CE – 648: Disaster Mitigation and Management

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CE – 648: Disaster Mitigation and Management

Syed Muhammad Ibrahim Department of Civil Engineering Aligarh Muslim University Aligarh

Syllabus CE 648 Disaster Mitigation and Management

UNIT 1 Understanding of disasters

Earthquake, flood, cyclone, landslide etc.

UNIT 2 Preparedness and mitigation

Disaster mapping, predictability, forecasting and warning, disaster preparedness plans, Land use zoning for disaster management.

UNIT 3 Reconstruction and rehabilitation

Disaster resistant housing, retrofitting, repair and re- strengthening

UNIT 4 Man-made disasters Nuclear, chemical and biological disasters, building fire

UNIT 5 Disaster management and awareness

Human behaviour and response, community participation and awareness, public awareness programmes.

UNIT 1 Understanding of disasters

Earthquake, flood, cyclone, landslide etc.

UNIT 3 Reconstruction and rehabilitation

Disaster resistant housing, retrofitting, repair and re- strengthening

UNIT 4 Man-made disasters Nuclear, chemical and biological disasters, building fire UNIT 5 Disaster

management and awareness

Human behaviour and response, community participation and awareness, public awareness programmes.

 ―Any activities which actually eliminate or reduce the probability of occurrence of a disaster. It also includes long-term activities which reduce the effects of unavoidable disasters‖

(National Governors’ Association, 1981).

Mitigation

Definition

Mitigation programs are designed to prevent disasters or reduce their effects by discouraging behaviors that may put people and property at risk, such as building homes and businesses in hazardous areas.

 Voluntary mitigation programs rely upon individuals, organizations, and communities to recognize the dangers posed by hazards and to reduce their exposure to the risk.

 Nonvoluntary or mandatory mitigation programs use the threat of punishment to encourage compliance with established standards, although some individuals, organizations, and communities may risk punishment rather than change their behaviors (such as restricting development in floodplains).

Mitigation programs

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Mitigation programs (continued)

 Tax incentives, information concerning hazards and how to avoid them, and information on safe building practices, for example, only work if individuals, organizations, and communities decide that the risk of certain behaviors (such as building in wildfire areas) outweighs the benefits.

 Nonvoluntary or mandatory mitigation programs use the threat of punishment to encourage compliance with established standards, although some individuals, organizations, and communities may risk punishment rather than change their behaviors (such as restricting development in floodplains).

 The voluntary approach

 The regulatory approach

 The preemption approach

 The punishment approach

 The incentive approach

Strategies for disaster mitigation

Types

 The voluntary approach—using public information programs to inform people about hazards and encourage them to reduce the level of risk to their property, their families, their communities, and themselves;

 The regulatory approach—adopting land-use regulations and building standards to ensure that people build safely and reduce the risk to themselves and to others;

 The preemption approach—purchasing high-risk properties to prevent development and to ensure land uses that reduce the risk to people and property;

Strategies for disaster mitigation (contd…)

 The punishment approach—refusing to provide disaster assistance to individuals, families, and businesses that do not use disaster mitigation strategies to reduce the risk of property losses, injury, or death; and

 The incentive approach—rewarding builders, residents, officials, and others for behaviors deemed desirable, such as reducing taxes or insurance costs for residents who install storm shutters, use disaster-resistant building designs, or choose to locate their homes away from areas prone to flooding.

Strategies for disaster mitigation (contd…)

General mitigation measures include

 building standards and codes,

 tax incentives/disincentives,

 zoning ordinances,

 land-use regulations,

 preventive health care programs, and

 public education to reduce risk (National Governors’

Association, 1981).

Mitigation techniques are generally categorized as structural or nonstructural, as well as voluntary or mandatory.

 Building standards and codes and land-use regulation are two of the most used nonstructural mitigation techniques to reduce threats to property and potential loss of life.

 Building standards specify what materials can be used in the construction of homes, businesses, and institutional structures based upon criteria such as strength, durability, flammability, resistance to water and wind, etc., and appropriate designs for the environment.

Structural and nonstructural mitigation

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 Building codes are regulations adopted by states and/or communities that specify what kinds of building materials and designs are appropriate for particular locations, general standards to reduce the risk of fire and/or damage from earthquakes or other kinds of disaster, and specific mitigation measures to reduce the potential damage from winds or other hazards.

Structural and nonstructural mitigation

 Structural mitigation techniques include building dams, levees, breakwaters, and containment ponds to hold water or slow its flow; building civil defense shelters; and other physical means to reduce potential loss of life and property.

 Public agencies and officials are often liable to use structural or nonstructural mitigation measures rather than seek other options.

• For example, engineers tend to be oriented toward structural solutions and lawyers tend to be oriented toward nonstructural solutions.

Structural mitigation

Disaster mapping

• Mapping of areas that have been disturbed through extreme – natural

– human

caused disruptions to the normal environment such that there is a – loss of life

– value to the area.

• The delineation can occur through the use of – ground based observations

– use of remote sensing devices (aerial photographs, satellite images).

• From the information gathered it is possible to – map the affected areas and

– provide the information to groups that will provide relief.

•

Discuss the significance of zoning in disaster management

•

Discuss the do’s and don’ts for pre-, during and post earthquake and cyclone.

Questions for assignment

Area liable to floods (http://www.ndma.gov.in/en/zone-maps.html) Area liable to earthquakes (http://www.ndma.gov.in/en/zone-map.html)

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Area liable to earthquakes(https://isr.gujarat.gov.in/sz-map-india)

Area liable to winds/cylcones (http://www.ndma.gov.in/en/cyclones-zone-map.html)

Dos and don'ts

What to Do Before an Earthquake

• Repair deep plaster cracks in ceilings and foundations. Get expert advice if there are signs of structural defects.

• Anchor overhead lighting fixtures to the ceiling.

• Follow BIS codes relevant to your area for building standards

• Fasten shelves securely to walls.

• Place large or heavy objects on lower shelves.

• Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches. Hang heavy items such as pictures and mirrors away from beds, settees, and anywhere that people sit.

• Brace overhead light and fan fixtures.

Dos and don'ts

• Repair defective electrical wiring and leaky gas connections. These are potential fire risks.

• Secure water heaters, LPG cylinders etc., by strapping them to the walls or bolting to the floor.

• Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.

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Dos and don'ts

• Identify safe places indoors and outdoors.

• Under strong dining table, bed

• Against an inside wall

• Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over

• In the open, away from buildings, trees, telephone and electrical lines, flyovers and bridges

• Know emergency telephone numbers (such as those of doctors, hospitals, the police, etc)

• Educate yourself and family members

6.8 Earthquake In Bengal, Bihar And Assam, Epicentre In Myanmar

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Disaster risk reduction

CE – 648: Disaster Mitigation and Management

Syed Muhammad Ibrahim Department of Civil Engineering Aligarh Muslim University Aligarh

• Disaster Risk Reduction is: ‘Actions taken to reduce the risk of disasters and the adverse impacts of natural hazards, through systematic efforts to analyze and manage the causes of disasters, including through avoidance of hazards, reduced social and economic vulnerability to hazards, and improved preparedness for adverse events. [UN International Strategy for Disaster Reduction (ISDR)]

• The conceptual framework of elements considered with the possibilities to minimize vulnerabilities and disaster risks throughout a society, to avoid (prevention) or to limit (mitigation and preparedness) the adverse impacts of hazards, within the broad context of sustainable development [United Nations Office for Disaster Risk Reduction]

Disaster risk reduction

What is Disaster Risk Reduction (DRR)?

• Ensure that DRR is a national and local priority with strong institutional basis for implementation;

• Identify, assess, and monitor disaster risks – and enhance early warning;

• Use knowledge, innovation, and education to build a culture of safety and resilience at all levels;

• Reduce the underlying risk factors;

• Strengthen disaster preparedness for effective at all levels.

Disaster risk reduction

Steps for Implementing DRR Strategy

• Mitigation;

–Measures to be taken before and after an event

• Preparedness;

–Measures to be taken before and after an event

• Response;

–Measures to be taken during and immediately after an event

• Recovery;

–Post disaster measures

Disaster risk reduction

Components of Disaster Risk Reduction

• Mitigation is the effort to reduce loss of life and property by lessening the impact of disasters.

• It is permanent reduction of the risk of a disaster. Mitigation lessens the likelihood and severity of disaster by implementing sustained actions, such as improved construction practice, to reduce or eliminate long-term risk to people and property.

• Mitigation of hazard impacts reduces the possibility of disaster and reduces the need for assistance.

• Mitigation includes recognizing that disasters will occur; attempts are made to reduce the harmful effects of a disaster, and to limit their impact on human suffering and economic assets

Disaster risk reduction

Mitigation

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• Primary Mitigation.

–Primary mitigation refers to increasing the resistance to the hazard and reducing vulnerability.

• Secondary Mitigation.

–Secondary mitigation refers to reducing the effects of the hazard (preparedness).

Disaster risk reduction

Types of Mitigation

• Risk Identification.

–The first step in disaster mitigation is to identify areas that are at risk to hazard. Once the priority zones have been identified, comprehensive and integrated risk reduction programs should be initiated.

• Land-Use Planning.

–Land-use planning includes the mapping of disaster prone area which should contain number of livestock per unit area, crop density, population density, road network, location of shelter etc.

• Structural and Non-Structural.

–Mitigation measures may involve construction (e.g. dykes and flood protection walls, and also ecosystem-based approaches to flood and erosion control, such as planting mangrove forests) and non-material measures (e.g.

land-use restrictions in flood risk areas).

Disaster risk reduction

Various Approaches / Strategies of Disaster Mitigation

• Disaster Relief and Rehabilitation.

–Supply emergency humanitarian aid to victims for survival and relocate the peoples whose residence have been destroyed very badly, inappropriate for living.

• Disaster Management Training and Education.

–Trained up group of personnel need to be formed in local, national and regional context to mitigate and reduce disaster risk and damages.

Disaster risk reduction

• Role of Media in Disaster Risk Reduction.

–Media is the effective means to circulate the news and bulletins about hazard warning and mitigation processes.

• Institutional Capacity Building

–Several institutional bodies are engaged with disaster mitigation processes such as local community, organization, local and national government, NGOs, international organization etc. Ability and capacity of those institutions should be as high as they are capable to mitigate the disaster

Disaster risk reduction

• Preparedness refers the measures that ensure the organized mobilization of personnel, funds, equipment, and supplies within a safe environment for effective relief. Preparedness lessens the severity of disasters by preparing people for disaster, developing plans to ensure an effective response and recovery and training people to implement plans after a disaster occurs.

• Preparedness includes

–Forecasting and Warning for Different Hazards –Emergency Preparedness

•Organized personnel for monitoring, alert and evacuation; Medical team; Search and rescue team; Availability of food reserve; Emergency monetary fund and seed reserve;

Distribution of disaster supplies and equipment

–Education, Training and Public Awareness

Disaster risk reduction

Disaster Preparedness

• Forecast

• Weather forecasting  predict the state of the atmosphere for a given location.

• Quantitative data collection about the current state of the atmosphere at a given place/scientific understanding of atmospheric processes to project how the atmosphere will change.

• Tools

–Various types of tools like Barometer, Satellite (Geostationary and Polar Orbit), Radar, and other equipments.

• Early Warning System

–Early warning is a major element of disaster risk reduction. It prevents loss of life and reduces the economic and material impact of disasters. early warning systems can be used to detect a wide range of events, such as vehicular collisions, missile launches, disease outbreaks, and so forth

Disaster risk reduction

Weather Forecast and Early Warning

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• Communication

• Indigenous Knowledge

• Media

• Instruction

Types of Early Weather and Forecasting: Based on Duration

• Short Range: 48 – 72 Hours (e.g. Cyclone, Hurricane, Bombing, Flood etc.)

• Medium Range: 3 Days to 3 Weeks (e.g. Cold and Heat Wave, Floods etc.)

• Long Range: Over a Season (El-Nino, La-Nino etc.)

Disaster risk reduction

Tasks Related to Early Warning

• Aviation

• Shipping

• Local

• Agricultural Base

Disaster risk reduction

Types of Early Weather and Forecasting: Based on Purposes

• Family

• Community –Volunteering activities

–Protesting environmental degradation –Awareness building

–Emergency steps

• National: Developing principles and laws, executing rules, funding etc.

• International / Regional: Seminar, Conference, Exchange of Technology and knowledge.

Disaster risk reduction

Level of Preparedness

• Disaster response is the implementing phase of the disaster preparedness step. The focus in the response phase is on meeting the basic needs of the people until more permanent and sustainable solutions can be found.

• To be ready for response with capability to provide rapid and efficient medical, rescue and emergency supplies, and equipment to those in need, following steps of task should be implemented:

–Mobilization –Assessment –Requirement Analysis –Rescue and Evacuation

–Emergency Assistance (e.g. medical care, shelter, distribution of food, water and supplies).

Disaster risk reduction

Response

• Disaster recovery (DR) involves a set of policies and procedures to enable the recovery or continuation of vital technology infrastructure and systems following a natural or human-induced disaster. In other words, recovery is implementation of actions to promote sustainable redevelopment following a disaster, including new building code standards and land-use planning controls.

• Recovery consists of:

• Rehabilitation

Disaster risk reduction

Recovery

• Reconstruction (During reconstruction it is absolutely necessary to consider mitigation measures including relocation, land use zoning etc.)

–Rebuilding of house and public buildings –Financing for rebuilding

–Repair of roads, bridge, water system etc.

• Psychological counselling

• Long-term assistance to rebuild the community.

Disaster risk reduction

Recovery

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Floods

Impact on built and natural environments;

Disaster mitigation strategies

• The most important consequence of floods is the loss of life. There is huge loss of livestock caused by drowning.

• In floods, deaths usually exceed injuries.

• Surgical needs are low and are generally only during the first 72 hours.

• Lack of proper drinking water facilities, contamination of water (well, ground water, piped water supply) leads to outbreak of epidemics, diarrhoea, viral infection, malaria and many other infectious diseases.

• Floods may create conditions that promote secondary threats of waterborne and vector-borne diseases.

Health-related effects

Floods - Impact on built and natural environments

• In most flood prone countries where economies are based on agriculture, the largest economic flood-related losses are in the agricultural sector.

• Obviously most losses to agriculture result from the drowning of crops.

• Other agricultural losses occur in the submersion of crop storage facilities. e.g. grains.

• An additional negative impact on the agricultural sector is the erosion of topsoil by the floods - resulting in the reduced productivity of the land and possibly eventual abandonment.

Impact on Agriculture

Floods - Impact on built and natural environments

• Flooding, however, is not all bad. For some agricultural areas flooding is a positive and necessary event.

• Some low-lying lands depend on the periodic silt deposits for added nutrients to the soil.

• Flooding also serves other advantages including:

–the filtering or dilution of pollutants that enter the waterways, –flushing of nutrients in river systems,

–preserving of wetlands, –recharging of groundwater, and

–maintaining of river ecosystems by providing breeding, nesting, feeding and nursery areas for fish, shell fish, migrating waterfowl, and others.

Impact on Agriculture

Floods - Impact on built and natural environments

• Structures like houses, bridges; roads etc. get damaged by the gushing water. Boats and fishing nets also get damaged.

• Widespread floods can have a significant effect on the long-term economic growth of the affected region. Indirect and secondary effects on the local and national economy may include reduction in family income, decline in the production of business and industrial enterprises, inflation, unemployment, increase in income disparities, and decline in national income.

• In addition, relief and reconstruction efforts often compete with development programs for available funds. In countries where flooding occurs frequently, floods can create an enormous financial burden.

Impact on development

Floods - Impact on built and natural environments

• The loss of crops and the need to find alternate sources of income have often caused small-scale migrations of farmers and skilled workers from rural areas to cities. Once established in a city, few return to their homes or farms.

• Small marginal farms usually cannot survive economically following a major flood. Farmers are often forced to sell their land because they cannot afford to rehabilitate it. This may result in a substantial increase in the number of people migrating to urban areas, and thus a related housing shortage.

Floods - Impact on built and natural environments

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• The loss of crops and the need to find alternate sources of income have often caused smallscale migrations of farmers and skilled workers from rural areas to cities. Once established in a city, few return to their homes or farms.

• Small marginal farms usually cannot survive economically following a major flood. Farmers are often forced to sell their land because they cannot afford to rehabilitate it. This may result in a substantial increase in the number of people migrating to urban areas, and thus a related housing shortage..

Floods - Impact on built and natural environments

• The ability to forecast flooding is limited to the time during which changes in the hydrological conditions necessary for flooding to occur have begun to develop.

• Warning time for peak or over bank conditions can range from a few minutes in cloudburst conditions to a few hours in small headwater drainages to several days in the lower reaches of large river systems.

• Methods for warning the public should be well thought out, documented, and practiced on an annual basis. Ways to disseminate warnings include radio, television, warning sirens and public address systems.

Forecasting & Warning

Floods – Forecasting & Warning

• The majority of the deaths and much of the destruction created by floods are largely preventable.

• Mitigation measures to reduce flood damage includes actions on three fronts:

–reducing the vulnerability of the physical settlements and structures in which people live;

–reducing the vulnerability of the economy; and

–strengthening the social structure of a community so that community coping mechanisms can help absorb the impact of a disaster and promote rapid recovery.

Disaster mitigation strategies

Floods – Disaster Mitigation Strategies

• Mapping of the flood prone areas

• Land use control

• Construction of engineered structures

• Flood Control –Detention –Flood proof –Channeling

• Flood Management. Possible risk reduction measures

Floods – Possible risk reduction measures

• Historical records give the indication of the flood inundation areas and the period of occurrence and the extent of the coverage.

• Warning can be issued looking into the earlier marked heights of the water levels in case of potential threat.

• In the coastal areas the tide levels and the land characteristics will determine the submergence areas.

• Flood hazard mapping will give the proper indication of water flow during floods.

Mapping of the flood prone areas

Floods – Possible risk reduction measures

• The number of casualties is related to the population in the area at risk.

• In areas where people already have built their settlements, measures should be taken to relocate to better sites so as to reduce vulnerability.

• No major development should be permitted in the areas which are subjected to high flooding.

• Important facilities like hospitals, schools should be built in safe areas.

• In urban areas, water holding areas can be created like ponds, lakes or low-lying areas.

Land use control

Floods – Possible risk reduction measures

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• Construction of engineered structures in the flood plains and strengthening of structures to withstand flood forces and seepage.

• The buildings should be constructed on an elevated area. If necessary build on stilts or platform.

Construction of engineered structures

Floods – Possible risk reduction measures

• Flood Control aims to reduce flood damage. This can be done by decreasing the amount of runoff with the help of :

–planting trees reforestation, –protection of vegetation,

–clearing of debris/desilting from streams and other water holding areas, –conservation of ponds and lakes etc.

Flood control

Floods – Possible risk reduction measures

• Detention facilities, such as dams store flood waters and release them at lower rates, thus reducing or eliminating the need for major downstream flood control facilities, the construction of which would disrupt the developed areas.

• Perhaps the greatest disadvantage of detention facilities is the false sense of security that such structures create among the general public. These facilities are almost never designed to contain the probable maximum flood. Thus they require a spillway to pass discharges in excess of the design flood.

Detention facilities

Floods – Possible risk reduction measures

• Active flood-proofing is temporary, requiring some positive action on the part of building owners and/or occupants immediately before a flood event. E.g. sand bags to keep flood water away, blocking or sealing of doors and windows of houses etc

• Active flood-proofing requires some type of flood detection and warning system to give time for the personnel to install the flood- proofing devices. In flash flood situations the personnel may not be available to respond in time.

• Passive flood-proofing is permanent and does not require any action at the time of the flood. Base floor elevation, provision of flood vents, etc.

• Active flood-proofing is most effective in areas with long warning lead times; it should not be relied upon, if possible, in flash flood areas.

Flood-proofing

Floods – Possible risk reduction measures

• The construction of open channels is a commonly used method of reducing the size of a floodplain or floodway.

• To prevent erosion, channels can be lined with grass, wire-enclosed rock, concrete, riprap or cobblestones placed a few layers deep.

• Open channels allow water to enter them at almost any point, thus compensating for inadequate tributary collection systems..

Channelization

Floods – Possible risk reduction measures

• In India, systematic planning for flood management commenced with the Five Year Plans, particularly with the launching of National Programme of Flood Management in 1954.

• During the last 6 decades, different methods of flood protection structural as well as nonstructural have been adopted in different states depending upon the nature of the problem and local conditions.

Flood management

Floods – Possible risk reduction measures

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• Structural measures include storage reservoirs, flood embankments, drainage channels, anti erosion works, channel improvement works, detention basins etc. and non-structural measures include flood forecasting, flood plain zoning, flood proofing, disaster preparedness etc.

• The flood management measures undertaken so far have provided reasonable degree of protection to an area of ≈15.81 million hectares through out the country.

Flood management

Floods – Possible risk reduction measures

• Permanent Flood wall

• Temporary Flood wall

• Embankment

• Bypass drain

• Storage basin

• Flood gate

Typical structures for flood prevention

Floods – Possible risk reduction measures

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General rules of disaster resistant design

Syed Muhammad Ibrahim Department of Civil Engineering Aligarh Muslim University Aligarh CE – 648: Disaster Mitigation and Management

Basic rules of disaster resistant design

Examples of better understanding of disaster resistant construction principles

Basic rules of disaster resistant design

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Basic rules of disaster resistant design

Rules described here apply to different hazards.

But all the rules help in making the building stronger and lasting longer.

With each rule a special symbol is assigned for its applicability to a particular hazard.

Basic rules of disaster resistant design

• Locating the building

• Building plan & form

• Walls – length, height, thickness & connection

• Walls - openings

• Building components

• Roof & chajja

Basic rules of disaster resistant design

Locating the building

Basic rules of disaster resistant design

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Basic rules of disaster resistant design

Building plan & form

Basic rules of disaster resistant design

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Basic rules of disaster resistant design

Walls – length, height, thickness & connection

Basic rules of disaster resistant design

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Basic rules of disaster resistant design

Walls - openings

Basic rules of disaster resistant design

Walls - openings

Basic rules of disaster resistant design

Walls - openings

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Basic rules of disaster resistant design

Walls - openings

Basic rules of disaster resistant design

Walls - openings

Basic rules of disaster resistant design

Building components

Basic rules of disaster resistant design

Building components

Basic rules of disaster resistant design

Building components

Basic rules of disaster resistant design

Roof & chajja

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Basic rules of disaster resistant design

Roof & chajja

Basic rules of disaster resistant design

Roof & chajja

Basic rules of disaster resistant design

Earthquake Repair and Retrofit

Basic rules of disaster resistant design

Earthquake repairing is to make the existing damaged structure safer for future earthquake so that it can perform better during any future earthquake. It includes renewal of any part of a damaged or deteriorated structure to provide the same level of strength and ductility, which it had prior to the damage.

Seismic retrofitting is to upgrade the earthquake resistance of the structure up to the level of present-day building codes by appropriate techniques. The concepts of retrofitting include repairing and remolding, thereby upgrading of the structural system to improve the performance, function or appearance.

Earthquake Repair and Retrofit

Basic rules of disaster resistant design

Retrofitting Strategies for RC Structures Global Strategies

• Adding shear wall

• Adding infill wall

• Adding bracing

• Adding wing walls or external buttressing

• Wall thickening

• Mass reduction

• Supplemental damping

• Base isolation Earthquake Repair and Retrofit

Basic rules of disaster resistant design

Local Strategies

• Jacketing of Beams

• Jacketing of Columns

• Jacketing of Beam-Column joints

• Strengthening of individual footings

Repairing and Retrofitting Strategies for Masonry Structures

• Injecting grout or epoxy

• Injecting cement mortar and flat chips

• Wire mesh and cement plaster

• Shotcrete

• Adding reinforcements

• Confining with RC or steel Earthquake Repair and Retrofit

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Basic rules of disaster resistant design

Four Serious Configurations Conditions

• Four configuration conditions (two vertical and two in plan) that originate in the architectural design and that have the potential to seriously impact seismic performance are:

1. Soft stories

2. Discontinuous shear walls

3. Variations in perimeter strength and stiffness 4. Re-entrant corners

Basic rules of disaster resistant design

Additional features (to be taken care of) to minimize structural damages during an earthquake

• Avoid short columns

• Provide structural redundancy

• Avoid strong beam-weak column

• Provide adequate anchorage

• Separate adjacent buildings by joints

• Use closely spaced transverse reinforcement with 135°hooks in structural walls and columns

• Anchor free standing parapets walls & other elements attached to the structure

Basic rules of disaster resistant design

Ductility and Seismic Detailing

• Ductility may be broadly defined as the ability of a structure to undergo inelastic deformations beyond the initial yield deformation with no decrease in the load resistance.

• While ductility helps in reducing induced forces and in dissipating some of the input energy, it also demands larger deformations to be accommodated by the structure.

• Modern building codes provide for reduction of seismic forces through provision of special ductility requirements.

Basic rules of disaster resistant design

• In order to maintain overall ductile behavior of the structure with minimal damage, it becomes necessary to achieve, in relative terms, combinations of:

• Continuity in construction (i.e., avoid sudden changes in plan or elevation);

• Strong foundations and weak structure (i.e., the foundations should not fail before the structure);

• Strong columns and weak beams (i.e., the columns should not fail before the beams);

• Members stronger in shear than in flexure (i.e., they should not fail in shear before failing in flexure, because shear failure in much more brittle and sudden).

Basic rules of disaster resistant design

• Since ductility is a major concern for RC structures that are widely used in building construction, seismic detailing of RC structures is a topic of particular interest. The main design considerations in providing ductility of RC structures include

• Using materials of ‘medium strength’; i.e., materials strong enough to avoid brittle tensile failure but not too strong to result in brittle tensile/compressive failure;

• Using a low tensile steel ratio and/or using compressive steel in order to avoid concrete crushing before yielding of steel;

Basic rules of disaster resistant design

• Providing adequate stirrups to ensure that shear failure does not precede flexural failure;

• Confining concrete and compressive steel by closely spaced hoops/spirals;

• Proper detailing with regard to anchorage, splicing, minimum reinforcement, etc, so that the structural members can develop the forces they are designed for.