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.

The use of FRP for reinforcing is not as popular as its use for prestressing because the modulus of elasticity to strength ratio of most FRP bars is relatively small compared to steel, and the unit price is significantly higher than steel. Therefore, to control deflection and crack width under service conditions, FRP reinforced sections often need to be greatly over-reinforced, which increases the overall cost of the structure. This paper offers an innovative solution to the latter problem by suggesting the use of tension elements as reinforcement. The CFRP tension elements developed in the present investigation are concentrically pretensioned prisms of small cross-section. Such elements would reduce the need for high reinforcement ratio while simultaneously endowing the member with greater flexural rigidity. This paper will briefly explain the concept of FRP prestressed tension elements used for reinforcement of concrete beams, followed by the description of an experimental investigation related to the development of CFRP tension elements and their use as flexural reinforcement in concrete beams. The effectiveness of the tension elements in controlling crack width and deflections under service loads is demonstrated.

The development of Arapree, about fifteen years ago in the Netherlands, can be considered as one of the initiatives, which started the use of FRP reinforcement for concrete structures. Today, although no longer produced in the Netherlands, Arapree is still commercially available. Hence, over the years a considerable amount of information on the use of this type of AFRP has become available, including test data and practical experience. Several approaches have been developed regarding the design philosophy. Based on the information available to the authors, and their own experience concerning the use of Arapree, a design philosophy for concrete elements prestressed with Arapree is given in this paper.

Investigation of the long-term characteristics of the Highly Expansive Material (HEM) anchorage for CFRP strands is very important. In the post-tensioning type of prestressed concrete structures, considerations should be made for the loss of prestressing force due to the pull-out displacement which is caused by the creep of the HEM. The long-term characteristics of the HEM anchorage were investigated by creep test on five specimens. From the creep test, some important characteristics of HEM anchorage were observed, for example, time-dependent change of pull-out displacement at the loaded end, unit shear “q” distributions and the tensile force distributions “Tp”. An analytical relationship on how the long-term behavior of prestressing force can be predicted by using the measured values for the time-dependent change of pull-out displacement at the loaded end is presented. Also from the simulated results of this relationship, it was found that the loss of prestressing force is negligible in practice when the CFRP strand is 10 meters long. Normally the expansive pressure of HEM at prestressing is 50MPa. However, when the expansive pressure is 100MPa, the pull-out displacement at the loaded end and the loss of prestressing force can be reduced to more than the half of one with 50MPa.

In this paper, an experimental study on the frictional coefficient of fiber reinforced polymer (FRP) tendons is made and reported. Tests on FRP tendons fixed in cement mortar and confined with highly expansive material (HEM), and placed all together inside a steel sleeve pull-out test were conducted. Tests were carried out at various levels of confining pressure. The initial bond and the friction coefficient are presented for the FRP tendon with the surrounding HEM. A newly developed pressure transducer was placed in the same manner as the FRP tendon to monitor the confining pressure due to the HEM. The previous results are compared with the present one on Carbon FRP are reported using this monitoring system. The Vinyl on FRP is tested for the first time and the large size Carbon FRP are also introduced as they are prime candidates for use in practice.