Currently, the need of constructing strong bridges on highways and streams is increasing day by day because of the unbelievable environmental changes and to cope with contemporary needs, the architects are needed to pay specific attention towards the designing of the bridges. Nowadays, there has emerged a vast variety in bridge constructions and hence, it has become really difficult to select which one is suitable for which locality. However, this thing can be assessed through scrutinizing environmental factors since it is the contemporary environment that can give an overview of what is the need of local people.
In this paper we examine bridge construction, the light is thrown upon several kinds of bridges and their designing, which factors are pondered upon while designing scrutinizing the bridge and how the environmental factors are scrutinized while making a bridge design. The first part of this paper throws light upon different elements which are contemplated in order to make a bridge, including span, material, placement and form of the bridge. The second part throws light upon three different kinds of fundamental structures that are used in order to formulate bridge design, including beam, truss and ach structure. The third part of this paper gives an overview of what challenges the architect has to face while designing a bridge and the last paper gives the example of bridge designing from three perspectives i.e. steel made bridge, covered bridge and Earthquake Bridge. The entire paper is developed keeping the scholarly articles and journals in view.
However, before throwing light upon which bridge is constructed in which sort of circumstances, it is vital to analyze the kinds of bridges and their requirements.
Bridge and its Requirements
If the analysis of all kinds of bridge is done, there are millions of bridges which are constructed using dissimilar structures but the basic architecture of all these bridges is the same. However, these bridges are constructed to help people in crossing valleys and streams without any apprehension but the main thing is that how these bridges are constructed?
A bridge architect has to consider lots of things including bridge span, size, look, shape of bridge, distance from ground or stream or material used for the construction according to environmental needs etc. However, four different factors which are required for constructing the bridge that can compete with natural forces, involve span, material, placement and form of the bridge.
As far as span is concerned, there are three different types of spans which can be contemplated for the construction of the bridge keeping environmental factors and whereabouts under consideration. These three are simple, continuous and cantilever types of span.
Keeping the material needs in view, to construct a bridge concretely and with extreme accuracy, stones, metal, concrete etc are required to mixed up with harmony so that the constructed bridge can easily cope with environmental hitches. Suppose, if the bridge is constructed over stream, it is vital to use concrete material with appropriate mixing of stones so that the bridge can be build in a strong way that enable it for coping water hitches.
The bridge surface also matters a lot as far as the placement of bridge is considered. This surface can be deck, thorough and pony which is employed appropriately. While constructing this kind of bridges, trusses type and surface level matters a lot. The bridge form such as beam, truss, arch etc also considered while constructing a bridge keeping the environmental factors in view. The next part of this paper will through light upon all these three types and how they work in different environments.
How Bridge Construction Works In Different Environments
Every bridge is constructed keeping environmental and constructional issues in view and hence the architecture is designed accordingly. The demand of material and method of construction is assessed by scrutinizing the whereabouts of the construction site. However, these three kinds of bridges are suitable for different kind of environments and these are as follow.
The beam bridge
The beam bridge is suitable for temperate environment since the construction of such bridges is done using horizontal beams which are used to give support on the end of each pier. Usually the beam weight pushes on the piers straightly. While using beams for bridge construction, usual span is observed is no more than 250 feet.
The trusses bridge
Truss bridge construction structure is one of the widely used bridge structure in United States and thousands of bridges have been constructed using this structure. Basically, in this bridge structure, the triangular steel bars are assembles in a sharp series. Cantilever bridge is the most complex kind in this structure and Earth of Forth Bridge of Scotland is the most appropriate example in this regard.
While constructing bridge using the structure, rigid arm of every two piers are extended from each side and steel bar is projected between each two pier from top to bottom. The arms are projected in the middle in order to hold and support one side so that the bridge remains strong. These arms support the central span.
Usually this kind of bridges are good for the places where the weather is strong, dynamic, always changing and strong winds blow since, this kind of weather requires a strongly constructed bridges.
The Arch Bridge
This structure of bridge is innovated by Romans using stones in order to make bridge carrying great strength. However, today, these arch bridges have been made using concrete or steel in order to construct the bridge in a strongest and modern way. Usually the span of such bridges is more than 800 feet. This kind is also good for aggressive environment.
Though these are three basic structures which are employed in order to get ultimate architecture but mostly, two of them are amalgamated to get ultimate bridge that can aid the architect to meet the bridge construction requirement. Most of these amalgamated structures involve trussed through arch, trussed deck arch, covered trussed etc.
Environmental Challenges for Bridge Construction
Different kinds of bridges are constructed in different ways keeping environmental needs under consideration but during this process, there are several severe challenges appear as the strong hindrances during the construction process. These obstacles varies according to the type of the bridge structure i.e. beam, arch or truss one, along with the environmental factors which are pondered well before hand while constructing bridge from its core. Some major challenges which involve during bridge construction include the traffic load during bridge construction, geometric and construction challenges, environmental changes and deformation (ICE, pp. 217, 2001) However, for making a bridge that tallies the environmental factors, the bridge designing plays an inseparable role and all three basic units of bridge design needs particular attention from architects.
Bridge Construction Design Steps
The construction of a bridge involves several sensitive issue which are employed in order to meet the objectives since the life of thousand people rely upon the construction of the bridge. However, while constructing a bridge, there are lots of factors that are kept in limelight and the entire design of bridge is constructed. While making design of a bridge, either the architect is eager to place it on highway, stream, busy post or some small canal, it is divided into three major parts. These parts involve superstructure, substructure and foundation. Each part is needed to pay special attention while designing so that the ultimate objective can be met. (Bangash, pp.5, 1999) The example of steel bridge construction, Earthquake Bridge and covered bridge building can be taken as evidences in this regard. The next part of this paper will show different types of bridges and the way these are build.
Steel Bridge Building
Steel bridge structure is one of the widely exploited structures worldwide and utilized in order to control and handle heavy traffic load. However, the construction of steel bridge is also a matter of challenge for the architect since the architects have to keep several issues under consideration.
While constructing steel bridge, first it is essential to keep superstructure and substructure in view. Before doing bridge designing and paperwork, the form of bridge is also selected; either the choice should be beam structure, arch structure or the trusses based one. It is also vital to throw light upon the need of surface whether which one is suitable according to the environment, deck or covered one. All these factors are pre-planned before starting designing of the bridge in formulated. Hence, the capability and accuracy of the bridge very much depends upon the above mentioned factors and the architect has to pay attention to all these factors so that a bridge can be formulated in order to meet the environmental requirements.
Why steel bridges are preferred over other structures? The reason is very obvious since it has the capability of coping environmental challenges, either it is related to whether or the circumstances. It is its strong capability to bear heavy load of traffic and strength of tolerating speeds. The reason behind this fact is the steel based surface which is strong enough to handle environmental and crowd related issues.
There is no lit-up problem with steel based bridges since the quality of such bridges is very high. Since the hostile environmental factors are minimized, the result appears in the form of safety and economic benefits.
Covered Bridge Building
Another type of bridge is covered bridges that are structured with wooden trusses. Basically this kind of bridges are good for the places where the threat of climatic changes is at its apex and the masses have threat of being injured because of this environmental change.
In this kind of bridges, the surface of bridge is protected with enclosed roof in order to keep the whether related issues aloof from the bridge users. However, this kind of bridges is stronger as compared to some other in the sense of weather since the safety from climatic effect widens their life span. Most of these bridges are constructed using trusses and the most renowned design in this regard is Brown trusses.
Basically these bridges are constructed for one way lane of traffic and used for local purpose. Hence, these are made of wooden and if they are not protected in a righteous way, their life span gets shortened soon. According to researches, an uncovered wooden bridge may last within 10 to 15 years of its construction as compared to covered one which has long life span. However currently, there are lots of covered bridges which are constructed using metal, steel or similar other material but these types of bridges also need protection to widen their lifespan. However, the reason behind covering metal based bridges is to provide convenience to the users rather than safety of bridge.
Earthquake Safer Bridge Construction
Another example of bridge design and environment compatibility can be assessed through the bridge design which is formulated to keep the harms caused by earthquake aloof from the bridge and its users. According to Buffalo (2007), “Bridges that “dance” during earthquakes could be the safest and least expensive to build, retrofit and repair.”
Apart from climatic factor, another environmental factor ‘earthquake’ has been given specific attention that causes severe loss if the bridges got hitches and get down in such circumstances.
The contemporary researchers have developed the first seismic bridge design and tested this methodology successfully observing how it moves and jumps off during the course of earthquake. During the test session, this bridge has proved itself a stronger one since the steel truss made towers are used to support the decks of bridge and the construction of this bridge has been less expensive as compared to others. U.S highway administration has funded this research in order to build a safe and earthquake free bridge design which can come up with the needs of dealing with earth hitches.
While designing this bridge structure, the emphasis is laid on having strong foundation since the earthquake issue always caused broken bridges from their foundation. So, the construction of foundation structure is given more importance as compared to superstructure and substructure.
For construction of the bridge, it is essential to keep the environmental needs, material and designing of the bridge under consideration and according to the assessed specifications, the appropriate bridge construction design should be adopted. There are lots of pre-formulated designs for this cause but all of them needs some basic elements to get changed and this change is made possible through constructing the bridge using a structure that tallies with the environment of that respective place.
In this regard, this paper has given an overview of what the basic requirements of the bridge construction are, how the environmental needs can be assessed, which structure will be appropriate for which kind of circumstances and what sort of material should be used in order to cope with such environmental changes. Moreover, all these basic designs can be used to formulate specific design for some special place, keeping the environmental challenges in view.
Bangash, M. H., (1999) Prototype Bridge Construction Structures: analysis and design Front Cover M. Y. H. Bangash.
Thomas Telford, 1 (999) Great Britain (Bridge Construction section): Thomas Telford.
BUFFALO, N. Y., (2007) Bridge Construction Will Rock Safely with New Quake Design.
ICE (2001) Current and future trends in bridge construction and maintenance 2: safety, economy, sustainability and aesthetics; proceedings of the international conference organized by the Institution of Great Britain: Thomas Telford.
Orchard (2007) Student guide to steel bridge design – Bridge Construction. North Lincolnshire: orchard Resource Base.