Lecture Notes on Bridge Engineering and Types

Introduction

• Earth’s topography can hinder easy movement.
• Bridges help us traverse areas that are too wet, steep, etc.
• Bridges are often seen as magnificent structures, worthy of admiration.
• The classification of bridges usually depends on how they manage structural forces.

Beam Bridges

• Definition: Simplest structural form; a horizontal member across two supports.
• Types:
  • Rolled steel beams (stringers)
  • Steel plate girders
  • Concrete girders (modern overpasses)
  • Box girders (efficient material use)
• Limitations: Can't span large distances due to self-weight challenges.

Truss Bridges

• Definition: Utilizes a truss assembly for a lightweight, rigid structure.
• Characteristics:
  • Members experience axial loads (compression or tension).
  • Truss designs have specific names based on arrangements.
• Types:
  • Through truss (deck at bottom)
  • Deck truss (deck atop)
  • Lenticular truss: lens-shaped
  • Bailey Bridges: portable, temporary trusses

Arch Bridges

• Definition: Use a curved element to transfer weight via compression.
• Types:
  • Deck arch (arch below roadway)
  • Through arch (arch extends above roadway)
  • Moon bridges (exaggerated arch)
  • Tied arch bridges (use a cord for thrust force resistance)
• Challenges: Requires strong abutments or temporary supports during construction.

Cantilever Bridges

• Definition: Use beams or trusses projecting horizontally for balance.
• Characteristics:
  • Central piers bear compression loads.
  • Effective for long spans.

Cable-Stayed Bridges

• Definition: Deck supported by cables (stays) attached to towers.
• Characteristics:
  • Can have central or multiple towers.
  • Simplicity leads to various configurations.

Suspension Bridges

• Definition: Use cables to suspend the deck.
• Types:
  • Simple suspension (basic rope bridge)
  • Stressed ribbon (cables integrated into deck)
  • Suspended deck bridge (iconic long spans)
• Features: Require stiffening with girders/trusses.

Movable Bridges

• Definition: Can move to allow ship passage.
• Types:
  • Bascule bridge (rotates upward)
  • Swing bridge (rotates horizontally)
  • Vertical lift bridge (raises deck horizontally)

Floating Bridges

• Definition: Use buoyant supports without needing a foundation.
• Applications: Common in military, some permanent examples exist.

Viaducts

• Definition: Long bridges with multiple spans over land.
• Usage: Often referred to as elevated expressways.

Creative Combinations

• Bridges often combine elements:
  • Phyllis J. Tilly Bridge (arch and stress ribbons)
  • Third Millennium Bridge (concrete tied arch with suspension cables)

Concluding Thoughts

• Bridges display a variety of designs and engineering creativity.
• Understanding basic structures helps appreciate complex designs.
• Examples include the use of living tree roots or bridges for specific purposes like pipelines or animals.

Additional Insights

• Importance of understanding and contextualizing news stories through platforms like Ground News.
• Bridges not only connect places but also have a significant cultural and functional impact.