Key Engineering Materials Vol. 920

Abstract: This study focuses on the experimental analysis of concrete-filled double-skin tubular (CFDST) short columns with double circular inner steel tubes under concentric axial loading. This cross-section layout promises to increase the ductile behavior of the compressive element and its energy absorption capacity, not to mention its ultimate axial strength. This research analyses main twofold variables: (i) Hollow ratio and (ii) eccentricity ratio (i.e., distance ratio between the inner tube’s separation and the sandwiched concrete width). As a result, load Vs. Axial deformation, load Vs. Axial strain curves, ductility index, strength index, energy absorption capacity, and ultimate axial capacity formulae for square CFDST columns with double circular inner tubes are reported. Key findings of this study show that (a) ductility is an intrinsic property of these types of sections; (b) the variation effect of hollow ratio influence inversely in the confined concrete strength of the element, (c) Eccentricity ratio has proved to be the least ultimate strength capacity influencer. However, its impact increases when it is jointly analyzed with the hollow ratio values. (d) The formulae proposed for predicting the ultimate capacity of CFDST columns showed good agreement with the experimental results. Thus, these expressions could be extended to the design of composite CFDST elements, provided a resistance factor based on a reliability analysis is incorporated.

Abstract: This study investigated numerically the effect of small and large rectangular web openings in unstrengthened and strengthened steel I-beams and columns. With the use of a numerical model, 25 simply supported steel I-beams were subjected to a four-point bending test. In addition, 25 steel I-columns were tested numerically under axial compressive load. All steel I-beams and columns were compared with solid reference specimens without web openings (control specimen), where all specimens have the same 400 mm depth and 177 mm width steel section dimensions. Twelve of the 25 steel I-beams and columns with openings were strengthened with steel plates, and all had different web openings that were symmetrically located near the support areas. The performance of all steel I-beams and columns was compared before and after a strengthening procedure. The selected opening depths ranged from 40 to 280 mm. Aspect ratios of opening length to opening depth of 1.0, 2.0, and 3.0 were chosen. ABAQUS software was used to perform numerical analysis on I-sections (beams and columns) that were either unstrengthened or strengthened. All specimens were analyzed in terms of their load-displacement characteristics and failure modes. Finite element analysis showed that those beams and columns with small web openings have a slight decrease in strength and stiffness, which is considered to be within acceptable limits unlike solid steel beams and columns (control specimen). I-section beams and columns that have been strengthened have significant effects on increasing the load-displacement characteristics.

Abstract: Road construction on sulfate-bearing soils is a worldwide concern because it is associated with a volume swelling stability issue due to the ettringite formation. Several treatment techniques were developed to solve this problem and improve geotechnical soil properties, including using pozzolanic materials and applying the mellowing process. This research evaluated the combined effect of cement and waste glass powder (WGP) on stabilizing sulfate-bearing soil before and after the mellowing procedure. Total six mixtures were developed, which includes 4% cement, 4% cement + 2% WGP, and 4% cement + 6% WGP before and after soil mellowing. The experimental program included particle size distribution of soil and stabilizers, chemical analyses of stabilizers, soil properties, unconfined compressive strength, and three-dimensional (3-D) swelling for the high sulfate-bearing kaolin clay. The test results demonstrated that the use of WGP in soil with a high sulfate content WGP improved strength development, decreased volumetric swelling, and reduced moisture susceptibility.