The aim of the present study is to experimentally investigate the behaviour of concrete-filled steel tubular columns under axial loading. The grade of concrete used is M20 and the yield strength of the steel is 250 MPa. Fly ash is used as partial replacement (25%) of cement and 0·5, 1·0 and 1·5% polypropylene fibres are added to the concrete; the optimum mix is selected based on the mechanical properties of the concrete and used as a filler material for the columns. Twenty-seven columns of different cross-sections, such as circular, rectangular and square cross-sections with length-to-depth ratio of 2 to 11·83, and two different concrete infills are tested. The load–deflection response of axially loaded columns is obtained. The strength of the columns is predicted theoretically by various international design standards, including Eurocode 4 (BS EN 1994-1-1). A comparative study is made between the experimental and theoretical values. From the investigations, it is inferred that the partial replacement of cement by fly ash and addition of fibres in the concrete is advantageous as infill material in concrete-filled steel tubular columns.
Concrete-filled steel tube structures have experienced rapid development in recent decades. Simplified methods have been proposed in design codes, such as BS EN 1994-1-1:2004 (Eurocode 4), Mander and co-workers, as well as Lu and Zhao, have proposed a simplified model to determine the load-bearing capacity of concrete-filled steel tubular columns. This paper presents an analysis of the test results of 311 specimens of axially loaded, concrete-filled steel tube circular columns available from the literature with length/diameter (L) ratio greater than 4. The test results are compared with international design codes and equations. A comparative study of the variable parameters such as concrete compressive strength, yield strength of steel and diameter/thickness (D) ratio is also presented. Their influence on the estimation of ultimate load capacity of concrete-filled steel tube columns and their impact on the proposed design codes and theoretical equations are analysed.
Settlement is the major problem that arises after the construction of a structure on a soil mass. Consolidation characteristics of soil such as coefficient of consolidation cv, compression index cc, recompression index cr, preconsolidation pressure σ′p play a major role in the settlement behavior of fine grained soil mass. cv represents the rate of consolidation of soil mass. cc and cr are essential in calculating settlement of normally and over consolidated clays respectively. σ′p is determined to find whether the clay is under, normally or over consolidated. These consolidation properties are obtained from graphical constructions after conducting several one dimensional consolidation-oedometer tests. Since this is time consuming, many correlations have been derived between consolidation properties and index properties of soil. Different researchers have used various soil parameters such as liquid limit (wL), plastic limit (wp), natural moisture content (wn), initial insitu void ratio (eo), dry unit weight (γd), plasticity index (Ip), void ratio at liquid limit (eL) etc., as correlative parameters for deriving the correlations. Hence, it is desirable to predict the value of cv, cc, cr and σ′p from the known correlations rather than conducting several tests, to ease the procedures.
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