International Concrete Abstracts Portal

This paper discusses the procedure and results from in-situ load tests performed on strengthened double tee beams in a precast parking garage. The load tests were performed to evaluate and confirm the performance of the double tees after the members had been strengthened in shear. Carbon FRP sheets were used as shear reinforcement at a 0/90° combination on the stem of each double tee. Load tests were performed on twenty double tees at various locations and floor levels of the parking structure. Each complete load test, including assembling and dismantling of the test equipment, was completed in approximately three hours. Results indicate that the shear strengthening systems increased the capacity of the double tee beams to meet the design load requirements.

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.

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 the aftermath of the 1995 Hyogo-Ken Nanbu Earthquake in which many severe failures of bridge piers occurred, numerous studies have been conducted on ways to retrofit existing RC columns and piers. As a result of this research, it has been found that continuous fiber sheet offers a feasible means of retrofitting. Consequently, several design guidelines on the use of FRP sheets for retrofitting highway, railway and subway structures have been proposed in recent years. The JSCE (Japan Society for Civil Engineers) Concrete Committee on FRP Sheet, which was setup in 1998, has been commissioned to establish a new design method for seismic retrofit of bridge columns and piers. It seeks to unify all the existing guidelines on a performance-based design concept. This paper describes mainly the new design method of shear strength and ductility of retrofitted RC structures using FRP sheet. Design equations for shear strength and ductility are also presented.

Prevalently compressed concrete columns can be transversely confined in order to obtain increase in strength and ductility. Generally, two principal methodologies of advanced confinement are used: the “Wrapping” technique which consists of wrapped concrete columns using thin carbon or glass flexible straps epoxy-bonded concrete surface; and concrete filled FRP tubes (CFFT) in which the tube is the pour form, protective jacket, confining mechanism, and shear and flexural reinforcement. The purpose of this paper is to theoretically model the stress-strain behavior of concrete confined by FRP straps or tubes, evidencing the straight dependence of s - e curve on the hoop mechanical properties of the transverse composite reinforcement. The proposed model consists of a generalization of the theory of elasticity, i.e. a step by step application of Navier classical relations which define the stress-strain laws in states of triaxial stress. The theoretical results are compared with experimental compression tests carried out on ten cylindrical concrete specimens confined with two different typologies of fiber composite tubes.