Fire behavior and design of steel columns reinforced by prestressed CFRP strips

This study analyzes the behavior of steel columns reinforced by prestressed (PS) carbon fiber reinforced polymer (CFRP) strips exposed to fire. First, tests are performed to study the CFRP material degradation under high temperatures. The elastic modulus and strength of the CFRP decrease with increasing temperature. Second, a thermal–mechanical coupling analysis is conducted with finite element method (FEM) to study the behavior of composite members exposed to fire. Under compressive preloading, the columns are exposed to the ISO 834 standard fire curve. The fire exposure time of columns with different initial CFRP prestressing forces is obtained. All the specimens fail because of global buckling either due to the slacking of the concave side of the CFRP or the plastic deformation of the steel. Subsequently, parametric studies are performed considering different initial CFRP prestressing forces, preloadings and column slenderness values. Finally, a design method is proposed for steel columns with PS CFRP that are exposed to fire, followed by a design example. Columns with protections can achieve high buckling capacities at room temperature and long fire exposure time.