Bridges are structures that span an obstacle. They connect us from one point to another in a much easier and most times quicker way. The physical obstacles may be a body of water, a valley or even a road. Sometimes the passage provided over the obstacle is otherwise impossible to cross.
Bridges of any kind, vehicular or rail or other types, are important to any nation’s infrastructure. The design of these bridges varies fundamentally with their function.
Earlier bridges were constructed using trees and sometimes their roots, while in later centuries, stone bridges came into the picture. These stone bridges though safer and more sturdy were also bulky and heavier. But with today’s technological advancements our bridges are lightweight, quicker to build and are more customised to suit our present demands.
Along with the material, the design approach and the people involved in the design process have also changed. In present times, bridges are not just designed by civil engineers but also by the government body and local communities.
Many variables influence the design of the bridge. Here are some broader principles and points to remember while designing a vehicular bridge.
1. Need
One of the most important and foremost parts of designing is understanding and acknowledging the need for the said structure. One must see where there is a need for it, and how does the intervention help people.
It is of utmost importance that we look for the simplest possible solution for a given problem and not dive directly into design and construction.
2. Operation
The next step in the process of design is understanding how things work. One must try to recognise who the users are, what their needs and requirements are and things like how many people might use it.
For example, a vehicular bridge may or may not need a pedestrian sidepath. This depends on the users and their needs.
3. City and Bridges
Bridges are designed to span over an obstacle. And they do so without closing the way underneath them. Their main function is to connect different geographical areas. But the bridges also serve as social connectors as the city expands.
Any new structure adds value to the existing cityscape. Bridges create a shortcut between city parts and provide a unique experience to the user.
4. Traffic Structure
A design for the vehicles must delve into the structure of traffic. Aiming at understanding their movement; not just where the bridge is to be designed but also considering the area surrounding it.
Not just the design of the bridge as to how and where the traffic will go, this information is crucial in calculating the live loads that the structure will have to bear. It is one of the greatest uncertainties in this design.
5. Terrain and Hydrology
Unlike any other structure, humans have designed. Bridge design is influenced more by the site conditions. The structure has to be carefully designed, keeping in mind both safety and serviceability.
There are many factors that one has to look at. These include the terrain details; elevation of land, soil type, soil bearing capacity, the groundwater table, pH of the soil and water (in case the bridge is designed over a water body).
All these factors heavily influence the design, the structure and mostly the material choices and their treatment (a type of polish, waterproofing chemicals, etc).
6. Site Context
Very much like the buildings and other built forms around us, the design of bridges too should be sensitive about the site context. Though these bridges are constructed majorly over roadways and water bodies, they must be designed such that they fit in the larger cityscape.
7. Durability
The conditions to which this structure is subjected are harsh. The outdoor sun and winds and the wear and tear by the use itself, and the various loads it encounters are a challenge to any designer.
The bridge is also required to stand strong for a very long time. And henceforth it is important that when designing, one must take into consideration, this requirement of the structure.
8. Low Maintenance
With the unstoppable traffic and frequently taken routes, it is very difficult to make any repairs to the bridges if a situation demands it. Hence, a bridge must be designed so that it requires low maintenance.
The process of repair must be quick, easy and efficient. This can be achieved by the virtue of design and planning for any such situation.
9. Construction
A design is not a good design if it cannot be constructed. Along with being low maintenance and being durable, the first thing a bridge should be is to be possible to construct. One has to choose the material palette of the structure keeping in mind various interrelated factors. Along with this comes the technology with which the bridge has to be constructed.
The finance and cost implications must also not be separated from the design aspect in any given structure.
10. Aesthetics
Contrary to popular belief, the design of the bridges not only concerns safety and their purpose of connecting one place to another, but the bridges also need to be aesthetically appealing.
The aesthetic quality of the bridges is not a superficial addition on the surface but it is an integral part of the bridge itself. Most times its structure.
Numerous bridges around the world are known for their aesthetic appeal and have also become a tourist attraction.
The design of a structure, like the vehicular bridges, depends on and is to an extent influenced by many factors. These factors are almost always interrelated and a designer must pay attention to each one of them to make their design successful.
