28.02.2013 Views

Building Design and Construction Handbook - Merritt - Ventech!

Building Design and Construction Handbook - Merritt - Ventech!

Building Design and Construction Handbook - Merritt - Ventech!

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

STRUCTURAL THEORY 5.129<br />

roof girder is supported at one end by a column <strong>and</strong> near the other end by a cable<br />

that extends diagonally upward to the top of a vertical mast above the column<br />

support (cable-stayed-girder construction, Fig. 5.100). Cable stress an be computed<br />

for this case from the laws of equilibrium.<br />

Cables also may be used in building construction instead of girders, trusses, or<br />

membranes to support roofs, For the purpose, cables may be arranged in numerous<br />

ways. It is consequently impractical to treat in detail in this book any but the<br />

simplest types of such applications of cables. Instead, general procedures for analyzing<br />

cable-supported structures are presented in the following.<br />

5.16.1 Simple Cables<br />

An ideal cable has o resistance to bending. Thus, in analysis of a cable in equilibrium,<br />

not only is the sum of the moments about any point equal to zero but so is<br />

the bending moment at any point. Consequently, the equilibrium shape of the cable<br />

corresponds to the funicular, or bending-moment, diagram for the loading (Fig.<br />

5.101a). As a result, the tensile force at any point of the cable is tangent there to<br />

the cable curve.<br />

The point of maximum sag of a cable coincides with the point of zero shear.<br />

(Sag in this case should be measured parallel to the direction of the shear forces.)<br />

Stresses in a cable are a function of the deformed shape. Equations needed for<br />

analysis, therefore, usually are nonlinear. Also, in general, stresses <strong>and</strong> deformations<br />

cannot be obtained accurately by superimposition of loads. A common procedure<br />

FIGURE 5.100 Two types of cable-stayed girder construction for roofs.<br />

FIGURE 5.101 Simple cable: (a) cable with a uniformly distributed load; (b) cable with<br />

supports at different levels.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!