= 6 /8 Q - + 6) 20 Marks An innovation in structural engineering is the Concrete Filled Double Skinned Tube (CFDST). A C

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6 8 Q 6 20 Marks An Innovation In Structural Engineering Is The Concrete Filled Double Skinned Tube Cfdst A C 1 (360.57 KiB) Viewed 39 times

= 6 /8 Q - + 6) 20 Marks An innovation in structural engineering is the Concrete Filled Double Skinned Tube (CFDST). A CFDST consists of a hollow section placed inside another larger hollow section, and the space in between filled with concrete. The inside of the inner tube is not filled. Once filled, the CFDST acts compositely. The CFDST has the following properties: ● Aluminium outer tube with dimensions 100 mm × 5 mm, and Ealuminium = 70000 MPa. Steel inner tube with dimensions 50 mm x 2.5 mm, and Esteel = 200000 MPa. ● Concrete infill, with Econcrete = 30000 MPa. ● All materials behave linear elastically. ● The member is used as a column, 4 m in length, and is subjected to an axial compression. ● The design engineer wants to ensure that the stress in the concrete does not exceed fconcrete, max = 25 MPa. a) When the concrete reaches its maximum permissible stress of 25 MPa, give values for the following: 100 mm Concrete strain and stress Aluminium strain and stress ● Steel strain and stress Total axial shortening 5.0 mm ● Total axial force Steel has a coefficient of thermal expansion of 12 × 106 (°C)¹¹, concrete has a value of 12 × 106 (°C)¹, and aluminium a value of 24 × 106 (°C)¹¹. Ignoring any directly applied external axial load, what would happen to the steel, aluminium and concrete portions of this column if it experienced a temperature increase? How could the design of the column be changed to reduce any possible issues? b) O 50 mm (inner thickness 2.5 mm) Typical column cross-section 4 m