Earthquake Resistive Structures/Methods/Construction PDF

EARTHQUAKE RESISTIVE STRUCTURES/ METHODS/ 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 co...

EARTHQUAKE RESISTIVE STRUCTURES/ METHODS/ 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 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 or structure control systems may be classified as passive, active, semi-active or hybrid 1. passive control devices/systems 2. active control devices 3. Semi-active control devices 4. hybrid control devices PASSIVE CONTROL DEVICES  passive control devices have no feedback capability between them, structural elements and the ground (TMD, TLD, viscous fluid and friction, base isolation); it does not require an external power source and being utilizes the structural motion to dissipate seismic energy or isolates the vibrations so that response of structure can be controlled. Passive control devices includes 1. Base isolation 2. Passive energy dissipating (PED) devices  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. A base isolation system is a method of seismic protection where the structure (superstructure) is separated from the base (foundation or substructure). By separating the structure from its base the amount of energy that is transferred to the superstructure during an earthquake is reduced significantly. Seismic Base Isolation  Seismic Base Isolation The isolation can be obtained by the use of various techniques like rubber bearings, friction bearings, ball bearings, spring systems and other means. Seismic Base Isolation Mausoleum of Cyrus, the oldest base-isolated structure in the world 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. Passive Energy Dissipating Devices (PED) Mechanical devices to dissipate or absorb a portion of structural input energy, thus reducing structural response and possible structural damage. Metallic yield dampers Friction dampers Visco-elastic dampers Viscous fluid dampers, and Tuned mass dampers and tuned liquid dampers  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. SEISMIC VIBRATION CONTROL TECHNOLOGIES b. Lead rubber bearing https://youtu.be/2yXgu4aS8HE Lead Rubber Bearing or LRB is a type of base isolation employing a heavy damping. It was invented by Bill Robinson, a New Zealander. 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES c. Spherical sliding 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES d. Tuned mass damper 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES d. Tuned mass damper Tuned mass damper in Taipei 101, the world's third tallest skyscraper SEISMIC VIBRATION CONTROL TECHNOLOGIES d. Tuned mass damper SEISMIC VIBRATION CONTROL TECHNOLOGIES d. Tuned mass damper SEISMIC VIBRATION CONTROL TECHNOLOGIES e. Friction pendulum bearing 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. FPB shake-table testing SEISMIC VIBRATION CONTROL TECHNOLOGIES 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 SEISMIC VIBRATION CONTROL TECHNOLOGIES f. Building elevation control Shake-table testing of a regular building model (left) and a model with the vertical control (right) Transamerica Pyramid Bldg. SEISMIC VIBRATION CONTROL TECHNOLOGIES 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES Hysteretic dampers SEISMIC VIBRATION CONTROL TECHNOLOGIES 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 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. SEISMIC VIBRATION CONTROL TECHNOLOGIES Illustration of diagonal, chevron brace, scissor-jack- damper, and toggle-brace- damper configurations, magnification factors, and damping ratios of a single- story structure with linear fluid viscous devices.  SEISMIC VIBRATION CONTROL TECHNOLOGIES Hysteretic dampers Fluid viscous damper installed in a building structure Friction dampers (FDs) SEISMIC VIBRATION CONTROL TECHNOLOGIES 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. ACTIVE CONTROL DEVICES Active control system is a new invention compared with passive systems. When an earthquake hits a building, the sensors of active control system determine the direction and the weight of the counterbalance force to be induced in opposite direction so that the building remains motionless and structure remains safe.  active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure; (AMD) ACTIVE CONTROL DEVICES Active control systems include active tuned mass dampers, distributed actuators, active tendon systems and active coupled building systems. Semi-active control systems include: magnetorheological (MR) fluid dampers, semi-active stiffness dampers, semi-active tuned liquid column dampers, and piezoelectric dampers. https://www.slideshare.net/NamanKantesaria/nama n-act https://slideplayer.com/slide/14183150/  ACTIVE MASS DAMPER SYSTEMS It evolved from TMDs with the introduction of an active control mechanism.  ACTIVE TENDON SYSTEMS Active tendon control systems consist of a set of pre-stressed tendons whose tension is controlled by electro-hydraulic servomechanisms SEMI-ACTIVE CONTROL SYSTEMS It compromise between the The action of control forces can passive and active control maintained by using external devices. power supply or even with battery The structural motion is utilized to develop the control actions or forces through the adjustment of its mechanical properties SEMI-ACTIVE CONTROL DEVICES 1. Stiffness control devices 2. Electro-rheological dampers 3. Magnetorhelogical dampers 4. Friction control devices 5. Fluid control devices 6. Tuned mass dampers 7. Tuned liquid dampers HYBRID CONTROL SYSTEMS Combine controls system Hybrid control devices have together combined features of active Passive+ Active and passive control devices Passive + Semi-active Smart base-isolation The Yokohama Landmark Tower Hybrid mass damper (a combination of tuned mass damper and an active control actuator) as well as something called “bandage pillars”  SEISMIC RETROFITTING https://www.luxdevla.com/soft-story-seismic- retrofitting-techniques/ SEISMIC RETROFITTING SEISMIC RETROFITTING is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Common seismic retrofitting techniques fall into several categories: a. External post-tensioning. 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. SEISMIC RETROFITTING SEISMIC RETROFITTING is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Common seismic retrofitting techniques fall into several categories: a. External post-tensioning. 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. SEISMIC RETROFITTING a. External post-tensioning 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 SEISMIC RETROFITTING b. Supplementary dampers 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 SEISMIC RETROFITTING 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. SEISMIC RETROFITTING c. Slosh tank One Rincon Hill South Tower, USA SEISMIC RETROFITTING 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. SEISMIC RETROFITTING 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. SEISMIC RETROFITTING e. Ad hoc-addition of structural support/reinforcement e.1. Connections between buildings and their expansion additions 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 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. SEISMIC RETROFITTING e. Ad hoc-addition of structural support/reinforcement e.4. Infill shear trusses 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. SEISMIC RETROFITTING e. Ad hoc-addition of structural support/reinforcement 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) https://www.slideshare.net/slideshow/seismic-retrofitting- techniques/10114660