What are the Common Bridge Construction Materials?
Choosing a bridge construction material involves considering the following the points- maintenance requirements, lifecycle costs, and lifespan of material.
The following are the few of types of materials used in bridge construction:
1. Concrete for Bridges
Concrete is more widely used as a bridge building material as it has demonstrated a continued confidence regarding its performance and durability. Concrete bridges are known for their flexibility and versatilityboth in terms of the final forms as well as the methods of construction that are difficult to match. The reasons for which it is considered as the best construction material for any form or size of project are- durability, aesthetics, economic solutions, simplified construction and rapid deployment techniques.
The flexibility as a construction material can be understood by the various forms of concrete easily available nationwide which make concrete an adaptable resource which is suitable for deployment even for the most difficult of bridge types or even construction sites. All sorts of structural forms can be achieved that the designer wants with concrete, which is why elegant bridges can be created which can blend seamlessly with natural surroundings.
Concrete can unite both function and elegance in a very safe, robust structures whatever be the scale. With the proper architectural surface finish it can even add to visual impacts while at the same time the need for cladding, painting and ongoing maintenance activities are eliminated.
Types of concrete Bridge:
• Slab: Single or multiple spans can be used for the composition of slab bridges.
It is simple and easy to construct
It is suitable for spans up to 50 feet.
Continuity with abutments and piers can be able to mobilize frame action for longer span.
• Arch: The concrete arch bridges consist of either a single arch or multiple arches which is supported by abutments and intermediate piers.
It is simple and easy to construct.
It is very well suitable for spans which are up to 50 feet.
Continuity with abutments and piers can be able to mobilize frame action for longer span.
• Cable-Stayed: The decks are reinforced or segmental.
It is both economical and aesthetically pleasing.
It is a structurally efficient way of using materials.
• I-Girder: Here a beam bridge is used for moderate spans.
The variations of the precast I-girder lie in the PCI bulb-tee or bulb-tee sections which is developed by various states.
It is one of the most popular bridge types.
Its usual depths are: 20in, 36in, 45in, 54in and 72in.
• Box Beams: Just like simple or continuous beam bridge, a box beam bridge is supported by abutments and piers.
It is a common bridge choice for low-volume roads.
It is well suited for spans ranging from 50 feet to 120 feet.
The common widths are 36 or 48in.
• Segmental: These can be cast-in-place or even precast, a span-by-span or balanced cantilever construction can be used.
It is best suited for gradual or sharply curved alignments.
The maximum span here is more than 300 feet.
Short span repetition is from 70 feet to 150 feet.
2. Prestressing Concrete for Bridges
To build a prestressing concrete bridges the following materials are required- casting concrete beams with longitudinal holes for steel tendons which can be cables or bars such as reinforced concrete, but the holes for the tendons are curved upward from end to end, and the tendons which when once fitted inside can be stretched and then anchored at the ends. When under high tension the tendonspull the two anchored ends together which then puts the beam into compression. Along with this, the curved tendons also exert an upward force and with this the designer can make the upward force counteract much of the downward load expected to be carried by the beam. The amount of steel and concrete required in a structure is reduced in prestressed concrete which leads to lighter designs that are mostly less expensive than designs of reinforced concrete.
• Steel as a bridge construction material: From large to small, steel is vastly used as a bridge construction material. Due to its versatile nature and since it is also an effective material it has proved to be efficient and sustainable solutions. For a wide range of bridge steel has long been considered as it is an economic option.
Now in products of various shapes and sizes are considering structural steel which is a high-quality material that is now readily available worldwide in certified grades. With the prefabrication of steelwork in controlled factory conditions a high-quality work can be achieved at minimum cost. The prefabrication process consists of an excellent quality control which is achieved with the help of a thorough testing regime at the steel mills, thenin the fabrication processes cutting and drilling, assembly, welding, and protective treatment takes place. Flat products (steel plate and strip) and Long products (rolled sections, which can be both standard open sections for example beams, channels, angles or even hollow sections) are the two forms in which steel material is supplied.These products are then cut (to size and shape) and welded, one component with another to be used for the construction of bridge. Structural steel functions in a linear elastic mannerup to the ‘yield point’ which is why it has a significant capacity for plastic straining before failure. These features are kept in mind by the designer when steel bridges are constructed.
• Structural steel as bridge construction material: The high strength-to-weight ratio of steel helps in reducing the structural weight of superstructures which then reduces the substructure costs, which is of help in poor ground conditions. The minimum self-weight plays a key in the cost of transporting and in the handling of components. The use of steel also allows shallow construction depthswhich overcomes problems with headroom and flood clearances and therefore reduces the length and cost of approach embankments.
Since steel is the most recycled construction material therefore selecting it for bridges represent a sustainable management of natural resources. The process of recycling steel is when a steel bridge reaches the end of its fruitful life the girders are then cut into manageable sizes so that they can be demolished, and then can be returned to steelworks for recycling. around 99% of structural steel usually finds its way back into the steelmaking process or it is reused. The recycled steel shows no degradation in the performance. The alternative use is by using the component parts of steel bridges in other structures; If the ease with which the bridge can be relocated is kept in mind then the design can be of such where the entire bridge can be relocated in the future.A wide range of architectural possibilities can be imagined with steel. Another benefit of steel bridge is that it can be made to look light or even reassuringly solidand can be sculptured according to our desired shape or form. With the high surface quality of steel clean sharp lines are created and it allows attention to detail. With modern fabrication methods curvature can be made possible in both plan and elevation. The painting of steelwork helps in introducingcolour and contrast to the bridge and the repainting helps in making changes in looks and also gives a refreshing appearance to the bridge.
• Cast-iron as a bridge construction material: Since cast iron has a very high resistance to compression it is ideal for use in arch bridges.
The advantage of cast-iron columns is it is extremely slender when compared to materials which can support equal amount of weight.
It is also useful for other kinds of buildings which ranges from architectural work at theaters, churches, synagogues, it is used to improve sight lines for supporting balconies.
It became a popular construction material from the 1700s.
Due to the introduction of blast furnace the cost of cast iron has reduced which was not the case earlier.
3. Timber for Bridge Construction
Timber bridge has been used from ancient times. In European countries there has been an interest in timber or wood bridges in the last two decades.
As it is a sustainable material it is recently becoming an option for bridge construction. Stress laminated timber decks are now used for better connections.
Bridges can be divided into two categories- footbridges and road bridges.
Footbridges are made with decks of timber; simple timber boards are cross layers along with the usage of various laminated decks.
For road bridge the construction is more complicated as water prevention is important for which some sort of impermeable membrane is used between the timber deck and asphalt.
4. Stone for Bridges Construction
It is strong in compression as well as in shear but cannot resist force when in tension.
Masonry arch bridge are designed in such a way that it is in constant compression.
For thousands of years stone bridges have been used. The ancient form of bridges was made with large flat slabs of granite or schist which were supported on stone or were rested on the banks of streams.
The cost of masonry arch bridge is similar to that of concrete bridge or steel bridge as no expensive machinery is needed. It is mostly built with the help of manual labour and simple lifting equipment.
The maintenance cost masonry arch bridge is less than other bridges and can outlast other bridges as well if maintained well.
5. Advanced Composites for Bridge Construction
It is important to remember that to achieve the materials tested in the laboratory in the field quality control specifications are required.
Composites can be divided into two phases- matrix phase and dispersed phase. The matrix phase has a continuous character, where it is ductile and less hard. The disperse phase is within the matrix phase in a discontinuous form. The dispersed phase is stronger than the matrix phase which is why it is called the reinforcement phase.
Even though there is awareness regarding the advantages of composite bridge yet due to skepticism over how the material will work and resistance to change along with the question of cost and materials it is not that widely used.
Example of composite bridge: A highway which consists of hollow carbon-composite tubes and lightweight concrete built on State Highway Route 86 near Palm Springs, California was constructed in 2000.