Extraction of nonlinear hysteretic properties of seismically isolated bridges from quick - release field tests

A time domian system identification method is used to identify the hysteretic properties of lead-rubber bearings installed in seismically isolated bridge systems. The longitudinal or transverse motion of the superstructure is idealized as a single degree of freedom (SDOF) system, where the total damping effect has been divided two parts.

Implications of spatial variation of ground motion on the seismic response of bridges : Case study

Linear and non-linear analytical studies were conducted for evaluating the performance of the southbound separatin and overhead bridge at the SR14/15 interchange during the Northridge earthquake of January 17, 1994. The analyses are focused on potential implications of the spatial variability of ground motion on the collapse of the structure. The influences of vertical ground motion, soil-structure interaction and non-linear contact effects at the expansion joints and abutments, are also examined. The parameter studies help to determine some of the causes of collapse and offer insight on the complex seismic behavior of long multi-span concrete bridges. (AU)

A seismic retrofitting manual for highway bridges

In 1993, the Federal Highway Administration (FHWA) published a set of guidelines for the seismic retrofitting of highway bridges. These guidelines has been prepared by the Applied Technology Council (as ATC 6-2) and represented what was then the state-of-the-art for screening, evaluating, and retrofitting of seismically deficient bridges. In the 10 years since the publication of these guidelines, there has been significant progress in understanding the seismic response of bridges and the development of new and improved retrofit technologies. It therefore appeared timely to revise this material based on this accumulated experience and to reissue it as a retrofit manual. The change from guideline to manual reflects the fact that this is a field which is changing rapidly, both in design and construction practice. In addition, there are several active research programs in progress at the present time and new techniques are being developed and tested which may greatly influence the state-of-the-art in the near future. It is therefore intented that this revision be an interim one which will be revisited in four or five years time for a second review based on the results of ongoing research and development activities.(AU)

Specifications for the seismic design of new highway bridges

The current seismic design criteria and procedures in the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges were developed in the late 1970s following the 1971 San Fernando earthquake in California. Although these provisions were notable for their innovation at the time, experience with their use over the intervening years and the perfomance of bridges during recent damaging earthquakes in California (and elsewhere) led to the decision by AASHTO to have the specifications reviewed and modified as appropriate. NCEER was awarded a contract for this purpose by the National Academy of Sciences on behalf of the Transportation Research Board and AASHTO. This revised set of specifications has been prepared which include new or modefied provisions for soil effects, site-specific spectra, important bridges, temporary structures, seat widths for skewed bridges, analysis methods, and minimum requirements for bridges in low and moderate seismic zones.(AU)

Critical loads of elastomeric isolators at high shear strain

This paper describes both analytical and experimental studies to determine the effect of high shear strain on the critical loads of a set of 5 inch and 10 inch square elastomeric bearings with shape factors ranging from 1.7 to 10.0. The results from ADINA finite element solutions are described and compared against experimental tests. Demonstration of significant axial load capacity at high shear strain is presented, and the effect of end (boundary) conditions is illustrated. It is proposed that three regions be defined on the critical load-shear displacement plot which identify stable, unstable and transition conditions respectively.(AU)

The Northridge, California earthquake of January 17, 1994 : Perfomance of highway bridges

On January 17, 1994 at 4:31 a.m., a magnitude 6.6 earthquake struck the Los Angeles metropolitan area. Epicentered in the San Fernando Valley town of Northridge, California, the earthquake caused serious damage to buildings and sections of elevated freeways; ignited at least one hundred fires as it ruptured gas pipelines; and disrupted water supply systems. As a consequence, 57 people died, another 1,500 were seriously injured, and 22,000 were left homeless. Over 3,000 buildings, most of which were residential structures, were declared unsafe for reentry due to earthquake damage. Los Angeles, a city which has extensively prepared itself for earthquakes, found that it had experienced the most destructive event since the 1906 San Francisco earthquake. Direct economic losses are estimated currently at over $20 billion. This reconnaissance report provides an analysis of major bridges damage with occurred during the earthquake. Eight highway bridges are described in terms of their geometry, site ground motions, observed damage and likely failure modes.(AU)

Part II : Lifelines. Chapter 7 : Highways and railroads

Transportation systems such as highways and railroads are a diverse collection of structural, mechanical and electrical components which individually play a vital role in modern society. Until recently, their seismic vulnerability was largely ignored. But damage sustained by highways and bridges in the Loma Prieta, Costa Rica and Philippine earthquakes over the last three years has heightened awareness concerning their fragility and the potential for major economic losses should they fail. Although the state-of-the-art is generally immature, seismic bridge specifications are well developed and a set of performance criteria (based on acceptable damage) are available for highway bridges. Other components such as tunnels, retaining structures, slopes and pavements are not however covered by these specifications and except for some major projects, are not designed for seismic loads, even in high risk zones. Further, there are no accepted methods for making a vulnerability assessment of an entire, or even a partial, highway or railroad system. Thus the issues of redundancy and consequences of closure are not rationally considered when establishing design criteria for new systems or evaluating existing networks. Much can be done to implement existing knowledge in order to improve the state of practice and some recommendations are made in this monograph in this regard. Recommendations are also made for advancing the state-of-the-art, for developing new knowledge, and for ensuring that this knowledge addresses national needs.(AU)

Part II : Lifelines. Chapter 12 : Standards for lifelines

In this chapter the status of standards and guidelines for the seismic safety of existing and new lifeline systems is described to provide a framework for end users who are presently collaborating on a national study to plan for the development and adoption of seismic guidelines and standards for lifelines. Although nationally recognized seismic standards are not yet available for all lifelines, advances are being made for: a) electrical power systems, b) gas and liquid fuel systems, c) telecommunications systems, d) transportation systems, and e) water and sewage systems.(AU)

History and application of seismic isolation to higway bridges in the United States

Seismic isolation is used in buildings to decouple these structures from the damaging components of earthquake ground motion. It is also in bridges where it involves the separation of the superstructure from the substructure, usually at the bent cap level. But unlike a building application the primary intent in a bridge is to protect the structure below the plane of isolation - the superstructure being relatively rigid to in-plane loads and of adequate strength to resist these loads. Bridges are particularly suitable for isolation and literature surveys indicate that more than 90

of the world's isolated structures are, in fact, bridge structures. Applications include both new construction and retrofit work. Implementation within the United States has only occurred within the last few years and then predominantly as a retrofit measure rather than in new construction. This activity is reviewed in this paper along with some potential innovations in the use of isolators for protecting monolithic continuous bridges.(AU)

AASHTO seismic isolation design requirements for highway bridges

In October, 1990 the American Association of State Highway Transportation Officials (AASHTO) adopted Guide Specifications for the Seismic Isolation Design of Highway Bridges. This paper overviews the basic concepts and design principles of seismic isolation and discusses the objectives and philosophy of the provisions. A summary of the provisions is presented and the paper concludes with a procedure to compare the perfomance of isolation systems with different damping values.(AU)

The need for earthquake education

In 1977 the United States Congress found that 1) all 50 States are vulnerable to the hazards of earthquakes, and at least 39 of them are subject to major or moderate seismic risk, including Alaska, California, Hawaii, Illinois, Massachusetts, Missouri, Montana, Nevada, New Jersey, New York, South Carolina, Utah, and Washington. A large portionof the population of the United States lives in areas vulnerable to earthquake hazards; and 2) earthquakes have caused, and can cause in the future, enormous loss of life, injury, destruction of property, and economic and social disruption. With respect to future earthquakes, such loss, destruction, and disruption can be substantially reduced through the development and implementation of earthquake hazards reduction measures, including A) improved design and construction methods and practices, B) land-use controls and redevelopment, C) prediction techniques and early-warning systems, D) coordinated emergency preparedness plans, and E) public education and involvement programs. Education is seen in this extract from the Earthquake Hazards Reduction Act of 1977 to be one of five reduction measures to be undertaken under Public Law 95-124