Plate girder web slenderness control: the maximum permissible clear panel dimension of a web of thickness t (between stiffeners) is limited to what multiple of t?

Introduction / Context:
Thin webs in plate girders must be stiffened at intervals to prevent shear buckling. Traditional exam problems reference legacy limits by relating panel clear dimension directly to web thickness t.

Given Data / Assumptions:

• Web thickness = t.
• Clear panel dimension measured between adjacent transverse stiffeners.
• Mild-steel plate girder under shear.

Concept / Approach:
When the web panel becomes too slender, elastic shear buckling occurs. A prescriptive limit ties the maximum clear dimension to a multiple of t. A commonly cited limit in older practice for mild steel is approximately 270 t, beyond which transverse stiffeners must be provided or spacing reduced.

Step-by-Step Solution:

Verification / Alternative check:
Modern codes use rational shear buckling models with limits based on yield strength and panel aspect ratio; this legacy 270 t rule is a quick check aligning with exam-style questions.

Why Other Options Are Wrong:
Smaller multiples (180 t, 220 t, 230 t, 260 t) are more conservative than this traditional limit and not the typical maximum stated in such questions.

Common Pitfalls:
Confusing clear dimension along depth versus along length; ignoring end/bearing stiffener requirements; overlooking weld-induced distortions affecting slender panels.

Final Answer:
270 t