When designing plate girders, it's crucial to ensure the stability of the web. The web of a plate girder is often very thin compared to its depth, making it susceptible to buckling under shear and bending stresses. To prevent this, vertical stiffeners and sometimes horizontal stiffeners are provided.

Plate Girder Web Stiffening Purpose

Plate girders are structural elements primarily used to carry heavy loads over long spans. They typically consist of a top and bottom flange connected by a thin web plate. The web's primary function is to resist shear forces, while the flanges resist bending moments.

• Web Buckling: Due to their slender nature, the webs of plate girders can buckle under compressive or shear stresses. This phenomenon, known as web buckling, can lead to structural failure if not properly addressed.
• Stiffeners: To enhance the buckling resistance of the web, stiffeners are welded to the web plate. These stiffeners act like columns or beams, increasing the out-of-plane stiffness of the web panel and preventing it from buckling.
• Vertical Stiffeners: These are commonly provided at points of concentrated loads, support reactions, and at regular intervals along the span. Their main purpose is to subdivide the web into smaller panels, which significantly increases the buckling capacity of the web. This subdivision is essential because the buckling strength of a plate is inversely proportional to its aspect ratio (ratio of panel dimensions).

Web Panel Clear Dimension Limit

For a plate girder web that is vertically stiffened, specific code provisions limit the dimensions of the resulting panels to ensure adequate buckling resistance. These limits are based on the thickness of the web, denoted by '\(t\)'.

According to standard design codes for steel structures, such as IS 800:2007 (Indian Standard Code of Practice for General Construction in Steel), for webs provided with only vertical stiffeners, the clear depth of the web panel (distance between flanges) or the clear length of the panel (distance between vertical stiffeners) must be controlled.

The question specifically asks about the "smallest clear dimension of a panel" not exceeding a certain multiple of the web thickness \(t\). This limit ensures that the web panels are not excessively large, which would make them prone to buckling under shear.

For a plate girder web that is stiffened vertically, the generally accepted limit for the maximum clear depth of the web, or the maximum clear distance between vertical stiffeners, is based on code provisions. The clear depth of the web (distance between flange angles/plates) or the clear distance between vertical stiffeners should not exceed a certain multiple of the web thickness \(t\).

Specifically, for a web stiffened vertically, the smallest clear dimension of a panel (which is typically the clear depth of the web, or the clear spacing of stiffeners if that dimension is smaller) should not exceed:

• \(180t\)

This limit is crucial for preventing the shear buckling of the web plate between the vertical stiffeners and the flanges, thereby ensuring the structural integrity and safety of the plate girder.