Earthquake Spectra

An experimental investigation was conducted to evaluate the seismic performance of common types of architectural glass used in a typical storefront wall system. Two seismic loading histories were developed and employed in the laboratory to simulate the effects of moderate and severe earthquakes on a full-scale storefront wall system test assembly. Serviceability limit states and ultimate limit states of storefront glass and related glazing components were defined and assessed at moderate and severe earthquake loading levels. Experimental results indicated that for all glass types tested, serviceability limit states of glass edge damage and gasket seal degradation in the storefront wall system were exceeded during the moderate earthquake simulation. Ultimate limit states of major cracking and glass fallout were reached for the most common storefront glass type, 1/4 in. annealed monolithic glass, during the severe earthquake simulation. Annealed laminated glass, fully tempered monolithic glass, and insulating glass units constructed with either annealed or fully tempered glass were highly resistant to glass fallout and major cracking during the severe earthquake simulation.

A need exists to improve the effectiveness of the network of communities, organizations, and agencies that are concerned with reducing the negative impact of natural hazards in the USA. The issue is to find ways to integrate community need assessment, research and development, education and training, policy formulation, implementation, and evaluation to improve practices that reduce vulnerability at the community, regional, and national levels. To this end, we propose to create a disaster reduction network that supports a cycle of development and application activities relating to natural hazards mitigation standards, diffusion of loss reduction practice, and consensus building in communities and in technical and professional associations. The expected benefit is a more efficient use of resources and a sustained and effective national infrastructure.

structural design, Limit design, Spectra

The seismic design provisions of most building codes in the United States specify ground motion parameters for various regions of the country and provide simple formulas to determine a distribution of lateral forces for which the structure should be designed. The simple formulas typically involve the use of one or more “factors” to account for anticipated inelastic behavior of the structure, relative importance of the structure, and site soil effects. Although these code provisions are very simple to use, they oversimplify a complex problem and are based on many implicit assumptions which many designers may not appreciate. Furthermore, the reliability of the final design is not known. This paper describes the key features of an alternative seismic design procedure in which the underlying assumptions are more clearly defined and which provides a more uniform level of reliability in the final design. The procedure requires the designer to consider two levels of earthquake excitation. An “equivalent” single-degree-of-freedom model and uniform hazard response spectra are used to predict structural performance. The alternative procedure should enable designers to achieve code-specified target performance objectives for moderate and severe levels of earthquake excitation.

This report examines the state-of-the-art of in situ methods of estimating liquefaction potential in sands. In situ methods are especially important since “undisturbed” samples of loose sand for laboratory testing are virtually unobtainable. Various penetration test methods are examined, such as the SPT, DMT, and the CPT and variants. These methods are completely empirical in nature, and have worked well to date. The current state-of-practice is an SPT-based method. Intrusive, seismic-based tests are also examined: the cross-hole, down-hole tests, and down-hole logger. The seismic velocity-based predictors have a stronger physical basis than the penetration test-based estimation methods, but need a larger database. A non-intrusive test, the Spectral Analysis of Surface Waves technique, seems especially suited for examining sites of large areal extent.

On October 12, 1992, the metropolitan area of Cairo, Egypt and surrounding villages in the Nile Valley sustained the effects of a moderate earthquake of magnitude M _B 5.9 (M _S 5.2). To identify mortality- or injury-prevention strategies for communities at risk, we investigated deaths and injuries that were associated with the event and modeled the time that patients spent in the hospital because of earthquake-related injuries. Populations in areas closest to the epicenter experienced increased death and injury rates (4.6 deaths per 100,000 and 80.6 injuries per 100,000) compared to those located further from the epicenter (0.8 deaths per 100,000 and 23.7 injuries per 100,000). The distribution of earthquake-related admissions in one hospital peaked within 36 hours after the earthquake. A general linear model predicted that older people were hospitalized longer than younger people and people with fractures to the trunk were hospitalized longer than those with injuries at other anatomical sites (p = 0.008). While recognizing that other characteristics are also important, we recommend that emergency managers consider proximity to the epicenter when planning response operations, and that health officials focus on ensuring appropriate medical care for older people and for people who have suffered severe injuries to the trunk.

The catastrophic collapse of the Cypress Street Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of older elevated freeway bridge structures. One part of a joint Caltrans/University of California at Berkeley research project is the investigation of outrigger knee joints found in elevated freeway bents. This project has two principal goals: to evaluate the behavior of the existing outrigger knee joint systems under a combined transverse and longitudinal loading, and to design and experimentally verify upgrading strategies and repair techniques suitable for application on the existing elevated freeways. The primary focus of this paper will be to present the behavior of the as-built and upgraded systems, but an overview of the design method and the analytical tools used in the upgrade will also be presented.