Plate Girder Stiffener: Preventing Web Compression Buckling

In structural engineering, plate girders are deep beams used for large spans. The web plate of a plate girder is susceptible to different types of instability under load.

Function of Horizontal Stiffeners

Horizontal stiffeners are specifically added to the web plate of a plate girder to address a particular failure mode:

• Prevent Compression Buckling: When a plate girder bends, the top portion of the web experiences compressive stress, similar to the top flange. If the web plate is relatively thin and deep (high slenderness ratio), it can buckle locally under this compression before the material yields. Horizontal stiffeners act as intermediate supports along the web's depth, increasing its resistance to this compressive buckling.

Why Other Options Are Incorrect

• Yielding: Yielding is a material failure due to exceeding the stress limit. It's primarily managed by selecting appropriate steel grades and ensuring the flanges and web have sufficient cross-sectional area. Stiffeners do not directly prevent yielding.
• Shear Buckling: Shear buckling is a concern for the web plate, especially under transverse loads. However, vertical stiffeners are typically used to prevent shear buckling by stiffening the web against shear deformation.
• Excessive Deflection: Deflection is primarily controlled by the girder's stiffness (moment of inertia), which is significantly influenced by the size of the flanges and the overall depth of the girder. While stiffeners add some stiffness, their main purpose is stability (buckling), not controlling overall deflection.

Therefore, the primary reason for providing horizontal stiffeners is to prevent the web plate from buckling under compression.

The correct option is Compression buckling of web plate.