T-beam

A T-beam is a structural section whose cross section resembles a capital T: a vertical web carries a horizontal flange at the top. The beam derives its strength from this geometry. Load applied to the top flange transfers down through the web to the supports below. The flange resists compression; the web resists shear. This arrangement is efficient because material is positioned where stress is greatest, avoiding the waste of a solid rectangular section.

T-beams fall into two categories: rolled and built-up. Rolled T-beams are produced directly from a rolling mill, common in steel mills as a standard product. A typical metric rolled T-beam might carry a designation like T-section 80x80x6, meaning an 80 mm flange width, 80 mm total height, and 6 mm web thickness. Built-up T-beams are fabricated by welding a flat plate (the flange) to a rolled beam or plate (the web), allowing custom dimensions when standard rolled sections do not suit the design.

The asymmetric T-beam is distinct from the symmetric I-beam, which has flanges at both top and bottom. A T-beam has only one flange, making it suitable for applications where load acts primarily downward onto a single surface. Composite T-beams are also common in precast concrete construction, where concrete is molded in the T shape and prestressed steel is tensioned to improve load capacity.

Typical uses and failure modes

T-beams appear in bridge decks, where the flange forms the road surface and the web carries the load to piers. They are used as purlins in industrial buildings and as shelf supports in warehouse racking. The primary failure mode is web buckling under high shear stress, particularly in slender webs. Lateral torsional buckling can also occur if the flange is not properly braced. Coping with these risks requires checking slenderness ratios and, in some designs, adding stiffeners (internal webs) perpendicular to the main web.

The name T-beam is descriptive rather than derived; it simply reflects the profile when viewed in cross section. In older civil engineering texts, particularly British practice, the rolled steel T-section is sometimes called a T-iron or T-steel. The section is favored over other shapes when material cost and fabrication speed matter equally, and when load is strictly one-directional.