International Concrete Abstracts Portal

SP160 This publication brings out a wide spectrum of the state research and practice in the rehabilitation of concrete structures for improved earthquake resistance. It also covers seismic rehabilitation with regard to elements of the structures as well as the whole structure.

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.

A rational retrofit of a non-ductile RC frame structure requires an assessment of its seismic behavior as limited by the strength and ductility capacity of its critical regions. From this assessment, the critical regions can be prioritized for retrofit. This paper presents part of the research at Lehigh University that is investigating the seismic performance of non-ductile RC frame structures and developing retrofit strategies. The paper describes the design of 12-story and three-story prototype non-ductile RC frame structures, modeling of these structures for inelastic static analyses, their seismic behavior as obtained from these analyses, and the implications of this behavior on their retrofit. The seismic behavior of the prototype structures was controlled by the non-ductile behavior of their critical regions. Critical column end regions must be retrofit to increase the global ductility capacity. However, such a retrofit would not significantly increase the base shear capacity of the 12-story structure; pullout regions at the beam-column joints must be retrofit to increase the base shear capacity of this structure. Possible non-ductile behavior within the beams is not considered to be critical to the base shear or global ductility capacity of the prototypes. However, if the pullout regions are retrofit to increase their ultimate moment/rotation capacity, the other regions in the beams should be carefully evaluated.

Reports tests of a three span reduced scale segmental box girder bridge model post-tensioned with external tendons. The objectives of this study included the determination of the effect of using external tendons discretely bonded at an intermediate diaphragm in each segment and/or using grouted internal tendons on the strength and ductility of external tendon bridges. The scope included experimentally determining and analytically predicting the external tendon maximum stress and the flexural capacity of the bridge. The flexural tests, performed on the three span model, were conducted in three phases. In the first phase, the external tendons were discretely bonded at only two or four intermediate diaphragms in each span. In the second phase, the external tendons were discretely bonded at all ten intermediate diaphragms in each span. In the third phase, supplementary ungrouted or grouted internal tendons were added. The test results indicated that discrete bonding of external tendons and/or using grouted internal tendons substantially improved the strength and ductility of this kind of construction.