B R I D G E S
History of Bridges
Bridge study has revealed that people have been carrying out bridge construction since humans first assembled into groups. The initial bridge design was basically felled trees that were utilized for moving over the ditches and rivers, and concrete bridges were rare. With the advance of civilization, techniques were discovered to use rocks, stones, mortar, and other materials for the creation of stronger and extended bridges. Subsequently, as the engineers and physicists advanced in the design, materials, and construction technology, modern materials like steel and aluminum were introduced for bridges.
The bridge construction skills progressed rapidly during the 20th century. At the end of the century, new techniques were developed that improved the design, strength, and durability of the bridges. Steel bridges were strongly riveted instead of the previous practice of using bolts. Concrete bridges were being cast at the desired place, instead of being precast. Huge bridge elements made from bars and small sections were used, and not rolled as one part. Before the 1980s, the majority of bridge designs included expansion joints for decks, including expansion and fixed support bearings. This technique was used to permit structural expansion and contraction. However, the expansion joints are likely to be filled with debris, and bearings often weaken over time. Thus, the structure is hardened, and maintenance requirements are increased. The bridge engineers explored methods to reduce this trouble, and finally the expansion joints and bearings were eliminated to develop a joint-less bridge. This type of bridge is constructed on a flexible foundation that may expand or contract with negligible trouble.
New technologies are expected to meet the challenging and varying requirements, and also offer options that will guide to innovative engineering and bridge construction standards. With the beginning of the new century, bridge construction is being revolutionized. Modern construction methods and the latest advanced materials are being evolved. Construction technologies like post tensioning, reinforced ground walls, and soil freezing are being developed. Modern surveying techniques are being used that have facilitated the soil selection, and other design parameters, through the use of optical and infrared technology. Progress in the deck technology is creating lighter and stronger decks. Bearings, joints, and seismic elements have become more effective since advanced testing facilities have been introduced. Consistent, economical, fast, and programmed inspection systems will emerge
Materials with improved characteristics will be used that will make the bridge construction safe, durable, and reliable. Materials like high-performance concretes, polymer concretes, and plastics will be utilized. As the fiber reinforced composites are becoming more tolerant towards temperature, they will be used extensively for bridge construction. Use of larger steel fibers will be used in the
Bridge Construction and planning
Bridge construction has been improved tremendously with the advancement in science and technology. Better and lighter materials are now available that can endure greater loads. The construction is now much faster due to the introduction of a variety of heavy construction equipment.
Bridge construction tends to involve huge projects that encompass the utilization of skills related to several engineering disciplines including geology, civil, electrical, mechanical, and computer sciences. Therefore, integrating the efforts of all involved must be meticulous. The initial plans are prepared regarding the project, including the characteristics of the desired bridge, the site details, and the requirement of resources. The bridge design will be determined by the type of bridge being constructed. The main types of the bridges are beam, arch, truss, cantilever, and suspension. The beam bridge is one of the popular types. Bridges can also be categorized by the planned use, like road and rail bridge, pedestrian pavement, material to be used like steel or concrete, and fixed or moveable. Moveable bridges are constructed when the ship height may be more than the bridge floor. In such situations, the road has the capability to be lifted or pivoted, to permit marine traffic movement under it.
Bridges are structures that connect two land masses separated by valleys or rivers, but they serve a greater purpose as they bridge the gap between different places, cultures, and societies. Discover how civil engineers construct bridges that win out over the deepest valleys and turbulent waters. Millau Viaduct in France, a concrete structure supported by cables 270 meters high above the road level is a pinnacle of civil engineering achievement. It crosses over the valley of the River Tarn, and its overall length is 2460 meters. Across the globe, civil engineers have constructed bridges over such valleys and rivers, enabling the public to commute from one place to another efficiently. What we finally see is a structure carrying hundreds of vehicles from one point to another; however, the real story of a bridge is not that simple. Constructing a structure over rivers and valleys requires a lot of money, expertise, and patience. In this guide to bridge design and construction, we will get to know about the different aspects of bridge construction through many linked articles. Today, the study and advancement of bridge construction and design technology has diversified like never before, and we will discuss everything you should know about construction of bridges in this guide.
First we plan and then we design and then we start with the construction of a bridge. However, the planning needs to be fail-safe because unless we know what to construct, how to construct, where to construct, we would not be able to erect a safe structure. Planning becomes extremely important when we have to deal with vehicles running at altitudes as high as 300 meters above ground level. Planning includes analysis of topography of the site, studying soil features, effect on wetlands, and surroundings.
Earthquake prone areas always exert great pressure on economy and social security. Safety is the most important aspect of bridge building for earthquake areas. Modern technology has now enabled engineers to build earthquake resistant bridges economically yet keeping the reliability factor intact
Bridges do not just connect two far-off places; they serve a greater purpose. They minimize distance and help humans win over natural obstructions, rivers in particular. Building earthquake resistant buildings is important for human safety, but if a bridge is destroyed, connected places can be completely isolated from each other. The 1989 San Francisco Bay Area earthquake suspended traffic for more than twenty hours because of the damage done to a bridge deck. In 2011, Japan suffered a major earthquake resulting in many bridge collapses, but the losses were minimized because the Japanese implemented earthquake resistant design practices. There have been many incidents in the US and other countries where post-earthquake studies have reported that a seismic design would have minimized the losses- or even absorbed the earthquake jolts.
Construction of the foundations is the first step toward building a bridge. This process involves detailed geotechnical investigations of the bridge site. The type of bridge foundation has to be selected, such as the well foundation, pile foundation, and the opened foundation. Each foundation is suitable for specific soil strata, and the desired bridge characteristics. The soil characteristics will determine the load bearing capacity, and other important parameters. The superstructure is basically designed in accordance with the technical requirements, aesthetic reasons, and the construction methodology. Excavation required for the foundations may need to be executed to sizeable depths, involving hard ground, before the solid rocks are reached. Engineering feats will be involved to avoid water, and prevent collapse of the diggings. Tunnels specifically may be subjected to sudden failures.
· Bridge Construction Equipment
Heavy equipment will be used extensively during the bridge construction including bulldozers, excavators, asphalt mixers, formworks, and fabrication equipment. The construction and other equipment needs to be identified thoroughly, according to their capability and other desired functions. The foundation and the superstructure design will need to be considered. This expensive equipment should not remain idle, and must be used cautiously to obtain optimum advantage.
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Several loads act on a bridge, and the bridge is designed accordingly. Dynamic loads are particularly of prime significance. A bridge is designed to endure the normal vehicle loads, and other forces created due to winds and earthquakes. Several bridges have collapsed due to high speed winds. Even if the wind speeds are reasonably low, the dynamic forces can become excessive for the bridge to resist. Initially, the bridge may vibrate violently, causing the bridge structure to fail at a few weak elements, or even damage the major components. Investigations conducted after bridge failures have revealed that the real forces on bridges that collapsed were significantly less compared to the loads for which the bridge was designed. However, the oscillations created due to the winds were enough to cause the failure. Therefore, special reinforcement may be necessary for prevention against high speed winds and earthquakes. Thus, lighter materials are used that are arranged in suitable geometric structures, and it is ensured that the configuration is aerodynamically stable.
Since bridge construction is an expensive project, it is essential that all necessary tests may be conducted prior to the actual construction. These tests and investigations can reveal the bridge behavior under different dynamic loads. Computer aided design and testing are powerful tools that must be used to assist in the bridge design. Bridge design has benefited considerably due to the growth of computer programs. Such computer programs reveal immense information concerning the effect of different forces being applied on a bridge. Wind tunnels are being used extensively for the analysis of aircraft designs. Now these techniques are also being applied for bridge design examination. A wind tunnel is basically a space that is enclosed. Air at a fast speed is moved through the bridge model. Likely design and structural defects can be discovered by photography and study of the air movement pattern over the model.
The Brooklyn Bridge was once considered the eighth wonder of the world; it is still called one of the greatest civil engineering feats of the 19th Century. America is proud of the Golden Gate Bridge in San Francisco, and it stands witness to the political and social changes the country has seen in the last century. Here we have articles mentioning the greatest civil engineering feats of the modern times, which include the Panama Canal bridges, the 126 meter high Bandra Worli Sea Link (BWSL) in India, and the tallest cable bridge in France.
ProduceD by : Nima hassanpour and Saeed ebrahimzadeh
amir hossen | 1394/12/5 ساعت 9:50 |
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علی | 1394/12/4 ساعت 23:05 |
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