What are Girders?
Girders are large structural members that carry loads from beams, joists, slabs, or other framing and pass those loads to columns, walls, piers, or foundations.
Definition
Purpose
Girders are an integral part of the structural load path. Girders receive loads from smaller members in the frame and transfer them to columns, walls, piers, or even the foundation. Girder size is determined by factors such as span, load, material, loading conditions, and permissible deflection. In buildings and bridges, girders are used with beams, columns, slabs, connections, and foundations.
Examples of Use
- Steel Girders: Steel girders are usually used in commercial buildings, factories, parking garages, and other structures where large loads must span long distances.
- Bridge Girders: Bridge girders lie below the bridge deck and transfer loads from traffic to piers or abutments.
- Building Framing: Girders can carry floor beams, joists, slabs, and other framing members, particularly where several smaller members meet at one location.
- Transfer Structures: Transfer girders support framing above open areas when columns or walls below cannot line up with the loads above.
- Fabricated Members: Some girders are built from steel plates or assembled sections when a standard rolled shape does not provide the required depth, strength, or dimensions.
Notes
- A girder is usually considered a primary framing member, while a beam often carries loads from one area of framing to a girder or another support.
- Girders vs. beams is mainly a distinction based on their role in the framing system, although girders are often larger and carry heavier loads.
- Steel girders may be rolled steel sections or welded members made from separate plates.
- Bridge girders come in several forms, with the choice depending on span length, loading, site conditions, clearance, and structural design.
- Girder connections must be detailed to handle the forces transferred between the girder and its supporting or supported members.
- Girder takeoffs can cover member lengths, sizes, weights, connection plates, stiffeners, bearing plates, and other steel items needed for fabrication and estimating.
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