SP-188 This volume presents 24 papers from the Fourth International Symposium and represents a significant expansion in the state of knowledge that has occurred since the First Symposium in 1993.

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.

It was determined that additional flexural strength, ductility and crack-control, and shear strength were needed in the Myriad convention center unbonded post-tensioned street-level floor system. Fiber reinforced polymer (FRP) reinforcement was designed to correct the insufficiencies. The challenge in the project, aside from the mechanics unique to FRP reinforcement, was to present the design in such a way as to allow and encourage as many bidders as possible to bid on the construction. In particular, since there are no standardized properties for any given type of FRP, the possibility that not all bids would involve the same properties had to be accommodated—especially in the flexural design. Generally, for each strengthening location, two flexural designs were completed: one giving required FRP force level at minimum ultimate FRP strain and one required FRP force level on concrete crushing at the limit state of failure, the latter associated FRP ultimate strain termed “High-Threshold” ultimate strain. Required force level for any ultimate strain could then be obtained by linear interpolation. Ability to use FRP for shear reinforcement was limited due to low available beam stem development length. Both glass, with restrictions, and carbon FRP were allowed for shear reinforcement.

For the purpose of investigating the bond splitting behavior of continuous fiber reinforced concrete (CFRC) members, two series of investigations were conducted. The first series was performed in order to obtain the local bond behavior in the case of splitting failure of the concrete cover for members with or without lateral reinforcements. For specimens without lateral reinforcement, test results show that the bond splitting strength is not influenced by the Young's modulus of the reinforcement and that it is approximately proportional to the thickness of the cover concrete. On the other hand, for specimens with lateral reinforcement, the local bond splitting strength is greater than the case where there is no lateral reinforcement. The strength is also independent of the mechanical property of the lateral reinforcement and is determined solely by the thickness of concrete cover. For both types, a new relationship between the bond stress (t) and the slip of reinforcements (s) is proposed. The second series was an analytical study to investigate the average bond behavior of CFRC members, which had several bond lengths and Young's moduli. Analytical results show that in the case of large bond lengths, the analytical bond splitting strength is inversely proportional to the bond length, and is clearly influenced by the Young's modulus of the reinforcement. It is considered that continuous bond failure from the loaded end causes a remarkable decrease in the bond strength especially for large bond lengths and low Young's moduli.

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.