Presents the theoretical analysis of load bearing capacity and ductility of reinforced concrete (RC) strengthened sections. The analysis is performed first, stating the equilibrium equations at the ultimate limit state for combined bending and axial load and for pure bending of reinforced concrete sections strengthened by adding new concrete parts incorporating additional steel reinforcement. A detailed discussion of the load bearing capacity and of the related ductility which can be reached by means of prescribed strengthening procedures is then performed, pointing out the basic prerequisites that have to be satisfied to obtain a good deformational behavior, together with a significant increase of the load bearing capacity. The results derived from a parametric study and from some numerical examples previously performed by the author allow application of the proposed procedure to practical cases, showing how it can be used as an efficient tool in solving the problems connected to everyday practice.

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.

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.

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.

Various techniques are available for the seismic rehabilitation of existing structures, such as adding cross bracings, structural/shear walls, base isolation systems, etc. The cross bracings and structural/shear wall help reduce the drift and increase the ductility of the structures. The base isolation systems reduce the effect of the peak ground acceleration and, hence, the drift. In this paper, the base isolation systems have been considered to rehabilitate the existing reinforced concrete frame structures. Review of various base isolation systems used in reinforced concrete structures for seismic response is evaluated. An analytical procedure is described for a frame building supported on isolation bearings. The study is based on a single degree of freedom (SDOF) with appropriate hysteretic properties. Different geometries, variation of bearing stiffness, and ground motion are considered. Inelastic behavior by increasing the effective natural period of vibration and the damping ratio of frame is considered. The viscous damping coefficient and hysteretic damping ratio for isolation bearing were considered from the shear load deflection relationship of isolation bearings. The proposed procedure is applied to evaluated the Uniform Building Code (UBC) requirements of reinforced concrete frame buildings.