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Composite column

Steel spandrel

Concrete topping on composite metal deck

Gravity steel framing

Steel spandrel

Concrete topping on composite metal deck

Gravity steel framing

Floor beam ji-ii ir h iL

Steel column

Erection column Steel spandrel Composite column

Column vertical reinforcement Column ties

FIGURE 22.42 Composite tubular system: (a) plan view and (b) beam-to-column connection.

hollow perforated tube. The overturning moment under the action of lateral load is resisted by compression and tension of the leeward and windward columns, which are called the flange columns. The shear is resisted by bending of the columns and beams at the two sides of the building parallel to the direction of the lateral load, which are called the web frames.

Deepening on the shear rigidity of the frame tube, there may exist a shear lag across the windward and leeward sides of the tube. As a result of this, not all the flange columns resist the same amount of axial force. An approximate approach is to assume an equivalent column model as shown in Figure 22.43. In the calculation of the lateral deflection of the frame tube it is assumed that only the equivalent flange columns on the windward and leeward sides of the tube and the web frames would contribute to the moment of inertia of the tube.

The use of exterior framed tube has the following distinct advantages: (1) It develops high rigidity and strength for torsional and lateral-load resistance, since the structural components are effectively placed at the exterior of the building forming a three-dimensional closed section. (2) Massiveness of the frame tube system eliminates potential uplift difficulties and produces better dynamic behavior. (3) The use of gravity steel framing in the interior has the advantages of flexibility and enables rapid construction. If a composite floor with metal decking is used, electrical and mechanical services can be incorporated in the floor zone.

Composite columns are frequently used in the perimeter of the building where the closely spaced columns work in conjunction with the spandrel beam (either steel or concrete) to form a

Distribution without shear lag

Distribution without shear lag

Actual axial stress distribution

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