The Upper and Lower Bridge Structure & Its Components

Bridges have upper and lower structures that function to support the loads above them. The construction of a bridge involves a deep understanding of appropriate construction technology as well as mathematical and physical principles. Bridges are also built to be durable and long-lasting.

The types of bridge constructions also vary depending on field conditions. The structure of a bridge follows the type of construction used. To understand the upper and lower bridge structures more deeply, read this article carefully.

Types of Bridge Structures Based on Their Position

A bridge is a structure designed to connect two points separated by obstacles, such as rivers, valleys, or highways.

In general, bridge structures can be divided into two main parts, the lower structure and the upper structure. Each of these structures has its own components.

Lower Bridge Structure

The lower bridge structure is the part that transfers the load from the upper structure to the ground or riverbed. The function of the lower bridge structure is to serve as the main support for the entire bridge.

This part must have a strong bearing capacity to withstand various loads. Below are its main components:

1. Foundation

The foundation is the main element that supports the entire bridge load and transfers it to the ground or underlying rock. The type of foundation used depends on the soil conditions at the construction site. With a solid foundation, a bridge can last for a long time and withstand various environmental pressures.

2. Abutment

An abutment is a supporting structure located at both ends of the bridge, functioning to resist the pressure from the upper structure. Additionally, abutments also help retain the soil behind them to prevent landslides in the area beneath the bridge. The construction of abutments must be strong enough to bear both horizontal and vertical loads.

3. Pillars

Pillars are vertical elements that function as additional supports for bridges with long spans. These structures are placed between two abutments to help distribute the load evenly. With pillars, a bridge can have a longer span without losing stability and strength.

Upper Bridge Structure

The upper bridge structure is the part that supports traffic loads and distributes them to the lower structure. This section must be designed to be strong enough to withstand vehicle loads, wind, and other environmental factors.

Below is an explanation of some key components of the upper bridge structure:

1. Main Girder

The main girder is the primary beam that bears the heaviest load from traffic passing over the bridge. This crucial bridge structure is typically made of steel or reinforced concrete and is installed parallel to the bridge's direction. The load received from above is evenly distributed to the lower structure.

The design of the main girder must consider various factors, such as traffic load, wind pressure, and temperature changes that may cause material expansion or contraction. Using high-quality materials is essential to ensure the main girder remains strong over time.

There are several common types of main girders used in bridge construction, such as box girders and truss girders. Box girders have higher resistance to torsion and bending, while truss girders are more suitable for long-span bridges due to their lightweight yet strong structure.

2. Cross Girder

The cross girder is a beam installed perpendicular to the main girder, functioning to enhance the stability of the upper structure. This element helps distribute the load from the bridge deck to the main girder more effectively. With the presence of cross girders, the bridge becomes sturdier.

Cross girders also serve to unify multiple main girders into a single integrated structure. This prevents the main girders from shifting over time due to the increasing loads the bridge endures. Strengthening this structure helps reduce the risk of bridge deformation.

3. Bridge Deck

The bridge deck is the surface that comes into direct contact with vehicles and functions as the traffic lane. This component must have high durability to withstand heavy loads and extreme weather conditions to prevent damage.

The materials used are typically reinforced concrete, which has high resistance to pressure.

4. Approach Slab

The approach slab is a transitional component that connects the bridge deck to the abutment and surrounding roadway. It functions to reduce shocks when vehicles transition from the road to the bridge or vice versa.

With the presence of an approach slab, the ride becomes smoother, and the bridge structure remains durable.

5. Wearing Course

The wearing course is an additional layer placed on top of the bridge deck to provide better traction for vehicles. This component is often textured or made from specialized materials to prevent vehicles from slipping, especially in wet conditions.

Additionally, the wearing course serves as extra protection for the bridge deck, preventing rapid wear and tear due to continuous friction.

That is the complete explanation of bridge structures, both lower and upper ones. These two types of structures have different locations and functions. The lower structure is directly connected to the ground, while the upper structure directly supports the vehicle loads passing over the bridge.

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