Precast Solutions - September/October 2008 - (Page 11) practice, a relatively new reinforcing material technology, like CFRP, faces conservative caution from civil engineers who view CFRP applications as unproven systems. That caution toward CFRP use in highway infrastructure is changing as monitoring data on successful CFRP performance for in-service structures continues to grow. Worldwide research using innovative construction materials such as CFRP requires detailed documentation and continuous monitoring of implemented innovative structures over a long period of time. Only data showing long-term predictable behavior for this new technology can foster confidence for the specifier, producer and owner to bring the use of these materials into mainstream applications in transportation construction. Growing in-service performance data on CFRP and continued advances in research will form the foundation for design standards for innovative materials like CFRP. Currently, ACI Committee 440 has produced the “Guide for the Design and Construction of Concrete Reinforced with FRP Bars.” (Top left) With the cradle design, cable stay strands serve as tensile elements that are individually threaded from the bridge deck through a high-density polyethylene sheath. (Bottom left) A view of a CFCC anchor sleeve with nut and strand. (Top right) Research continues at Lawrence Tech’s new Center for Innovative Materials Research. Photo shows the recently installed fire/loading chamber that can test structural components up to 2,300 F, approximating the conditions that precipitated the collapse of the World Trade Center on Sept. 11, 2001. THREE BRIEF CFRP CASE STUDIES Bridge Street Bridge The first CFRP prestressed concrete bridge constructed in the United States in 2001 was the Bridge Street Bridge Structure B in Southfield, Mich., funded by the Federal Highway Administration (FHWA), Michigan Department of Transportation (MDOT), the City of Southfield and the National Science Foundation (NSF). Long-term automated monitoring of unbonded longitudinal external CFRP post-tensioning strands and TYPICAL TENSILE PROPERTIES OF VARIOUS REINFORCING BARS* (Table from ACI Guide for the Design and Construction of Structural Concrete Reinforced with FRP Bars, ACI Committee 440.1 R-06. Steel Nominal yield stress, ksi (MPa) Tensile strength, ksi (MPa) Elastic modulus, ×103 ksi (GPa) Yield strain, % 40 to 75 (276 to 517) 70 to 100 (483 to 690) 29.0 (200.0) 0.14 to 0.25 Glass Fiber Reinforced Polymer (GFRP) N/A 70 to 230 (483 to 1600) 5.1 to 7.4 (35.0 to 51.0) N/A Carbon Fiber Reinforced Polymer (CFRP) N/A 87 to 535 (600 to 3690) 15.9 to 84.0 (120.0 to 580.0) N/A Aramid Fiber Reinforced Polymer (AFRP) N/A 250 to 368 (1720 to 2540) 6.0 to 18.2 (41.0 to 125.0) N/A Rupture strain, % 6.0 to 12.0 1.2 to 3.1 0.5 to 1.7 1.9 to 4.4 *Typical values for fiber volume fractions ranging from 0.5 to 0.7. SEPTEMBER/OCTOBER 2008 | PRECAST SOLUTIONS 11
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