THE COEFFICIENT OF LONGITUDINAL BENDING FOR COMPOSITE STEEL-CONCRETE RODS UNDER SHORT-TERM LOADS
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Abstract
The norms (codes) for calculations of compressed composite steel and concrete columns, as well as experimental and theoretical studies by other authors, are considered. An experimental study of compressed columns with small eccentricity at a range of flexibility 䠇㐋/ℎ from 6 to 20 was performed. Finite-elements modeling of various variants of structures has been performed: with concrete class from B30 (С25/30) to В100 (С90/105), with I-beam core, with square form core. The experimental and FEM data obtained are compared with theoretical curves of the longitudinal bending coefficient. It was found that the coefficient curves in SP 266.1325800 and Eurocode 4 are not in the correct shape and do not reflect actual work of composite compressed columns. The use of SP 266.1325800 curve, based on the curve for reinforced concrete structures, as well as Eurocode 4 curves, which are accepted as for steel sections by Eurocode 3, does not provide load-bearing capacity reserve and does not ensure reliability. Both codes ignore different work of low- and high-strength concretes. As a result of the research, it was found that class of concrete affects the stability of columns with flexibility 䠇㐋/ℎ from 6 to 10, while there is no influence on the shape of the cross-section of the core (type of rigid reinforcement). For flexibility 䠇㐋/ℎ from 10 to 20, a uniform coefficient curve can be adopted for all concretes. Curves of the coefficient have been developed for calculating compressed elements at small eccentricities and short-term action of loads; a formula for calculating the bearing capacity of compressed racks has been proposed.
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