International Concrete Abstracts Portal

The characteristics of 1994 Northridge motions with respect to permanent slope deformations are consistent with much larger world-wide database of excitations. The paper describes the application of a recently developed procedure to compute abutment fill settlements caused by earthquakes to predict fill settlements. The study used 58 excitations from 1994 Northbridge earthquake recorded in the free field with acceleration higher than .1g to investigate the influence of vertical acceleration on permanent abutment fill settlements. It was found that the influence of vertical accelerations is insignificant. The comparison between predicted and observed abutment fill settlements aft4r the 1994 Northbridge earthquake using data from 18 bridge sites near the epicentral area has been reported. The study indicates that the existing computational model yields conservative estimates and it may be used as a first approximation for evaluating abutment fill settlements in moderate to large earthquakes.

This paper describes current practices and proposed changes for the seismic analysis and design of bridges at Caltrans. It includes an explanation of the new performance criteria for ordinary and important bridges. It provides a description of Caltrans' new site-specific ground input motions which are based on magnitude, acceleration, and the shear wave velocity of the surrounding soil. A variety of new bridge analysis tools and new bridge models, many of which seek to describe the nonlinear behavior of bridges and bridge elements, are described in the paper. Finally, current and proposed seismic design procedures for columns, joints, and superstructures are briefly illustrated. Caltran's seismic bridge procedures reflect the geological, industrial, and economic conditions of California. California's high seismicity requires analysis and design methods that are state-of-the-art. Often, new procedures are implemented only days after the research is completed. Since most bridges in California are made of cast-in-place reinforced concrete, there are few breaks in the structure for the placement of isolators or dampers. Dissipation of energy must occur in ductile columns rather than in special devices. Because, California's economy is dependent on its highway system, methods of protecting vital transportation arteries during and after disasters are being studied.

In order to provide experimental background for current seismic design of bridge footings, a 0.4:1 scale circular-column footing model was tested. The model was designed and constructed based on a footing of an actual prototype bridge which was built following current bridge design standards. The model pier was tested in a vertical cantilever condition with cyclic horizontal displacements and constant axial load applied to the top of the column. The pier was supported on rubber pads simulating the compressive flexibility of pile foundation, with high tensile strength bars simulating the compressive flexibility of pile foundation, with high horizontal displacement, the pier developed a satisfactory hysteretic response with a full plastic hinge formed at the bottom of the column. However, test results and theoretical analyses revealed potential problems in current bridge footing design, in particular, the lack of the column/footing joint shear design as well as non-conservative flexural and shear designs which are based on full effectiveness of the entire footing width.

A comprehensive research project focused on investigation and repairing the vulnerable elevated freeway bridge structures was initiated and jointly conducted by the California Department of Transportation and the University of California at Berkeley after the 1989 Loma Prieta earthquake. One part of this project was the investigation of outrigger knee joints, a structural sub-system found in elevated freeway bridges. This investigation had two principal goals: to evaluate the behavior of existing outrigger knee joint systems under a combined transverse seismic upgrading of existing outrigger knee joints. The focus of this paper is the design procedure for seismic upgrade of existing outrigger knee joint systems. This design procedure comprises a performance objective, quantified in terms of system drift demand, and a displacement-based capacity design process that centers around an interaction for computing the level of column plastic hinge confinement pressure. To further explore the upgrade design framework. Four damage indices are examined as candidates for the role of a response measures that relates a global performance objective to a local design parameter. Directions for new research derived from this exploration are discussed in the conclusion.

As low cycle fatigue failure in the longitudinal reinforcement is unavoidable, it necessitates the concept of using replaceable plastic hinges in which specially-detailed reinforcing fuse-bars are installed. Three one-third scale model pier specimens were constructed. The first renewable-hinge column was tested and repaired five times. The second pre-cast column was also constructed using the fuse-bar connections and subsequently repaired ten times. For comparative purposes, a conventionally reinforced column was constructed and tested. It was found that each of the repaired columns performed as well as the undamaged virgin columns. This new approach to construction enables rapid restoration to full service following a damaging earthquake.