Pultruded FRP structural profiles — including wide‑flange beams, channels, angles, and square tubes — may share familiar shape nomenclature with steel sections, but their orthotropic material properties commonly require a different engineering approach to structural design. Key considerations include directional dependence of stiffness, deflection‑governed span selection, and local buckling resistance characteristics. This guide identifies the engineering factors relevant to pultruded FRP profile design in industrial structural applications.
Material Directionality
Pultruded FRP is an orthotropic material. The longitudinal direction — along the profile length, parallel to the pultrusion direction — commonly exhibits different stiffness characteristics than the transverse direction — across the flange width, perpendicular to the pultrusion direction. The shear modulus may also differ from both longitudinal and transverse values. This directional dependence means that standard beam formulas commonly applied to isotropic materials can be adapted for FRP by using material properties appropriate to the relevant direction for each design check. Shear deformation may be a more significant consideration in FRP beams than in steel beams of similar proportions, particularly for configurations with lower span‑to‑depth ratios.
Deflection and Span Considerations
In FRP beam design, the section depth for a given span is commonly evaluated against deflection criteria. The allowable bending stress and the deflection limit can be compared to determine which governs the section selection. At loading levels typical of industrial walkway and platform applications, deflection limits may control the section depth before bending strength limits are reached. The span capability of an FRP beam for a given depth and loading can be determined according to the specific section properties and material stiffness values of the selected profile. Structural weight differences between FRP and steel sections may be a relevant factor when evaluating overall structural layout and support spacing.
Section Properties and Standard Shapes
Pultruded structural shapes are commonly available in standard dimensional series. Section properties — including moment of inertia, section modulus, and radius of gyration — are typically published by profile manufacturers and can be compared across different section depths and configurations. Wall thicknesses in FRP shapes may differ from those in steel sections of similar nominal depth, which can influence section properties and local buckling resistance. Width‑to‑thickness ratios for FRP flanges and webs are commonly evaluated against applicable buckling criteria. Lateral‑torsional buckling may be a relevant limit state for long, unbraced FRP beams, and can be assessed according to the applicable structural design methodology with FRP‑specific material parameters.
For section property tables and manufacturer‑published data for standard pultruded profiles, refer to the individual product pages under FRP Structural Profiles.