The pultruded beam will be designed for deflection, strength and buckling.


Fiberglass Pultruded Beams exhibit both flexural and shear deflections. Shear deflections are most apparent when the span to depth ratios are less than 20. At short spans, the shear deflections comprise a significant portion of the actual deflections; therefore, the designer should always account for shear deflections when designing with composites.

Fiberglass support beams

Although coupon testing is a good quality control method, composite materials are not homogeneous and will exhibit different properties in the web and flange areas. Deflection predictions should be made with values based on full section testing.

fiberglass pultruded beam

The following formula was used to predict the deflections in The Allowable Uniform Load Tables for simply-supported beams subjected to a uniform load:

Δ = 5wL4/384 ExTm I + w L2/ 8A′GTm  Where A′ = kAw (in2)

The following formula is used to calculate the deflection of a simply-supported beam with a concentrated load P applied at mid-span of span L:

Δ = PL3 /48 ExTm I + PL/4A′GTm   Where A′ = kAw (in2)

Refer to the back of the section for other loading conditions, or use standard accepted engineering practices for calculating deflections of beams subjected to other loadings.

Aw = Shear area (in2) (Ref. Table 2)
k = Shear coefficients (Ref. Table 2)
Ex = Full-section modulus of elasticity, LW (psi)
G = Gxy = Modulus of rigidity (Shear Modulus) (psi)
I = Moment of inertia (in4)
L = Length of span (in)
Δ = Deflection (in)
w = Uniform load on the beam (lbs./in)
P = Concentrated point load applied at mid-span of the beam (lbs)
Tm = Temperature Modulus Reduction Factor

Basic Flexural Stress Formula
Acting Longitudinal Flexural Stress fbx = M/Sx
Acting Minor Axis Flexural Stress fby = M/Sy

On 06, 6, 2013, posted in: FRP Profile News by

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