What is an I-beam? An I-beam, also known as H-beam, W-beam (for "wide flange"), Universal Beam (UB), Rolled Steel Joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an I or H-shaped cross-section. The horizontal elements of the "I" are known as flanges, while the vertical element is termed the web. I-beams are usually made of structural steel and are used in construction and civil engineering. Why do we use I Beam, instead of rectangular beam? On the left side we have a simple rectangular beam, whereas on the left hand side on the above image, we have an I section beam. The question that is most commonly asked as to why do I section beam most frequently used in construction as compared to simple rectangular beam. And also why only I beam is used and not a beam of any other shape. When a beam is subjected to stresses, the outer layer is compressed, with the inner one undergo tension. The m