Short vs. long column behavior of pultruded glass-fiber reinforced polymer composites

Analytical and experimental studies were conducted for the purpose of establishing a distinguishing criterion between short and long FRP composite column behaviors. The results of investigating 24 full-scale GFRP composite columns are presented. The experimental studies utilized specimens with commonly used 'Universal' and 'Box' cross-sections which were manufactured by the pultrusion process using E-glass fibers in various forms as reinforcement and polyester and vinylester as binding matrices. The effective slenderness ratios (L/r) of the investigated columns were 3.79, 32.7, 47.9, 63.1 and 75.4 for the 'Universal' section and 9.38, 53.9 and 78.9 for the 'Box' section. The specimen lengths were 18 inches (0.46 m), 8 foot (2.44 m), 12 foot (3.66 m), 16 foot (4.88 m) and 19.25 foot (5.87 m). All columns were tested in a vertical position and under compressive axial static loading and the fundamental pinned-pinned end-conditions. The columns' compressive strains, buckling and crippling loads, lateral displacements, initial curvatures, and modes of failure were documented during the course of this investigation. Orthotropic mechanical properties of the composites were experimentally obtained utilizing 44 coupons cut from the column specimens. Analytically, Euler's formula was employed to obtain critical loads for the slender columns. For short columns, the classical plate theory was used to predict columns' buckling loads. Based on experimental evaluations and analytical results, a slenderness ratio based criterion was established for distinguishing between short and long composite column behaviors. Further conclusions and design recommendations were made. (C) 2001 Elsevier Science Ltd. Ail rights reserved.