Bridges are essential infrastructure elements that facilitate transportation and connect communities by spanning various obstacles. They come in various designs and types, each carefully engineered to suit specific requirements. In this article, we will explore the components that make up a typical bridge and delve into its classification based on different criteria, such as materials, span length, function, etc.
What is Bridge?
A bridge is a structure that is built to span a physical obstacle, such as a river, valley, road, railway, or any other obstacle that hinders the movement of people, vehicles, or goods. The primary purpose of a bridge is to provide a passage or crossing over the obstacle, enabling continuous connectivity and facilitating transportation and communication.
Bridges consist of several components, each playing a crucial role in the overall structure’s stability and functionality. The main components of a bridge include:
The foundation is the lowest part of the bridge, and it supports the entire structure by transferring the loads from the bridge superstructure to the ground. Depending on the soil conditions and the bridge design, foundations can be shallow, such as spread footings or mat foundations, or deep, such as piles or drilled shafts.
The substructure comprises the piers, abutments, and any other supporting elements between the foundation and the superstructure. Piers are vertical supports that carry the bridge deck and transfer the loads to the foundation. Abutments are supporting structures at the ends of the bridge that hold the backfill and support the end of the bridge deck.
The superstructure is the main load-carrying part of the bridge, located above the substructure. It includes the deck, girders, trusses, or arches, depending on the bridge type. The superstructure is designed to safely carry the weight of traffic, pedestrians, and any other loads applied to the bridge.
The deck is the uppermost surface of the bridge, and it is the part that vehicles, pedestrians, or trains directly travel on. The deck is made of materials like reinforced concrete, steel, timber, or composite materials.
Girders or Beams
Girders or beams are the horizontal load-carrying members of the bridge that support the deck and transfer the loads to the piers or abutments. They can be made of reinforced concrete, steel, or other materials.
Trusses (in Truss Bridges)
Trusses are triangular frameworks made of steel or other materials that provide additional structural support and rigidity to the bridge. Truss bridges use trusses as the primary load-carrying members.
Arch (in Arch Bridges)
Arch bridges have a curved superstructure known as an arch, which transfers the load horizontally to the abutments at each end of the bridge.
Cables (in Suspension and Cable-Stayed Bridges)
A suspension bridge and a cable-stayed bridge use cables for primary support. In suspension bridges, cables hang from towers and support the deck, while in cable-stayed bridges, cables connect the deck directly to the towers.
Bearings are devices placed between the superstructure and the substructure to accommodate movements caused by temperature changes, vibrations, and loads, while ensuring stability and preventing damage.
Expansion joints allow the bridge to expand and contract due to temperature variations without causing structural damage. They also accommodate movement caused by traffic loads and help maintain the integrity of the bridge over time.
Classification of Bridge
Bridges come in a variety of types and designs, each serving specific purposes and adapting to different conditions. Let’s explore various classifications of bridges based on different criteria:
Based on the Construction Materials Used
Historically, wooden bridges were prevalent, but they are less common in modern times due to the availability of more durable materials. Some wooden bridges still exist in certain locations for their aesthetic or historical value.
These bridges are built using stone, brick, or other masonry materials. While masonry bridges were common in the past, they are now rarely constructed for major transportation routes.
A steel bridge is constructed using structural steel components. They are known for their strength, flexibility, and ability to carry heavy loads. Steel bridges are commonly used for long-span structures and movable bridge
The R.C.C. Bridge
An RCC (Reinforced Concrete) bridge is a type of bridge constructed primarily using reinforced concrete as the main building material. RCC bridges are widely used worldwide due to the durability, strength, and versatility of reinforced concrete. They are commonly used for various types of roadways, highways, pedestrian crossings, and small to medium spans.
Prestressed Concrete Bridge
Prestressed concrete is defined as concrete that has been compressed prior to the application of loads. To build a prestressed concrete bridge, prestressed concrete blocks are arranged as deck slabs and supported by girders. These blocks are suitable for bridges with shorter spans as well as those with longer spans.
Based on Alignment
This is the simplest and most common type of bridge alignment. They span a straight path across the obstacle they are designed to cross, such as a river, valley, or road.
Skewed bridges have an alignment that is not perpendicular to the abutments or piers. They are used when the roadway must cross the obstacle at an angle due to terrain constraints or road layout requirements.
Based on Span
Typically have spans up to 30 meters and are commonly used for pedestrian crossings, culverts, or small streams.
Have spans between 30 meters and 120 meters, often used for urban roadways and regional transportation
Have spans exceeding 120 meters and are used for major river crossings, straits, or deep valleys. Examples include iconic suspension bridges and cable-stayed bridges.
Based on the type of Super Structure
Arch bridges have an arched superstructure that transfers the load horizontally to the supports at each end. The arch shape provides natural structural stability, allowing for longer spans and elegant designs. Arch bridges can be made of stone, concrete, steel, or a combination of materials.
Truss bridges use a framework of interconnected triangular elements (trusses) to support the bridge deck. Truss bridges can be made of steel, concrete, or timber, and they are used for medium to long spans.
Suspension bridges have a superstructure supported by steel cables that hang from massive towers. The deck is suspended below the cables, allowing for long spans and significant flexibility. Suspension bridges are commonly used for very long spans, such as crossing wide bodies of water or deep gorges.
Girder bridges have one or more girders (longitudinal beams) supporting the bridge deck. They can be made of steel, concrete, or a combination of materials. Girder bridges are versatile and can be used for various span lengths and load-carrying capacities.
Based on Level Crossing
An overpass bridge is a type of bridge that allows one transportation route (such as a road or railway) to pass over another transportation route without any intersection or level crossing. This design ensures smooth traffic flow and safety by eliminating the need for vehicles or trains to stop at the crossing point.
An underpass bridge is a type of bridge that allows one transportation route to pass under another transportation route without any intersection or level crossing. This type of bridge is commonly used to separate roadways from railways or pedestrian paths from vehicular roads.
Based on Function
A footbridge, also known as a pedestrian bridge or footpath bridge, is a specialized type of bridge designed primarily for pedestrians and cyclists to cross over obstacles such as rivers, streams, roads, railway tracks, or other transportation routes.
Footbridges provide a safe and convenient passage for people on foot or using non-motorized modes of transportation. They play a vital role in enhancing pedestrian connectivity, promoting active transportation, and improving overall urban mobility.
A highway bridge is a type of bridge designed specifically to carry vehicular traffic, including cars, trucks, buses, and motorcycles, over obstacles such as rivers, valleys, railways, other roads, or any physical barrier that interrupts the flow of a highway or roadway.
Highway bridges are a crucial component of transportation infrastructure, facilitating the movement of goods and people across various terrains.
Rail Way Bridge
A railway bridge is a specialized type of bridge designed to carry trains and other rail vehicles over water bodies, valleys, roads, other railways, or any physical barrier that interrupts the flow of a railway line. Railway bridges are essential components of the railway infrastructure, allowing trains to cross obstacles safely and efficiently.
Aqueduct bridges are simply water-carrying structures built to transport water from a source to a system.
Road cum Railway Bridge
A road cum railway bridge, also known as a combined bridge or a multi-use bridge, is a specialized type of bridge designed to accommodate both road and railway traffic.
Based on Inter Span Relation
A simple bridge is a simple, supported beam with two supports at its ends. Simple bridges are appropriate for shorter spans.
A continuous bridge consists of two or more spans that are connected together without any hinges or expansion joints between them. The deck is continuous over the supports, which allows for load sharing between adjacent spans. Continuous bridges are more structurally efficient and can have longer spans compared to simply supported bridges.
Cantilever bridges are formed by constructing two arms or cantilevers from opposite sides of the obstacle and connecting them at the center or using a suspended span. The cantilevered arms balance each other and provide support without the need for central piers.