International Concrete Abstracts Portal

Upgrading often becomes a necessity due to changes in usage of buildings due to factors such as deterioration and aging, change in occupancy, or the need for installation of facilities such as air-conditioning, heating, escalators, elevators, additional skylights, or new façade structures. In a number of cases upgrading is related to changes which affect the load bearing components of the structure. Fiber reinforced polymer matrix composites provide an efficient means of both strengthening slabs for enhanced load carrying capacity and for strengthening slabs after installation of cut-outs. This paper reports on a series of tests conducted to assess the comparative efficiencies of a commercially available strip form and a fabric form of material vis-à-vis strengthening ability and ductility. It is shown that material tailoring can result in significant changes in efficiencies. The extension of this to the rehabilitation of cut-outs is also detailed and aspects of an on-going full-scale test program in that area are elucidated.

In this paper the results of a series of tests, which were carried out using a total of 16 specimens of reinforced concrete (R/C) columns having wing walls retrofitted with fiber reinforced polymer (FRP) sheets as shear reinforcement, are described. In this work, the FRP sheets were adhered with epoxy resin. The specimens before retrofit were designed by the abolished Japanese seismic code before 1971. The primary test variables were the widths of the wing walls stretching from the columns, the kind of FRP sheets and its amount as shear reinforcement. It was observed that all specimens failed in a shear mode except for one specimen and that the ultimate shear strengths increased linearly in proportion to the amount of the fiber as shear reinforcement. ( i.e., the product of tensile strength and equivalent reinforcement ratio which corresponds to an replaced rectangular cross section of the column and the wing walls as a whole.) Based on the test results of regression analysis, an equation to evaluate the ultimate shear strength of R/C columns having wing walls retrofitted with FRP sheets is proposed.

This paper summarizes the recent research developments of a new structural concept for the design of the hybrid RC circular columns confined in aramid fiber reinforced polymer (AFRP) tube impregnated with epoxy. The AFRP tubes have the dual function of stay-in-place formwork and transverse reinforcement for the structural elements. Although the AFRP tube is not structural member by itself, it will turn into an important seismic resistance member by hybridizing the AFRP tube and the RC column. However, in this lateral cyclic loading test under a constant axial force the bond splitting failure happened on these specimens for lack of bond strength because high strength and large diameter longitudinal reinforcement were arranged excessively. If the hybrid RC columns confined in AFRP tube prevented the bond splitting failure from happening, their high seismic performance could be expected.

FRP materials such as carbon, aramid, and glass provide a potentially economical means of strengthening unreinforced and under-reinforced masonry. Potential applications include strengthening for a change in occupancy or loading; repair of inadequate construction; or possibly as an alternative reinforcing method for new construction. At the University of Wyoming, seven unreinforced concrete masonry walls were tested in out-of-plane flexure with carbon, aramid, and glass tape reinforcing. The initial three walls were tested with carbon tow sheets, laminates, and aramid tapes applied to the exterior surface of the wall. These initial tests indicated that the FRP strengths were well above the strength of the masonry causing shear failures in the unreinforced masonry. In addition, cost comparisons of the strengthening materials indicated that they were cost-prohibitive when compared to traditional strengthening methods. The four remaining walls were strengthened with narrow strips of unidirectional fiberglass fabric applied to the surface with epoxy. The objective of the second set of tests was to force a tension failure in the FRP rather than a shear or compression failure in the masonry. The failure modes included fracture of the GFRP, combination delamination/fracture, and complete delamination. Tension tests were also conducted on single lengths of the GFRP tape. The tension test was developed to provide a method of predicting the flexural tensile strength of the GFRP tape. Observed and potential failure modes are presented based on test observations along with a discussion of the desirable failure modes for the strengthening system.

In this study, the tests of 12 types of FRP (fiber reinforced plastic) rods were carried out to investigate the characteristics of bond between the rods and concrete. The experimental results of bond strength and bond stress-slip relationship of FRP rods are presented and discussed. Four types of bond failure were observed. The type of bond failure of a FRP rod was principally determined by its configuration. All of the tested samples, which failed due to full frictional pullout or local frictional pullout, had an almost identical pattern in the ascending branch of the curve. The bond strength of AFRP rods was smaller than that of CFRP and GFRP rods. The bond strength of FRP rods is greatly affected by the surface configuration of the rod. The deformed FRP rods had approximately the same bond strength. The bond strength of the deformed CFRP rods was equal to, or greater than, that of the steel bar. An equation is proposed to predict the bond strength of FRP rods. The predicted values have rather good agreement with the experimental results.