International Concrete Abstracts Portal

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.

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.

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.

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.