Performace of Muiti-bar GFRP Tiebacks-Paper

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The paper evaluates ASTM D8505-compliant multi-bar GFRP tiebacks for temporary and long-term anchoring, focusing on creep, creep rupture, bond performance, and field application. Compared with steel, GFRP is lighter, corrosion-resistant, easier to handle and cut, and may reduce environmental impacts. Its lower elastic modulus and brittle failure behavior require careful design, particularly because sustained loading can cause creep rupture.<br /><br />Laboratory tests on #3 GFRP bars found limited creep strain at 45% of ultimate tensile strength (UTS) over 1,780 hours, with little additional deformation after 1,000 hours. In creep-rupture testing, specimens loaded at 80% UTS or above failed within hours, while some at 70–75% lasted thousands of hours; specimens at 65% remained unbroken after up to 8,000 hours. Extrapolation estimated a creep-rupture strength of about 62% UTS at one million hours, though this projection is based on the tested product and methods.<br /><br />The Kipling Station Condos project in Toronto used multi-bar GFRP tiebacks for excavation support near electrical transmission infrastructure and a retaining wall expected to be redeveloped. Four #8 bars were specified per anchor, with conservative stress limits based on existing design standards. Field tests reached up to 52% UTS without bar failure. Wall movements of 7–12 mm were consistent with the predicted 11 mm, and the system performed as expected during excavation.<br /><br />The authors conclude that multi-bar GFRP tiebacks offer a promising alternative to steel for temporary and potentially permanent applications. They recommend continued product-specific testing and development of design guidance that accounts for creep and service life.

Keywords

GFRP tiebacks

ASTM D8505

creep rupture

bond performance

temporary anchoring

long-term anchoring

multi-bar GFRP bars

excavation support

Kipling Station Condos

corrosion-resistant alternative