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.

This paper clarifies, experimentally, the degradation of aramid fiber, glass fiber and carbon fiber, used as reinforcement for concrete, in various solutions (alkaline solution, hydrochloric acid aqueous solution and pure water) at different temperatures. A calculation model is proposed to estimate the progress of the degradation by the solution. The accelerated degradation test, immersing fibers in several solutions, was carried out at the temperatures of 20, 40 and 60 degrees Celsius and the strength of the fiber after the immersion test was examined. Observation of the fibers was carried out by scanning electron microscope (SEM) in order to clarify the degradation of the fibers. As a result of this study, the strength changes of Kevlar 49 and Technora were quantitatively estimated using the weakest link theory of Weibull.

In Japan, continuous fiber bars are not allowed to replace reinforcing steel and prestressing steel for load-bearing members, mainly because: 1) Fibers and binders forming continuous fiber bars are made of combustible materials, for which the permissible temperature in case of fire is unknown. Also, these reinforcements are difficult to evaluate by the fire test methods currently practiced in Japan. 2) Safety factors according to members and durability, which are necessary for determining the design strength of continuous fiber bars, are not known, and no performance evaluation methods have been established. The Architectural Institute of Japan (AIJ), Japan Society of Civil Engineers (JSCE) and other institutions proposed about ten test methods for evaluating continuous fiber bars. However, the deteriorating external forces are not known yet in regard to durability, and few reports have been made regarding fire resistance. This paper reports on the commercial use of continuous fiber bars for load-bearing members related to performance evaluation methods and standards on the basis of the proposed standard test methods and state-of-the-art technology on their durability and fire resistance.

The external bonding of FRP to concrete beam is an effective method in order to increase the structural capacity of such beams. The test under fatigue loading of RC beam reinforced with FRP shows that the strengthening of beam with carbon epoxy composite increases fatigue durability [1]. To design composite reinforcement for a RC beam under fatigue solicitation, one has to determine the mechanical behavior of each material and above all, of the concrete composite interface. We have carried out a set of tests with fatigue solicitation on the concrete/composite interface and a set of tests on composite plate. Those tests set up the fatigue life for several levels of shear stress in the interface and in the composite plate and so allow to assess the maximum fatigue stress curve. The second part of the work is based on the information obtained from the first one to design the reinforcement. The design of the composite reinforcement is determined by a software developed by P. Hamelin and H. Nasseri [2,3] using a non-linear calculation method. The design method of those reinforcements is based on classical methods used for RC structures, taking into account the slip phenomena at the interface and considering the mechanical behavior of each material. Suitable range of stress for concrete, steel, composite and interface are determined to predict the fatigue life of the reinforced concrete beams. So, the load range for the test on the beam is set up. Safety factor are determined for the structure loading.

Much research has been conducted on the short-term behavior of concrete members prestressed with FRP tendons, but relatively little is known about the long-term behavior of these members. This lack of knowledge is one important factor hindering the widespread use of FRP for prestressing. Therefore, a comprehensive study on the long-term response of FRP prestressed concrete members is necessary before FRP can gain acceptance as a viable construction material. This paper describes a part of an on-going test program to investigate the long-term behavior of CFRP prestressed concrete beams. The scope of the program includes eight large-scale T-beams constructed with different levels of prestress. The study considers fully prestressed and partially prestressed sections. For the long-term tests, the specimens are subjected to a sustained loading, higher than the cracking load of the partially prestressed members, maintained constant for several months (about 10,000 hours). The results of the long-term test show similar behavior between beams prestressed with CFRP tendons and that prestressed with steel strands. The ratio of long-term to instantaneous deflection was higher for beams prestressed with CFRP tendons than for the beam prestressed with steel strands. The overall deflection of the CFRP tendons was however smaller than that of the steel prestressed beams.