Earthquake Spectra

Public education programs intended to increase individual and household preparations for earthquakes often prove to be disappointingly ineffective, especially in reaching minorities and ethnic groups outside the mainstream of community life. This paper argues that the success of such programs can be improved by understanding the ebb and flow of earthquake saliency as well as the complex social structure of our cities. In particular, earthquakes and other major disasters in the ancestral homeland represent “teachable moments” when receptivity to earthquake safety information may be especially high among members the ethnic community with a variety of psychological and personal links to that nation. The paper presents specific suggestions for taking fullest advantage of these teachable moments.

A number of new code developments, largely initiated in California, are taking place in the USA for the seismic design of steel structures. The principal ones are reviewed and commented upon in the paper. Key experimental support for some of the changes is indicated. Major attention is directed to the three main types of steel construction: moment-resisting frames, concentrically braced steel frames, and, the relatively new method for seismic design, eccentric bracing. Some of the proposed and possible practical improvements in moment-resisting connections are given; the reasons for some concern over the use of concentrically braced frames for severe seismic applications are discussed; and a brief overview on the application of eccentrically braced steel frames is presented. The paper concludes with a few remarks on future trends and needs in structural steel seismic design.

In iron or steel pipelines subjected to ground shaking from wave effects, leaks are often related to corrosion and other types of chemical or physical deterioration associated with normal aging. This paper examines the performance of water, sewage and gas pipelines in Coalinga, California for five years prior to and two years after the May 1983 earthquake. It is found that water and sewer pipelines are suffering the effects of the earthquake two years later. Thus, in addition to causing prompt damage, the 1983 earthquake accelerated aging of pipeline systems which may have shortened their effective life and permanently increased maintenance costs.

The potential damage to lifelines from even moderate earthquakes can have significant and widespread effects on community well-being. Recently, under the sponsorship of the United States Geological Survey, researchers from California cooperated with a utility in Utah to analyze the seismic safety of natural gas facilities in Utah. They identified pipelines by system importance, size, and material, and then assessed the probability of structural damage to these components. These estimates, which reflect knowledge of Wasatch Front fault mechanisms, and an ability to model numerous seismic events by computer, are yielding significant knowledge of possible piping responses.

Project results included the number and location of possible pipeline breaks for various seismic events. This information was used to estimate gas loss and resultant system pressures. This, in turn, is currently being used to guide future system reinforcements, replacements, and installation of emergency system isolation valves. This project, involving the close interaction of both the utility and the research firm, is a good example of the type of practical research needed by industry.

Consensus-opinion earthquake damage and loss estimates and companion loss estimation and inventory methdology have been developed for existing facilities in California. These data and methodology are needed to provide input into computer simulation methodologies developed by the Federal Emergency Management Agency (FEMA) that estimate the economic impacts of real or hypothetical California earthquakes on the state, region, and nation. Data and methodology developed include: consensus opinion damage-factor estimates (expected physical damage due to ground shaking); methodology to adjust damage-factor estimates to account for construction quality; methodology to estimate the effects of collateral hazards such as ground failure, fault rupture, and inundation; loss-of-function data and methodology to estimate the time it takes to restore damaged facilities to their pre-earthquake usability; methodology to estimate deaths and injuries; and inventory data and methodology for all types of existing industrial, commercial, residential, utility and transportation facilities in California. Damage-factor estimates are provided for Modified Mercalli Intensities VI through XII in the form of Damage Probability Matrices. Seven damage states are considered: 0%, 0-1%, 1-10%, 10-30%, 30-60%, 60-100%, and 100% damage. Loss-of-Function estimates, which specify the time required to restore a facility to 30%, 60%, and 100% of the pre-earthquake usability, are provided for these same seven damage states.

In the design of reinforced concrete multistorey buildings, in which lateral load resistance has been assigned to structural walls, the emphasis should be on a rational strategy in the positioning of walls and the establishment of a hierarchy in the development of strengths to ensure that in the event of a very large earthquake brittle failure will not occur. The preferred mode of energy dissipation should be flexure in a predictable region. Therefore failures due to diagonal tension or compression, crushing of concrete in compression, sliding along construction joints, instability of wall elements or reinforcing bars and breakdown of anchorages should be suppressed. These aims may be achieved with the application of a deterministic design philosophy and they necessitate special detailing and dimensioning of potentially plastic regions of walls. In several areas differences exist between code provisions and practices in the United States and New Zealand.

Following an overview of the special problems inherent in the design and construction of earthquake-resistant buildings in regions of high seismic risk, the techniques that will be required to solve these problems in the U.S. are discussed. Some lessons learned from recent earthquakes, particularly those in Chile and Mexico in 1985, are discussed as are some results of integrated analytical and experimental research at the University of California, Berkeley. The implications of the ground motions recorded during the 1985 Mexican and Chilean earthquakes, the performance of buildings during the Mexican earthquake, and the research results previously discussed are then assessed with respect to seismic-resistant design regulations presently in force (UBC) as well as those formulated by ATC 3-06 and the Tentative Lateral Force Requirements recently developed by the Seismology Committee of SEAOC. The rationale for and reliability of the values suggested by the ATC for the “Response Modification Factor R” and by the SEAOC Seismology Committee for the “Structural Quality Factor R _w ” are reviewed in detail. In the conclusion to the paper, two solutions for improving the earthquake-resistant design of building structures are proposed: an ideal (rational) method to be implemented in the future, and a compromise solution that can be implemented immediately.