Experimental and numerical study of high-strength aluminum alloy circular hollow sections after exposure to fire

Concrete-filled double skin steel tubular (CFDST) beam–columns subjected to cyclic bending

Experimental and numerical investigations of concrete-filled double-skin aluminium stub column with a circular hollow section as the outer skin and a square hollow section as the inner skin are presented in this article. A test program was carried out to study the influences of aluminium tube geometric dimensions and concrete strength on structural performance and strength of composite columns. A series of composite columns was tested on outer circular hollow section tubes and inner square hollow section tubes; the spaces between them had been filled with concrete of different nominal cylinder strengths of 40, 70 and 100 MPa. The tubes were fabricated by extrusion using 6061T6 heat-treated aluminium alloy having a nominal 0.2% proof stress of 240 MPa. A non-linear finite element model was developed and verified against experimental results. The test and numerical results were compared with the design strengths to evaluate the applicability of the design rules in the American specifications for aluminium and concrete structures. In addition, the proposed design equations, developed by the authors for concrete-filled double-skin aluminium tubular stub columns with circular hollow section as both outer and inner skins, were used to calculate the design strengths and compared with the experimental and numerical results obtained in this study. The proposed design equations also predicted the ultimate strengths of the concrete-filled double-skin aluminium tubular stub columns accurately with circular hollow section as the outer skin and square hollow section as the inner skin.

Effect of the presence of perforations on thin structure has been extensively investigated for decades. Various perforation parameters were investigated in past studies. However, study on thin cylinder with multiple perforations has not been carried out. In searching for lighter structural members, the concept of perforated hollow section has been inspired by the shape and arrangement of multiple perforations observed in the Cholla skeleton. Effects of multiple perforation parameters on circular hollow section have been the main interest. This paper presents the verification of FEM simulation with test results. A non-perforated circular hollow section (control model) and a circular hollow section penetrated with 12 nos. of circular shape perforations in array arrangement were selected for the verification process. Both test specimen and FEA models were subjected to compression, flexural and torsional loads. For result comparison within the material linear range, FEA models show good agreement with test results for compression and flexural load cases, and for control models under torsional load case. For perforated models under torsional load, FEA results correspond well with the inclined strain gauge readings. FEM analysis method is considered capable to produce reliable result for loading within the material linear range for circular hollow sections with multiple perforations.

An experimental study on composite columns of square and circular steel hollow sections filled with normal concrete has been held in this paper. The concrete used in this study have two different compressive strength with mixing ratios of (1:2:4) and (1:1.5:3); the compressive strength of concrete were (22.9 MPa) and (31.8 MPa) respectively. Square steel hollow sections of (7.5×7.5 cm) and 2 mm thickness used with a yield stress of (352 MPa) while the circular hollow sections have (7.5 cm) diameter and 2 mm thickness with a yield strength of (327 MPa). Samples tested under the effect of concentric and eccentric axial loads with one case in which the column tested horizontally as a beam to evaluate the maximum bending resistance. The interaction curves for both shapes of columns and for two different concrete compressive strength are presented with a simple analysis for the pattern of failure in columns for each case of loading and for each type. The results show that the increase in compression strength of concrete provides more capacity for the composite columns in axial loading more than bending due to the confinement, and the failure in columns with square cross-sections are different from those which have circular cross-sectional area.

Structural steel hollow section members are extensively utilized in civil engineering due to their excellent mechanical performance, favourable geometry for corrosion protection, and aesthetic appeal. Degradation in material properties of steel and thermal expansion at high temperatures must be regarded in designs for fire situations. The closed inner space of hollow sections presents challenges at elevated temperatures. The present study examines the effect of expanding air on the stress state in section walls of hermetically sealed circular and rectangular hollow sections. The effect of the gas pressure is calculated analytically and numerically. The pressure of the expanding air may substantially reduce the capacity of a tubular member. The influence on resistance depends on temperature, volume of the air in the tubular member, and geometry of the hollow section. The results of the study indicate that rectangular hollow sections with relatively large width-to-thickness ratios are more sensitive to internal pressure than circular hollow sections. The temperature range where the adverse effect of internal pressure occurs can include realistic critical temperatures in practical design and therefore deserve special attention to ensure the required safety.

Flexural buckling of high-strength aluminium alloy CHS columns

This paper aims to develop a new continuous strength method (CSM) to more accurately predict the strain-hardening characteristics of high-strength aluminum alloy circular hollow sections (CHSs) under axial compression. A total of 11 stub column specimens made of 7A04-T6 and 6061-T6 aluminum alloys underwent testing. Additionally, 16 sets of experiment data were gathered from open sources, encompassing various aluminum alloy types such as 6082-T6, 6061-T6, and 6063-T5. Validated by experimental result, the finite element (FE) model was applied in a series of comprehensive parameter studies, supplementing the limited test result of high-strength aluminum alloy stub columns. Based on the experiment and FE results, this paper proposes a new CSM relation to determine the cross-sectional resistance of high-strength non-slender CHS aluminum alloys under compression. The cross-sectional resistance obtained from tests are compared with predicted strengths determined using the European code, as well as the solution of the CSM proposed in a previous study and in this paper. The comparison illustrates that the strength predictions in the European code and the previous study are conservative. Compared with the European code and the previous study, the strength prediction formula proposed in this paper improves accuracy by 11% and 5%, respectively, while reducing scatter by 8.4% and 2%, respectively.

Despite many papers on the structural response of thin circular sections, the effect of large imperfections – largely imposed due to damage, collisions, etc. – still leaves many open questions. Over the past few years however, there has been a significant body of tests on steel members with large imperfections, conducted by the authors at the University of Tasmania, with a particular focus on circular hollow sections under different loading conditions. The effect of geometrical irregularities of such structures was examined and subsequently presented in several papers. This paper incorporates these new advances into an organized summary, including key findings of the mentioned experimental data on the effect of local damages on the capacity of different structures with various geometrical features. Discussions are presented on the topic and some general recommendations made in relation to real structures in practice.

Circular hollow sections are usually used in long-span roof truss systems due to the advantages they offer. One of the typology for connecting elements in such structures involves the flattening of bar ends, in order to provide a simpler and more economical connection. A new flattening typology called stiffened flattening is proposed, characterized by a non-flat geometry, with the creation of stiffeners in the lateral edges of the bar flattened ends. A theoretical, numerical and experimental study was carried out on the behavior of a plane truss composed of circular hollow sections, in which diagonal bars have stiffened flattening ends. The diagonal connecting system with the chord members uses connecting plates. The plates are welded to the chords and the diagonals are connected to latter through a single bolt. This work presents the numerical analysis of a circular hollow section bar with stiffened flattening ends subjected to compression. This is a study of the behavior of an isolated bar compressed from the truss, which corresponds to the most requested diagonal composed by circular hollow sections with stiffened flattening ends. The numerical analysis using finite elements method was developed through ANSYS software with the Parametric Design Language (APDL), in which parameters such as geometry, material, element type, definition of the finite element mesh, boundary conditions and application of compression loads are specified. A non-linear analysis was performed using shell element on the bar with stiffened flattened ends. The numerical analysis result satisfactorily represented the structural behavior of the isolated circular hollow section bar with stiffened flattening ends. It was possible to observe the buckling effect of the compressed circular hollow section bar and the effect of the axial load eccentricity due to the stiffened flattening of bar ends.

Effect of concrete infill on local buckling capacity of circular tubes

Study on the Bending Capacity of Cold-formed Stainless Steel Hollow Sections

The number of buildings higher than 30 floors has shown remarkable growth; many of them are supported on foundations of hollow circular piles. This increasing of height of constructions causes an increment of the shear stresses that are transmitted to their foundations, however these elements are more shear critical due to the hollow core. Most of the existing codes are based on shear models for rectangular sections, and guidelines for assessment of shear strength of members with hollow circular cross sections are practically non-existent. This study evaluates, on a comparative basis, the shear strength of elements with hollow circular cross sections, obtained from experimental tests, with values computed using the Canadian Code (CSA A23.3) and using a proposed simple procedure based on the Brazilian standard (NBR 6118).

The Beams subjected to the axial force and lateral force simultaneously are known as beam-columns. Bridge pier is idealized as a column subjected to axial load and biaxial moment. Slender member subjected to axial force and biaxial bending moment fails due to buckling effect. This buckling is caused due to slenderness effect also known as ‘PΔ’ effect. The objective of the research reported in this paper is to obtain a theoretical formulation, using beam column theory for studying the behavior of straight hollow circular section and tapered hollow circular section of the bridge pier. Study is carried for different heights of bridge pier for straight hollow circular pier and tapered hollow circular pier. Study is carried by considering two lane box type bridge girder. Providing a straight hollow circular section for a direct & flexural action proves to be uneconomical. The straight hollow circular section of bridge pier is replaced by a tapered hollow circular pier section in the present study.

Bending tests to determine slenderness limits for cold-formed circular hollow sections

An experimental study on stress concentration factors of stainless steel hybrid tubular K-joints