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Structural Concrete - Hassoun

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562 Chapter 16 Continuous Beams and Frames<br />

Figure 16.6<br />

(a) Gable and portal frames (schematic) and (b) multibay, multistory frame.<br />

Figure 16.7<br />

Assumption of fixed column ends for frame analysis.<br />

concrete sections are used. Once the moments are calculated, the sections assumed previously are<br />

checked and adjusted as necessary. More accurate analysis can be performed using computers,<br />

which is recommended in the structural analysis of statically indeterminate structures with several<br />

redundants. Methods of analysis are described in many books on structural analysis.<br />

16.4 PORTAL FRAMES<br />

A portal frame consists of a reinforced concrete stiff girder poured monolithically with its supporting<br />

columns. The joints between the girder and the columns are considered rigidly fixed, with the<br />

sum of moments at the joint equal to 0. Portal frames are used in building large-span halls, sheds,<br />

bridges, and viaducts. The top member of the frame may be horizontal (portal frame) or inclined<br />

(gable frame) (Fig. 16.8). The frames may be fixed or hinged at the base.<br />

A statically indeterminate portal frame may be analyzed by the moment–distribution method<br />

or any other method used to analyze statically indeterminate structures. The frame members are<br />

designed for moments, shear, and axial forces, whereas the footings are designed to carry the forces<br />

acting at the column base.

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