Munaf A. Al-Ramahee

Construction and demolition waste is recognized as a major waste stream made by humans around the world. The use of crushed old concrete in a type of recycled aggregate concrete (RAC) has been a promising technique to promote construction sustainability. However, the mechanical behaviors and the durability of RAC are inferior to those of concrete incorporating natural aggregate. Therefore, the creation of effective methods to lessen these harmful consequences is crucial. It stands to reason that the dilatation of concrete can be restricted by placing it in a confinement state. Due to the confinement provided by the steel casing, a steel tube filled with concrete can be considered suitable for improving the working mechanism of the RAC. In this paper, a series of comparison tests were conducted to investigate the behavior of square double skin steel tubes filled with self-compacting concrete (SCFDST) columns under different loading conditions. Ten specimens consisting of five normal SCFDST and five recycled aggregate self-compacting concrete filled double skin steel tube (RSCFDST) columns were tested under (axial, uniaxial, and biaxial) compression loads. Loading eccentricity and full replacement of coarse aggregate were adopted as the main parameters in the experiments. Overall, the failure mode, ultimate capacities, and general deformational behavior have been presented in this paper. According to the results, comparable structural behavior and failure shapes were observed between the RSCFDST columns and their normal SCFDST counterparts with an acceptable reduction in ultimate bearing capacity. The ultimate bearing capacity of both RSCFDST and conventional SCFDST are significantly harmed by eccentricity, while the ductility of the columns was improved by the RAC replacement. The failure mode of normal SCFDST and RSCFDST columns was overall buckling under a uniaxial and biaxial compression load, whereas compression failure was the failure mode of the axially loaded columns. As expected, due to the confinement effect of the steel tubes, the strength of the sandwich concrete was enhanced, and all tested columns exhibited ductile failure.

This research studies the structural behavior of self-compacted reinforced concrete deep beams by using steel plates as an alternative to traditional shear reinforcement. Seven specimens were fabricated and tested to evaluate the effectiveness of steel plate substitution based on force equivalency principles. The experimental program includes one specimen with traditional stirrup reinforcement as a control specimen and six specimens divided into two groups. The first group included three beams with web reinforcement substituted with 2 mm, 3 mm, and 4 mm steel plates. The second group included three beams with skin reinforcement replaced by steel plates of the same varying thicknesses. Experimental results showed that using 4 mm-thick web steel plates enhances the load-carrying capacity by 11% compared to the control specimen. Other specimens, especially those with skin reinforcement steel plates, showed comparable performance to the control beam, suggesting that steel plate substitution maintains structural integrity without significant strength degradation. Finite element analysis was carried out using ABAQUS software to validate the experimental results. The numerical outcomes showed good agreement with those from the experimental program in terms of ultimate load capacity. The study concludes that steel plates can serve as a viable alternative to traditional shear reinforcement in self-compacting concrete deep beams, with optimal performance achieved using 4 mm-thick web steel plates.

While concrete filled double skin steel tubes offer superior structural performance, their behavior after fire exposure, particularly under eccentric loading conditions has not been adequately investigated, limiting the development of comprehensive fire safety design guidelines. They exhibited excellent load carrying capacity when compared to conventional columns. In this research, the performance of concrete filled double skin steel square tubular columns consisting of outer and inner square tubes with self-compacting concrete (SCC) infill between them after exposed to fire was studies experimentally. Twelve specimens were fabricated and tested under concentric and eccentric loading. For each loading conditions, two columns were exposed to 60 min fire, two were exposed to 90 min fire, and two columns were considered as control specimens which are not exposed to fire. These two columns, one with solid section and one with hollow section. The filling by SCC increased the capacity by 18-26% for concentric condition through enhanced confinement. Fire exposure reduced capacity by 8-25% due to steel softening and concrete thermal degradation with stiffness degrading more severely (44-59%), indicating interface deterioration. Eccentric loading caused 65-68 capacity reduction across all conditions. Failure modes included concrete crushing and local buckling with fire exposed specimens showing more sever buckling and concrete spalling from thermal damage. The dominant mode of failure was crushing of concrete at loaded end followed by tube local buckling. These findings contribute to understanding the fire resistance behavior of SCC-filled double skin steel tubes and provide essential data for developing fire safety design guidelines for such structural systems in building construction.

Different techniques were employed for the passage of different utilities through structural elements. The reduction of the overall building weight was the main concern that needs to be achieved, especially for a multistory building. It can be done with the eliminating of a suspended ceiling with a portion of the beam’s weight by taking the advantages of the hollow sections. In this study, an equivalent reinforcement to the traditional ribbed reinforcement was employed to fabricate a reinforced concrete (RC) beam with a hollow section along the length of the beam. A steel pipe was used based on the equivalent moment from section analysis. Two diameters were selected of steel pipes as an equivalent to the commercial reinforcement. A total of four RC beams were cast and tested, two of them with traditional reinforcement and the other with steel pipe reinforcement. The comparison showed a promising result in terms of ductility, cracking pattern, ultimate strength, and mode of failure compared to the reference beam. The peak loads for the specimens with steel pipe were 160.6 kN and 184 kN, while they were 192 kN and 203.5 kN for the beams with traditional reinforcement.