Benefit of Ultra-High Strength Infill in Concrete-Filled Steel Tubular Columns

Concrete filled steel tubes (CFST) represent a composite building member suitable especially for the construction of columns of a skeleton frame. Filling the steel tube with concrete allows the use of suitable properties of both materials and their interaction. This is very beneficial in a fire exposure, where a circular column has slightly better fire resistance than a square column. In case of an assessment of columns at the ultimate limit state (ULS), a buckling resistance decides. In previous research, it was found that increasing the strength of concrete increases buckling resistance only to a certain extent. The main aim of the article is to show through a theoretical study what benefit the use of ultra-high strength concrete has for buckling resistance of CFST.

An Experimental Investigation on Concrete Filled Steel Tube Columns Under Axial Compression

This paper presents an experimental investigation on the behaviour of concrete filled steel tube columns under axial compression. The steel columns were filled with self-compacting and self-curing concrete instead of normal conventional concrete. A test program consisting of square column, circular column and rectangular column was firstly conducted. The behaviour of three concrete filled steel tubular sections (CFSTs) under axial load is presented. The effect of steel tube dimensions, shapes and confinement of concrete are also examined. Measured column strengths are compared with the values predicted by Euro code 4 and American codes. Euro code 4, gives good estimation of self-compaction concrete. However, lower values as measured during the experiments were predicted by the American Concrete Institute (ACI) equation. Also, the effect of thickness of steel tubes, concrete cube strength and steel percentage is also studied. In addition to CFST column the steel tube also acts as confinement for concrete.

Analisis Kekuatan Kolom Beton Bertulang Berdasarkan Diagram Interaksi Kolom

The column interaction diagram is a boundary area graph showing the various combinations of axial loads and moments that the column can safely hold. The benefit of a column interaction diagram provides an overview of the strength of the column in question. This study aims to analyze rectangular and circular columns using column interaction diagrams and then compare the strength of the columns in withstanding a combination of axial loads and bending moments with the same area. In this study, square and circular columns have the same number of reinforcement, diameter of reinforcement, steel strength, concrete quality, and cross-sectional area. The column is reviewed based on five conditions, namely pure axial load conditions, pure bending moment, and three failure conditions. Based on the five conditions that occurred, a column interaction diagram was created by using Microsoft Excel. Results of the analysis show that in the same area, the square column is stronger in withstanding the bending moment (Mu) of the circular column by 0.015 - 0.61%, while the circular column is stronger in resisting the axial force (Pu) of the square column by 1,9 - 4.4%.

Stiffness of Concrete-Filled Thin-Walled Steel Tubular Slender Columns

Concrete-filled thin-walled steel tubular slender columns are studied in this paper to evaluate their stiffness. The slender columns have various steel tube thicknesses, length/diameter (width) ratios, and concrete compressive strengths. The columns are loaded by axial and eccentric loads. Two experimental tests of the slender and stub columns are described. Also, the finite element software ABAQUS is utilised to simulate and analyse the columns. The tested columns are simulated taking into account all their features in the tests to verify the simulation of the columns. The simulation results are compared with the tests results which reveal that good agreements exist between them. Thus, the proposed simulation method of the columns is verified. In order to assess the stiffness of the columns under different conditions, various load eccentricities (0 mm, 25 mm, and 50 mm), cross-sectional configurations (circular, rectangular, and square), and steel tube thicknesses (2 mm, 3.35 mm, and 5 mm) are adopted for the developed columns. The columns are simulated and analysed based on the verified simulation method considering the mentioned conditions. As a conclusion, the stiffness of the columns is generally reduced by the increase of the load eccentricity from 0 mm to 25 mm and 50 mm. Further, more uniform distribution of the stiffness is witnessed for the columns with lower eccentricities. In addition, the enhancement of the load eccentricity increased the reduction slope of the stiffness graph for the columns. Although the initial stiffness of the circular column is slightly lower than the rectangular and square columns, the stiffness has more uniform distribution which is preferred. Larger stiffness is achieved for the columns by increasing the steel tube thickness from 2 mm to 3.35 mm and 5 mm.

Punching Strength of Reactive Powder Reinforced Concrete Flat Slabs

This research is devoted to investigating experimentally the punching shear strength of reactive powder concrete slabs under monotonic loading. All slabs have the same flexural reinforcement and same dimensions (1000mm length,600mm width,50mm thickness). The experimental program includes casting and testing of sixteen slabs tested under monotonic loading. The major parameters adopted in the current research include the shape of column (circle, square), column size (twocolumn sizes), number of columns (one, two), and the distance between two columns (3d,5d,7d). Results showed that, the slabs with circular column sections have slightly higher ultimate load than those with square column sections. An increasing column area increases the load of punching shear failure. It was found that the ultimate failure load for slabs with two columns is greater than the slabs with one column. Related to the effect of distance between the two columns for monotonic, it was found that the slabs maximum load reaches the maximum value at distance between the two columns equal to(7d) for a circular section with a diameter of 85mm and 113mm and square section with dimensions of (100*100)mm. While the maximum failure load reaches the maximum value when the distance between two columns (d) for a square section with the dimension of (75*75)mm. Related to the crack patterns, it was noticed that for slabs with larger columns sections with the distance between columns equal to 7d, the failure zone extended (in a large direction) to the slab sides.

Performance Comparison of High Strength Reinforced Concrete Circular and Square Columns Subjected to Flexural Controlled Cyclic Loading

In existing design practices selection of circular or square column shape mostly depends upon architectural needs rather than structural behavior. The behavior of equivalent area (circular and square), high strength reinforced concrete columns is reported to be same under monotonic loading conditions but their behavior under fatigue loading is not well-established. This paper presents the comparison of high strength reinforced concrete circular and square equivalent area columns’ performance (load-deflection behavior) under fatigue loading. Columns were casted in four configurations: square and circular shapes and with and without shear stirrups. Experimental results showed that in case of columns without shear stirrups, the square column resisted 38% more loading cycles as compared to circular column while the maximum deflection was 78% more than the circular column. Similarly, in case of columns with shear stirrups, square shaped column resisted 55% more loading cycles with only 5% more maximum deflections as compared to circular column. The results show that the square columns might be considered more ductile as compared to circular columns under the application of cyclic loading conditions like wind forces or seismic forces. Therefore, it might be concluded that square columns should be recommended for highly seismic regions as compared to circular columns with equivalent area. Doi: 10.28991/cej-2021-03091639 Full Text: PDF