10. Design method for concrete filled tube members with rectangular section

  • A method was proposed to estimate the flexural capacity and deformation performance of rectangular CFT members.
  • The cross section of rectangular CFT members can be made up to 30% smaller than other existing members.
  • Improving the connectivity of these members to building columns in station buildings etc. can reduce construction costs for connection work by 10%.

Concrete Filled Tube (CFT) members, as the name suggests have a relatively simple structure and are made of steel tubes filled with concrete. In addition, even small cross sections have good flexural capacity, and are easy to use in construction. There are already established design standards for circular cross-section CFT members which are already employed extensively in structures, however there are no set standards yet for rectangular CFT members.

Rectangular CFT members are in demand however to improve connectivity with beams, and building columns used in station buildings (Fig. 1).

Loading tests were conducted on a test model, and the results were used to propose a method for estimating deformation performance, flexural capacity and for setting damage levels, based on the principles required for a design standard (Fig. 2). Based on this, rectangular CFT members can be adapted for used on actual structures. The proposed estimation method was used to produce a normal CFT column following the trial design. The result of this trial showed that the rectangular CFT column had a similar section size to that of the circular CFT column, however the cross-section size would be approximately 30% smaller than using reinforced concrete columns (Fig. 3).

The present method can be used to design CFT members with the same dimensions as building columns, as early as from the design stage for station buildings. This would mean greater connectivity of these members and allow cost savings for connections of about 10%. These results were taken into account to draft in an inspection handbook and develop analysis tools.

Fig. 1 Example of rectangular CFT columns being used on a station building
Fig. 2 Comparison of experimental values and those estimated using the proposed method
Fig. 3 Comparison of cross-section
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