Concrete Filled Double Steel Tube (CFDST) columns are a modern technique of composite structural element that has fire resistance and has been adopted in high-rise building structures. The Concrete Filled Steel Tube (CFST) columns also have high strength and ductility due to composite action. This type of column CFST can sustain a heavy load with high performance and has been adopted in recent years in many countries around the world. The aim of the present work is to study the behavior and strength of rehabilitation of composite columns that are made from concrete core and surrounded steel tubes under the effect of axial compression loads with different height to diameter ratios such as 5.46, 10.91, and 16.37, respectively, by experimental tests. Double skin methodology is adopted to repair the damaged columns that were tested up to 85% of the ultimate load. Strength column capacity of double skin columns, axial and buckling deformations with axial and buckling strains are investigated. Test results showed that the repaired specimens up to 85% of the ultimate load had the same strength carrying capacity as compared with the control specimens, which had the same geometry. The ductility of an 800 mm specimen’s height is greater than the other tested specimens, while the stiffness of short specimens becomes high. Doi: 10.28991/CEJ-2022-08-03-013 Full Text: PDF

In this study, six full-scaled models of RC floors supported by cold-form steel sections have been tested. Each model consists of RC 75mm thick slab supported on two parallel cold-formed steel beams with a span of 3m and spacing of 500mm. The slab has an overhang part of 250mm on each side. In the first and fourth models, the slab has been casted directly on the top flanges with no shear connector to simulate the effectiveness of friction in resisting of the lateral-torsional buckling. Shear studs have been drilled in the second and fifth models to ensure the composite action. Finally, the flanges have been embedded for the third and sixth models. A single channel beam is used in the first, second, and third models while a built-up beam is used in the fourth, fifth, and sixth models. Each model has been loaded up to failure under a pure bending with two-line loads located at the third points. Data for loads, deformations, and strains have been gathered. Except the fourth and the sixth models that failed in local buckling modes, all other models failed in global lateral-torsional buckling modes. For the single beam models; the load carrying capacity of the non-composite model is 82.9% less than the capacity of the composite models with shear studs and embedded flange. For the built-up models; the load carrying capacity of the non-composite model is 44.2 % less than the loads of the composite model with shear stud and 48.7% less than the model with the embedded flange.

This study aims to show, the strength of steel beam-concrete slab system without using shear connectors (known as a non-composite action), where the effect of the friction force between the concrete slab and the steel beam has been investigated, by using finite element simulation. The proposed finite element model has been verified based on comparison with an experimental work. Then, the model was adopted to study the system strength with a different steel beam and concrete slab profile. ABAQUS has been adopted in the preparation of all numerical models for this study. After validation of the numerical models, a parametric study was conducted, with linear and non-linear Regression analysis. An equation regarding the concrete slab-steel beam system strength in non-composite action has been pointed out. Where the actual strength of the beam without using shear connectors has been located in between the full composite action and non-composite action. However, partial-composite action has been noted, due to the effectiveness of friction force which makes the beam behave as composite before the slip occurs.

In recent years, more researches on structural reliability theory and methods have been carried out. In this study, a portal steel frame is considered. The reliability analysis for the frame is represented by the probability of failure, P_f, and the reliability index, β, that can be predicted based on the failure of the girders and columns. The probability of failure can be estimated dependent on the probability density function of two random variables, namely Capacity R, and Demand Q. The Monte Carlo simulation approach has been employed to consider the uncertainty the parameters of R, and Q. Matlab functions have been adopted to generate pseudo-random number for considered parameters. Although the Monte Carlo method is active and is widely used in reliability research, it has a disadvantage which represented by the requirement of large sample sizes to estimate the small probabilities of failure. This is leading to computational cost and time. Therefore, an Approximated Monte Carlo simulation method has been adopted for this issue. In this study, four performances have been considered include the serviceability deflection limit state, ultimate limit state for girder, ultimate limit state for the columns, and elastic stability. As the portal frame is a statically indeterminate structure, therefore bending moments, and axial forces cannot be determined based on static alone. A finite element parametric model has been prepared using Abaqus to deal with this aspect. The statistical analysis for the results samples show that all response data have lognormal distribution except of elastic critical buckling load which has a normal distribution.

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