Basic recommendations for earthquake protection_8 docx

STRATEGIES FOR EARTHQUAKE PROTECTION 191 in e-commerce or use the internet for essential business communications need disaster plans and back-up servers located outside the region likely to be affected by earthquake. Cellular phone networks have also been found vulnerable to disruption in major earthquakes. Radio systems are less vulnerable to earthquake disruption and may be worth installing as a back-up for communications. Internal communications within an organisation can be maintained through UHF radio systems – these are usually sufficient to cover a large site or campus. City-wide communications can be maintained on VHF radio, within specific wavebands usually requiring a licence. Conversations over a radio system of this sort are less secure – that is, other people can eavesdrop – but could be critical in an emergency. A larger radio communication system can enable contact to be maintained with places far beyond the area likely to be damaged in an earthquake. Maintaining Transportation Links More serious disruption to an organisation’s operations may be the possible enforced isolation if road and rail linkages are cut either locally or in the region. Inability to receive or make deliveries for any length of time may cripple the oper- ation of an organisation, particularly manufacturing operations unable to receive raw materials or spare parts and unable to get finished products to market. An ability to be flexible in transport mode will help, using road if rail links are cut and vice versa. A storage capability to stockpile several days (or weeks) of output, with freezing or preservative capabilities for perishable goods, may make immediate despatch less critical. Similarly, increasing the margins of stock operations, although perhaps expensive in warehousing capacity, will make the operation less vulnerable to disruptions in delivery of supplies. The less reliant the organisation can be made on continuous services being provided from outside, the less vulnerable it will be to disruption from a future earthquake. 6.3.7 Information Protection and Business Contacts Many businesses, particularly small businesses, suffer badly from the loss of information or records in the earthquake damage. Files can be lost in destroyed buildings, ruined by fires or by water leakages caused by the earthquake, wiped from computer memories or simply thrown into disarray by the overturning of filing cabinets. Protection of commercial records from earthquake damage is an important consideration. It is possible to formulate filing and archiving procedures to protect against earthquake-induced information loss. A measure of protection can be ensured by keeping copies of important documents on back-up servers, or physically in separate filing cabinets, preferably steel cased and low level. Archives may be safer if kept in a separate building. Hard copies of important computer files, and back-up disks, should be similarly ‘hard filed’. 192 EARTHQUAKE PROTECTION The chaos ensuing after a major earthquake is also extremely disruptive, again particularly for a small business. Communications may be cut and routines shat- tered. If the business itself has lost its premises, or is forced to close temporarily, potential customers trying to make contact will be unable to do so. Contact should be re-established as soon as possible by informing customers and clients about the continued delivery of services and goods, and any relocation address, through advertising, mail, telephone or personal contact. Disruption is likely to be minimised if part of the organisation’s normal activities involve informing clients and customers, suppliers, subcontractors, staff and other business contacts of emergency plans that would affect them, including information channels likely to be used to confirm continued operations, contingency plans and enquiry con- tact points. Information about an organisation’s emergency plans is unlikely to frighten off customers and may encourage confidence if it is presented in the context of a range of activities being undertaken by the organisation to improve earthquake protection for staff and customers. 6.4 Urban Risk Management 6.4.1 Urban Planning The layout and development of cities, the location of infrastructure, key buildings and utilities and the physical development of the built environment all affect the consequences of an earthquake. The urban planner, the regional planner, engineers designing the layout of utility networks, transportation routes or key installations, and anyone whose job is to locate facilities within a city or whose decisions affect the use of land, all have a role to play in reducing potential earthquake impact. Urban planning departments are usually a part of local or regional government, and activities of the management of private building stock, seismic design code enforcement and other local government measures for earthquake protection may well be a central part of the responsibilities of an urban planning department. If not, the linkages between land-use master planning for earthquake protection and other urban planning protection measures and the control of building quality are so interrelated that the development of effective earthquake protection measures needs a strong coordination between the groups with those responsibilities. As with all urban planning, effective management of the development of a city depends on understanding the processes that are making it the way it is. The trends in land prices, the locational preferences for various industries, activities and communities, the demographic trends of the population and many other factors are all driving forces shaping the city. Urban planning is the attempt to direct those forces using limited means and a small repertoire of legislative and economic powers. The concerns of urban planning are many: to ensure a sanitary, pleasant and safe environment for the population, to provide adequate services to the people and workers in the city, to enable the city’s activities to be carried out STRATEGIES FOR EARTHQUAKE PROTECTION 193 more easily and to plan ahead for the future. Many of the concerns of earthquake protection also parallel these objectives: limiting the densities of development and concentrations of population, protection of service provision and facilitation of continued economic activities. By its nature, urban planning is long term. Master plans have to encompass decades of expected growth, and it is evident that earthquake protection is nec- essarily a long-term process. Adding Building Stock Management to Land Use Where earthquake protection may be different to normal urban land-use planning is in the emphasis on building stock management, i.e. the influencing of the process of creation and maintenance of privately owned buildings in addition to land use and location. This process-orientated approach in combination with locational aspects may require a slight reappraisal of planning methodology. Earthquake protection should be seen as an additional element of normal urban planning. It should not be a separate activity from other planning operations, but rather an integral part of the planning process – another factor to be weighed in the decision-making and balanced against other factors: when siting a new school or planning a new residential suburb, earthquake risk should be weighed against the transportation implications, cost of land, suitability of the local environment, cost of providing services and so on. Where there is a choice of sites with an identifiable difference between them in earthquake susceptibility, this should influence the choice – if all other factors are equal the less susceptible site should be chosen. If not, the cost of building the school to higher standards of earthquake resistance or imposing stricter controls on the residential structures should be balanced against other costs and advantages of the sites. Where a site of higher seismic hazard is chosen, the facilities and building stock built on that location must be built to higher standards of earthquake resistance. Thus the integration of seismic building code enforcement and building stock management with land-use planning becomes critical. Microzoning and Vulnerability Mapping From the discussion in the next few sections it will be seen that earthquake protection planning at an urban scale involves both the location of elements in the city and the quality of elements in those locations. Earthquake protection planning at the urban scale requires two additional maps to the urban planner’s usual map collection: (1) the seismic microzoning map of the geological earthquake hazards and (2) the seismic vulnerability map of the buildings and facilities of the city. The addition of a seismic microzoning map in preparing land-use plans or development master plans may be fairly straightforward and comparable to other 194 EARTHQUAKE PROTECTION preparation and study maps that contribute to the planning process. However, the seismic vulnerability map encompasses the physical attributes of the building stock in a more comprehensive way than is usually needed for other planning activities. In addition to the characteristics of function, plot development, density and perhaps number of storeys that are commonly used to map the building stock for land-use planning, earthquake protection needs information on construction materials, structural form, height and size, engineering design quality and age and other broad indicators of seismic vulnerability (see Chapters 8 and 9 for vul- nerability classification of building types) with which to classify the earthquake resistance of the building stock. Building Stock Data Information is needed across the city, from district to district, about the numbers of different types of building classified by their seismic vulnerability together with their functions and occupancy. This is usually built up from building cen- sus data if it already exists or can be obtained by carrying out building surveys on a street-by-street basis, but useful data on the physical characteristics of the building stock can also be gathered from aerial survey interpretation, planning applications or other documentation, or assumed from historical urban devel- opment patterns and existing land-use plans or zoned from other information sources. Seismic vulnerability mapping and building stock inventories can be time con- suming if carried out in detail, but may only be needed at an approximate level to give enough information for urban protection plans. The broad identification of the building types most at risk from a future earthquake and the parts of the city which are likely to be worst affected may be relatively easily identified. The policies of upgrading the most vulnerable building stock sector and proposing land-use plans that reduce earthquake risk in the city are likely to be obtainable from relatively simple analyses. Land-use Planning and Seismic Microzoning Some types of ground are safer than others in earthquakes. In addition to the numerous ground failures caused by earthquake vibrations, such as landslides, slope failures, liquefaction and rockfalls, it is well known that different types of ground vibrate more severely in earthquakes and so cause higher damage levels to the buildings built on them. Siting considerations for earthquake protection are discussed in Chapter 7. Seismic microzoning, or the identification of various ground conditions in terms of their earthquake hazard across an area at the scale of a city or conurbation, is an important tool for urban planning to incorporate earthquake protection. Methods of microzoning are described in Section 7.4. The seismic microzoning STRATEGIES FOR EARTHQUAKE PROTECTION 195 map, even if fairly coarsely defined, can be used as an additional information resource for urban planners to incorporate earthquake protection considerations into their normal land-use planning decisions. The map may define areas of likely ground motion amplification, potential slope failures, landslides or rockfalls and potential liquefaction. The delineation of the city and its environs, particularly its potential areas of expansion, into areas of relative severity of ground motion shaking likely to be experienced in a future earthquake can help shape a safer city. It may be possible to avoid building on some areas of potentially higher hazard altogether – a zone of very high hazard might be left as park area or the areas of city expansion might be encouraged out in an opposite direction (through preferential provision of transportation routes, urban services, etc.). By building on areas of potentially lower hazard, future earthquake damage can be reduced. This method of damage reduction has the advantage that if locational planning is possible, there is no direct capital investment required to bring about increased safety. There are a number of indirect costs involved – land prices may be higher in one area than another, or there may be increases in transport costs or needs for additional infrastructure – but in many cases the total costs to the community can be far less than those involved in the construction of stronger building stock. Where choices of location are limited, or the arguments for locating in an area of higher seismic hazard for other reasons are convincing, structures or infrastructure built in that location must be built to a higher standard of earthquake resistance. The matching of engineering code requirements and building stock management with land-use planning therefore becomes critical. High-intensity Amplification The potential effectiveness of land-use planning for safety will vary considerably from case to case. Different types of ground affected by the same earthquake waves may vary in their severity of shaking and consequent destructiveness by one or more degrees of intensity. Stiffer soils, or hard rock, may be shaken with ground motion of intensity VIII while softer ground close by, like shallow alluvium, is shaking more severely, closer to intensity IX. From the vulnera- bility studies outlined in Chapter 9, this would mean that around 75% of weak masonry buildings built on the soft ground could collapse, killing perhaps 14% of their occupants, whereas only 40% of the same building types built on the rock would collapse, killing less than 5% of their occupants. There is generally more difference between the performance of different ground types at higher inten- sities, so for moderate levels of earthquake shaking locational planning is less effective in reducing losses. But where high intensities are possible, the micro- zoning of a city or town can play an important part in earthquake protection. An example of using urban land-use planning for earthquake protection is shown in Figure 6.1. 196 EARTHQUAKE PROTECTION In a case study of the effectiveness of strategies to reduce losses in the rapidly expanding city of Bursa in Turkey, one of the options considered was locational control over the expected future growth of the city suburbs. The constraints on development are considerable, but if some of the predicted expansion of the suburbs could be redirected away from their expected sprawl across the alluvial valley, and could instead be encouraged to take place on the stiff soils at the neck of the valley floor, the city would be significantly safer against a future earthquake. A magnitude 7.2 earthquake occurring 30 km or so away from the city in the year 2010 would be likely to cause an estimated 1200 deaths in the city. If by then land use controls have redirected the expansion, fatalities would be only about 980 - a reduction of 17% in life loss. This increase in safety would be independent of any changes in the quality of the building stock, which would of course, give further safety. Bursa 2010 (Expected Growth) Bursa 2010 (Land Use Control) Figure 6.1 Study of earthquake implications for planning of new city suburbs in Bursa, Turkey (after Akbar 1989) Unfortunately the science of microzoning ground conditions and predicting their likely performance in future earthquakes is relatively young and there are large uncertainties. Estimates of likely response characteristics of different ground types are only approximate, and detailed knowledge of the sub-strata underneath sites is difficult to obtain. There are only a few places where earth- quakes have recurred and where detailed observations have been made of how the ground conditions affect the intensity experienced. In most other places, the detailed effect of ground condition on ground motion severity can only be crudely estimated. STRATEGIES FOR EARTHQUAKE PROTECTION 197 Frequency Characteristics of Soils The information provided by microzoning studies cannot predict very accurately the severity of shaking and the amplitudes of acceleration likely to be experi- enced in a future earthquake, but it can be much more reliable in determining the frequency content of vibration due to different local ground conditions. This is important because certain building types are more vulnerable to different fre- quencies of ground motion vibration than others. (See Section 7.5.) Seismic microzoning can be used to ensure that a match does not occur between buildings vulnerable to certain frequencies of vibration and ground conditions that are likely to vibrate in that frequency range. This is chiefly a problem for taller high-rise buildings and soft soils that may amplify earthquake motions in the long-period range. To avoid buildings being damaged by resonance effects in zones where the ground is likely to vibrate in certain frequency ranges, buildings should be designed either to have frequencies of natural vibration well outside the critical range or, more problematically, for the much higher seismic forces they are likely to experience. An example would be a zone where restrictions might be imposed on building structures of 10 storeys high, likely to have a natural period of about 1 second, because the zone consists of deep deposits of soft soil that are also likely to have natural periods of vibration of about 1 second so resonance would occur. Uncertainties about ground conditions and their likely performance in an earth- quake may be too great for major decisions on location to be solely based on seismic safety considerations, but they can add useful information to help decision-making for protection. Limitations of Land-use Planning There are a number of other important restrictions to land-use planning as a tool of the earthquake protection planner. The first is that land-use planning is essentially opportunistic: there has to be a need for the location of new buildings (e.g. an expanding city), a choice between alternative areas in which location is possible, and a difference between the expected earthquake performance of the different areas. The second and possibly greater restriction is that land use has to be controllable. In many very rapidly expanding cities, principally in developing countries, urban planning authorities have almost given up attempting to control detailed land use, because the administrative framework for planning controls is impossible to maintain. The more stable cities, e.g. in the developed world, have well-established planning control mechanisms but the opportunity for changing their risk through land use is very limited because the city already exists and will largely retain its historical layout. 198 EARTHQUAKE PROTECTION Land Price and Earthquakes A major factor in shaping cities is land price. Earthquake risk may itself change the shape of the city to reduce future risk without planning measures. Earthquakes have been known to have marked effects on land price, changing the character of urban areas in the longer term: poor ground conditions in a district of a city, highlighted by concentrations of earthquake damage, are likely to make that dis- trict less desirable and suppress land prices there. 4 Land prices and commercial forces also change the nature of urban areas in other ways. Higher land prices tend to make high-rise buildings more economic and this has implications for urban form, occupant densities and safety levels in the event of future earth- quakes. Control of land prices directly is not normally part of urban planning in democratic countries, but is strongly influenced by planning decisions, by zoning and by planning permissions. Provision of services affects how desirable an area is and residential densities may be influenced by levels of provision of utilities and other services. Understanding the dynamics of urban land price economics is often important in planning a safer city. Deconcentration of Cities The worst earthquake disasters have occurred in ‘direct hit’ earthquakes – an earthquake epicentre directly underneath or very close to a large town. The concentrations of people and buildings represent targets of high potential loss. Deconcentration of cities spreads the elements at risk by reducing densities and decentralising facilities. Deconcentration and density limitations are desir- able in cities for other reasons too, including environmental improvements and limitations on service provision. Most urban plans already limit densities of devel- opment. Limitations of density, height restrictions, plot development regulations and other controls can all be used to limit concentrations of building stock. It is, of course, very difficult to change the densities of existing urban districts, and much easier to limit densities on areas of future development. Reducing Densities in Existing Cities The densities of existing urban areas can be reduced by city authorities buying up plots and demolishing to create open space among the blocks or redevel- opments at lower densities. After some earthquakes in the past this has been achieved by the city authorities buying up the sites of collapsed buildings and 4 After the 1985 earthquake in Mexico City, a number of banks relocated their office buildings from the badly damaged Reforma area to the more desirable and firmer ground condition of the nearby Polanco district to avoid problems of disruption to bank activities from future earthquakes. This had a significant effect on land price in the Reforma area and affected the development process. STRATEGIES FOR EARTHQUAKE PROTECTION 199 making them into urban memorial parks. 5 Such urban parks, even if they are small, add greenery to the city, help with urban hydrology, humidity and micro- climate, and provide areas for emergency facilities or population evacuation or temporary shelter housing in the event of any future disasters. Some cities now have large budgets for the re-greening of their built-up areas, buying up plots as they become available on the open market. In Japan, earthquake protection objectives (chiefly deconcentration for fire risk and the provision of refuge areas for the population) have been set at the provision of 3 square metres per per- son of parkland in all major cities. With the price of land in Tokyo currently the highest in the world, this is an expensive and long-term policy: Tokyo Metropolitan Government has achieved nearly 1 square metre per person so far, but other cities in Japan are closer to their target of 3 square metres per person. 6 Limiting Densities in New Settlements In the planning of a new town in a seismic area it is important to limit the size and potential for high-density over-concentration of development. Density controls include restrictions on building height, limitations on the plot ratio of allowable development for any site, and limitations on access to basic services. Where direct density controls are not easily enforceable, other methods of achieving lower densities include the design of street patterns, wider streets and limiting plot sizes by physical planning means, using the design of the layout of the town and positioning of street furniture to maintain street frontages and to limit plot developments. There are, however, no absolute levels or recommendations about density tar- gets for earthquake safety. Urban population densities vary considerably from country to country and town to town, and the vulnerability of the building stock is the overriding factor in determining how much the population is at risk from earthquakes. In a neighbourhood of fairly vulnerable buildings (masonry, for example) the height and proximity of buildings, particularly buildings on a slope, should at a minimum be constrained to prevent one building collapsing onto or into a neighbour. The ‘domino’ collapse of buildings, particularly down a slope, has been one of the causes of high fatalities in earthquakes. Similarly street lay- out road widths, particularly major routes needed for emergency access, should be wide enough not to be made impassable by the rubble of a collapsed struc- ture. Vitally important routes should be wide enough to survive the collapse of structures on both sides of the road simultaneously. 5 After the 1985 earthquake, the sites of several collapsed buildings in Mexico City were turned into urban parks. 6 Itoh (1985), Ashimi (1985). 200 EARTHQUAKE PROTECTION It is also important to reduce densities by designing open spaces in the city, particularly spaces within the built-up areas. Such spaces also form safe congre- gation areas for the population, away from the possibility of injury from pieces falling from the fa¸cades of buildings and, in areas at risk from fires, provide some safety refuge in the event of multiple fires. Deconcentration and Fire Deconcentration is particularly important to reduce the risk of fire spreading from building to building in cities of flammable buildings. The danger of conflagra- tions following earthquakes is particularly acute with timber frame structures or those with combustible roofs: in such cases deconcentration becomes a major earthquake protection measure. The division of urban areas into small cells by wide roads, rivers, parks and other fire-breaks limits the potential for con- flagration. The chief risk for fire or earthquake disaster in many cities is in squatter areas or informal housing sector developments. These are likely to be beyond conventional planning measures, but general programmes to upgrade squatter areas should include reductions of density, access routes for fire and other emergency service vehicles, and discouragement of siting on hazardous slopes. Decentralisation of Major Cities In many countries, there are efforts to decentralise capital cities and other major regional centres. There may also be programmes to reduce the rate of urbani- sation generally and to discourage large-scale migration of rural populations to the cities. Both of these measures reduce earthquake risk in a seismic region. Decentralisation of major conurbations reduces earthquake risk by reducing the concentration of people and building stock, and earthquake protection is an addi- tional argument for decentralisation. Decentralisation is commonly tackled using a number of methods including the development of ‘satellite centres’ (local ser- vices in the suburbs), ‘necklace’ development (suburban development beyond green belts), the promotion of secondary towns in the region, or moving min- istries and other key facilities to other cities, or promoting relocation grants for industry and preferential provision of services in order to reduce development pressures on an over-centralised city. After the city of Tangshan was devastated in 1976 by the most lethal earthquake of the twentieth century, the Chinese planners rebuilt the city as three separate smaller towns, several kilometres apart, partly in order to reduce the potential for an earthquake to cause another similar disaster. 7 7 Wu Liang Yong (1981). [...]... needed to import heavy equipment Important for public information Power supply very important for industry and public safety Drinking water needed for public Important for industry and public comfort Important for public health Important for economic business Critical Important Important Are the fire station buildings that house the vital fire tender trucks sufficiently earthquake resistant to remain serviceable... of political campaigns for earthquake legislation, like the prolonged campaign for legislation on unreinforced masonry in Los Angeles,14 14 See Section 10.7 212 EARTHQUAKE PROTECTION demonstrate very clearly that the occurrence of a lethal earthquake, either in a neighbouring country or more significantly within the area of jurisdiction, is the main spur for government action An earthquake is unlike... to reduce future earthquake losses were taken within a broad-ranging overall strategy for earthquake protection – perhaps coordinated with protection strategies for other natural hazards in a national disaster preparedness plan An integrated earthquake protection plan for a nation would decide on what levels of risk are acceptable (see Chapter 10), identify what are the priority areas for action and... injury in future earthquakes But an earthquake design code that is too stringent may also cause problems In developing countries where capital for development is precious, the level of earthquake protection aimed for is more critical than in countries more easily able to invest in higher cost infrastructure Every 1% added to the cost of a structure by higher earthquake codes means that for every 100 hospitals,... STRATEGIES FOR EARTHQUAKE PROTECTION 213 bodies may prove suitable vehicles for institutionalised national earthquake protection strategies The aspects of earthquake protection that can only be carried out at national level, e.g the measures that are needed in legislation, financing, building code, professional standards, curriculum, etc., have to be implemented by the government A national earthquake. .. insurance, before a licence is granted Public display of certification is an added aid to enforcement and reinforces public awareness of earthquake protection Targeting Weakest Buildings Unless the probability of an earthquake is high, or the consequences of failure of a particular structure or class of structures are severe, it may be difficult to justify making structural interventions or forcing owners... be integrated with training initiatives for building designers and with support for the dissemination and clear understanding of what the codes are requiring them to do Code enforcement is primarily a concern of urban authorities rather than national governments and is discussed in Section 6.4.2 above National Earthquake Insurance Compulsory earthquake insurance for buildings has been considered in a... building should be strengthened if their continued function after an earthquake is essential Routing of networks – the piped services, electrical and communication systems cabling and the road and railway links that make up the transportation network of the city – is also important for earthquake protection A grid network STRATEGIES FOR EARTHQUAKE PROTECTION 205 is more robust than a radial network because... owners to carry them out to increase earthquake resistance Costs of structural reinforcement of strengthening existing buildings are high – anything from 10% to 50% of the value of the building; generally it costs far more to increase the earthquake resistance of an existing building than it does to design a new building to a higher standard of earthquake resistance For a building that may already be... risk from future earthquakes and whose buildings commonly make up the most vulnerable sector of the building stock are usually those who are least able to contribute to their own safety Their abilities to make choices about where they live or what they live in are minimal and their priorities for food, income, housing quality and basic living standards may eclipse any concern for earthquake safety . can play an important part in earthquake protection. An example of using urban land-use planning for earthquake protection is shown in Figure 6.1. 196 EARTHQUAKE PROTECTION In a case study of. activities to be carried out STRATEGIES FOR EARTHQUAKE PROTECTION 193 more easily and to plan ahead for the future. Many of the concerns of earthquake protection also parallel these objectives:. important tool for urban planning to incorporate earthquake protection. Methods of microzoning are described in Section 7.4. The seismic microzoning STRATEGIES FOR EARTHQUAKE PROTECTION 195 map,