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ACI SP-230 VOL 1

2005 Edition, October 2005

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Superseded By: ACI SP-230

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Over the past decade, there has been a significant increase in the application of fiber reinforced polymers (FRPs) for strengthening and rehabilitation of aging and deteriorated infrastructure. However, the use of these innovative materials in new construction has not reached its full potential, mainly because of their high cost in comparison with other conventional construction materials such as concrete and steel. The advantages of FRPs, such as the high strength, light weight, easy handling, enhanced durability and low maintenance, can be more realized when FRPs are used as load-carrying structural elements. Reduction of construction costs can be achieved when the design offers reduced amounts of materials, simplified fabrication and construction procedures, lighter weight and shorter construction time. The use of FRP in new structures, particularly bridges, can be limited if all the structural components are made of FRP, mainly due to its relatively small rigidity. This limitation can be eliminated when the structural system combines FRPs with other conventional materials in a hybrid form.

A few researchers around the world have attempted to develop new bridge systems that employ FW structural components as load-carrying elements. In Japan, for example, a new composite concrete-FRP prestressed box-girder bridge system has been proposed (Gossla and Yoshioka 2000; Niitani et al. 2001). In this system, the heavy concrete web of conventional box girders is replaced with pultruded glass FRP panels. In the United States, two modular bridge systems have been developed: one is made of FRP box sections supporting conventional concrete slab cast on stay-in-place FRP deck panels (Seible et al. 1998; Cheng et al. 2005), and one consists of carbon fiber shells filled with concrete and used as primary flexural members connected in the span direction along their length to a conventional reinforced concrete slab by means of steel or special FRP dowel connectors (Zhao et al. 2001a). This latter system was used in construction of the 20 m long Kings Stormwater Channel Bridge on California State Route 86 (Zhao et al. 2001b).

The concrete-filled FRP tube system utilizes the best characteristics of both the FRP and the concrete. Under compression, the tube provides confinement to the concrete core and, hence, increases its compressive load carrying capacity. The concrete on the other hand provides local stability to the thin-walled tube and, hence, prevents premature local buckling (Fam 2000). Under tension, when properly bonded to concrete, the FRP provides corrosionresistant tensile reinforcement. Use of concrete-filled tubes primarily as flexural members is, however, less efficient than their use as axially-loaded tension or compression members. Fam (2000) has shown that for concrete-filled FRP tubes used as flexural members, the shear strength provided by the tube is small, unless filament-wound tubes with fibers mainly oriented in the circumferential direction are used. Also, the confining effect of the tube on concrete in the compression zone of flexural members is insignificant as compared to that of similar members under pure axial compression. The FRP tubes, however, serve as stay-inplace formwork for the concrete, protect it from the environment, and enhance its durability.

This paper is concerned with the development of a system for short- and medium-span bridges. In the proposed system, the superstructure is built entirely from materials that are not vulnerable to corrosion. The system consists of precast prestressed concrete truss girders and cast-in-situ concrete slab (Fig. 1). Each girder has top and bottom concrete bulbs (flanges) connected by precast vertical and diagonal truss members. In addition to concrete, the materials used are FRP and stainless or any other type of corrosion-resistant steel, which are utilized as described in the following section. In addition to being immune to corrosion, the new system is light in weight and durable. The light weight reduces the load on the supports and allows for longer spans, resulting in reduction in the size of the substructure and in the number of supporting piers in multi-span bridges and, hence, reduction in the initial cost. The improved durability reduces the maintenance cost and extends the life span of the structure.