Closed-form equations for compressive local buckling of pultruded thin-walled sections

• Closed-form equations for local buckling of typical pultruded GFRP sections are proposed.
• Approximate deflected-shape functions addressing end conditions and continuity between plate elements are assumed.
• The Rayleigh energy method is used to obtain equations.
• Results are compared with those obtained using the finite strip method.
• Comparison is made with equations proposed by current available standards and guidelines.

Closed-form equations to determine the local buckling critical stress of typical pultruded fiber reinforced polymer (FRP) sections – angles, I-shaped, channels and rectangular tubes – comprised of orthotropic thin walls subject to concentric compression are developed. Approximate deflected-shape functions addressing boundary conditions and compatibility of rotation between plate elements are chosen for each section having uniform thickness and material properties. The Rayleigh energy method is used to obtain equations for the local buckling critical stress. Results are compared with numerical analyses using the finite strip method (FSM) for isotropic and orthotropic sections with typical ranges of properties. Comparison is also made with the method recommended by current available standards and guidelines.