I-beams are typically made from steel or from concrete


that is reinforced with pre-stressed steel rods to improve

its tensile strength.  The top and bottom horizontal parts

of the steel I-beam are called flanges, and the middle,

vertical section, is called the web. Load bearing Ι-beams

are called girders.  Another advantage of the I-beam

design is that sections can be riveted, bolted, or welded

together to make longer members and fix them to their

supports.  This enables the creation of extended steel

Fig. 149 - Steel Ι-beam skeleton

Ι-beam and column skeleton frameworks for multi-story

framework of a building

buildings like skyscrapers.

(visualization model)


Truss beams


There are limits to how much material can be removed from the middle of an Ι-beam and

placed at its outer edges before the web becomes too slender for its height and is prone to

twisting and buckling under load.  To repeat, the material in the middle of the beam's

cross section resists the tendency of the upper and lower edges of the beam to slide past

each other, or shear, when loaded.  One design solution is to use a truss beam where the




Fig. 150 - Truss beam

(demonstration model)

click image to enlarge



web consists of a triangulated arrangement of small diameter struts instead of being one

continuous section of material.  A force applied to the top edge of the truss beam is

distributed throughout the struts as axial forces.  The diagonal struts should be angled 45o

relative to the flanges of the beam for maximum resistance to shear stresses.  Truss beams

are commonly used for floor support joists and rafters in buildings.


Back to Knowhere

Page 98 - Building stability - Truss beam

home   sitemap   products   Polywood   .networks   contact us   Knowhere   3Doodlings