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.

Octaform(TM) system is a stay-in-place concrete forming system that consists of interconnected PVC polymer-based elements. These elements are assembled on the construction site to form a hollow wall shell structure, which is then filled with concrete to complete the wall. This paper reports on the flexural behavior of these specimens. Eight of the tested specimens were fabricated using the Octaform system and the remaining four acted as control specimens (without forming system). All specimens were 305 mm (12 in.) wide and 2.5 m (8.25 ft) long. The specimens were reinforced with two 10M bars. The variables studied were the depth of the specimen (150 mm [6 in.]) or 200 mm [7.87 in.]) and the connector configuration. Two types of connectors were used: flat in the middle or inclined (45o) at the corner. The specimens were monotonically tested in horizontal position (to simulate flexural behavior) in four -point bending. Test results showed that the Octaform system increased the cracking load, yield load. And ultimate load by 36%, 78% and 36% on average, respectively, compared to the control specimens. Also, the ductility index for specimens encased with Octaform increased by 25%. The type of the connectors had no effect on the general behavior of the Octaform-encased specimens. A simple limit state model was proposed to predict the flexural capacity of the Octaform-encased specimens. In general, the predicted values compared well with the experimental values.

This paper presents an analytical procedure for modeling concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) subjected to reversed cyclic bending, including a method for predicting their fatigue life. The model employs procedures to account for creep and stiffness degradation of FRP and concrete. The predicted behavior compared reasonably well with experimental results of three large-scale CFFT specimens tested under reversed high-cycle fatigue. It was shown that excessive slip between the concrete core and FRP tube reduces fatigue life and, hence, the accuracy of prediction was better at lower moments as slip was less. A parametric study conducted showed that time-dependant properties of concrete and FRP affect the long-term deflection of CFFTs subjected to reversed cyclic bending. Increasing the loading frequency, for the same number of cycles, decreases the deterioration in the response in terms of excessive deflection. Finally, CFFT members with a larger diameter-to-thickness (D/t) ratio (that is, smaller FRP reinforcement ratio) suffer a slightly larger deterioration in their cyclic response than CFFTs with smaller D/t ratio.

In recent years, the application of concrete-fi lled fi ber-reinforced polymer (FRP) composites tubes (CFFT) for different structural applications (piles, column, girder, bridge piers) has begun. The FRP tubes benefi ts are in confi nement, protective jackets, providing shear and/or flexural reinforcement and permanent formwork. Most of the experimental investigations conducted to study the behavior of the CFFT columns under compression load were without internal longitudinal reinforcement. This paper presents the experimental results of small- and medium-height CFFT columns with internal steel bars. The parameters used in this investigation include the effect of laminate thickness of FRP tubes, concrete strength, slenderness ratio (height-to-diameter ratio) and presence of longitudinal steel bars. Sixteen CFFT specimens and one steel spiral reinforced concrete column were tested under axial compression load. The diameter of the tubes used was 152 mm (6 in.), and the fi ber orientations were mainly in the hoop direction. The results indicate signifi cant decrease of the ultimate load capacity by increasing the slenderness ratio, which also yields to different failure modes. The internal longitudinal reinforcements improve the ductility of the CFFT columns, as well as the load-carrying capacity. The ultimate strength of the reinforced CFFT columns is mainly dependent on the stiffness of the GFRP tubes. The benefi t of CFFT technique is more effective for normal-than that medium-strength concrete.

The State of Wisconsin recently constructed a highway bridge as part of the FHWA Innovative Bridge Research and Deployment Program. The superstructure is composed of precast concrete I-girders acting compositely with the concrete bridge deck that uses a fiber-reinforced polymer stay-in-place (FRP-SIP) formwork system that serves as positive flexural reinforcement. In-place load test strain data are used to compute wheel load distribution widths and estimates for bending moments acting on unit widths of bridge deck. These widths are compared with those computed using the AASHTO-LRFD and AASHTO Standard specifications. The in-place field data indicate that bending moments within the deck system are reasonably close to predictions made using the Standard and LRFD specification bridge deck approximate analysis procedures. The Standard specification estimates for bending moment per unit width of bridge deck were found to be conservative for interior and exterior deck spans. The LRFD specification estimates for strip width resisting wheel loads are also conservative for interior and exterior deck spans when compared to field-measurement-based predictions.