What is the difference between a bridge pier and abutment?

The fundamental difference between a bridge pier and an abutment lies in their location and primary function within a bridge structure: piers are vertical supports located between spans, while abutments are horizontal supports found at the very ends of the bridge.

Bridge construction relies on robust support structures to safely carry traffic over obstacles like rivers, valleys, or other roadways. These essential components ensure the bridge deck remains stable and transfers loads effectively to the ground.

Understanding Bridge Supports: Piers vs. Abutments

Both piers and abutments are critical substructure elements that bear the weight of the bridge deck and transfer it to the foundation below. However, they serve distinct roles based on their position and the types of forces they manage.

Bridge Piers

Bridge piers are vertical structures positioned between spans to support the bridge deck, acting as intermediate supports. They are designed to carry the vertical loads from the bridge deck and transfer them down to the foundation, which then distributes the weight into the underlying soil or rock.

• Location: Piers are situated within the main span of the bridge, standing in the water (for river crossings) or on land between different sections of the bridge.
• Primary Function:
  • Vertical Support: Directly support the bridge deck and superstructure.
  • Load Transfer: Transmit dead loads (weight of the bridge itself) and live loads (traffic, pedestrians) from the deck to the foundation.
  • Aesthetic Element: As noted, piers are often serving as aesthetic elements, contributing to the visual appeal and architectural design of the bridge.
• Forces Resisted: Piers must withstand not only vertical compressive forces but also significant horizontal forces such as:
  • Wind loads
  • Seismic (earthquake) forces
  • Water currents and ice pressure (for bridges over water)
  • Impact from vessels (for navigable waterways)
• Types of Piers:
  • Column Piers: Simple, slender columns.
  • Wall Piers: Solid, continuous walls providing broad support.
  • Hammerhead Piers: Feature a wider top to support multiple girders.
  • Pier Bents: A frame of columns connected by a cap beam.
• Practical Insight: In multi-span bridges, each pier allows for shorter, more economical spans of the deck, reducing the need for excessively long girders.

Bridge Abutments

Bridge abutments are horizontal support structures at the ends of the bridge, connecting it to the embankment or foundation. Unlike piers that are internal, abutments mark the beginning and end of the bridge structure, forming the transition from the approach road to the bridge deck.

• Location: Abutments are located at the extreme ends of the bridge, where the bridge deck meets the land or roadway leading up to it.
• Primary Function:
  • End Support: Provide the final support for the bridge deck at its termination point.
  • Connection: Connecting it to the embankment or foundation, seamlessly linking the bridge structure with the land approach.
  • Earth Retention: Retain the earthen approach fill, preventing the road embankment from sliding into the bridge opening.
  • Load Transfer: Transmit vertical and horizontal loads from the bridge to the foundation.
• Forces Resisted: Abutments handle various forces, including:
  • Vertical loads from the bridge deck.
  • Horizontal earth pressure from the retained soil behind them.
  • Thermal expansion and contraction forces from the bridge deck.
  • Braking and acceleration forces from traffic.
• Types of Abutments:
  • Full Height Abutments: Extend from the bridge seat down to the foundation, retaining the full height of the approach fill.
  • Stub Abutments: Shorter abutments that rest on a fill embankment, typically used when the approach fill is stable.
  • Integral Abutments: Designed to move with the bridge deck, eliminating expansion joints and often used for shorter bridges.
• Practical Insight: Abutments are crucial for managing the transition from the flexible roadway to the rigid bridge structure, often incorporating features like wing walls to retain the soil at the sides of the approach embankment and prevent erosion.

Key Differences: Pier vs. Abutment

The table below summarizes the core distinctions between these two vital bridge components:

Both piers and abutments are indispensable elements in bridge engineering, each meticulously designed to fulfill its specific role in ensuring the bridge's stability, longevity, and safe operation. Their distinct locations and functions highlight the complex interplay of forces and structural requirements in bridge design.