Flexural creep tests and modeling of concrete-filled fiber reinforced polymer tubes

An experimental and analytical investigation was made into the flexural creep behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFT). While creep effects reduce the flexural stiffness of CFFT specimens, ultimate strength is not significantly altered. The slow rate of loading and short-term creep at 70% of static capacity may cause premature rupture of the tube. Fiber analysis of CFFT beam-columns by discretizing the section into filled and hollow FRP tubes can adequately simulate the flexural creep behavior. Isochronous sustained stress-creep strain curves are used as a constitutive nonlinear relationship for creep analysis in flexure. Creep deflection of CFFT beam-columns is much less than that of CFFT beams, mainly because axial compressive loads tend to retard the cracking of concrete and tensile creep of FRP The stiffness ratio of FRP tubes with respect to the concrete core has a pronounced effect on the creep deflection of CFFT beam-columns. As the stiffness ratio increases, creep deflection decreases. However, there exists a threshold beyond which stiffer tubes do not provide additional benefit. CFFT beam-columns under high levels of sustained axial loads have a lower creep rupture life expectancy, mainly because failure moments under large axial forces are lower. The creep rupture life expectancy of CFFT beam-columns with diameter-to-thickness ratios of 40 or less is at least 50 years at transverse loads as high as 60% of the static capacity.