CHAPTER 3

REINFORCING ELEMENTS FOR CONCRETE STRUCTURES

This chapter addresses the use of composite (carbon fiber and aramid fiber reinforced) elements as replacements for conventional steel reinforcements in concrete structures. The description includes the use of cables, bars and tendons, as well as the use of linear reinforcements as ground anchors. Emphasis is placed on the use of composite elements as cables and tendons for prestressing or post-tensioning rather than as replacements for conventional rebar.

INTRODUCTION

Over the last decade, considerable attention has been devoted to the development of composites as alternative reinforcement for concrete in place of conventional steel rebar and tendons. A significant amount of this effort stems from the Japanese composites community, especially in the development of carbon fiber and aramid fiber-based reinforcing elements ranging from round and deformed (spirally wound) bars to ribbon-like elements and even grids. Over 10 firms in Japan manufacture and supply various types of reinforcing elements (Table 1.1, p. 3). More striking, a large number of projects—demonstration or otherwise—have been completed over the last 10 years and are still functional.

In addition to the projects, there have been concerted efforts, both by the materials and composite manufacturing companies and by the Japanese Ministry of Construction (through the Building Research Institute, and the Public Works Research Institute) to develop comprehensive design guidelines and standards for using these materials. The PWRI instituted a series of national collaborative projects involving multiple vendors to develop the necessary technology for the use of these elements. Between 1989 to 1992, these projects included extensive materials characterization and development of draft guidelines. The Japan Railways Corp. has made similar, and sometimes independent, efforts. Applications for these composite elements range from their use in floating marine structures (Fig. 3.1), pontoon bridges (Fig. 3.2), non-magnetic structures such as tracks for linear motors (Fig. 3.3), girders for conventional pre-stressed and post-tensioned bridges (Fig. 3.4), decks of stress-ribbon bridges (Fig. 3.5) and ground anchors (Fig. 3.6). Novel applications such as the use of composites in shield-cuttable shaft walls combine structural factors with increases in construction speed and efficiency. The following sections provide a brief overview of these and other activities.


Fig. 3.1. Use of Leadline elements for the tensioning of diagonals of a floating marine structure.


Fig. 3.2. Use of FiBRA elements as tendons in the pontoon bridge at Takahiko Three Country Club.


Fig. 3.3. Use of CFCC and Technora elements for pretensioning of girders at the Yamanashi Linear Car Test Track.


Fig. 3.4. Use of Technora tendons for prestresssing and post-tensioning of girders of bridges at the Sumitomo Oyama Works.


Fig. 3.5. Use of Leadline, CFCC and Arapree elements in a stress ribbon bridge at the Southern Yard Country Club (Birdie Bridge).


Fig. 3.6. Use of Technora elements as ground anchors along the Meishin Expressway.


Published: October 1998; WTEC Hyper-Librarian