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Structural

Span

In Plain English

The distance a beam or other member bridges between its two supports.

Definition

The horizontal distance between supports of a structural member such as a beam, joist, girder, or truss. Span length is a primary factor in determining member size, deflection, and the type of structural system required. Longer spans require heavier or deeper members and may require more sophisticated structural systems.

Why It Matters in Bidding

Span dictates member size, depth, and structural system, all of which flow straight into material quantities and cost during a bid. Longer spans push estimators toward heavier steel, deeper joists, or engineered systems, and they affect coordination with mechanical and ceiling heights, so understanding span lets an estimator validate the takeoff and flag where a column-free requirement is driving cost.

Example

Reviewing a gymnasium with a long clear-span roof, the estimator confirms the design uses deep open-web steel joists and prices the heavier members and larger crane accordingly, rather than the lighter sizes used over the shorter classroom spans.

Related Terms

BeamGirderJoistTruss

Frequently Asked Questions

Longer spans require larger or deeper members, stronger connections, and sometimes specialized systems like long-span joists, post-tensioned slabs, or trusses, all of which raise material and erection costs. They can also increase floor-to-floor heights and crane requirements, so an estimator weighs the cost premium against the owner's demand for open, column-free space.
Beam depth controls stiffness and deflection, and as span increases, a deeper section is needed to limit sag and carry load efficiently. Deeper members use more material and may affect mechanical routing and ceiling height. Estimators rely on the structural drawings for sizes rather than assuming a member, since the engineer sets depth for each span.
Span generally measures center-to-center of supports, while clear span is the unobstructed distance between the inside faces of supports. Clear span matters when an owner wants column-free area, since it usually drives larger members and higher cost. Estimators confirm which definition the drawings use so member sizing and pricing match the structural intent.

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