This thesis investigates strengthening slender steel columns with carbon fibre reinforced polymer (CFRP) plates of various moduli. Three different types of CFRP were used in the study: Ultra-high modulus (430GPa), High modulus (212GPa) and Normal modulus (168GPa). In this study, specimens were grouped according to measured initial out-of-straightness values. The first section examines the effect of adding CFRP plates to the column flanges when buckling about the weak axis. Twelve columns, with a slenderness ratio of 197, were tested, of which nine were strengthened with CFRP. The main parameters tested were the level of initial out-of-straightness (length (L)/8387 to L/1020), CFRP modulus (168 to 430 GPa), CFRP reinforcement ratio (13% to 34%) and the length of CFRP plate (33% to 95% of L). The gain in axial strength due to CFRP retrofitting ranged from 11% to 29%, depending on the various parameters. The gain generally increased as CFRP modulus, initial out-of-straightness, or CFRP reinforcement ratio increased. Global buckling consistently governed the maximum load. In the case of the 430 GPa CFRP, buckling was followed by CFRP crushing in compression, then rupture in tension. The second section of the thesis examines the effect of CFRP plates added to the flanges and tested for buckling in the strong axis. Eight columns, with a slenderness ratio of 83, were tested of which five were strengthened with CFRP. The main parameters examined were the level of initial out-of-straightness (L/28889 to L/1635), CFRP modulus (168 to 430 GPa), CFRP reinforcement ratio (13% to 34%) and the axis of bending. The gain in axial strength due to CFRP retrofitting ranged from 0% to 25%, depending on the various parameters. The gain generally increased as initial out-of-straightness, or CFRP reinforcement ratio increased. The higher modulus did not perform as expected, showing no gain in strength, because the compressive strains were too large and the CFRP crushed before the specimen experienced any gain. Specimens compared with the weak axis, strengthened with normal modulus CFRP, had similar percentage gains in strength. / Thesis (Master, Civil Engineering) -- Queen's University, 2014-06-27 15:19:03.397

Three full-scale experimental tests were conducted to investigate the strength and stiffness of weak-axis moment end-plate connections. Each test consisted of two girders connected to a column web with four-bolt extended moment end-plates. Two tests were conducted with bare steel. One test included a composite concrete slab that confined the top extension of the end-plate. Finite element models of the tests were created with the commercial software SAP2000. A simplified modeling procedure was developed to overcome the contact problems between the end-plates and column web, and between the bolts and holes in the end-plates and web. The simplified modeling procedure accurately predicted the experimental elastic stiffness, in the form of column web rotations, of the connections. Yield line theory was used to investigate the plastic strength of the column web. Several yield line patterns were examined. Analytical plastic moment strengths were very conservative when compared to the observed behavior of the column web. The experimental stiffness of the test with the concrete slab confining the top extension of the end-plate was compared to the stiffness of a similar test without a slab. The slab increased the elastic stiffness of the connection; however, after the concrete began cracking and crushing around the connection, the stiffness was greatly decreased. / Master of Science

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