Vertical stiffener spacing in plate girders (without horizontal stiffeners): If d is the distance between the flange angles (i.e., clear depth between vertical legs), the minimum spacing of vertical stiffeners should not be less than which fraction of d?

Introduction / Context:
Vertical stiffeners prevent web buckling and help distribute concentrated loads in plate girders. Codes and handbooks prescribe limits on the maximum and minimum spacing, often expressed as fractions of the clear web depth d (between inner faces of flange angles) when horizontal stiffeners are absent.

Given Data / Assumptions:

• Plate girder without horizontal stiffeners.
• Clear depth between vertical legs of flange angles is d.
• We seek the minimum recommended spacing between consecutive vertical stiffeners.

Concept / Approach:
Too-close stiffeners are uneconomical and can cause fabrication congestion, while too-wide spacing risks web instability. Traditional guidance sets a lower bound around one-third of the clear depth, i.e., ≥ 0.33 d, to ensure a rational panel aspect ratio and practical detailing.

Step-by-Step Solution:
Identify the reference dimension: d (clear depth).Apply the empirical minimum spacing criterion: s_min ≈ 0.33 d.Choose the listed value 0.33 d.

Verification / Alternative check:
Sample designs using typical web slenderness limits show vertical panel widths between about 0.33 d and 1.5 d depending on shear demand and web thickness, consistent with the stated minimum spacing.

Why Other Options Are Wrong:

• 0.15 d and 0.22 d: unnecessarily close spacing; impractical and uneconomical for standard girders.
• 0.44 d: acceptable but not the minimum commonly cited; the question asks for the minimum lower bound.

Common Pitfalls:

• Confusing minimum spacing with maximum spacing; both limits exist but serve different stability and economy concerns.
• Using overall depth instead of clear depth when computing spacing ratios.

Final Answer:
0.33 d