Open Web Steel Joists

Open Web Steel Joists (OWSJ)

Open web steel joists are one of the most efficient and widely used structural members in commercial and industrial construction. Manufactured to SJI (Steel Joist Institute) standards, these triangulated steel trusses span long distances at a fraction of the weight of wide-flange beams, making them the go-to solution for large roof and floor framing systems.

Their open-web geometry isn’t just structural economy; it’s coordination economy. Mechanical ducts, electrical conduit, and plumbing runs thread through the web openings without requiring costly dropped ceilings or beams punched with penetrations.

Types and Applications

K-Series Joists are the lightest and most common, used for roof spans up to approximately 60 feet. They’re specified by depth and load capacity, and they work with both metal deck and concrete-over-deck assemblies.

LH-Series (Longspan) Joists handle roof spans from 25 to 96 feet where K-Series reaches its limits. They’re common in warehouses, big-box retail, and manufacturing facilities.

DLH-Series (Deep Longspan) Joists extend spans up to 144 feet and are used where column-free space is paramount: arenas, aircraft hangars, and large industrial buildings.

Joist Girders act as the primary framing members that support the joists themselves. They are designed with the joist spacing built into their geometry, simplifying connection detailing and load transfer.

Engineering Considerations

Joist selection requires careful attention to both gravity loads and lateral bracing requirements. OWSJs have relatively low torsional stiffness and must be adequately braced (both top chord by deck and bottom chord by bridging) to prevent instability during construction and in service. Bridging must be installed in the correct sequence per the erection drawings before any loads are applied.

Vibration is a key serviceability concern for floors framed with open web joists. We evaluate joist systems using AISC Design Guide 11 criteria to ensure occupant comfort, especially in offices, healthcare facilities, and other sensitive environments.

Concentrated loads from mechanical units, hangers, or partition walls must be reviewed against the standard uniform load capacity. Many joist specifications include allowances for specific panel point loads, but field-added loads require engineering analysis.

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Frontier Structural Engineering brings 20 years of commercial and residential design experience to projects across Colorado and California. Whether you're in schematic design or already in the field, we're available.