🌉Bridge Engineering Unit 6 – Arch Bridges – Types and Behavior

What Are Arch Bridges?

• Arch bridges are a type of bridge that use an arch as the main structural element to span a gap or obstacle
• The arch shape allows the bridge to transfer the weight of the bridge and any traffic loads to the supports at each end (abutments or piers)
• Arch bridges have been used for thousands of years, with early examples dating back to ancient civilizations (Romans, Greeks)
• The arch can be made from various materials (stone, brick, concrete, steel)
• The shape of the arch can vary (semicircular, segmental, pointed)
  • Semicircular arches have a full half-circle shape
  • Segmental arches are a portion of a circle, with a shallower curve than semicircular arches
  • Pointed arches have a more angular, Gothic-style shape
• The arch is typically located under the bridge deck, but can also be above the deck (through arch) or in between two separate deck levels (deck arch)

Types of Arch Bridges

• There are several types of arch bridges, each with distinct characteristics and design features
• Deck arch bridges have the arch located entirely below the bridge deck
  • The deck is supported by vertical members (columns or hangers) that transfer loads to the arch
  • Deck arch bridges are commonly used for medium to long spans
• Through arch bridges have the arch extending above the bridge deck
  • The deck is suspended from the arch using vertical cables or hangers
  • Through arch bridges are often used for longer spans and can have a more dramatic appearance
• Tied-arch bridges are a variation of through arch bridges, where the ends of the arch are connected by a horizontal tie beam
  • The tie beam resists the outward thrust of the arch, allowing for more slender arch designs
• Arch culvert bridges are used for short spans, typically over small streams or drainage channels
  • The arch is usually made of precast concrete or corrugated metal sections
• Rigid frame bridges combine the arch with the deck and supports into a single, rigid structure
  • This design eliminates the need for separate bearings or expansion joints

Key Components of Arch Bridges

• Arch bridges consist of several key components that work together to support the structure and transfer loads
• The arch is the primary load-bearing element, which can be made of various materials (stone, concrete, steel)
  • The shape and size of the arch depend on the span length, loading conditions, and aesthetic considerations
• Abutments are the supports at each end of the bridge that transfer the loads from the arch to the ground
  • Abutments also provide lateral stability to resist the outward thrust of the arch
• Piers are intermediate supports used for longer spans or multiple-arch bridges
  • Piers help distribute the loads and provide additional stability
• The bridge deck is the surface on which vehicles, pedestrians, or trains travel
  • The deck can be made of concrete, steel, or timber, and is supported by the arch through various means (columns, hangers, spandrel walls)
• Spandrel walls are the vertical walls built on top of the arch to support the bridge deck
  • Spandrel walls are commonly used in stone or concrete arch bridges
• Hangers or suspenders are vertical cables or rods used to suspend the deck from the arch in through arch bridges

How Arch Bridges Work

• Arch bridges work by transferring the loads (weight of the bridge, traffic, etc.) through the arch to the supports at each end
• The arch shape is efficient in compression, allowing it to resist the downward forces and transfer them to the abutments or piers
• As the load is applied to the bridge deck, it is transmitted through the vertical supports (columns, hangers, or spandrel walls) to the arch
• The arch experiences compression forces along its length, which are resisted by the abutments at each end
• The abutments also resist the outward thrust of the arch, which is caused by the tendency of the arch to flatten under load
• In deck arch bridges, the load is transferred from the deck to the arch through columns or spandrel walls
• In through arch bridges, the load is transferred from the deck to the arch through vertical hangers or suspenders
• The arch shape and materials used determine the load-carrying capacity and efficiency of the bridge
  • Deeper arches are generally more efficient in transferring loads, but may require taller supports
  • Materials with high compressive strength (stone, concrete) are well-suited for arch construction

Materials Used in Arch Bridges

• Arch bridges can be constructed using various materials, each with its own advantages and characteristics
• Stone was one of the earliest materials used in arch bridge construction
  • Stone arches are durable, long-lasting, and have high compressive strength
  • Granite, limestone, and sandstone are common types of stone used
  • Stone arch bridges are labor-intensive to construct and require skilled craftsmen
• Brick is another traditional material used in arch bridge construction
  • Brick arches are composed of individual brick units bound together with mortar
  • Brick is relatively inexpensive and easy to work with, but has lower strength compared to stone
• Concrete has become the most common material for modern arch bridge construction
  • Reinforced concrete combines the compressive strength of concrete with the tensile strength of steel reinforcement
  • Precast concrete segments can be used for faster construction and improved quality control
  • Concrete arches can be cast in various shapes and sizes to suit different design requirements
• Steel is used in arch bridges for its high tensile strength and flexibility
  • Steel arches are typically used in through arch designs, where the arch is above the deck
  • Steel can be used in combination with concrete (composite construction) to optimize strength and stiffness
• Timber was used historically in arch bridge construction, particularly for short spans and temporary structures
  • Modern timber arch bridges are less common but can be found in some pedestrian and park bridges

Design Considerations

• Designing an arch bridge involves considering various factors to ensure structural integrity, functionality, and aesthetics
• Span length is a primary consideration, as it determines the size and shape of the arch
  • Longer spans require deeper arches or stronger materials to efficiently transfer loads
• Loading conditions must be carefully analyzed, including dead loads (weight of the bridge) and live loads (traffic, wind, seismic)
  • The arch and supports must be designed to withstand these loads with an appropriate factor of safety
• Site conditions, such as the foundation soil, topography, and environmental factors, influence the design and construction of the bridge
  • Poor soil conditions may require deep foundations or ground improvement techniques
  • Topography can affect the height and positioning of the arch and supports
• Aesthetics play a role in arch bridge design, as these structures are often considered landmarks or iconic features
  • The choice of materials, arch shape, and overall proportions contribute to the visual appeal of the bridge
• Constructability is an important consideration, as arch bridges can be complex and challenging to build
  • The construction method (e.g., centering, cantilevering) must be carefully planned and executed
  • Access to the site, material availability, and skilled labor are factors that affect constructability
• Maintenance and durability should be considered in the design process
  • The choice of materials, drainage systems, and access for inspection and repairs impact the long-term performance of the bridge

Advantages and Limitations

• Arch bridges offer several advantages over other bridge types, but also have some limitations
• Advantages:
  • Efficient load transfer: The arch shape is excellent in compression, allowing for efficient transfer of loads to the supports
  • Long spans: Arch bridges can span longer distances than beam or girder bridges, making them suitable for crossing wide valleys or rivers
  • Aesthetic appeal: Arch bridges are often considered visually attractive and can serve as iconic landmarks or tourist attractions
  • Durability: Well-designed and constructed arch bridges can have a long lifespan, with some historic examples lasting centuries
• Limitations:
  • Complex construction: Building arch bridges requires specialized skills and equipment, particularly for larger spans or challenging site conditions
  • Higher cost: The complexity of design and construction often results in higher costs compared to simpler bridge types
  • Sensitivity to foundation settlement: Uneven settlement of the abutments or piers can cause cracks or damage to the arch
  • Limited clearance: The arch shape can limit the vertical clearance for traffic or navigation below the bridge
  • Longer construction time: The construction process for arch bridges can be time-consuming, especially for larger or more complex designs

Famous Arch Bridges

• Many arch bridges around the world are renowned for their engineering, history, or aesthetic qualities
• The Ponte Vecchio in Florence, Italy, is a medieval stone arch bridge known for its shops built along the span
• The Charles Bridge in Prague, Czech Republic, is a 14th-century stone arch bridge featuring baroque statues and a rich history
• The Mostar Bridge in Bosnia and Herzegovina, originally built in the 16th century, is a reconstructed stone arch bridge that symbolizes the city's resilience
• The Sydney Harbour Bridge in Australia is a steel through arch bridge and a major landmark of Sydney, known for its distinctive design and scale
• The Hejiang Pavilion Bridge in China is a traditional stone arch bridge with a pavilion built on top, showcasing Chinese architecture and engineering
• The New River Gorge Bridge in West Virginia, USA, is a steel arch bridge with a 518-meter main span, one of the longest in the world
• The Viaduct de Millau in France is a modern cable-stayed bridge with a steel arch supporting the tallest pier, showcasing contemporary arch bridge design