Steel Plate Girder Bridges: Design, Types, and Applications

Steel plate girder bridges are among the most commonly used bridge types worldwide, consisting of fabricated steel girders that support the bridge deck. These bridges offer an excellent balance between strength, economy, and constructability, making them ideal for short to medium spans (typically 20-100 meters).

Key Components:

1. Main Girders:

   • Welded or bolted steel plates forming I-shaped sections

   • Typically deeper than rolled steel beams for greater strength

2. Flanges:

   • Top flange (compression)

   • Bottom flange (tension)

   • Width and thickness vary along span based on bending moments

3. Web Plate:

   • Vertical plate connecting flanges

   • Resists shear forces

   • Often reinforced with stiffeners

4. Stiffeners:

   • Transverse stiffeners (vertical plates) prevent web buckling

   • Longitudinal stiffeners increase bending capacity

5. Bracing System:

   • Provides lateral stability during construction and service

   • Includes cross frames and diaphragms

Types of Steel Plate Girder Bridges:

1. Non-Composite vs. Composite:

   • Non-composite: Steel girders act independently from deck

   • Composite: Steel girders and concrete deck work together (most common today)

2. Deck Types:

   • Concrete deck on steel girders (most common)

   • Orthotropic steel deck (lighter weight)

3. Span Arrangements:

   • Simply supported (single span)

   • Continuous over piers (multiple spans)

   • Cantilevered construction

Advantages:

• High strength-to-weight ratio

• Faster construction than concrete alternatives

• Adaptable to various geometries (curved, skewed)

• Easily modified or strengthened

• Cost-effective for spans up to 100m

Disadvantages:

• Requires corrosion protection

• More susceptible to fatigue than concrete

• May require more maintenance

• Less aesthetically pleasing than some alternatives

Construction Methods:

1. Piece-Small Erection:

   • Girders assembled in shop

   • Transported in segments

   • Field-bolted on site

2. Full-Span Erection:

   • Complete girders lifted into place

   • Requires large cranes

3. Incremental Launching:

   • Assembled at one end

   • Pushed/pulled into position

Design Considerations:

• Fatigue resistance (especially for highway bridges)

• Lateral-torsional buckling prevention

• Web crippling at supports

• Deflection limits

• Connection detailing

Typical Applications:

• Highway overpasses

• Railway bridges

• Pedestrian bridges

• Urban viaducts

Notable Examples:

1. I-35W St. Anthony Falls Bridge (USA): Replaced collapsed bridge with modern plate girders

2. Second Severn Crossing (UK): Continuous plate girder approach spans

3. Tappan Zee Bridge replacement (USA): Uses twin steel plate girders

Maintenance Requirements:

• Regular painting/coating

• Inspection for cracks and corrosion

• Bearing maintenance

• Deck joint maintenance

Innovations:

• High-performance steels (HPS)

• Corrosion-resistant alloys

• Improved welding techniques

• Advanced coating systems

Steel plate girder bridges continue to be the workhorse of medium-span bridge construction due to their reliability, economy, and well-understood behavior. Modern fabrication techniques and materials have extended their capabilities while reducing life-cycle costs.