FAQ – Joists

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How can the correct joist series be determined by the date of original construction of the building in question?
The chart below gives the dates for each joist series from the beginning of the Steel Joist Institute in 1928.

1929-1958  SJ-Series 1953-1958 Longspans
1958-1961  S-Series 1958-1961 L-Series
1961-1978  J-Series 1961-1966 LA-Series
1961-1986 H-Series 1967-1978 LJ-Series
1986- K-Series 1970-1978 DLJ-Series
1962-Present LH-Series
1970-Present DLH-Series


Are bearing seat depths helpful in determining the joist series?
Typical seat depth for short span joists (SJ, S, J, H & K) is 2 ½”. Typical seat depth for long span joists (Longspan, L, LA, LJ, DLJ, LH, DLH) is 5″. For DLH-Series with chord section 18 through 25, the seat depth is 7 ½”.


Can bearing seat depths vary from the K series and LH series joists?
Yes, but the minimum depths are 2.5” and 5” respectively.


Why can’t hole to hole bearing seat connections be used?


Why are the bottom chord extensions not welded?
So that a moment is not developed in the joist or joist girder.


How far can I extend the top chord?
That depends on the loads and the configuration of the TCX. Refer to the Top Chord Extension section in the current Specification.


How large of an additional top chord axial load can I have in my joist?
That depends on the bearing depth and type of joist. The manufacturer can provide this information.


How much extra capacity is built into a joist?
Almost none. Joists are designed for efficiency and a very high strength to weight ratio.


What duct size can I fit through a joist or girder?


Chord widths for joists?


End panel lengths and distance between panel points?
This determined by the manufacturer and is design specific.




How do you calculate the maximum moment for a joist?








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