Introduction

Earthquakes are a major geological phenomena. Man has been terrified of

this phenomena for ages, as little has been known about the causes of

earthquakes, but it leaves behind a trail of destruction. There are

hundreds of small earthquakes around the world everyday. Some of them

are so minor that humans cannot feel them, but seismographs and other

sensitive machines can record them. Earthquakes occur when tectonic

plates move and rub against each other. Sometimes, due to this

movement, they snap and rebound to their original position. This might

cause a large earthquakes as the tectonic plates try to settle down. This is

known as the Elastic Rebound Theory.

Every year, earthquakes take the lives of thousands of people , and

destroy property worth billions. The 2010 Haiti Earthquake killed over

1,50,000 people and destroyed entire cities and villages. Designing

Earthquake Resistant Structures is indispensable. It is imperative that

structures are designed to resist earthquake forces, in order to reduce the

loss of life. The science of Earthquake Engineering and Structural Design

has improved tremendously, and thus, today, we can design safe

structures which can safely withstand earthquakes of reasonable

magnitude.

The most destructive of all earthquake hazards is caused by seismic

waves reaching the ground surface at places where human-built

structures, such as buildings and bridges, are located. When seismic

waves reach the surface of the earth at such places, they give rise to what

is known as strong ground motion. Strong ground motions cause’s

buildings and other structures to move and shake in a variety of complex

ways.

Many buildings cannot withstand this movement and suffer damages of

various kinds and degrees. Most deaths, injuries, damages and economic

losses caused by earthquake result from ground motion acting on

buildings and other manmade structures not capable of withstanding such

movement.

Experience in past earthquakes has demonstrated that many common

buildings and typical methods of construction lack basic resistance to

earthquake forces. In most cases this resistance can be achieved by

following simple, inexpensive principles of good building construction

practice. Adherence to these simple rules will not prevent all damage in

moderate or large earthquakes, but life threatening collapses should be

prevented, and damage limited to repairable proportions. These principles

fall into several broad categories:

(i) 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.

(ii) Lay out and general design of the structural framing system

with special attention to furnishing lateral resistance, and

(iii) Consideration of highly loaded and critical sections with

provision of reinforcement as required.

Earthquakes cause massive vibrations in the Earth’s crust. This can cause

a number of problems in the ground, which in turn becomes a hazard to

all life and property. The effect depends on the geology of soil and

topography of the land.

For categorising the buildings with the purpose of achieving seismic resistance at economical cost, three parameters turn out to be significant:

(i) Seismic intensity zone where the building is located,(ii) How important the building is, (iii)How stiff is the foundation soil.

A combination of these parameters will determine the extent of appropriate seismic strengthening of the building.

The importance of the building should be a factor in grading it for strengthening purposes,and the following buildings are suggested as specially important:

IMPORTANT . Hospitals, clinics, communication buildings, fire and police stations, water supply facilities, meeting halls, schools, dormitories, cultural treasures such as museums, monuments and temples, etc.

ORDINARY . Housings, hostels, offices, warehouses, factories, etc.Severity of ground shaking at a given location during an earthquake can be minor, moderate and strong. Thus relatively speaking, minor shaking occurs frequently; moderate shaking occasionally and strong shaking rarely. For instance, on average annually about 800 earthquakes of

magnitude 5.0-5.9 occur in the world while about 18 for magnitude range 7.0-7.9. So we should design and construct a building to resist that rare earthquake shaking that may come only once in 500 years or even once in 2000 years, even though the life of the building may be 50 or 100 years

Design Philosophy of Earthquake Resistant Structures

Engineers do not attempt to make earthquake proof buildings that will not get damaged even during the rare but strong earthquake; such buildings will be too robust and also too expensive. Instead the engineering intention is to make buildings earthquake-resistant; such buildings resist the effects of ground shaking, although they may get damaged severely but would not collapse during the strong earthquake. Thus, safety of people and contents is assured in earthquake-resistant buildings, and thereby a disaster is avoided. This is a major objective of seismic design codes throughout the world.

Design Philosophy

1. Under minor but frequent shaking, the main members of the buildings

that carry vertical and horizontal forces should not be damaged;

however buildings parts that do not carry load may sustain repairable

damage.

2. Under moderate but occasional shaking, the main members may

sustain repairable damage, while the other parts that do not carry

load may sustain repairable damage.

3. Under strong but rare shaking, the main members  may sustain

severe damage, but the building should not collapse.

Earthquake resistant design is therefore concerned about ensuring that the damages in buildings during earthquakes are of acceptable variety, and also that they occur at the right places and in right amounts. This approach of earthquake resistant design is much like the use of electrical fuses in houses: to protect the entire electrical wiring and appliances in the house, you sacrifice some small parts of electrical circuit, called fuses; these fuses are easily replaced after the electrical over-current. Likewise to save the building from collapsing you need to allow some pre-determined parts to undergo the acceptable type and level of damage.

Earthquake resistant buildings, particularly their main elements, need to be built with ductility in them. Such buildings have the ability to sway back-and-forth during an earthquake, and to withstand the earthquake effects with some damage, but without collapse.

Impact of Earthquakes

Earthquakes do not kill people, but buildings do. We are heavily dependent upon the civic amenities or life-lines like water supply, electric power supply, drainage. Earthquake can disturb civic amenities in a major way. Lifeline like hospitals, health care centers have major role in natural catastrophe like earthquake. Hence additional care while designing these

structures is needed. A severe earthquake can have very damaging consequences upon a region’s development and economy.

Its has its impacts on

(a) Lifeline and society(b) Affects a Large number of People. (c) Losses to Lives, Livelihoods, Property. (d) Civic amenities(e) Heritage(f) Loss of housing. (g) Damage to infrastructure (h) Disruption of transport and communication. (i) Disruption of marketing systems. (j) Breakdown of social order. (k) Loss of business. (l) Loss of industrial output.

Among all disasters that can take place, earthquake has the maximum loss of life and limbs. Tremendous loss of property, especially buildings is caused, leaving a large mass of population shelter less. Buildings as badly damaged as this require demolition.

Our heritage connects us with our ancestors and give a sense of pride and belongings. The new structures can be often rebuilt but the loss of heritage is a huge loss. Since the reconstruction is difficult as well as the very sense of it being built historically is lost forever.

The healthcare center where everyone looks for healing, itself looking for health touch is the sad scene during earthquakes. These type of facility needs to be given extra level of earthquake protection. Since healthcare buildings have to play a major role in case of catastrophe, additional care is needed in their design. Seismic code provisions require these buildings to be designed for higher levels of earthquake loads.

Effects of Earthquakes

In a comprehensive design approach, it should be recognized that damage to structures and facilities may result from different seismic effects.  These effects can be classified as ‘Direct’ and ‘Indirect’ (or Consequential) as follows:

Direct Effects:

1. Ground failures (or instabilities due to ground failures)             Surface faulting surface or fault rupture)

             Vibration of soil (or effects of seismic waves)                   Ground cracking                   Liquefaction                   Ground lurching                   Differential settlement                   Lateral spreading                   Landslides

2. Vibrations transmitted from the ground to the structure.

Indirect Effects (or Consequential Phenomena):

      (3)  Tsunamis       (4)  Seiches      (5)  Landslides      (6)  Floods      (7)  Fires

The seismic effect or damage that usually concerns the structural engineer, and which is taken into account by code seismic-resistant design provisions, is the vibration of the structure in response to ground shaking at its foundation.  Although damage due to other effects may exceed that due to vibration, procedures for gauging the probability of these effects and for coping with them are outside the scope of the structural engineering discipline and so are usually not included in seismic-resistant codes.  Nonetheless, the structural engineer should be aware of the different seismic hazards and should advise the client of potential damage involved in locating structures at certain sites.  Thus the first step in the design procedure of a future structure should be the analysis of the suitability of the site selected with proper consideration for the potential of any one of the above types of damage.

The effects of earthquakes include, but are not limited to, the following:

Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicenter, and the local geological and geomorphologic conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphologic, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

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. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

Landslides and avalanches

Earthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.

Fires

Earthquakes can cause fires by damaging electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started.

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. This can be a devastating effect of earthquakes.

Tsunami

Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. In the open ocean the distance between wave crests can surpass 100 kilometers (62 miles), and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600-800 kilometers per hour (373–497 miles per hour), depending on water depth. Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes. Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.

Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have

been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.

Floods

A flood is an overflow of any amount of water that reaches land.[34] Floods occur usually when the volume of water within a body of water, such as a river or lake, exceeds the total capacity of the formation, and as a result some of the water flows or sits outside of the normal perimeter of the body. However, floods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which then collapse and cause floods.

Human impacts

Earthquakes may lead to disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse or destabilization (potentially leading to future collapse) of buildings. Earthquakes can also precede volcanic eruptions, which cause further problems.

Construction Materials

In India, most non-urban buildings are made in masonry. In the plains, masonry is generally made of burnt clay bricks and cement mortar. However in hilly areas, stone masonry with mud mortar is more prevalent. But now a day we are very familiar with R.C.C. buildings, and a variety of new composite constructions materials.

Brittle and Ductile Building Materials

I. Masonry

Masonry is made up of burnt clay bricks and cement or mud mortar. Masonry can carry loads that cause compression (i.e. pressing together) but can hardly take load that causes tension (i.e. pulling apart). Masonry is a brittle material, these walls develop cracks once their ability to carry horizontal load is exceeded. Thus infill walls act like sacrificial fuses in buildings: they develop cracks under severe ground shaking but they share the load of the beams and columns until cracking.

II. Concrete

Concrete is another material that has been popularly used in building construction particularly over the last four decades. Cement concrete is made of crushed stone pieces (called aggregate), sand, cement and water mixed in appropriate proportions. Concrete is much stronger than masonry under compressive loads, but again its behavior in tension is poor. The properties of concrete critically depend on the amount of water used in making concrete, too much and too little water both can cause havoc.

III. Steel

Steel is used in masonry and concrete buildings as reinforcement bars of diameter ranging from 6mm to 40mm. reinforcing steel can carry both tensile and compressive loads. Moreover steel is a ductile material. This important property of ductility enables steel bars to undergo large elongation before breaking. Concrete is used with steel reinforcement bars. This composite material is called as reinforced cement concrete. The amount and location of steel in a member should be such that the failure of the member is by steel reaching its strength in tension before concrete reaches its strength in compression. This type of failure is ductile failure, and is preferred over a failure where concrete fails first in compression. Therefore, providing more steel in R.C. buildings can be harmful even

Earthquake Construction Typologies

Earthquake construction means implementation of seismic design to enable building and non-building structures to live through the anticipated earthquake exposure up to the expectations and in compliance with the applicable building codes.

Design and construction are intimately related. To achieve a good workmanship, detailing of the members and their connections should be, possibly, simple. As any construction in general, earthquake construction is a process that consists of the building, retrofitting or assembling of infrastructure given the construction materials available. The destabilizing action of an earthquake on constructions may be direct (seismic motion of the ground) or indirect (earthquake-induced landslides, soil liquefaction and waves of tsunami).

A structure might have all the appearances of stability, yet offer nothing but danger when an earthquake occurs. The crucial fact is that, for safety, earthquake-resistant construction techniques are as important as quality control and using correct materials.

To minimize possible losses, construction process should be organized with keeping in mind that earthquake may strike any time prior to the end of construction. Each construction project requires a qualified team of professionals who understand the basic features of seismic performance of different structures as well as construction management.

Adobe structures

One half of the world's population lives or works in the buildings made of earth. Adobe type of mud bricks is one of the oldest and most widely used building materials. The use of adobe is very common in some of the world's most hazard-prone regions, traditionally across Latin America, Africa, Indian subcontinent and other parts of Asia, Middle East and Southern Europe.

Adobe buildings are considered very vulnerable at strong quakes. However, multiple ways of seismic strengthening of new and existing adobe buildings are available.

Key factors for the improved seismic performance of adobe construction are:

Quality of construction. Compact, box-type layout. Seismic reinforcement.

Limestone and sandstone structures

Limestone is very common in architecture. Many landmarks across the world, including the pyramids in Egypt, are made of limestone. Many medieval churches and castles in Europe are made of limestone and sandstone masonry. They are the long-lasting materials but their rather heavy weight is not beneficial for adequate seismic performance.

Application of modern technology to seismic retrofitting can enhance the survivability of unreinforced masonry structures.

Timber frame structures

Timber framing dates back thousands of years, and has been used in many parts of the world during various periods such as ancient Japan, Europe and medieval England in localities where timber was in good supply and building stone and the skills to work it were not.

The use of timber framing in buildings provides their complete skeletal framing which offers some structural benefits as the timber frame, if properly engineered, lends it to better seismic survivability.

Light-frame structures

Light-frame structures usually gain seismic resistance from rigid plywood shear walls and wood structural panel diaphragms. Special provisions for seismic load-resisting systems for all engineered wood structures requires consideration of diaphragm ratios, horizontal and vertical diaphragm shears, and connector/fastener values. In addition, collectors, or drag struts, to distribute shear along a diaphragm length are required.

Reinforced masonry structures

A construction system is used where steel reinforcement is embedded in the mortar joints of masonry or placed in holes and after filled with concrete or grout is called reinforced masonry.

There are various practices and techniques to achieve reinforced masonry. The most common type is the reinforced hollow unit masonry. The effectiveness of both vertical and horizontal reinforcement strongly depends on the type and quality of the masonry, i.e. masonry units and mortar.

To achieve a ductile behavior of masonry, it is necessary that the shear strength of the wall is greater than the tensile strength of reinforcement to ensure a kind of bending failure.

Reinforced concrete structures

Reinforced concrete is concrete in which steel reinforcement bars (rebars) or fibres have been incorporated to strengthen a material that would otherwise be brittle. It can be used to produce beams, columns, floors or bridges.

Prestressed concrete is a kind of reinforced concrete used for overcoming concrete's natural weakness in tension. It can be applied to beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would, otherwise, experience due to a bending load.

To prevent catastrophic collapse in response earth shaking (in the interest of life safety), a traditional reinforced concrete frame should have ductile joints. Depending upon the methods used and the imposed seismic forces,

such buildings may be immediately usable, require extensive repair, or may have to be demolished.

Prestressed structures

Prestressed structure is the one whose overall integrity, stability and security depend, primarily, on a prestressing. Prestressing means the intentional creation of permanent stresses in a structure for the purpose of improving its performance under various service conditions. Naturally pre-compression is used in the exterior wall of Colosseum, Rome.

There are the following basic types of prestressing:

Pre-compression (mostly, with the own weight of a structure) Pretensioning with high-strength embedded tendons Post-tensioning with high-strength bonded or unbonded tendons

Today, the concept of prestressed structure is widely engaged in design of buildings, underground structures, TV towers, power stations, floating storage and offshore facilities, nuclear reactor vessels, and numerous kinds of bridge system.A beneficial idea of prestressing was, apparently, familiar to the ancient Rome architects; look, e.g., at the tall attic wall of Colosseum working as a press for the wall piers beneath.

Steel structures

Steel structures are considered mostly earthquake resistant but their resistance should never be taken for granted. A great number of welded steel moment frame buildings, which looked earthquake-proof, surprisingly experienced brittle behavior and were hazardously damaged in the 1994 Northridge earthquake. After that, the Federal Emergency Management Agency (FEMA) initiated development of repair techniques and new design approaches to minimize damage to steel moment frame buildings in future earthquakes.

For structural steel seismic design based on Load and Resistance Factor Design (LRFD) approach, it is very important to assess ability of a structure to develop and maintain its bearing resistance in the inelastic range. A measure of this ability is ductility, which may be observed in a material itself, in a structural element, or to a whole structure.

All pre-qualified connection details and design methods contained in the building codes of that time have been rescinded. The new provisions stipulated that new designs be substantiated by testing or by use of test-verified calculations.

Base Isolation

It is easiest to see the principle at work by referring directly to the most widely used of these advanced techniques, known as base isolation. A base isolated structure is supported by a series of bearing pads, which are placed between the buildings and building foundation.

Base Isolation Technique

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, 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. 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.

oncept of Base Isolation

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.

Response of Base Isolated Buildings

The base-isolated building retains its original, rectangular shape. The base isolated building itself escapes the deformation and damage-which implies that the inertial forces acting on the base isolated building have been reduced. Experiments and observations of base-isolated buildings in earthquakes to as little as ¼ of the acceleration of comparable fixed-base buildings.

Acceleration is decreased because the base isolation system lengthens a buildings period of vibration, the time it takes for a building to rock back and forth and then back again. And in general, structures with longer periods of vibration tend to reduce acceleration, while those with shorter periods tend to increase or amplify acceleration.

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

Guidelines

  One of the most critical decisions influencing the ability of a superstructure to withstand earthquake ground shaking is the choice of its basic plan shape and configuration.  The importance of a proper selection of the superstructure configuration will be discussed and illustrated for the case of building structures.

      Building structures may be of many types and configurations and there is, of course, no universal ideal configuration for any particular type of building.  However, there are certain basic or guiding principles of  seismic-resistant design that can be used as guidelines in selecting an adequate building configuration structural layout, structural system,

structural material and the non-structural components.  These basic guidelines are as follows:

1. Building (superstructure and non-structural components) should be light and avoid unnecessary masses.

2. Building and its superstructure should be simple, symmetric, and regular in plan and elevation to prevent significant torsional forces, avoiding large height-width ratio and large plan area.

3. Building and its superstructure should have a uniform and continuous distribution of mass, stiffness, strength and ductility, avoiding formation of soft stories.

4. Superstructure should have relatively shorter spans than non-seismic-resistant structure and avoid use of long cantilevers.

5. The non-structural components should either be well separated so that they will not interact with the rest of the structure, or they should be integrated with the structure.  On the latter case, it is desirable that the structure should have sufficient lateral stiffness to avoid significant damage under minor and moderate earthquake shaking, and toughness with stable hysteric behavior (that is, stability of strength, stiffness and deformability) under the repeated reversal of deformations which could be induced by severe earthquake ground motion.  The stiffer the structure, the less sensitive it will be to the effects of the interacting non-structural components, and the tougher it is, the less sensitive it will be to effect of sudden failure of the interacting non-structural elements.

6. Superstructure should be detailed so that the inelastic deformations can be constrained (controlled) to develop in desired regions and according to a desirable hierarchy.

7. Superstructure should have the largest possible number of defense lines, that is, it should be composed of different tough structural subsystems which interact or are interconnected by very tough structural elements (structural fuses) whose inelastic behavior would permit the whole structure to find its way out from a critical stage of dynamic response.

8. Superstructure should be provided with balanced stiffness and strength between its members, connections and supports.

9. The stiffness and strength of the entire building should be compatible with the stiffness and strength of the soil

Research alone is not enough; analytical and experimental studies must be augmented by development work [27].  Specific educational and integrated analytical and experimental research and development needs have been discussed in detail in several publications [12, 13, 28, 29].

RESEARCH CONDUCTED IN THE LAST TWO DECADES

      Despite many unresolved problems in predicting the behavior of buildings and civil engineering structures in general, under the combined effects of normal environments and extreme earthquake ground motions, our understanding has advanced significantly in the last two decades.  There is a significant body of knowledge regarding the problems caused by extreme earthquake shaking that has been gained through integrated experimental and analytical research conducted in different research institutions in the world.  A few example of the experimental research conducted in the Structural Laboratories of the University of California at Berkeley are illustrated in Slides J109-J113.

   

J109.  Test set-up for studying the seismic behavior of short column-spandrel deep girder subassemblages. 

      A series of integrated analytical and experimental studies has been conducted to investigate the behavior of this type of main assemblage that has been used frequently in buildings located in regions of high seismic risk.  Methods to improve the hysteretic behavior of the short columns have been developed.  By using the correct amount and detailing of longitudinal and particularly lateral reinforcement it has been possible to attain tough short columns

capable of dissipating a significant amount of energy before resistance is lost [30].

J110.  Two-story column-deep girder assemblage after being subjected to severe hysteretic behavior, simulating the expected behavior of this assemblage in tall buildings subjected to severe ground shaking.  Note the excellent behavior of the properly confined concrete [30].  The need for improving the behavior of short columns has been emphasized by the numerous failures of this type of column in recent earthquakes.

 

J111.  Strong column-weak girder assemblage of a ductile moment-resistant reinforced concrete frame.  In the experiments conducted on subassemblages of ductile reinforced concrete moment-resistant frames it has been observed that there was significant degradation in stiffness and strength of frames with repeated cycles of deformation reversal.  The main sources of this problem have been identified as high shear and/or high bond stress through the joint.

      The design can avoid or minimize this problem by avoiding the formation of the critical regions (plastic hinges) at the faces of the columns.  Experiments conducted at Berkeley on subassemblages in which the plastic hinges have been moved away from the columns as illustrated in this slide, and therefore keeping the joint elastic, have shown that it is possible to achieve good stable hysteretic behavior [31, 32].  Note in this slide that all the inelastic deformations occurred in the beams in regions away from the face of the column.

J112.  Weak column-strong girder assemblage of a steel moment-resistant frame.  Slide showing the local buckling of a column of the subassemblage that has been subjected to high axial forces and shear reversals simulating the effect of seismic excitations.  From this

study and similar integrated experimental and analytical research, a series of recommendations has been made regarding the compactness of steel structural shapes as well as the design of beam-column joints in steel moment-resistant frames subject to severe seismic shaking and requiring significant dissipation of energy through inelastic behavior (ductility).

 

J113.  A 1/5 scale model of the US-Japan 2-story reinforced concrete test structure on the shaking table of the earthquake simulator facility at the University of California, Berkeley.  This is the 1/5 scale model of the prototype studied experimentally using a pseudo-dynamic technique at the large testing facility of the BRI at Tsukuka, the Science City of Japan.  These studies have been conducted as part of a comprehensive US-Japan Cooperative Research Program, planned to improve the seismic-resistant design and construction of buildings [34].

      The results of the tests conducted have indicated the importance of the three-dimensional interacting behavior of walls and surrounding frames and of the significance of rocking and growth of the wall at the base, and the consequential outriggering action that the surrounding frames will exert on the walls.  The results obtained have also indicated the need for considering the contribution of slab reinforcement to the negative moment capacity of the girders cast monolithically with the floor slabs.  Important recommendations for improving the states of the practice and of the art in seismic-resistant design and construction of reinforced concrete frame-wall systems have been made, based on the results offered in this cooperative research program.

References

http://articles.architectjaved.com/earthquake_resistant_structures/tag/earthquakes/

http://nisee.berkeley.edu/bertero/html/earthquake-resistant_construction.html