Direct Answer
A seated connection is one where the beam bears on a shelf or seat angle welded to the support, with a top angle or clip providing stability (but minimal moment transfer). It is used where beam rotation (end rotation under load) must be accommodated freely, where shop-applied welded connections are preferred, or where the beam must be supported temporarily before permanent connections are made. Unstiffened seat angles handle small reactions; stiffened seat angles handle larger.
Full Explanation
Seat connection types: (1) Unstiffened — a horizontal leg of the seat angle bears the beam bottom flange; a flexible top angle provides lateral stability. Capacity is limited by the angle's bending capacity. (2) Stiffened — a vertical stiffener plate is welded to the seat angle, dramatically increasing capacity. AISC Manual Tables 10-8 and 10-9 provide unstiffened and stiffened seat capacity. Seated connections are simple to erect (beam drops onto seat before permanent connections are made) and are common in pre-engineered buildings and heavy industrial applications with large beam reactions.
What This Means for Your Shop
The bearing length on a seated connection is critical — too little bearing causes web crippling at the beam end; too much bearing can interfere with adjacent members. Verify bearing length matches the connection design, especially for long-span, heavily-loaded beams.
Common Mistakes
Not checking web crippling capacity at the beam end for stiffened seat connections. High reactions on slender webs can cause web crippling before the seat reaches its bending capacity. This must be verified by the engineer.
Recommended Process
For any seated connection with a reaction over 30 kips, confirm with the engineer that web crippling has been checked at the specified bearing length. Include the bearing length on the piece mark drawing as a critical dimension.