International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 04 | Apr -2017
p-ISSN: 2395-0072
www.irjet.net
An overview on Concrete Filled Double Skin Steel Tube (CFDST) column with FRP wrapping Anju Alias1, Susan Jacob2 1PG
Student, Department of Civil Engineering, FISAT, Angamaly, India Professor, Department of Civil Engineering, FISAT, Angamaly, India ---------------------------------------------------------------------***--------------------------------------------------------------------2Assistant
Abstract: CFDST is a composite construction which consists of two steel layers embedding a concrete layer in between The inner hollow steel section acts as formwork and reinforcement for the concrete. Concrete delays the local buckling of hollow steel section and hence improves the ductility of the section. CFDST have many advantages such as high strength, high bending stiffness, good seismic and fire performance. But the columns were proven to have certain shortcomings such as ageing of structures, corrosion of steel tubes. Therefore, the implementation of strengthening techniques with the new material is essential to eliminate this problem. Fibre reinforced polymer (FRP) can be used as an external reinforcement to strengthen the structure. Although significant research has been underway on advanced analysis for many years for better understanding of the behaviour of CFDST columns wrapped with FRP , the results of these various research works are scattered and unevaluated. Hence, a transparent understanding of more recent work on CFDST column is highly desired. The main objective is to give a clear vision about the CFDST column. This study would enable structural engineers for better understanding of the behaviour of CFDST column externally reinforced with FRP composites.
steel has a much higher modulus of elasticity than the concrete and is situated farthest from the centroid. This makes the greatest contribution to the moment of inertia. As a result the stiffness of the CFT is increased. The concrete forms a core to resist the compressive loading and it delays and often prevents local buckling of the steel, particularly in rectangular CFTs. The confinement of concrete core by steel increases the compressive strength and ductility for circular and rectangular CFTs respectively. Therefore, it is most advantageous to use CFTs for the columns subjected to the large compressive loading. In comparison with reinforced concrete columns with transverse reinforcement, the steel tube also prevents spalling of the concrete and reduces congestion of reinforcement in the connection region, particularly for seismic design. CFDSTs are structural members that have a double steel skin with concrete sandwiched between the two steel tubes. These structural elements can be concrete-filled double-skin rectangular tubes (CFDSRTs), concrete-filled double-skin circular tubes (CFDSCTs) or concrete-filled double-skin rectangular-circular tubes (CFDSRCTs). Similarly to CFTs, these members are economical and quicker to construct than conventional concrete-reinforced columns because the steel tube serves as form-work. This means that high rise buildings can be completed swiftly when CFDST columns are used. The concrete fill prevents the outer steel tube from buckling inwards whilst the steel prevents the concrete from deforming laterally, under compressive loads. CFDST columns have structural benefits similar to CFT columns. In addition they are lighter, stronger and possess better energy absorption.
Key Words: CFDST, FRP INTRODUCTION Composite columns are widely used in the construction of modern buildings, even in the regions of high seismic risk. Composite columns combines the advantages of both steel and concrete namely light weight and high strength of steel, speed of construction and stiffness, damping and inherent mass of concrete. Composite columns are of different forms: steel encased concrete section, concrete filled steel tubular section, concrete filled FRP tube, steel reinforced concrete section, concrete filled double skin tubular column (CFDST).
From structural point of view, this form of column has higher strength (uni-axial, flexural and torsion). By replacing the central concrete with a steel tube of much smaller crosssection area, the strength-to-weight ratio of the columns is improved significantly. Furthermore, the inner tube expands laterally during compression and hence improves the confining pressure provided to the concrete. Thus, the initial confining pressure builds up more rapidly than that in CFST columns that enhances the elastic strength and stiffness. From environmental point of view, CFDST column uses less concrete, which creates a more sustainable environment by reducing the embodied energy levels of the column. From cost effectiveness point of view, the tubes act as both the longitudinal reinforcement and form work that save the construction cost and cycle. Lastly, the cavity inside the inner
Concrete Filled Steel Tubes (CFSTs) are composite members consisting of a steel tube infilled with concrete. Concrete Filled Tubular (CFT) columns are mainly used in the primary lateral resistance systems of both braced and unbraced building structures. The CFT structural member has a number of distinct advantages over an equivalent steel, reinforced concrete, or steel-reinforced concrete member. The orientation of the concrete and steel in the cross section optimizes the stiffness and strength of the section. The steel lies at the outer perimeter where it performs most effectively in tension and in resisting bending moment. The
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