girders

A girder is a principal horizontal structural member that carries loads from beams, floors, or roofs and transfers them to vertical supports such as columns or walls. Girders are designed to resist bending and shear and are typically larger and stronger than ordinary beams. They play a central role in bridges, buildings, and industrial structures, where they span between supports and form the backbone of the structural frame.

Girders come in several forms. In steel construction, common shapes include I-beams (also known as wide-flange beams), which have a horizontal top and bottom flange connected by a vertical web; box girders are hollow rectangular sections; and plate girders are built from steel plates with flanges and web connected. In bridges, box and plate girders are widely used. Timber girders, built from sawn lumber or glulam, are used in traditional or lightweight constructions. Concrete girders may be cast-in-place or precast and are often integrated with a concrete deck.

Materials: steel girders offer high strength and ductility; reinforced concrete girders combine concrete stiffness with steel reinforcement; timber girders provide lightness and ease of fabrication but lower strength and durability in some environments.

Design and use: the capacity of a girder is determined by its cross-sectional shape and size, material properties, and the loads it carries. Engineers assess bending moments, shear forces, deflection limits, and connection details to columns or piers. Girders require proper detailing to ensure performance under service, fatigue, and environmental conditions.

Construction and maintenance: girders are installed with bracing and supports, connected to columns, walls, or piers. Regular inspection focuses on corrosion, cracking, settlement, and joint integrity; strengthening and repair are possible through retrofitting or replacement.