1. Failure mode 1, web crippling below the stiffener:
Yielding in the web below the bottom of the stiffener
with or without excessive yielding in the stiffener
led to the web crippling failure mode and was seen
in case of all half-depth stiffeners where the load was
applied through a plate. It was also seen in the case of
specimens with thick half-depth stiffeners subjected to
concentric loading through a roller. Figures 4 and 5
show test specimens that failed in this mode.
2. Failure mode 2, local stiffener crippling: This occurred
in beams with thin to moderately thick half-depth
stiffener under concentric loading through a roller. It
was also noted in all specimens subjected to eccentric
roller loads. In this failure mode, one of the stiffeners
crippled with either some or no crippling in adjacent
web. Figures 6 and 7 show test specimens that failed in
this mode.
3. Failure mode 3, global stiffener crippling: This was
found to occur in all specimens with deep stiffeners,
subjected to concentric loads through a roller or an
I-beam. In this failure mode, a cross-section comprised
of both stiffeners and part of the web on each
side of the stiffeners crippled together. Figures 8 and 9
show test specimens that failed in this mode.
It is worth noting that web crippling below the stiffeners
(failure mode 1) occurred where webs had half-depth stiffeners.
This type of failure, however, was not seen in webs
with three-quarters-depth stiffeners. This observation led to
one of the important conclusions and recommendations of
this paper.