Frequently Asked Questions

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By providing a complete load diagram to the manufacturer. See the SJI Code Of Standard Practice for additional information.

The SJI specification has some variations for determining the allowable stresses for the joist components, different from the AISC specification. Many of the software companies include these equations rather than the SJI variations, consequently the results of a SJI and AISC comparison don’t always match exactly – but they are very close.

No, KCS joists must be reinforced if the concentrated load is between panel points just like all other joists, unless the load is less than or equal to 100 pounds.

For nominal concentrated loads between panel points, which have been accounted for in the specified uniform design loads, a “strut” to transfer the load to a panel point on the opposite chord shall not be required, provided the sum of the concentrated loads within a chord panel does not exceed 100 pounds and the attachments are concentric to the chord.

There are no published inertias for J-Series joists and each manufacturer used a different array of chord angles, so there could be a small variance. You can use the tabulated live load values for l/360 deflection and back into the required inertia. Or you can physically measure the top chord and bottom chord and calculate a value.


Each member company may use various products and geometry in their designs that will meet the performance requirements. Their proprietary design is submitted and approved by the SJI consulting engineer prior to such approval by the SJI.

This determined by the manufacturer and is design specific.

For K-series the maximum width is 6 inches. Other series vary by size and manufacturer.

See the section in the Specification for the Approximate Duct Opening Sizes chart.

Slots are used due to fabrication and field tolerances. Also, hole to hole connections would encourage using joists to plumb the building.

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