International Concrete Abstracts Portal

This Symposium Publication contains 14 papers that were presented at technical sessions sponsored by ACI Committees 544 and 549, and Joint ACI-ASCE Committee 423 at the 2008 ACI Spring Convention in Los Angeles, CA. Topics covered in these papers include development, mechanical behavior, modeling and structural applications of fiber- reinforced concrete and thin laminate composites; repair and rehabilitation of reinforced and prestressed concrete members; and new developments in prestressed concrete bridges. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-272

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.

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.

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.

Four reinforced concrete T-beams were tested to study their behavior when strengthened for shear using near-surface mounted (NSM) bars. The objectives were to study the effects of the type of bars used (carbon fiber-reinforced polymer (CFRP) and conventional reinforcing steel) and the effects of the load level at which the bars are installed. It was observed that the CFRP bars bonded at zero load increased the shear capacity by up to 92%, while those bonded when the precracked beam was under load increased the capacity by 77%. For the steel bars, these values were 75% and 57%, respectively. The CFRP strengthened regions showed a slightly more favorable response than those strengthened with conventional steel bars. Strengthening provided an improved control of the diagonal crack width. In the beams with closer spacing of NSM bars, the increase in shear strength allowed the beam to fail after considerable flexural deformations.