Mohamed Elchalakani - Single Skin and Double Skin Concrete Filled Tubular Structures: Analysis and Design

The term composite structures refer to structures in which different materials such as timber, steel, concrete, and masonry are used together for construction. The most common type of composite construction is the use of steel and concrete to form steel-concrete composite structures. Steel-concrete composite structural members are known as economic members and have been used in construction for various structure types. It is a very well-known fact that steel members are susceptible to buckling, while their tensile strength is remarkable. Conversely, plain concrete members can withstand a large magnitude of compressive force; however, their tensile strength is very low. Therefore, the simultaneous use of steel and concrete allows the structural designers to take advantage of steel and concrete and neutralize each material's drawback by the advantage of the other material. By taking this viewpoint, most structural members such as slabs, columns, beams, and trusses can be constructed using steel-concrete composite members. The main focus of the current book is to understand the structural behavior of concrete-filled steel tubular (CFST) members and concrete-filled double skin steel tubular (CFDST) members as one of the most recent forms of composite members, and other structural members are beyond the scope of this book.

• 1. The outer steel usually takes a large part of the external axial load as compared to the concrete core because of its higher stiffness under composite action.
• 2. The concrete core close to the neutral axis has an insignificant contribution to the flexural strength.
• 3. The contribution of the concrete core in enhancing the torsional strength is insignificant.
• 4. The initial elastic dilation of concrete under axial compression is relatively small, and thus the confining pressure provided by the steel tube to concrete is relatively low during the elastic stage.
• 5. The heavy self-weight of the concrete can limit the performance of CFST due to the strength-to-weight ratio.

• 1. CFDST have higher flexural and torsional strength as compared to the CFST members. Additionally, their strength-to-weight ratio is improved significantly by replacing the central concrete with a steel tube of a much smaller cross-sectional area. Moreover, the inner tube expands laterally under compression loading, and, hence the confining pressure provided to the concrete also increases. Consequently, the initial confining pressure builds up more rapidly in CFDST as compared to CFST members so that their elastic strength and stiffness are enhanced.