aftershocks that became a continued source of anxiety for the populace. The Seismicity of the affected Area of Kutch is a known fact with a high incidence of earthquakes in recent times and in historical past. It falls in Seismic Zone V. The only such zone outside the Himalayan Seismic Belt. In last 200 years important damaging earthquakes occurred in 1819, 1844, 1845, 1856, 1869,1956 in the same vicinity as 2001 earthquake . An example of horrific failure due to earthquake

16. 16 An example of horrific failure due to earthquake Gujarat Earthquake is very significant from the point of view of earthquake disaster mitigation in India. The problems observed in this disaster are no different from other major recent earthquakes in the world. The issues in the recovery and reconstruction phase are: the proper understanding risk among different stakeholders, training and confidence building among the professionals and masons with appropriate development planning strategies. This quake has provided numerous examples of geo-technical and structural failures. The traditional wisdom of design and construction practices of engineered buildings prevalent in this country came under criticism for the first time. It has triggered comprehensive understanding on what needs to be done in this regard.

17. 17 . All these factors compounded the effects of the tremor and the material used in masonry just could not resist any lateral pressures for which it had no security. This amounted to large scale collapse of houses in the villages and also to some extent in the towns in the Katchchh  region. structures built in villages and urban areas by masons and builders with easily available materials and hybrid techniques Made by using contemporary materials. In the villages there was also an element of cheaper construction using waste stones and materials which were not particularly good for building purposes. sometimes use soil as a binding material and in many cases the soil used was of a very inferior quality heritage of building methods confined to the tribal cultures in the regions of Saurashtra and Katchchh sustained themselves in the event of such earthquakes and are more or less unaffected. . This was because of the form of the shelter and also the materials and techniques with which these were put together

18. 18 Case Study 2: Chamoli (Himalaya, India) Earthquake of 29 March 1999 The Chamoli earthquake of 29 March 1999 in northern India is yet another important event from the viewpoint of Himalayan seism tectonics and seismic resistance of non-engineered constructions. The earthquake occurred in a part of the Central Himalaya, which is highly prone to earthquakes and has been placed in the highest seismic zone (zone V) of India. There has been a bitter controversy during the recent years regarding the seismic safety of a 260-m-high rock-fill dam under construction at Tehri , about 80 km west of the epicenter. Fortunately, there are no major cities in the meizoseismal region and the population density is the second lowest in the state. The earthquake caused death of about 100 persons and injured hundreds more. Maximum MSK intensity was up to VIII at a few locations. The quake was felt at far-off places such as Kanpur (440 km south-east from the epicenter), Shimla (220 km north-west) and Delhi (280 km south-west). Maximum death and damage occurred in the district of Chamoli where about 63 persons died and over 200 injured; about 2,595 houses collapsed and about 10,861 houses were partially damaged. In all, about 1,256 villages were affected. A few buildings at the far away mega-city of Delhi sustained non-structural damages. No instances of liquefaction were reported. Longitudinal cracks in the ground were seen in some locations in the affected area. An example of horrific failure due to earthquake

19. 19 AN EXAMPLE OF ASTOUNDING SUCCESS Taipei 101 Taiwan is a horrible place to build a skyscraper. Not only is it right on the Ring of Fire, but its capital city lies right on top of multiple fault ones, one of which is just a few blocks away.

20. 20 AN EXAMPLE OF ASTOUNDING SUCCESS Taipei 101 SOME BASIC INFORMATION Architect – C.Y.Lee & Partners Structural Engineer – Shaw Shieh Structural Consult. – Thornton- Tomasetti Engineers , New York City Year Started – June 1998 (Mall already open) Total Height – 508m No . of Floors – 101 Plan Area – 50m X 50m Cost – $ 700 million Building Use – Office Complex + Mall Parking - 83,000 m2, 1800 cars Retail - Taipei 101 Mall (77,033 m2) Offices - Taiwan Stock Exchange (198,347 m2) ARCHITECTURAL STYLE Structure depicts a bamboo stalk Youth and Longevity Everlasting Strength Pagoda Style Eight prominent sections Chinese lucky number “8” In China, 8 is a homonym for prosperity Even number = “rhythm and symmetry” BUILDING FRAME Materials 60ksi Steel 10,000 psi Concrete Systems Outrigger Trusses Moment Frames Belt Trusses Lateral Load Resistance Braced Moment Frames in the building’s core Outrigger from core to perimeter Perimeter Moment Frames Shear walls

21. 21 CHALLENGES FACED Taipei being a coastal city the problems present are: Weak soil conditions (The structures tend to sink). Typhoon winds (High lateral displacement tends to topple structures). Large potential earthquakes (Generates shear forces). .   CONSTRUCTION PROCESS  380 piles with 3 inch concrete slab. Mega columns- 8 cm thick steel & 10,000 psi concrete infill to provide for overturning. Walls - 5 & 7 degree slope. 106,000 tons of steel, grade 60- 25% stronger. 6 cranes on site – steel placement. Electrical & Mechanical. Curtain wall placement . STRUCTURAL SYSTEM Braced core with belt trusses AN EXAMPLE OF ASTOUNDING SUCCESS

22. 22 TYPICAL PLAN UP TO 26TH STOREY TYPICAL PLAN FROM 27 TH TO 91 ST STOREY Gravity loads are carried vertically by a variety of columns. Within the core, sixteen columns are located at the crossing points of four lines of bracing in each direction. The columns are box sections constructed of steel plates, filled with concrete for added strength as well as stiffness till the 62nd floor. On the perimeter, up to the 26th floor, each of the four building faces has two ‘super columns,’ two ‘sub-super-columns,’ and two corner columns. Each face of the perimeter above the 26th floor has the two ‘super-columns’ continue upward. The ‘super-columns’ and ‘sub-super-columns’ are steel box sections, filled with 10,000 psi (M70) high performance concrete on lower floors for strength and stiffness up to the 62nd floor. The building is a pile through clay rich soil to bedrock 40 – 60 m below. The plies are topped by a foundation slab which is 3m thick at the edges and up to 5m thick under the largest of columns. There are a total of 380 1.5m dia. Tower piles. COLUMN SYSTEM AN EXAMPLE OF ASTOUNDING SUCCESS

23. 23 Tuned mass damper One of Taipei 101’s most famous engineering features is its tuned mass damper, which is the secret weapon behind its disaster survival techniques. It’s essentially a giant pendulum, which swings in the opposite direction of the sway of the building, preventing it from swaying too far. As you might imagine, for a building this size, the counterweight has to be huge, too; it’s the world’s largest, at 5.5 meters in diameter (18 ft ), and the heaviest, at 660 metric tons (730 short tons). But it doesn’t just swing back and forth on its suspension cables; it’s hydraulically controlled so its movements correspond precisely with the movement of the building, rather than swinging freely.  AN EXAMPLE OF ASTOUNDING SUCCESS

24. 24 AN EXAMPLE OF ASTOUNDING SUCCESS The trial quake Many of Taipei 101’s disaster prevention techniques were put to the test, when a 6.8 magnitude earthquake struck the building, partway through construction. Cranes collapsed, five construction workers died, and the city suffered major damage; but Taipei 101 was just fine, and after a thorough inspection, the crew got right back to work. Since then, Taipei 101 has faced typhoons and earthquakes, and still stands. Few other structures have to contend with the forces of nature endured by most East Asian skyscrapers, and although other structures have incorporated plenty of ingenious engineering techniques to combat these obstacles, Taipei 101 in many ways led the way for later designs. From concrete pouring techniques to the lifting of massive objects to disaster reduction methods, many later skyscrapers have built on the innovations that allowed Taipei 101 to reach its unprecedented heights .

25. 25 AN EXAMPLE OF ASTOUNDING SUCCESS The Taipei 101 uses a 800 ton TMD which occupy 5 of its upper floors (87 – 91). The ball is assembled on site in layers of 12.5-cm-thick steel plate. It is welded to a steel cradle suspended from level 92 by 3” cables, in 4 sets of 2 each. Eight primary hydraulic pistons, each about 2 m long, grip the cradle to dissipate dynamic energy as heat. A roughly 60-cm-dia pin projecting from the underside of the ball limits its movement to about 1 m even during times of the strongest lateral forces. The 60m high spire at the top has 2 smaller ‘flat’ dampers to support it . STRUCTURAL INNOVATIONS IN OTHER TAIPEI BUIDINGS The structural systems used in Taipei 101 draw a lot from other buildings in the Taipei region. They can generally be classified into 2 types a) Hysteretic Dampers - Triangular Added stiffness and damping damper (TADAS) - Reinforced ADAS damper (RADAS) - Buckling Restrained Braces (BRB) - Low Yield Steel Shear Panel (LYSSP) b) Velocity Dampers - Visco - Elastic dampers (VE) - Viscous Dampers (VD) - Viscous Damping Walls (VDW) Currently , there have been more applications using viscous dampers than other velocity type dampers. This may be due to the facts that the design procedure for implementing the viscous damper is relatively simpler and the analytical model is available in the popular computational tools such as SAP2000 and ETABS.

26. 26 ANCIENT EXAMPLE OF ASTOUNDING SUCCESS Japan has been struck by magnitude 7.0 or greater earthquakes a staggering 46 times since the pagoda at the Horyu -Ji Temple was built in 607AD. So, how did the 122 foot tall structure stay upright through all that shaking ? Multi-story pagoda technology arrived in Japan during the sixth century alongside Buddhism from China . On the mainland, pagodas were traditionally built of stone. However given Japan's seismic instability and higher annual rainfall, that design was simply untenable. But, after much experimentation, Japanese builders figured out how to adapt them to the shaky conditions through three design changes: the use of wide and heavy eaves, disconnected floors, and a shock-absorbing shinbashira . Japan is a wet country with roughly double China's annual precipitation. So, to keep rainwater from running off building and onto the soil surrounding the foundation, potentially causing the pagoda to sink, builders extended the eaves far away from the walls —constituting up to 50 percent or more of the building's total width. Builders employed a series of cantilevered beams to prop up the massive overhangs. Then, to combat the buildings' severe flammability, the eaves were then laden with heavy earthenware to prevent tinders from igniting the wooden structure underneath.

27. 27 ANCIENT EXAMPLE OF ASTOUNDING SUCCESS The Horyu-ji pagoda doesn't have any central load-bearing beams like you'd see in modern construction. Since the building tapers as it rises, no single load-bearing vertical beam connects to the one below it. The individual floors themselves aren't solidly connected to their neighbors either, just piled atop one another with loosefitting brackets. This is actually a big advantage in earthquake country. During a shake, the floors will sway in a slithering fashion, with each floor moving in the opposite direction of the ones immediately above and below. This allows the building to more fluidly ride the seismic wave than a more solid building would. To keep the floors from flexing too far, builders came up with an ingenious solution—the shinbashira . It looks like a large loadbearing column, but it doesn't actually support any of the building's weight (that weight is supported by a network of 12 outer and four inner columns). Built from a large pine trunk, the shinbashira is strung from the underside of the roof and hangs down a shaft in the center of the structure. Sometimes it's buried into the earth, sometimes it rests lightly atop the ground, and occasionally it doesn't even touch the ground—it just freely hangs. The shinbashira acts as a massive tuned mass damper, helping to mitigate the earthquake's vibrations. It also prevents the floors from swaying to the point of collapse and absorbs some of the momentum of the floors as they strike against it. Basically, it's a giant stationary pendulum with enough mass to prevent the lighter floors from freely swinging around.