FEDERAL EMERGENCY MANAGEMENT AGENCY FEMA 313 / January 1998 * Promoting the Adoption and Enforcement of Seismic Building Codes: A Guidebook for State Earthquake and Mitigation Managers Promoting the Adoption and Enforcement of Seismic Building Codes: A Guidebookfor State Earthquake and MitigationManagers ........ Robert B. Olshansky Project Director and Author ............ Research Assistants.................................................................... Robyn Bancroft Christopher Glick ................ Steve Otto, Roxanne Walker Editorial & Design .... Otto-Walker Communications Craig Chamberlain Media Consultant .................... University of Illinois News Bureau Educational Consultant .................... Marne Helgesen, University of Illinois Office of Instructional Resources Maeve Reilly .................... Copy Editing University of Illinois Office of Publications Gretchen Walters Design Consultant .................... Vicki Eddings Project Secretary .................... sponsored and funded by Federal Emergency ManagementAgency Promoting the Adoption and Enforcement of Seismic Building Codes: A Guidebookfor State Earthquake and Mitigation Managers Contents ir Background and Acknowledgments v Figures and Tables 1 Chapter 1: How To Use This Book 2 Chapter 2: Whyr Adopt a Building Code? Whyr Adopt a Seismic Code? 6 Chapter 3: 14 Chapter 4: How States Can Adopt Seismic Building Codes 22 Chapter 5: How Cities and Counties Can Adopt Seismic Building Codes Chapter 6: 28 Improving Code Enforcement: A Critical Link 33 Appendix A: History and Principles of Seismic Design 43 Appendix B: Examples, of Various States' Building Code Practices Sample State Enabling Codes 85 Appendix C: Examples of Building Code Administration by Local Governments 101 Appendix D: Model Code Organizations: Services and Resources Offered 114 Appendix E: Organizations Inv-olved in Seismic Safety: Contact Information 121 Appendix F: Recommended Readings and Resources 127 Appendix G: Sample Workshop Presentations 187 Appendix H: Sample Press Releases 193 Appendix I: Sample Brochures j: 203 Appendix Glossary and Acronyms Acknowledgments This report was prepared by the Department of Urban and Regional Planning, University of Illinois at Urbana-Champaign, under the direction of Associate Professor Robert B. Olshansky. The project team gratefully acknowledgesthe help of numerous public officials from the six states and six local governments that were the subject of our detailed case studies. Their names are listed in Appendices B and C. We also appreciate the help of our primary contacts at FEMA, Sheila Donahoe and Elizabeth Lemersal, as well as our numerous reviewers, including Lindsey Carter (SBCCI),Riley Chung (NIST), Susan Dowty (ICBO), Tom Durham (CUSEC), Brian Gore (Mass. Board of Bldg. Regula- tions and Standards), Cindy Hoover (Seattle Dept. of Construction and Land Use), Mike Mahoney (FEMA), Kathleen Mihelich (BOCA),Ugo MoreUi (FEMA), Christopher Rojahn (ATC), James R. Smith (BSSC), Stuart Nishenko (FEMA), Daniel Shapiro (SOH & Associates),Arthur Zeizel (FEMA),and Thomas Zimmerman (IllinoisEmergency Management Agency). V Figures and Tables 2 Figure 2.1 Photo of substandard housing stock 5 Figure 2.2 Map of general areas of building construction code influences 5 Figure 2.3 Map of states w,-ith mandatory stateride building codes Photo of earthquake damage in Loma Prieta, California, 6 Figure 3.1 1989 7 Figure 3.2 Photo of Back Bay area of Boston 8 Figure 3.3 Map of earthquake intensities in Loma Prieta, California, 1989 9 Figure 3.4 Photos and table of damage states for various ground- shaking intensities 10 Figure 3.5 U.S. seismic hazard map 12 Figure 3.6 Photo of earthquake damage in Armenia, 1988 14 Figure 4.1 Map of historic earthquake locations superimposed on map of states with mandatory building codes 20 Figure 4.2 Photo of state capitol building, Kentucky 25 Figure 5.1 Photo of new construction in Jonesboro, Arkansas 28 Figure 6.1 Photo of damage from Hurricane Andrewv, 1992 34 Figure A. 1 Photo of earthquake damage in Tokyo (Kanto), 1923 36 Figure A.2 Photo of new federal courthouse in Urbana, Illinois 37 Figure A.3 Photo of earthquake damage to Veteran's Administration hospital in San Fernando, California, 1971 3.9 Figure A.4 1948 seismic hazard map 44 Figure B.1 Map of states discussed in Appendix B 46 Figure B.2 Photo of earthquake damage to school building in Long Beach, California, 1933 50 Figure B.3 Photo of housing stock in Charleston, South Carolina 87 Figure C.1 Photo of commercial district in Carbondale, Illinois 89 Figure C.2 Photo of St. Louis, Missouri 91 Figure C.3 Photo of new construction in Jonesboro, Arkansas 92 Figure C.4 Photo of Memphis, Tennessee 94 Figure C.5 Map of earthquake intensities around Pacifica, California, 1906 95 Figure C.6 Photo of Las. Vegas, Nevada 40 Table A.1 State codes and code influence 50 Table B.1 South Carolina code enforcement 86 Table C.1 Overview of local building code administration by local governments Chapter I How To Use This Book Purpose Content This book provides background Chapters 2 and 3 of this book information and educational materi- contain background material on the als to help state officials promote the purpose, function, and effectiveness adoption and enforcement of state of building codes in general and and local model building codes that seismic codes in particular. Chapters contain the latest seismic provisions. 3,4, and 5 describe step-by-step processes for adopting state or local These codes can reduce the damage that will inevitably occur when codes and for administering codes. Several appendices contain: future earthquakes strike at-risk parts of the country. * the history and principles of seismic design Audience * current seismic design practices This book is intended for state in the United States officials, especially for earthquake * examples of state building code program managers and hazard mitigation officers in the emergency requirements management agencies of the states * examples of state legislation and territories prone to earthquakes. It is designed to help you convince * examples of local code your state and local governments administration that codes are effective, inexpensive, * the services of the three model and a good investment for the future code organizations in the United of our communities. States Additionally, this book is de- * sources of further information signed to be of use to local officials, and addresses state legislators, professional organizations, and concerned * recommended readings citizens. Portions of this book are educational material for making e meant to be copied and distributed local presentations to these various groups. sample press releases for the e media * sample brochures aimed at local audiences * a glossary of relevant terms 2 Chapter 2 Why Adopt A Building Code? categories with different perfor- Building Codes Protect Public mance requirements. Safety Building codes regulate building The validity of building codes is construction and use in order to based on state police powers, which protect the safety and health of allow regulation of activities and occupants. Codes address structural property to preserve or promote the public health, safety, and general integrity, fire resistance, safe exits, lighting, and ventilation. Codes also welfare. Zoning ordinances and regulate construction materials. environmental protection regulations are also founded in police powers. Building codes classify structures by use and apply different standards Building Codes Have a Long to each classification. For example, History in the U.S. office buildings and residential multi-unit buildings are in separate Building codes to reduce the loss of life, limb, and property have existed in North America since the seven- teenth century. The earliest building regulations addressed problems resulting from dense urban construc- tion, such as rapid spread of fire. New York City, then called New Amsterdam, first regulated chimneys and roofing material in 1648.These regulations were aimed at controlling the destructive force of fire in urban areas, as evidenced by London's 1666 fire, New York's 1835 and 1845 fires, and the great Chicago fire of 1871. Comprehensive building regula- tions were introduced in the mid- 1 1800s. Building regulations were of two types: housing codes and building codes. Housing codes were intended to reduce the ill effects of residential overcrowding, and their introduction paralleled Europe's housing and sanitation reform. New York City in the late 1850sadopted a citywide housing code in order to provide air and light into dwellings and reduce the risk of fatal hazards. Chicago followed by passing its initial tenement housing ordinance in 1874.Building codes were later FIGURE 2.1 Thefirst building codeswere enacted to comprehensively specify designed to improvesubstandardhousing. construction methods and materials. (Photo: Presidents Comnmissionon Urban Housing, 1968) In 1905 the National Board of Fire Underwriters published a model WhyAdoptA Building Code? In addition to writing and updat- building lawA aimed at reducing fire W-11mr., risks.' The three model building ing the codes, the organizations offer a variety of support services, includ- codes used today were initiated 1648 Chimneys and roofing materials ing such technical services as train- between 1927 and 1950. The use of regulated to prevent fire in Newv Amsterdam (nonv New York inog seminars, code interpretation, codes spread with the growth of City) technical and administrative publica- new building across the country iS50s (late) Comprehensive housing particularly after A/Vorld War II. By tions, customized consulting, plan- regulations introduced in NYC checking services, videos, and 1960 more than 60 percent of Ameri- 1874 Tenement housing ordinance software (see Appendix D). Each can municipalities had adopted passed in Chicago organization offers certification building codes. 1905 Model building law published programs to allow skilled inspectors by NBFU and plan reviewers to be recognized Model Building Codes 1906 San Francisco earthquake kills for their levels of knowledge and 3,000 A model building code is a docu- experience. For example, BOCA 1927 Uniform Building Code (UBC), ment containing standardized offers certification by examination in with seismic provisions, first building requirements applicable twenty-two categories and ICBO in published by ICBO throughout the United States. Model nineteen categories. SBCCI offers 1933 Long Beach earthquake kills 115 building codes are standards four levels of certification in various 1935 Charles Richter devises specifying the required performance categories to encourage professional magnitude scale for earthquakes of all structures. They are published growth through progressive levels of 1940 Standard Building Code (SBS) by private organizations, whose certification. published by SBCCI voting members are government 1949 UBC contains first national jurisdictions. Membership in model building seismic hazard map code organizations is open to It is the policy of the federal govern- 1950 Basic Building Code (nowv the governmental officials, private sector BOCA National Building Code) ment to rely on voluntary standards building and construction profes- published by BOCA whenever feasible and to encourage sionals, and students. Each member 1960 60% of American municipalities employees to participate in volun- participates in varying degrees had adopted one of the model tary standards-developing activities depending on membership ciassifi- codes (OMB Circ. A-119). cation. For all three organizations 1970s Study of earthquake-resistant design provisions funded by The United States has three only active governmental members prOmi- NSF may vote. Typically, these are local nent model building code organiza- 1971 San Fernando earthquake kills 65 and state officials responsible for tions: the International Conference 1972 CABO formed of Building Officials (ICBO), which enforcing the building codes. publishes the Uniformn Building 1973 UBC revised because of San The model building codes are Fernando quake Code (UBC); the Building Officials revised periodically by a democratic 1976 hBC includes new seismic and Code Administrators Interna- process. Each organization allows provisions tional, Linrc. (BOCA), which publishes the public to propose code amend- 1978 ATC releases ATC3-06 report the BOCA National Building Code ments and hear testimony in meet- 1979 BSSC formed (BNBC); and the Southern Building ings organized by the organization, Code Congress International, Inc. 1985 FEMIA releases NEHRP so members and nonmembers are provisions for new buildings (SBCCI), which publishes the equal participants. Active members 1989 95% of American municipalities Standard Building Code (SBC). Each of each organization vote on revi- covered by codes; Loma Prieta organization also publishes compan- sions after final testimony is heard earthquake kills 63 ion documents covering mechanical during their annual meeting. The 1990 EO 12699 requires all federal work, plumbing, fire protection, content of the codes has become agencies to incorporate seismic electrical work, energy, accessibility, resistant design in new buildings more similar over time, although and life safety codes. 1992 All three model codes require they still address regional conditions seismic designs consistent with and practices. The newest versions Simple one- and two-unit resi- NEHRP provisions; Northridge reflect a common code format so that dential structures also are covered earthquake kills 57 by another model building code: the similar topics can be found in 1993 E012699 provisions take effect consistently numbered chapters One- and Two-Flunily Dwelling Code, 1994 EO 12941 establishes seismic by the Council of American Building among the codes. standards for federally owned or Officials (CABO). 'CABO is com- leased buildings; ICC formed Although the code organizations posed of the three model building 2000 ICC codes to be finished have widespread membership, each code organizations: ICBO, BOCA, organization's model building code and SBCCI. Chapter 2 4 is predominantly adopted in one more time and money. A survey of portion of the United States (Fig. 2.2). Detroit area construction companies The BNBC is predominantly adopted in 1966 found that use of nonuniform in the northeast and north central building codes throughout the Building Officials and Code states, the SBC predominates in the metropolitan region increased hous- Administrators International, southern states east of the Missis- ing costs approximately 4 to 11 Inc. (BOCA). BOCA, headquar- percent. 4 In contrast, a 1953 study in sippi, and the UBC is predominant in tered in Country Club Hills, the western states, including Guam the San Francisco Bay Area found that Illinois, was formed in 1915. Its (see Figure 2.2).3 the restrictive effect of codes had been first code, the BOCA Basic Building Code now titled the greatly overemphasized, and that In addition, BOCA, ICBO, and BOCA National Building Code only 1 percent of housebuilding costs SBCCI have moved forward on the (BNBC), was published in 1950 in could be attributed to code inefficien- development of a single model code, cies.5 an attempt to standardize existing the International Building Code. On codes. The BNBC is revised every University studies6 based on 1967 December 9, 1994, the International three years, most recently in 1996, Code Council (ICC) was formed to and 1970 housing costs found that with a new edition due out in develop a single set of comprehen- building codes increased the cost of 1999. sive and coordinated national codes. housing by less than 2 percent, and International Conference of The advantages of a single code are up to as much as 5 percent for Building Officials (ICBO). ICBO numerous. Code enforcement offi- particularly restrictive codes. was formed in 1922 to integrate cials, architects, engineers, designers, To address these issues, the various design requirements into and contractors can have consistent one code. ICBO published its first National Commission on Urban requirements that can be used across model code, the Uniform Building Problems in 1968 recommended the country and around the world. Code (UBC), in 1927. ICBO, more uniformity in building codes, Manufacturers can put their efforts headquartered in Whittier, including adoption of state building into innovative products, instead of California, updates the UBC every codes.7 According to a 1989 Federal designing for all three regional codes. three years. The latest edition was Trade Commission study, because of To date, the ICC has produced codes published in 1994. the widespread adoption of model that address plumbing, mechanical codes, differences among codes no Southern Building Code Con- systems, and private sewage disposal. longer contribute to higher housing gress International, Inc. (SBCCI). The goal is for the complete family of costs. 8 Thus, the impact of codes on The third model building code international codes to be developed housing costs has always been organization, SBCCI was founded by the year 2000. relatively small, and is decreasing as in 1940. Located in Birmingham, Alabama, it publishes the Standard more localities adopt model codes. Compared to the Benefits, the Building Code (SBC). The SBC is Costs of Codes Are Small-and updated every three years, most Most States and Municipalities Uniform Codes Reduce Costs recently in 1994. Have Building Codes There are two costs associated with Council of American Building Constitutionally, states have jurisdic- building codes. One is the cost of Officials (CABO). CABO was tion over regulation of construction. additional material and quality of founded in 1972 by BOCA, ICBO, As of 1996, the Institute for Business workmanship, and the other is the and SBCCI. The One- and Two- and Home Safety (formerly IIPLR) cost of administration and enforce- Family Dwelling Code applies to reported that 23 states mandate a ment. In the studies cited below, the construction, prefabrication, model code or state code to cover all research has shown that building alteration, repair, use, occupancy, buildings, 9 relying mostly on local codes do not significantly increase and maintenance of detached one- municipal enforcement and adminis- or two-family dwellings and one- building cost, and adoption of tration (Fig. 2.3). An additional 18 family town houses not more than statewide codes can help reduce the states and Washington, D.C., man- three stories in height. costs. date the code for all buildings except Further information on these one-family dwellings. Ten states do Criticism of the cost of building organizations and their services is not have state-mandated codes. codes in the 1950s and 1960s centered included in Appendix D. around the inefficiencies of having Currently two states, New York numerous codes, inconsistently and Wisconsin, and one territory, applied. Builders often were required Puerto Rico, have written their own to alter their construction methods building codes. Other states and and materials from one community territories that enforce statewide to the next, which meant spending codes use one of the model building S Why Adopt A Building Code? WhyAdoptA Building Code? 5 codes described previously. (See Appendix A for a list of current state and territory codes.) I Usually county and local governments adopt a model building code by ordinance. As of 1992, 44,000 local governmental 0 units enforced building codes.' The Federal Trade Commission in 1989 estimated that 95 percent of all cities and towns are covered by building codes." These local governments have either adopted a model building code or are covered by a statewide building code. Codes Are Easy to Adopt State and local governments usually adopt an entire model building code, though sometimes with minor revisions or deletions. Model build- I. ing codes save governments the time and cost required to write an origi- nal code. They include sections detailing the administrative proce- dures for plan review, building Oc..n inspection, plan and building approval, and code enforcement. NOTES 1 National Conference of States on Building Codes and Standards Inc., Directoryof Building Codesand Regula- tions, Vol. , Code Primer, NCSBCS (Herndon, VA), 1989. 2 Ibid. Not coveredby model orstate code 1 3 Ibid. 4 Metropolitan Fund, Inc., A Study of Local 7 U.S. National Commission on Urban Building Codesand Their Administration Top, FIGURE 2.2 General areas of Problems, Building theAmerican City, building construction codeinfluence. in the SoutheastMichigan Six-County (Source: National Conference of States on report to the Congress and the President, Region,Public Administration Service Building Codesand Standards) House Document No. 91-34, December (Chicago), August 1966. 1968. Above, FIGURE 2.3 States with Maisel, Sherman J., Housebuilding in 5 mandatory statewidebuilding codes. 8 Reported by Korman, Richard, "A Much Transition,University of California (Source:Copyright 1996, Insurance Misunderstood Contraption," Engineer- Press, 1953. Institutefor Property Loss Reduction ing News-Record, June 22, 1989, 30-36. 6 For 1967 costs, see Muth, Richard F, and [now IBHS]) 9 Insurance Institute for Property Loss Wetzler, Elliot, "The Effect of Con- Reduction (now IBHS),Summary of straints on House Costs," Journalof Provisionsof State and LocalBuilding State-Mandated Codes, IIPLR (Boston), Urban Economics, Vol. 3, 1976, 57-67; for Codesand their Enforcement,NIST GCR April 1996. 1970 costs, see Noam, Eli M., "The 91.599, April 1992. Interaction of Building Codes and 10 National Conference on States on Housing Prices," AREUEA Journal, Vol. 11 Korman, Richard; see note 8. Building Codes and Standards, Seismic 10, 1983, 394-404. 6 Chapter 3 Why Adopt a Seismic Code? 7.1 on the Richter scale and was the strongest to affect a U.S. city since the 1964Alaskan earthquake.' It shook the San Francisco Bay Area and killed sixty-three people. Two-thirds of the deaths were a result of the Cypress viaduct collapse. Although the ground-shaking was intense within the metropolitan area, few buildings collapsed. Most of the damage occurred to unreinforced masonry buildings built before the adoption of seismic codes. Nearly all major reinforced concrete structures built after World War II survived without collapse. Even at the quake's epicen- ter new buildings and buildings located on firm ground suffered little damage. Informed observers attribute the success to the required UBC seismic codes.2 This example illus- The term seismic code refers to the FIGURE 3.1 Most of the butilding damage trates that code requirements reduced seismic design requirements in- in the 1989 Loma Prieta earthquake wvas to the damage and loss of life during olderunreinforcedmasonry buildings cluded within building codes. In the this moderate earthquake. built before the adoption of seismic codes. past, local governments sometimes The 1994 Northridge, California, (Photo: Rob Olshansky) viewed the seismic sections of the earthquake shows similar evidence. model codes as optional, adopted at Almost all the buildings in the local discretion. Now seismic affected area were built during the provisions are fully integrated into past fifty years under one of the UBC all three model codes. Local govern- seismic codes. Virtually all buildings, ments should adopt the latest even in the areas of strongest shaking, version of a model code in its remained standing and allowed for entirety, including the seismic safe evacuation of occupants. Regret- sections, in order to be operating at tably, one apartment building col- the current standard. This point is lapsed on its residents, and two high- very important and is emphasized occupancy concrete-frame buildings throughout this book. collapsed, fortunately with no 3 occupants at the time. Still, these Seismic Codes Are Effective three buildings were built under an Experience with recent earthquakes older version of the UBC code, and in the United States and throughout damage and life loss would have the world shows that seismic codes been immeasurably greater without work. Cities with seismic codes the seismic-resistant construction suffer much less damage than those prevalent in the San Fernando Valley. without such codes. A Kyoto University study of the The Loma Prieta earthquake 1995 earthquake in Kobe, Japan, clearly illustrates the effectiveness of Richter magnitude 6.9, found that seismic codes. Occurring on October damage to reinforced concrete 17, 1989,this earthquake measured buildings closely paralleled improve- WhyAdoptA Seismic Code? 7 ments to seismic provisions in the Japanese building code. More than 55 percent of pre-1970 buildings (old version of code) were severely damaged, compared with no post- 1980buildings (newest version of code). Similarly, steel buildings built before 1970 sustained severe dam- age, compared with little damage in post-1981 buildings. 4 Ohbayashi Corporation studied buildings it had constructed in Kobe and found that 58 percent of pre-1971 buildings were damaged, compared with 28 percent of 1972-80buildings and only 16 percent of post-1981 build- ings. 5 In contrast, a Richter magnitude 6.9 earthquake in Armenia in 1988 destroyed entire communities and tions are as important to building FIGURE 3.2 Lessons about underlying killed 25,000people. This disaster stability as the epicenter location. In soil conditions learned in the 1985 Mexico has been attributed to several City quake can help areas built on fill, response to this new information, factors: design deficiencies; poor such as the Back Bay area of Boston shown ICBO in the 1988 and 1991 UBC quality of construction; and the above, ninitnize damage. (Photo: Greater editions has emphasized soil Boston Convention & Visitors Bureau) earthquake's intensity exceeding conditions by increasing the force 6 that anticipated by the code. Similar requirements according to the type problems exist in much of the of underlying soil. The National United States. Earthquake Hazard Reduction Programn (NEHRP)Reconiended Provisions Even smaller earthquakes can (described on page 8) have also cause extensive damage where taken into account soil conditions in buildings are not designed for the latest edition. seismic shaking. A Magnitude 5.6 earthquake in 1993 at Scotts Mills, Today's Seismic Codes Are Based Oregon, caused significant struc- on More Than Sixty Years of tural damage to a number of Earthquake Experience unreinforced masonry (brick) buildings in the area.7 A high school Seismic codes in use now reflect a building was significantly damaged long history of learning from and vacated, 16 residences and 54 earthquakes and represent the businesses sustained major damage, collective knowledge of hundreds of and the Oregon State Capitol, in design and construction profession- Salem, suffered cracking in the als. The following is a brief account rotunda. The estimated damage cost of that history. See Appendix A for a to public facilities alone was nearly more detailed account. $13 million. This earthquake con- The earliest seismic design firmed the susceptibility of provisions in the U.S. were intro- unreinforced buildings to severe duced in the appendix to the 1927 damage, even in a minor earth- Uniforn Building Code, the first quake. edition of the UBC. By the 1950s, New lessons are learned from some California municipalities had every earthquake and incorporated adopted additional seismic-resistant into U.S. seismic codes. For example, design and material specifications. the 1985 Mexico City earthquake The 1949 edition of the UBC con- confirmed that the local soil condi- tained the first national seismic hazard map. After the 1971San Chapter 3 a Fernando earthquake, revisions were a.. - l. U1 Un U - j i' . ; L " _ made to the 1973 UBC, and new requirements were introduced in the Earthquake magnitude is a measure of the absolute size of an earthquake 1976 edition. 9 so that we may compare earthquakes with one another. Generally speaking, earthquakes that release more energy Early in the 1970s the National Science Foundation (NSF) funded a * shake for a longer amount of time, project, under the guidance of the * affect a wider area, and National Bureau of Standards (NBS, now the National Institute of Stan- * produce more violent shaking near the source. dards and Technology), to evaluate Because we cannot measure the energy released by an earthquake, existing earthquake-resistant design Charles Richter in 1935 devised a substitute measure-the Richter provisions. This extensive multi-year magnitude scale. The scale is based on what a seismograph would project relied on the input of a large measure; it has no inherent meaning of its own. The Richter scale is number of seismic design experts logarithmic, and each whole number increase in the scale represents and resulted in a 1978 report by the approximately a 31.5-fold Applied Technology Council titled increase in energy release: that X V 22'3 121;30 ioros Tentative Provisionsforthe Development is, a magnitude 7 earthquake e "a', vi of Seismic RegulationsforBuildings releases about 31.5 times more . 6 (ATC 3-06). , energy than does a magnitude 6 6 earthquake. Several different Under a contract with the Federal magnitude scales are now in3 Emergency Management Agency common use, and they all v (FEMA), the Building Seismic Safety vce share basic characteristics with Council (BSSC, formed in 1979 within the Richter Scale. i the National Institute for Building Sciences, NIBS) revised ATC 3-06 by Shortly after an earthquake ~ ~~~~ 37$\0' azn% , C S a consensus of its members. In 1985 occurs, the surface wave magnitude or body wave magni- FEMA released the NEHRP Recom- tude is often reported. The mended Provisionsfor the Development 7 scale that most accurately of Seismic Regulationsfor New Build- } I AL JX~~~~~~V represents the energy of an ings, commonly called the NEHRP earthquake is the moment Provisions. Although not a code, the 0 10 20 30MILES magnitude scale. For smaller NEHRP Provisions are designed to earthquakes (less than magni- provide guidance to the writers of FIGURE 3.3 The Loma Prieta, California, tude 6), the scales are nearly building codes. FEMA and BSSC earthquakeof 1989 had a magnitude of identical, but only the moment continue to update the NEHRP 7.1, but intensities in the affected area magnitude scale can distin- rangedfrom MlMI VII to IX. (Source: Provisions every three years, with the guish differences among very USGS Circular1045,1989) latest edition being published in large earthquakes. 1994. The 1997 edition is due out in Earthquake intensity is a measure of the actual shaking experienced at December 1997. a location. The United States uses the Modified Mercalli Intensity Scale, a twelve-point qualitative scale that describes observable effects of AllThree Model Codes Contain earthquakes. For example, Intensity VIII is described, in part, as "dam- State-of-the-Art Seismic age slight in specially designed structures; considerable in ordinary Requirements substantial buildings with partial collapse; great in poorly built struc- The past two decades have seen great tures ... fall of chimneys, factory stacks, columns, monuments, walls. strides in the knowledge of building Heavy furniture overturned." Whereas magnitude is an inherent quality responses to earthquakes. Based on of an earthquake, intensity generally decreases with greater distance the collective efforts of engineers, from the earthquake's center. Intensity is a very useful measure because scientists, and tradespeople, the it describes what is most important to society-the degree of damage to NEHRP Provisions contain seismic structures built by humans. design provisions that are technically advanced and widely accepted. Since 1992 all three model codes require seismic design standards consistent with the NEHRP 9 Why AdoptA Seismic Code? EQ Modified Mercalli Intensity Scale Figure 3.4 Percentage of Buildings Expected in Each Damage State for Various Shaking Intensities: Buildings Designed for Seismic Zone 4 under the I99 I UBC Size of Earthquake Standardized Damage States (Magnitude) A B C D E 6.0-6.5 7.5-8.0 None Slight Moderate Extensive Complete Distance t o Fault 30 mi. 50 mi. 60-90% 10-40% I-5%