Ultimate Bending Strength of Composite Beams

This paper deals with glass‐fiber‐reinforced plastic (GFRP) beams produced by the pultrusion process. Pultruded composite members are being used extensively as beams for structural applications. Widespread use is motivated primarily due to the light weight and corrosion resistance of composite materials. Low‐cost, mass‐produced pultruded beams are becoming competitive with conventional materials like steel and reinforced concrete. Common structural shapes have open or closed sections of thin composite walls. The ultimate bending strength of pultruded composite beams is limited by various failure mechanisms. Most failure modes are precipitated by local buckling of the thin walls. Analytical models for several local buckling modes are used in this work to model observed behavior in commercially available composite beams. Experimental data for composite beams are presented for comparison. Local buckling initiates a failure mode that eventually results in material degradation and total failure of the beam. Due to the large elongation to failure of the composite material, only postbuckling deformations can subject the material to deformations large enough to produce failure. Experimental results are shown to sustain these arguments. Analytical models for local buckling are developed and correlated with observed behavior.