Pultruded glass fiber reinforced polymer (pGFRP) composite profiles, having the advantages of high strength-to-weight ratio and light weight, have seen significant developmental progress and numerous practical applications in the field of civil engineering. However, the low modulus of elasticity and high anisotropy, in addition to the relative slenderness of the thin-walled profiles, result in complex local and global buckling behavior for pGFRP members and significant interaction between local and global buckling modes. In this work, the stability behavior of pGFRP I-sections subject to flexure was addressed. An extensive review of stability behaviors of pGFRP members, including: flange local buckling (FLB), global lateral torsional buckling (LTB) and interaction between local and global buckling (interactive buckling) behaviors, was carried out. Two experimental programs were conducted: 62 four-point bending tests to investigate FLB behavior and 86 three-point bending tests to investigate LTB behavior. Interactive buckling behavior was observed in both series of tests and was shown to be quite prevalent in results from the LTB tests. Experimental results were compared with existing design guides and analytical solutions. Uniform under-predictions were found for FLB behavior of the I-sections considered and over-predictions were generally found for LTB behavior, exhibiting the need of new design formulas with improved accuracy. Analytical studies were presented and non-empirical design formulas derived using energy methods were proposed with respect to the buckling behaviors observed in the experimental program. Supporting the experimental work, a series of material characterization tests were carried out to evaluate the mechanical properties of the pGFRP materials used. Both standard and nonstandard test methods that can be readily conducted using typically available test equipment as well as those requiring simple material preparations are recommended.
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