Skip to main content
Geosciences LibreTexts

7.5.6: Building Codes

  • Page ID
    6459
  • Overview

    One of the most important steps that can be taken by a community in defending itself against earthquakes is upgrading its building codes. Most codes are written such that a structure built under a seismic code should resist a minor earthquake without damage and resist severe earthquakes without collapse of the building. Building codes place life safety over property damage. They establish minimum standards based on average soil conditions. As discussed in Chapter 8, local ground conditions could generate seismic ground motions that exceed those in the code provisions.

     

    Regulations to reduce property damage and loss of life were in existence in America prior to the American Revolution, when the main concern was the spread of fire in densely populated New York City. Comprehensive building regulations were introduced in the mid-nineteenth century, and in 1905, the National Board of Fire Underwriters published a model building regulation aimed at the fire damage. Because of the cover-up of the role of earthquake damage in the 1906 San Francisco Earthquake, nothing was done at that time about extending building regulations to protect against earthquakes.

     

    As structural engineers began to recognize that buildings could be constructed to resist earthquakes, the situation began to change. Following the destructive Santa Barbara Earthquake of 1925, Santa Barbara and Palo Alto passed ordinances upgrading their building codes to take earthquakes into account. But it took the much more destructive Long Beach Earthquake of 1933 to produce statewide action, including an upgrade of building codes. The legislature passed the Field Act upgrading school construction standards and the Riley Act covering other buildings. Earthquake resistance was added to building codes in Los Angeles County and City, Long Beach, Santa Monica, Beverly Hills, and Pasadena, essentially putting an end to the use of unreinforced brick construction in California. Later, earthquake-resistance standards were applied to bridges, hospitals, and dams. Subsequent upgrades to the building codes, generally triggered by large earthquakes such as the 1971 Sylmar, 1989 Loma Prieta, and 1994 Northridge earthquakes, have produced the highest earthquake-resistant building standards in the United States.

     

    The starting point for building codes is the Uniform Building Code (UBC), published by the International Conference of Building Officials with its headquarters in Whittier, California. The UBC was developed following local ordinances in California in the 1920s and 1930s. In the Pacific Northwest, local governments began to base their code upgrades on the UBC, starting with the City of Seattle in 1946. The code established seismic zones in which earthquake reinforcing was recommended, but the Pacific Northwest, except locally, was placed in Seismic Zone 1, requiring no reinforcement against earthquakes.

     

    In 1952, following the 1949 Puget Sound Earthquake, the Puget Sound region was placed in Seismic Zone 3; the rest of Washington and the Portland area were placed in Zone 2. In the following year, Seattle and Tacoma adopted sections of the 1952 UBC, although Tacoma deleted the requirement that houses be bolted to their foundations. Further upgrades in Washington followed the 1965 Seattle Earthquake and the 1971 Sylmar, California, Earthquake. Action at the state level took place in 1974, when Oregon adopted the Structural Specialty Code and adopted the 1973 UBC, placing itself in Zone 2, and in 1975 when Washington adopted the 1973 UBC and established a Building Codes Council. Further upgrades followed the recognition that western Oregon and Washington are at risk from a subduction-zone earthquake, including upgrading most of the urbanized parts of Washington and Oregon into Seismic Zone 3 and placing part of the Oregon coast in Seismic Zone 4. The Washington legislature adopted the latest UBC in 2003.

     

    The increase in construction standards is illustrated for Oregon in Figure 14-2; the Washington increase is similar. If your house was built before the mid-1970s, there was no requirement that it be bolted to the foundation; in many areas, this requirement was not enforced until the early 1980s.

    clipboard_e31e45ad1a4665fb568885bf1cb7eba96.png

    The United States now has two model building codes The most widely used is the International Building Code (IBC), developed by the International Code Council, consisting of the three original model code organizations, the Building Officials and Code Administrators International, the Southern Building Code Congress International, and the Council of American Building Officials. The second was developed by the National Fire Protection Association and is called NFPA 5000; it has been adopted by California. The IBC, upgraded every three years, has as its objective “to provide minimum standards to safeguard life or limb, health, property, and public welfare while regulating and controlling design and construction.” Priority is given to protecting the inhabitants of a building over the prevention of damage to the building itself. Building codes represent minimum standards; the owner may well choose to have higher standards than those required by the code.

     

    Two cautions should be made about building codes. The first tradeoff is cost. Upgrading seismic resistance can add up to five percent of the cost of a new building, and for retrofitting, the percentage increase is higher. For a new building, the revised codes set the standard, and the owner must decide whether or not to exceed these standards to get better building performance in an earthquake—a decision similar to whether to obtain earthquake insurance. For a retrofit, the decision is harder, because of the added cost to a business, or the added cost to taxpayers if a public building is retrofitted. Without better insight into earthquake forecasting than is now available, the owner’s decision is a gamble. The estimation of average annual losses due to earthquakes for each county in the United States using HAZUS can be compared with the annual construction cost of upgrading the building code.

     

    The second caution is that upgrading the building code does not automatically make the area safe against earthquakes. New buildings will meet the standard, as will major remodels of buildings. But old buildings that are not remodeled will continue in the building inventory, and when these are unreinforced masonry (URM) or nonductile concrete, they are potential time bombs. The greatest loss of life in the 1971 Sylmar Earthquake was in those buildings on the campus of the Veterans Administration Hospital that had not been retrofitted after the 1933 Long Beach Earthquake (Figure 12-1).

     

    In 1988, California established the URM Law requiring local jurisdictions to inventory their URM buildings, establish loss-reduction programs, and report periodically to the state. As of early 2003, 13,303 buildings have been retrofitted and 3,458 demolished at a cost of $3 billion. Almost nine-thousand URM buildings remain in use, but this program is clearly working. Because of these retrofits, the northern California part of the subduction zone is clearly the best prepared for a subduction-zone earthquake.

    clipboard_e8b5e636732f8e3636b1196de92730bec.png

    Oregon and Washington have numerous school buildings, city halls, public-housing projects, retirement homes, churches, dams, and bridges that have not been upgraded. The 1993 Scotts Mills (Spring Break) Earthquake caused bricks to fall off Molalla High School that would have caused injury or death to students if school had been in session (Figure 14-3). The Klamath County courthouse was damaged in 1993, and the Grays Harbor courthouse was damaged in the 1999 Satsop Earthquake. The Oregon capitol was damaged in 1993, and the Washington capitol in 2001. However, significant efforts are underway in both states to retrofit schools and bridges. Despite the existence of seismic building codes since the mid-1970s in Washington and Oregon, there are still buildings constructed under earlier building codes that do not meet modern standards and are subject to collapse. It’s important to know the year of construction (or last retrofit) of the building where you work or live so that you can compare it with Figure 14-2.

     

    Following the 1993 seismic upgrade of building codes, the Oregon legislature, through Senate Bill 1057, established a Seismic Rehabilitation Task Force in 1995 to provide recommendations about how to eliminate those structures that are earthquake hazards. At the same time, the City of Portland, through its Bureau of Buildings, established its own task force to consider the seismic strengthening of existing buildings. Senator Peter Courtney strongly advocated for funds to seismically retrofit the State Capital building, but the Legislature failed to authorize the money.

     

    The state task force recommended that all unreinforced masonry (URM) buildings be rehabilitated within seventy years, with the more dangerous within thirty years, following a statewide inventory of buildings by the year 2004 to be conducted by the Building Codes Division. Mandatory strengthening would be required for appendages outside a building such as parapets and signs that could fall on people below during an earthquake. Essential and hazardous URM buildings would be repaired by the year 2019. Essential buildings would include fire and police stations and emergency communications centers. Hazardous facilities would include structures housing hazardous or toxic materials that could be released during an earthquake. A program for rehabilitating hospitals was also proposed.

     

    Other buildings would be rehabilitated based on passive triggers: actions within the control of the owner that would require the building to be strengthened. These triggers would include:

    1. Changes in use that would increase the risk to occupants
    2. Renovations that are substantial relative to the value of the building
    3. Renovations or additions that could potentially weaken the existing structure

    To encourage and facilitate the strengthening of buildings, a state tax credit was proposed that would be equal to 35 percent of the investment for seismic rehabilitation retroactive to the year western Oregon was upgraded to Seismic Zone 3, and a local property tax abatement equal to 35 percent of the seismic rehabilitation cost was proposed. Implementation of the program would be assigned to the Department of Geology and Mineral Industries (DOGAMI). These recommendations were incorporated into House Bill 2139, introduced in the 1997 legislative session. However, this bill failed to pass. The plan is presented here in the event that a future legislature in Oregon or Washington might adopt it when state finances improve.

     

    Although the state did not act except for critical facilities, the city of Portland is upgrading its URM building inventory through its Dangerous Building Code. Based on an ordinance passed in 1995, two hundred URM buildings have been retrofitted, most due to a change in building use or the installation of a new roof.

     

    An opinion survey was conducted among four hundred Portland residents. When asked to rank earthquakes among several social and environmental concerns, earthquakes were ranked relatively high, behind crime and violence, cancer, motor vehicle accidents, and fire. However, none of the categories was listed as “high risk.” Respondents were also asked to rank on a scale of 1 to 10 (1 = no money should be spent to strengthen the facility, 10 = it is absolutely essential to strengthen the facility) their priority ratings for strengthening key buildings and infrastructure facilities. Hospitals, buildings for storing hazardous wastes, emergency communications buildings, bridges and overpasses, and schools received ratings above 8.

     

    The insurance industry, through its Insurance Services Office, has established a system to grade the 454 building code enforcement departments in California on the effectiveness of their building codes, considering the quality of inspection and plan review as well as construction standards. The results of the grading will appear in an insurance publication called the Public Protection Classification Manual, which is read by more than a hundred thousand insurance agents and actuaries. A high grade should lead to discounts on insurance premiums for new construction, similar to discounts based on fire insurance grading systems.

     

    The problem, as stated elsewhere, is that building retrofits do not necessarily increase the ability of the building to generate additional income, and furthermore, the scientists cannot tell them how soon their buildings will be struck by a major earthquake. Should the building owner bear the total cost of upgrading, or should the cost be borne, at least in part, by local government?