Glass fiber reinforced polymer bars as top mat reinforcement for bridge decks
DeFreese, James Michael
Roberts-Wollmann, Carin L.
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The objectives of this research were to characterize the material and bond properties of three commercially available GFRP (glass fiber reinforced polymer) reinforcing bars, and evaluate the effects of the material properties and the current ACI design recommendations (ACI 2001) on the design of a bridge deck with GFRP as top mat reinforcement. The tensile properties evaluated were ultimate tensile strength, tensile modulus of elasticity and ultimate rupture strain. Ultimate bond stress and load-slip behavior of the three types of bars were evaluated using beam-end bond stress tests. For the tensile tests, for each type of GFRP bar, three bar sizes were tested: No. 4, No. 5, and No. 6. For each bar size and manufacturer, five samples were tested. The average ultimate tensile strengths varied from 80.4 ksi to 119 ksi, with coefficients of variation for the five-bar samples ranging from 2.6% to 8.0%. The average moduli of elasticity for the three manufacturers were very similar, with a high of 6340 ksi and a low of 5800 ksi. All bars showed linear elastic behavior to rupture. The bar rupture strains varied from 1.4% to 1.9%. The bars also had similar average maximum bond stresses, with a high of 2600 psi and a low of 2360 psi. The load-slip behaviors exhibited by the three bar types were each unique. Pre-peak behavior was similar, but post-peak behavior varied depending on the surface treatment of the bar. The design material properties for each bar type were determined using the recommendations of ACI Committee 440 (ACI 2001). These properties are presented in Table 14. of the report. The property with the greatest influence on the selection of bar size and spacing for a bridge deck reinforced with GFRP reinforcement is the modulus of elasticity. The reinforcing bar with the highest modulus of elasticity will result in the most economical design in terms of materials required. Realistically, however, a bridge deck design that is based on the lowest value of each measured material property will not greatly increase the quantity of GFRP reinforcing, and will enable any of the manufactures' products to be used successfully in a given project.