International Concrete Abstracts Portal

This CD-ROM consists of 11 papers which were presented in two special sessions sponsored by ACI Committee 440 at the ACI Spring Convention in Los Angeles, California, on March 31, 2008. The technical papers presented at the sessions and published in this volume cover both open and closed FRP forms, including bridge decks, concrete-filled tubes, and girders, and address important relevant aspects such as surface preparation, bond aspects, fatigue, constructability, confinement, and field applications.

Hybrid FRP concrete steel double-skin tubular columns (DSTCs) are a new form of hybrid columns recently proposed by the second author. The column consists of an outer tube made of fiber-reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. In this new form of hybrid columns, the three constituent materials are optimally combined to achieve several advantages not available with existing columns. This paper provides a summary of existing research on this new form of structural members, clarifying its structural behavior under axial compression, bending, and combined axial compression and bending. Test results of hybrid DSTCs are presented that demonstrate that they are very ductile under different loading conditions. A finite element (FE) model for its axial compressive behavior is also presented, which was employed in a parametric study leading to a simple stress-strain model for the confined concrete in hybrid DSTCs described in the paper. In addition, a conventional section analysis based on the plane section assumption and the fiber element approach is presented for predicting the behavior of hybrid DSTCs subjected to bending and eccentric compression. A variable confinement model that accounts for the effect of load eccentricity is adopted in this section analysis for the confined concrete, and is recommended for design use.

One of the applications of fiber-reinforced polymers (FRP) in building and bridge construction is stay-in-place formwork. FRP stay-in-place formwork, in the form of preformed tubes, provides easy form assembly protection of steel reinforcement and concrete against corrosion and chemical attacks while also improving the strength and ductility of structural elements in earthquakeresistant construction. Seismic performance of FRP tubes in building and bridge columns has been investigated through tests of large-scale specimens under simulated seismic loading. The experimental program consisted of tests of circular and square columns confined with carbon FRP (CFRP) tubes. The results indicate that the use of CFRP tubes increases column inelastic deformability significantly. Bridge columns under low levels of axial compression exhibit inelastic drift capacities in excess of 4% before failing in flexural tension due to the rupturing of longitudinal reinforcement. Building columns under higher levels of axial compression show drift capacities in excess of 8% when the behavior is governed by confined concrete. These observations and experimental results were used to develop a displacement-based design procedure for concrete confinement for FRP-encased concrete columns. The paper presents an overview of the experimental program and the design approach developed.

The cost-effective FRP-concrete composite structures represent the future of composites for corrosion-resistant and maintenance-free construction. The success of such structures is dependent on the bond between FRP and concrete to ensure a composite action. This paper is to present a study on the wet-bond technology to achieve the adhesive bond between prefabricated stay-inplace FRP form and cast-in-place concrete. Three wet bond agents were investigated, one employing conventional epoxy resins, one underwater resin, and one bonded aggregates, respectively. Three composite U-shape profiles of 2 m (6.6 ft) long were prefabricated, then coated with bonding agent, one type for each, and used as stay-in-place formwork for cast-in-place concrete beams. The FRP composite profiles also served as external reinforcements that incorporated high-modulus carbon sheets and high-ductility E-glass sheets to achieve required stiffness and ductility. With minimum internal steel reinforcement (r = 0.2%) to control the crack width, the composite beams had exhibited a comparable flexural stiffness and an enhanced resistance to first crack, post-cracking yielding and ultimate failure in comparison to RC beams of r = 1.5%.

The evolution of a new application for the use of fiber-reinforced polymer (FRP) formwork is described from its inception, through research and to actual implementation in a construction project. FRP formwork is becoming an attractive alternative to traditional wood forms in concrete floor construction and particularly for highway bridge decks. The recent development of new wide flange or bulb tee precast concrete bridge girders has resulted in short spans between girder flanges that need to be filled by formwork before the deck can be cast. FRP planks are an ideal solution for spanning this short gap and may be left as stay-in-place (SIP) forms. A commercial pultruded FRP floor plank was adopted for use as SIP forming for bridge decks. Rather than being used as intended, however, the plank is turned upside down before the concrete is placed and becomes bonded to the concrete. The testing of this SIP formwork system to prove its capacity in resisting static and impact loads during construction, its contribution to crack control in concrete under flexural loading, and its bond characteristics with a concrete deck are described. The results of the bond tests are used to create a "bond element" that could be used to predict the flexural behavior of concrete members with the FRP SIP formwork. A case study of construction of a highway bridge deck on U.S. Highway 12 with the new forming system is detailed after the FRP form capacities were proven through load testing. The advantages of using FRP planks for bridge deck construction are discussed and compared with traditional construction using wood forming that is subsequently removed.