Providing Safer Buildings Through Modern Building Codes

An Article from the January-February 2001 issue of Building Standards which is a publication of The International Conference of Building Officials.

by John R. Henry, P.E., Senior Staff Engineer, International Conference of Building Officials

Introduction

It is human nature to resist change, and life would certainly be easier if engineering practices and building codes remained unchanged. Although most of us would prefer less change where seismic design and building codes are concerned, that is an unrealistic wish. Advances in earthquake engineering and the code changes that follow are as dynamic as the world in which we live. In order to use the latest technology and ensure the highest level of safety in the built environment, it is imperative that members of the design and construction community as well as building code officials utilize the most current codes and standards available.

Whereas adopting the most current codes helps to ensure that the latest technology is used, this in itself is not enough. Without proper enforcement during plan review and inspection, having the latest code on the shelf is useless. In addition, it is important that building inspectors and trades workers understand the significance of the roles they play in the construction of seismic-resistant buildings. At present, there is a need to expand and improve the training materials available to building inspectors and trades workers where earthquake-resistant systems are concerned.

When Earthquakes Strike

On the morning of April 18, 1906, one of the most significant earthquakes in recent history ripped through the City of San Francisco. At 5:12 a.m., a foreshock was felt throughout the San Francisco Bay area, and about 20 seconds later the great quake produced violent shocks that lasted 45 seconds and were felt all the way from southern Oregon to Los Angeles. Estimated to have measured between 7.7 and 8.3 on the Richter scale,¹ some research indicates that the San Francisco earthquake caused as many as 3,000 fatalities, left up to 225,000 people homeless and destroyed an estimated 28,000 buildings.
On January 17, 1995, an earthquake with a moment magnitude of 6.9 struck the region of Kobe and Osaka, Japan, killing over 5,500 people and destroying or severely damaging nearly 180,000 buildings. The pre-dawn quake left 300,000 people homeless. The vast majority of fatalities occurred due to the failure of traditional, post-and-beam Japanese housing units with little or no lateral-force resisting systems.
On May 10, 1997, a 7.1 magnitude earthquake struck Northern Iran, killing over 1,500 people and destroying over 10,500 homes. The quake left 2,300 people injured and over 50,000 homeless.
On May 30, 1998, an earthquake measuring 6.9 on the Richter scale struck near Rostaq, Afghanistan, killing an estimated 4,000 people and leaving 45,000 people homeless. A similar quake with a magnitude of 6.1 struck the region on February 4th of that year, killing over 2,300 people and destroying more than 8,000 homes.
On September 21, 1999, a magnitude 7.6 earthquake struck Chichi, Taiwan, killing an estimated 2,000 people and causing severe damage to or collapse of an estimated 10,000 buildings. Some 100,000 people were left homeless.
On August 17, 1999, the industrial city of Izmit, Turkey, was struck by a magnitude 7.4 earthquake that killed an estimated 30,000 to 40,000 people and caused severe damage to or collapse of an estimated 20,000 buildings.
Statistics like these illustrate the kind of devastation that resulted from earthquakes that pre-dated building codes and present-day earthquakes that strike in areas where the codes are outdated, inadequately enforced or nonexistent.
On October 17,1989, the magnitude 7.1 Loma Prieta earthquake struck California's Santa Cruz Mountains. Sixty miles (97 km) away in downtown San Francisco, the 49-story Transamerica Pyramid building shook for over a minute, causing the top story to sway over 12 inches (305 mm) from side to side. The building, however, was undamaged and none of its inhabitants was seriously injured. All told, the Loma Prieta earthquake resulted in 63 fatalities.
On January 17, 1994, a magnitude 6.7 earthquake struck the San Fernando Valley area of Los Angeles County near Northridge. Although the epicenter was located in close proximity to a densely populated area, the quake resulted in only 57 deaths (although the number of fatalities was likely reduced considerably by the fact that it occurred in the early morning and on a holiday). The percentage of buildings that were totally destroyed was relatively small, and most of the severe damage was confined to an area within 16 kilometers of the epicenter.

While these recent events were tragic, they illustrate a significant reduction in fatalities and property damage; and one of the most important tools for minimizing loss of life and structural collapse is modern building codes. The lessons learned from each significant earthquake have resulted in many refinements and improvements in modern building codes.

Modern Building Codes: An Evolutionary Process

Over the course of the last century, major earthquakes severely damaged or destroyed many buildings and other structures. By carefully examining how buildings respond to earthquake forces, scientists, engineers, industry professionals and code officials have applied the knowledge gained from these unfortunate events to improve building codes so that modern structures have a better chance of surviving major earthquakes without collapsing or causing fatalities. In essence, the modern building codes are the result of an evolutionary process in which government and building code officials, the academic community, the engineering profession, and the construction industry have forged a cooperative relationship to produce a greater understanding of earthquake design.

Since its first edition in 1927, the International Conference of Building Officials' (ICBO) Uniform Building Code^TM (UBC) has included seismic force design requirements. When the 1933 Long Beach earthquake (M 6.3) devastated several schools, the State of California enacted legislation known as the Field Act that gave the state the responsibility for the review and approval of school buildings. In addition, the 1933 Riley Act required for the first time that earthquake loading be considered in the design of all buildings in California. The 1935 edition of the UBC reflected this by requiring that a lateral force equal to 2 percent of the dead load plus one-half of the live load, adjusted by a factor that depended on the seismic activity zone and the particular type of structural system involved, be applied to new buildings.

In 1940, the El Centro earthquake (M 7.1) occurred on the Imperial Fault, killing 9 people. Because the quake occurred in a well instrumented area, it produced the first real building response and building period data. Although it only lasted 10 seconds, a surprising ground acceleration of 0.33g was observed (1.0g is the ordinary force imposed by gravity). Based primarily on recommendations made by the Structural Engineers Association of California (SEAOC), the UBC seismic design provisions were revised in the 1961 edition to incorporate both a building's period as well as the type of lateral force resisting system used in its design.

The 1966 Parkfield earthquake, with a magnitude of only 5.5, produced a 0.5g ground acceleration, which was the highest recorded to date. This demonstrated that earthquake magnitude and ground acceleration were not as easily correlated as previously thought. During the period from 1933 to 1970, California and Nevada experienced over 70 earthquakes in excess of magnitude 5.0, but it was the 1971 San Fernando (Sylmar) earthquake (M 6.6) that most shocked the region by knocking out hospitals and collapsing several newly constructed concrete buildings. Although the prevailing viewpoint at the time was that the effective acceleration experienced by buildings in earthquakes was in the order of 0.5g, the Sylmar earthquake produced a remarkable ground acceleration of 1.24g at the site of Pacoima Dam. California responded by increasing the design requirements for hospitals, and state code officials responded by making further improvements in seismic design methodology. Accordingly, the 1976 edition of the UBC included an importance factor that accounted for the relative importance of a building and a soil factor that was intended to consider potential period resonance based on soil properties at a building site.

In 1972, the National Science Foundation and National Bureau of Standards initiated a program involving a multidisciplinary team of 85 nationally recognized experts who combined their skills and experience to completely re-think seismic design issues. Under the auspices of the Applied Technology Council (ATC), this concerted effort produced a document known as ATC-3-06.² In 1980, the SEAOC Board of Directors authorized a major overhaul of the association's Recommended Lateral Force Requirements and Commentary (also known as the SEAOC Blue Book)³ using a "clean-sheet of paper" approach to the problem. Armed with ATC-3-06 and the subsequent National Earthquake Hazard Reduction Program (NEHRP) provisions of the Building Seismic Safety Council (BSSC)⁴ (which were based on ATC-3-06), SEAOC fashioned a completely revised Blue Book in 1988. The 1988 SEAOC Blue Book formed the basis for the seismic design provisions of the 1988 UBC, which included new lateral force and building period equations based on the ATC-3-06/NEHRP provisions. It also included a dynamic analysis procedure, attempted to address irregular building features and nonbuilding structures, and provided material specific detailing requirements.

The earthquake design learning process continued with the next series of significant earthquakes to strike the region, beginning with the Loma Prieta earthquake (M 7.1), which struck the San Francisco Bay Area in October of 1989, and the Northridge quake (M 6.7), which struck the San Fernando Valley in January of 1997. These two earthquakes pointed out several important issues: (1) a significant increase in acceleration, velocity and displacement occurs near the fault source; (2) the deflection (differential movement) of a building results in damage to members and components that are not part of the lateral force resisting system; (3) more specific requirements for redundancy were needed to improve building performance; and (4) the influence of the specific soil properties at the building site should be refined. In an effort to address these and other issues, SEAOC developed extensive code changes in 1993, which were subsequently incorporated into the seismic design provisions of the most current, 1997 edition of the UBC.

The Future is Here: The 2000 International Building Code

In the past, the building codes used in the U.S. were based on one of three model codes: the Building Officials and Code Administrators International, Inc. (BOCA) National Building Code (NBC); the Southern Building Code Congress International, Inc. (SBCCI) Standard Building Code (SBC); and ICBO's UBC. As previously detailed, the seismic design provisions of the UBC are based on those published in the SEAOC Blue Book. With the complete overhaul of the Blue Book in 1988 and the subsequent SEAOC code changes, the UBC provisions have become even more similar to the NEHRP provisions. In addition, the 1997 NEHRP and 1997 UBC seismic design provisions were developed in parallel, with some degree of "cross-fertilization" occurring between the two. In contrast, the seismic design provisions of the 1999 NBC and SBC are based solely on BSSC's 1991 NEHRP Recommended Provisions, with the American Society of Civil Engineers' ASCE 7-95 (1994 NEHRP) as a permitted alternative.

The previous state of affairs, in which the three different model codes were used in different parts of the country, is undergoing a change. BOCA, ICBO and SBCCI recently joined forces to form the International Code Council® (ICC), with the purpose of producing a single, unified family of building codes for use throughout the U.S. Last year, ICC released the first edition of its flagship publication: the International Building Code® (IBC). The seismic design provisions of the 2000 IBC are based on the 1997 NEHRP provisions, with many modifications resulting from the ICC code development process. The monumental task of merging the three model codes into one represents the latest effort toward integrating the most current earthquake knowledge and seismic design technology into the building codes.

Measuring the Shake, Rattle and Roll

Although scientists began studying earthquakes as early as 1880, the actual magnitude of their vibrations was not accurately recorded up through the 1930s. The major obstacles to gathering accurate seismic activity data are that significant earthquakes occur at irregular and often long intervals and recording instruments must be in the vicinity when the events happen. Recording earthquake activity therefore represents a long-term commitment in that instrumentation must be in place and ready to capture the next earthquake when and where it happens. In the 1940s, seismic recording instruments began being installed in buildings in an effort to gather more reliable data on the response of structures to seismic activity. Still, it was not until the 1971 San Fernando earthquake that a significant amount of accurate building response data was able to be obtained. Although relatively primitive by today's standards, the seismic data collected from the 1971 San Fernando earthquake and 1979 Imperial Valley earthquake (M 6.6) were invaluable in developing a better understanding of building behavior and the effects of earthquakes on buildings.

Beginning with the 1967 edition, the UBC has included provisions for the installation of earthquake recording instruments in specific buildings located in areas of high seismic activity. In 1972, the California Division of Mines and Geology's (CDMG) Strong Motion Instrumentation Program (SMIP) was instituted to broaden the information database used to refine the design of structures subjected to earthquakes, and since then has placed sensitive instruments at strategic and seismically active locations throughout the state. Today, through the efforts of the CDMG program and others, instruments have been installed in a variety of buildings, bridges, dams, aqueducts and many other structures throughout the U.S., giving scientists and engineers a wealth of valuable data for use in improving building design and construction practices.

Pay Now or Pay Later

One of the most important lessons we have learned from many past earthquakes is that it costs much less to prepare for earthquakes than it does to repair the damage afterward. According to NEHRP research, the costs of providing seismic-resistant features for the protection of life rarely exceed two percent of the construction costs for new buildings. Given the immeasurable value of preserving lives, we must continue to marshal our resources and apply the collective knowledge of scientists, engineers, code and government officials, and the construction industry toward preventing fatalities due to earthquakes.

Section 1626.1 of the 1997 UBC states that the purpose of the earthquake provisions is primarily to safeguard against major structural failures and loss of life, not to limit damage or maintain function. Similarly, the 1997 NEHRP indicates that its design earthquake ground motion levels could result in both nonstructural and structural damage. In fact, engineers recognize that new buildings could sustain so much damage in a severe earthquake that they may have to be demolished and rebuilt, yet still not collapse. This may seem disconcerting until we focus on the hard realities. There is no question that we possess the necessary engineering expertise and technology to design and build highly earthquake-resistant structures, but they would not be affordable. Instead, we must continually balance economic considerations with minimum safety levels. We must set our goals with the objective that our buildings be both affordable and safe. We cannot expect buildings to resist the design magnitude earthquake without sustaining damage, anymore than we can expect buildings to be subjected to the design fire, flood or wind forces without sustaining damage. What is imperative is that our codes safeguard against catastrophic collapse and loss of life for both new and existing construction.

It Takes a Team to Build Safe Structures

The Building Design Team. The design team consists of architects and engineers who literally create a structure from a mental concept to a finished set of plans for the construction team to follow. The design team plays a vital role in the overall picture in that they must carefully balance form, function, safety and economy. The architect must create a building that is attractive to the owner, meets the code standards for safety and is economical. The engineer must create a structural framework that will support the concept that the architect has created while providing the structural integrity required by the code.

The Building Department Team. The building department team consists primarily of the building official, plan reviewer and building inspector. Charged with enforcing the currently adopted code, the building official sets the standard for the level of enforcement in his or her jurisdiction. The principal staff are the plan reviewer (or plan check engineer), who is charged with reviewing the building plans and specifications for compliance with all aspects of the code, and the building inspector, who must observe the field construction to ensure that it conforms to the documents approved by the plan review staff.

The Construction Team. The construction team consists of the job superintendent, foremen and a variety of trades workers. The superintendent manages the project as it progresses from foundation to finish and supervises the day-to-day tasks of the trades workers. The workers are skilled in their particular construction trades and are responsible for performing their specific jobs in the building construction process. The superintendent, foremen and trades workers must transform the symbolic information shown in the plans and specifications into a three-dimensional, physical structure in the real world. From making footing excavations, placing reinforcing, pouring concrete, welding and bolting structural steel, and installing interior and exterior finish to final painting and laying carpet, the workers ply their various trades.

The Specialty Inspection Team. In addition to the building department field inspectors, the building code requires that certain inspections be performed by special inspectors who have specific training in particular testing procedures and areas of construction. Special inspectors are required by the code to be employed by the owner, not the building department or the contractor. Some examples of special inspections are those addressing the placement of structural reinforcing, concrete strength testing, steel tendon prestressing, structural welding, the installation and tightening of high-strength bolting, and the observation and testing of structural masonry construction.

The Building Owner Team. The building owner and his or her team is of special importance. Without building owners there would be no buildings and, consequently, no design, building department or construction teams. The building owner is a consumer, and the building is the product he or she is purchasing. In that sense, building owners rely on the integrity, knowledge and skills of the other teams to ensure they get the best product for their money: safe buildings that meet their needs in terms of form, function and economy.

There is a final group: the people who are occupying buildings when disasters occur. Whether it is a crowded theater, a high-rise office building, a factory or a church that is filled to capacity on a Sunday morning, a building's occupants are the ones at risk when an earthquake strikes. They rightfully expect that the building they occupy is safe, and it is them the code specifically intends to protect.

Improving the Qualifications of the Construction Team

As noted, while adoption of the most current code helps to ensure that the latest technology in building safety is used, its benefits are greatly reduced without the proper level of enforcement in both plan review and inspection. In addition, it is vital that building inspectors and trades workers understand the importance of good workmanship to seismic-resistant construction. According to the Earthquake Engineering Research Institute (EERI) Construction Quality, Education, and Seismic Safety white paper,⁵ much of the damage caused by recent earthquakes (the 1994 Northridge quake in particular) resulted from poor quality design, plan review, inspection and construction practices. All of us must share the responsibility for this problem. The summary conclusion of the EERI white paper is that education and training hold the key to solving these problems.

Traditionally, efforts to improve the performance of buildings have been focused primarily on design engineering, materials science and keeping the codes as up to date as possible. It seems clear that a greater emphasis is needed on recognizing the significance of poor workmanship, which primarily involves trades workers and field inspectors. To use a popular metaphor, the day-to-day operations of the trades worker and building inspector take place "where the rubber meets the road." Trades workers and field inspectors must be provided the training necessary for them to sufficiently understand the negative effects of poor workmanship and inadequate inspection on the performance of buildings subjected to the seismic forces of earthquakes.

Although there have been a host of dramatic demonstrations of these effects, most are presented to audiences of design engineers-who already have a fair understanding of these consequences. The majority of earthquake engineering information begins as academic research and eventually becomes textbook or coursework material for engineers who design buildings, while the fact is that educational material intended to train engineers is generally not effective in training inspectors and trades workers.

Conclusion

One of the many lessons learned from past earthquakes is that it takes a large team of individuals to produce safe buildings. The team members include the architects and engineers who design the building, the plan reviewers who check the plans for code compliance, the trades workers who construct the building framework, the building inspectors who review the field construction for conformance with the approved plans, and the specialty inspectors who observe critical aspects of the construction process. We need to remind ourselves constantly that we are playing on the same team, charged with the common goal of producing safe buildings that afford a minimum level of protection to a trusting public. We must not view our individual expertise and specific role as being more or less significant than those of other team members, but strive to share our understanding of how our job relates to theirs and how it fits into the big picture. We should all be conscious of the profound importance that our particular role plays in producing buildings that will perform acceptably in the next earthquake.

Although training materials for seismic-resistant construction are readily available to engineers, additional emphasis is needed on developing and providing adequate training materials for the construction team. Most importantly, building inspectors, trades workers and specialty inspectors should have training programs that emphasize how earthquakes effect structures and how poor workmanship and inadequate inspection can contribute to structural damage or even failure. It is therefore incumbent on the academic institutions, engineering profession and model code organizations to help mitigate this problem by cooperating in the development of seismic-specific training materials suitable for the entire construction team.

The purpose of the building codes is to provide objective regulations that economically provide minimum levels of public safety in the built environment. We should strive to achieve this purpose through exemplary standards of quality and ethics in the design, plan review, construction and inspection processes. Utilizing the most current code ensures that we are applying the latest technologies to provide the highest level of safety in our built environment. We must work together as a team, bearing in mind that we each play a vital role in the construction of buildings that will perform in the next earthquake.

Notes

Earthquake magnitude is measured in two ways. The first, Richter magnitude (developed by Charles Richter at the California Institute of Technology), is based on the amplitude recorded by a seismometer and provides a measure of the energy produced by an earthquake. The second method, called "moment," is related to the slip and area of the fault and provides a measure of the total energy released during an earthquake. Moment is converted to generate a value similar to that used in Richter magnitude, called "moment magnitude" (M).
ATC-3-06: "Tentative Provisions for the Development of Seismic Regulations for Buildings," Applied Technology Council, 555 Twin Dolphin Drive, Suite 550, Redwood City, CA 94065. http://www.atcouncil.org/.
Recommended Lateral Force Requirements and Commentary, Sixth Edition, 1996, Seismology Committee, Structural Engineers Association of California, 555 University Avenue Suite 126, Sacramento, CA 95825-6510. http://www.seaoc.org/.
NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, 1997, Building Seismic Safety Council, 1090 Vermont Avenue Northwest, Suite 700, Washington, DC 20005. http://www.fema.gov/.
Construction Quality, Education, and Seismic Safety, April 1996. Earthquake Engineering Research Institute, 499 14th Street, Suite 320, Oakland, CA 94612-1934. http://www.eeri.org/.

John R. Henry earned a bachelor's degree in civil engineering with honors from California State University, Sacramento, in 1979. He is a Registered Civil Engineer, a member of the Structural Engineers Association of California and an ICBO Certified Plans Examiner.

Henry is a senior staff engineer at ICBO's Western Resource Center in Pleasanton, California. He is also an ICBO seminar instructor, involved in the development and presentation of a variety of structural seminars pertaining to wood frame construction.

The views expressed here are those of the authors and do not necessarily reflect the opinion or agreement of the International Conference of Building Officials.

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