Unstiffened knee joint design

[sdz]

How do you design an unstiffened moment knee joint?
These occur frequently in stair stringers such as shown in the attachment. So far I have found a method for rectangular hollow sections but not open sections.

 

[ishvaaag]

The bevel joint has along the seam line both compression to one side and tension to the other. These effects need to be cared for. You need to care for web buckling for the compression, and overall interaction of the stresses. This most likely can be cozily be made today with a 3D model of the Von Mises stressess checked against a reduced limit yield strength enough to care for web buckling effect.

 

[asixth]

For a 90 degree knee joint with deeper sections (such as a 410UB's/W16's), I have always provided stiffeners joining the flanges (to create a square in the panel zone).

For your example, I would calculate the flange forces and calculate the component which needs to be transferred into the web and design the web for that component of force. Similar to a bearing force.

 

[hokie66]

Most of us don't bother to do the calculations for stair stringers, as they are typically lightly loaded and the web can readily absorb the flange forces. For more heavily loaded members, use an end plate, with both sides butt welded to the plate.

 

[sdz]

Usually when I design these sorts of connections I use a stiffener to take out the unbalance flange forces but I am looking for a design method so I can check an existing connection.