The catastrophic collapse of the old Cypress Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of elevated freeway bridge structures. One track of the joint Caltrans and University of California, Berkeley, research project is the investigation of outrigger knee joints found in elevated freeway bents. This project has two principal goals: to evaluated the behavior of the existing outrigger knee joint subassemblies under a combined transverse and longitudinal loading and to devise and experimentally verify upgrading strategies and repair techniques suitable for application on the existing elevated freeways. The performance of the existing outrigger knee joint subassemblies was evaluated by testing two as-built models. After considering several upgrading strategies, two were tested on the remaining five specimens. In parallel with the experiments, a set of tools was developed for design and analysis of the upgraded subassemblies. A summary of the design, analytical, and experimental work conducted to date is presented in this paper.

Summarizes the findings of a research project performed by the American Iron and Steel Institute entitled, "Technical Review of Current and Proposed Seismic Design Provisions." In the last several years, both New York City and the Building Officials and Code Administrators International (BOCA) have proposed and drafted seismic provisions for their respective building codes. The purpose of this study was to compare the pertinent provisions of these proposed provisions to each other and to existing building codes (UBC, SEAOC, NEHRP, and ASCE 7). In addition, the American Institute of Steel Construction has adapted seismic provisions in their Load and Resistance Factor Design Specifications. BOCA has proposed a method of adapting these LRFD seismic provisions into its building code. This study also reviewed these proposed revisions with respect to applicability to east coast earthquakes, especially in New York City. The impact of both the NYC and BOCA provisions on design and construction costs is also addressed.

Applied Technology Council (ATC) is conducting a California Department of Transportation (Caltrans) sponsored project to review and revise existing standards, performance criteria, specifications, and practices for the seismic design and construction of new bridges structures within California. The goal is to provide standards and criteria that will insure that California bridge structures of all types perform well in earthquakes. Specifically, as affirmed by the Governor following the 1989 Loma Prieta earthquake, all transportation structures must be seismically safe and important transportation structures must maintain their function after earthquakes. The project builds on developments in bridge seismic design that have been made over the past 20 years. It uses results from current research plus observations made in recent earthquakes to identify several significant improvements that can be made to the current Caltrans Bridge Design Specifications (BDS). At the present time, a draft revised BDS and Commentary have been developed. The revised BDS is based on new performance criteria that was developed by Caltrans, its independent Seismic Advisory Board, and ATC. Specific improvements to design procedures are made in several areas, including seismic loading, foundation design, dynamic analysis, and concrete and steel design. The project is ongoing and the draft BDS will continue to be evaluated and, most likely, revised as the project continues. In addition to an overall review by the panel of 13 technical advisors selected for this project, independent external reviews will be conducted by selected experts in various aspects of seismic design. Several trial designs will also be performed using the draft provisions. The results of these trial designs will help point out deficiencies in the draft specifications that can then be improved prior to their being adopted for general use. In the end, this project will produce bridge seismic design criteria that reflect a consensus of expert opinion and provides a uniform approach to bridge seismic design in California.

Simply stated, shotcrete is sprayed concrete or mortar. Because of difficulty in obtaining good compaction and fully encasing large or closely spaced bars, it has traditionally been used in thin, relatively lightly reinforced sections. Unique to seismic repair and retrofit are heavily reinforced and often thick sections. Because of its ease of application in areas of poor access and the resulting reduction in construction time and cost, the process can be especially advantageous in seismic applications. Special procedures are required, however, to obtain good quality work under the common inherent constraints that often exist and overcome the limitations. Although not widely recognized, proven procedures are well established and have been successfully used in seismic repair and retrofit applications for nearly 50 years. Basic principles of the shotcrete process are reviewed in this paper; those special procedures required for proper placement in heavily reinforced and thick sections are discussed.

Existing beams coupling reinforced concrete walls are often found to be deficient. Common deficiencies include inadequate overall capacities, particularly shear capacities that are insufficient to develop flexural yielding of the beams. This research examines the use of steel plates to improve the shear resistance of reinforced concrete coupling beams in moderate seismic zones. Full-scale reversed cyclic loading tests of shear-deficient reinforced concrete coupling beams were carried out. The retrofit measures involved attaching thin steel plates on one side of the coupling beams to enhance their shear performance. A number of different ways of attaching the plate were investigated. Tests with the steel plate attached only with epoxy demonstrated a need for further connection to improve the hysteretic response. Additional specimens were constructed to investigate the influence of connecting the plate with both epoxy and bolting. The purpose of testing these retrofitted specimens was to develop a procedure for designing the plate connection details such that significant stresses are developed in the plate. The reversed cyclic loading responses of the retrofitted specimens are compared with a control specimen representing the deficient coupling beam before retrofit.