Engineering and Technology Journal

In this paper, concrete filled steel tubes columns (CFT) are investigated by using finite element program ANSYS 15.0. Analysis are done for four different shapes of columns (circular, square,hexagonal andoctagonal). Results of analytical solution (for circular and square) were compared with existing experimental data provided by [Alwash et al., 2013].Comparative resultsof failure load give 4% difference between experimental and ANSYS 15.0. Also, parametric studies have been carried out to investigate the effect of concrete filled steel tubes columns shapes (for hexagonal and octagonal) on load carrying capacity.Finally, a newformulaefor predicting the ultimate strength of CFT is proposedbased on experimental data of 148 CFT columns of different cross sections with side length ranging between 200 and 4000 mm. To check the validity of the proposed equation, the loads calculated from the designmethods (American Concrete Institute (ACI 318M-14), Eurocode (EC4),New Zealand Standard of concrete structures(NZS) and American Institute of Steel Construction (AISC)) are used to compare with it. The comparison shows least convergence percentageof the proposed equation.

This research studies the behavior of reactive powder concrete (RPC) circular short columns with and without steel fibers of different types, as well as change of the reinforcement kinds of lateral (hoops and spiral) and the spacing between them.
The experimental work consist study of fifteen short column specimens having an overall height of 1 m with circular cross-section of 150 mm diameter are loaded at ends with concentric loads. Six of the specimens are cast with the inclusion of steel fibers with aspect ratio of 75(group 1), and six of other specimens are cast with the inclusion of steel fibers with aspect ratio of 100 (group 2),and the other three specimens is without steel fibers, with hybrid steel fibers and high strength concrete. The concrete mix of fiber-reinforced samples contains 1% by volume of steel fibers of variable reinforcement longitudinal and lateral (hoops and spiral reinforcement).
Experimental data for strength, failure mode, lateral, and the ductility were obtained for each test.
The work concluded that the using of steel fibers in RPC was an effective way to prevent spalling of the concrete cover and increase the ductility and the using of high ratio of longitudinal reinforcement delays the pickling of the columns and increase strength.
The ultimate load capacity of RPC columns of spiral lateral reinforcement is greater than the load of RPC columns of tied lateral reinforcement by about 1.25 to 1.35 times for the two groups.