There are other buckling modes… everything depends on how your beam is constrained.
In gravity sewers, the pipe is laid in a straight and constantly sloping grade.
If we have simply supported beam a structure member which is supported at both end by column when load is applied on beam it will experience positive bending moment and bend in concave face structure in downward direction.
Persistent knee buckling may be remedied with surgical removal of these fragments or with the replacement of the knee.
The material is the same, the load is the same, applied in the same direction right? Several methods for approximating strength in the inelastic range have been used for different materials over the years.
As can be seen in Figure 6.