Limits to shape factor
it can be concluded that to make stiff and strong structures, efficient shape factors have to be made which is often limited by a number of factors as follows.
1. The range of shape factor for a given material is limited either by manufacturing constraints or by local buckling.
2. Steel, for example, can be drawn to thin walled tubing or formed (by rolling, folding or welding) into other efficient shapes; shape factors as high as 30 are common and they may reach 65.
3. Wood cannot be shaped so easily and shapes with values greater than 3 are rare. However, bamboo is a gift of nature and is already shaped in tubular fashion which possesses a high value of shape factor.
But it is very difficult to give it any other shape. Composites, too, can be limited by the present difficulty in making thin-walled shapes.
So far we have learned how the combination of material properties can be used to develop a material index for the selection of a suitable material for a given application under different loading conditions.
Similarly, the cross-sectional shape of a part can be used to enhance the load bearing capacity. An engineering material confirms to a modulus and strength, but it can be made stiffer and stronger when loaded under bending or twisting by shaping it into an I-beam or a hollow tube, respectively.