International Concrete Abstracts Portal

This paper presents the results of an experimental investigation under-taken for evaluating the cyclic lateral load-drift response of rectangular reinforced concrete (RC) columns which were damaged due to large drift reversals, but then repaired for upgrading the bond strength of the spliced reinforcement within the critical hinging region. The original specimens consisted of full-scale unconfined and fiber-reinforced polymer (FRP) confined columns having a relatively high section aspect ratio of 2.0. These original specimens were subjected to large drift reversals until complete bond degradation of the spliced reinforcement within the hinging zone and complete loss of flexural strength of the columns8. The repair procedure consisted of removing the deteriorated concrete within the damaged/splice zone and casting new concrete. Two types of concrete confine-ment for improving the bond strength and flexural capacity were investigated and compared, namely, internal confinement by transverse steel ties and external confinement using carbon fiber-reinforced polymer (CFRP) jackets. It was found that repairing the bond-damaged zone through concrete confinement leads to substantial regain of flexural strength up to or exceeding the strength of the original specimens, lower structural damage associated with concrete fracturing and bond degradation, and considerable improvement of the energy dissipation capacity under cyclic loading. Confinement by external FRP jackets was relatively more effective than confinement by internal steel ties. However, unlike columns with continuous reinforcement, columns with spliced reinforcement within the hinging region experienced significant bond and strength degradation beyond drift ratios between 3 and 4%, irrespective of the type and amount of confinement used. The experimental results are discussed, and a design expression for estimating the thickness of the FRP jacket required for seismic bond strengthening is presented and compared with the test data.

This paper reviews progress spanning a period of about four decades during which the author was intimately involved in research and teaching in three distinct yet related fields of civil engineering: prestressed concrete, fiber reinforced concrete, and ferrocement and thin cementitious products. In retrospect and for each area, key contributions are mentioned, milestones recalled, and prospects for the near future envisioned. Issues related to partial prestressing, external prestressing, high performance fiber reinforced cement composites, strain-hardening FRC composites, 3D textiles and the like are addressed. Technical advances are webbed with some personal milestones as well. Important research issues to address in the near future are pointed out.

The mechanical properties of cellulose fiber gypsum board have been investigated in bending, tension and compression. It shows a quasi-plastic behavior in the ultimate range and a strain softening behavior in the post-peak regime. Wall panels made of a timber frame and fiber gypsum board sheathing can be used as a lightweight structure in residential buildings. A cyclic test on such an element showed good deformability with high shear resistance which suggests the use of such panels in seismically loaded structures. For full understanding of the deformation potential, more tests are necessary.

Prestressed (PS)concrete technology is being used all over the world in the construction of a wide range of structures, particularly bridges. However, many PS bridges have been deteriorating even before the end of their design service-life due to corrosion and other environmental effects. In view of this, a number of innovative technologies have been developed in Japan to increase not only the structural performance of PS bridges, but also their long-term durability. These include the development of novel structural systems and the advancement in construction materials. This paper presents an overview of such innovative technologies on PS bridges including a brief discussion of their development and applications in actual construction projects. Some noteworthy structures, which represent the state-of-the-art technologies in the construction of PS bridges in Japan, are also presented.

There are a limited number of experimental results available on the retrofit of prestressed concrete structural elements. In addition, there is a lack of analytical models dealing with the flexural performance of such elements. This study addresses the latter problem by presenting a methodology for analysis and design of prestressed concrete flexural elements strengthened with externally bonded, fiber reinforced composites. The method provides systematic suggestions on the analysis and design of strengthened prestressed concrete beams with both bonded and unbonded tendons. The method can be used to determine the flexural capacity and to compute stresses and strains in concrete, tendons, and externally bonded fiber reinforcement. Compared to existing experimental data on carbon strengthened beams, the model provides very good prediction of the flexural performance of strengthened prestressed beams. The equations are also applicable to other fiber types including glass, steel, and aramid.