Concrete-filled Composite Columns Research Articles

Optimum design of steel columns filled with concrete via genetic algorithm: environmental impact and cost analysis

The use of concrete-filled tubular columns as part of structural systems has steadily increased throughout the years. The growing demand for structural elements of this nature is a direct result of the possibility to use various cross-section shapes that have increased strength, along with resistance to fire and other corrosive agents. The main objective of this article is to present the formulation for optimizing the design of composite columns in accordance with prescriptions from ABNT NBR 16239: 2013, considering financial cost and CO2 emission during manufacturing as objective functions. A Genetic Algorithm was used to solve three examples of composite tubular columns subjected to combined bending and compression, considering major axis and unsymmetrical bending. The financial cost in Brazilian currency and the CO2 emission in kilograms attributed to manufacturing concrete-filled composite columns were calculated and the optimization procedure was implemented on composite columns featuring CHS, RHS and SHS steel members. This study also considers the different concrete strengths and the optional inclusion of longitudinal rebar. For the cases analyzed, the financially and environmentally optimum design corresponds to a CHS composite column with no longitudinal rebar and the highest concrete strength tested, except when unsymmetrical bending is applied, in which case the optimum solution includes longitudinal rebar. Furthermore, results indicate that structural steel has the highest impact on the CO2 emission of the optimal designs. For the column with longitudinal rebar, the reinforcement steel presents the second highest financial impact, while concrete is responsible for the highest influence on CO2 emission.

Structural Fire Performance of Concrete-Filled Built-Up Cold-Formed Steel Columns.

Concrete-filled composite columns are widely used in the construction industry, exploiting the benefits of combining steel and concrete, providing, for instance, high load-bearing capacities and enhanced fire resistance. These solutions are extensively used in high-rise buildings and/or when high fire resistance performance requirements are imposed. In this exploratory research, a new type of concrete-filled composite column is investigated using fire resistance tests. Promoting the use of cold-formed steel products and developing innovative solutions for low-rise buildings with lower passive fire protection requirements led to the solutions presented in this research. Hence, a set of fire-resistance tests were undertaken on concrete-filled closed built-up cold-formed steel columns, where single cold-formed steel shapes are combined and fastened to create a box-shaped cross-section. The experimental results were then compared with the corresponding bare steel solutions to assess, in detail, the observed enhancements. Additionally, the effect of restraint on thermal elongation was assessed.

Experimental behavior of circular composite columns with different weld arrangements

Eighteen (18) circular short composite columns including 9 concrete-filled steel columns and 9 concrete-filled stainless steel columns, were experimentally studied in this paper. All composite columns have the same dimensions: D= 160 mm, H= 300 mm and t= 2 mm. The objective of this study is to shed light on the effect of the number and arrangement of lateral and longitudinal welds on the resistance and behavior of concrete-filled composite columns. Based on the results obtained, it was confirmed that weld joints have slight effect on the bearing capacity and instability modes of the studied composite columns. Lateral and longitudinal welds were very successful in conveying compression and bending efforts. The experimentally measured load-bearing capacities of the composite columns were compared to those predicted by Eurocode 4, AISC 360–16 and the equation proposed by Giakoumelis and Lam. All the results predicted by the AISC 360–16 code showed a good concordance with the experimental test results. However, the predictions calculated by the EC4 and the equation proposed by Giakoumelis and Lam were not conservative. This investigation shows that the use of lateral and longitudinal welds in composite columns applications would result in a reliable and economical design. This encourages designers to build their confidence in the use of this type of waste metal plates as structural components of locally produced materials.

Optimized design of concrete-filled steel columns

Abstract The objective of this paper is to present the formulation of the optimization problem and its application to the design of concrete-filled composite columns with and without reinforcement steel bars, according to recommendations from NBR 8800:2008, NBR 16239:2013 and EN 1994-1-1:2004. A comparative analysis between the aforementioned standards is performed for various geometries considering cost, efficiency and materials in order to verify which parameters influence the solution of the composite column that satisfies the proposed problems. The solution of the optimization problem is obtained by using the genetic algorithm method featured in MATLAB’s guide toolbox. For the examples analyzed, results show that concretes with compressive strength greater than 50MPa directly influence the solution of the problem regarding cost and resistance to normal forces.

Structural Performance of Welded Built-Up Mega Composite Columns Subject to Compressive Force and Moment

The width thickness ratio of a concrete-filled steel tube column is limited in order to prevent the local buckling of the tube. Determined by column width and steel tube thickness, width-thickness ratio decides whether the cross-section is compact, non-compact or slender. Different compressive strength formulas are applied depending on the type of the cross-section. This study suggests the shape of binding frames which are placed at a constant distance inside the steel tube of a mega column having large cross-sections to improve the composite effect and confinement effect. Structural tests are conducted on 9 welded built-up and generic CFT columns with different steel thicknesses to evaluate their structural performance under compressive force and moment applied simultaneously. The maximum load of the welded built-up specimens with compact, non-compact and slender cross-sections is approximately 38%, 30% and 20% higher when compared with their generic CFT counterparts. While the effective stiffness of the members of concrete-filled composite columns is calculated by one formula, the difference among the specimens is greater than 10% depending on the width-thickness ratio. Therefore, it is deemed that effective stiffness needs to be categorized depending on the width-thickness ratio as in the case of compressive strength and bending strength.

Finite element model for bolted shear connectors in concrete-filled steel tubular columns

This research presents a study on the numerical simulation of the structural behavior of bolted shear connectors used as force transfer device in concrete-filled composite columns. The numerical model was developed in ABAQUS software, using the constitutive model named Concrete Damaged Plasticity. In the study, the influence of different concrete stress-strain relationships on tensile and compressive strengths was analyzed, as well as the influence of the use of damage variables. Three different stress-strain relationships on concrete compressive strength were tested, and another three on concrete tensile strength, distinguished by the crack opening displacement. The obtained results were calibrated with the experimental results of four experimental models, and, next, the proposed calibration was compared with twelve other experimental results. Finally, the proposed parameters showed to be suitable to represent the structural behavior of bolted shear connectors applied in force transfer in concrete-filled composite columns.

Structural assessment of composite seam-welded rectangular hollow columns

Structural elements made of seam-welded hollow sections are considerably less expensive than their seamless equivalents. This is a strong incentive for their use, but the current steel design standards still contain recommendations for seam-welded hollow sections based on test results performed with sections produced using outdated steel grades and fabrication processes. These design procedures are even more conservative when applied to composite tubular seam-welded elements. This paper presents an experimental campaign performed to investigate the structural behaviour of steel- and concrete-filled composite columns made with seam-welded rectangular hollow profiles. The experiments involved columns with only steel sections, concrete-filled and concrete-filled plus additional reinforcing bars. The main aim of the tests was to identify the contribution of each component in the overall structural response. The results enable an evaluation of the design recommendations present in Eurocode 4 aiming to determine less conservative buckling curves to be used for the investigated composite columns made of seam-welded rectangular hollow sections.

Axial compressive strength of short steel and composite columns fabricated with high stength steel plate

The design of tall buildings has recently provided many challenges to structural engineers.rnOne such challenge is to minimise the cross-sectional dimensions of columns to ensure greater floorrnspace in a building is attainable. This has both an economic and aesthetics benefit in buildings, whichrnrequire structural engineering solutions. The use of high strength steel in tall buildings has the ability tornachieve these benefits as the material provides a higher strength to cross-section ratio. However as thernstrength of the steel is increased the buckling characteristics become more dominant with slendernessrnlimits for both local and global buckling becoming more significant. To arrest the problems associatedrnwith buckling of high strength steel, concrete filling and encasement can be utilised as it has the affect ofrnchanging the buckling mode, which increases the strength and stiffness of the member. This paperrndescribes an experimental program undertaken for both encased and concrete filled composite columns,rnwhich were designed to be stocky in nature and thus fail by strength alone. The columns were designedrnto consider the strength in axial compression and were fabricated from high strength steel plate. Inrnaddition to the encased and concrete filled columns, unencased columns and hollow columns were alsornfabricated and tested to act as calibration specimens. A model for the axial strength was suggested andrnthis is shown to compare well with the test results. Finally aspects of further research are addressed inrnthis paper which include considering the effects of slender columns which may fail by globalrninstabilities.

CONSTITUTIVE MODELS OF CONCRETE UNDER PASSIVE CONFINEMENT AND THEIR USE IN STRUCTURAL ANALYSIS

When a concrete cylinder is confined laterally by a steel tube, or it is strongly reinforced with closely-spaced hoop reinforcement bars, the axial strength and ductility of concrete are improved considerably. In such structures, large confining pressures are passively induced by steel due to the lateral expansion of concrete.The present paper proposes a constitutive model for describing the multiaxial deformational behaviour of concrete under passive confinement by using the work-hardening elasto-plasticity theory. The derivation of the proposed model is based on the use of experimental information obtained from tests in which concrete has been subjected to passive confinement. A computer program for finite-element (FE) analysis based on the use of the proposed model has been developed. The FE analysis successfully predicted the load-carrying capacities and deformational responses of concrete-filled composite columns subjected to eccentric loading.