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Bridge construction (RC girder bridges)

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Bridge construction (RC girder bridges)

  1. 1. Bridges Construction RC Girder Bridges
  2. 2. Bridges Construction  Page | 1 RC GIRDER BRIDGES ABSTRACT Girder bridges, also known as beam bridges, are the most common and simplest type of bridge. They basically consist of a horizontal beam supported at each end by a pier or other similar structure, longer girder bridges must be supported along their span by additional structures. Girder bridges are typically used over short to medium distances. The need for numerous additional supporting structures below the bridge makes them unsuitable for spanning greater distances. INTRODUCTION An important first step in understanding the principles and processes of bridge construction is learning basic bridge terminology. Although bridges vary widely in material and design, there are many components that are common to all bridges. In general, these components may be classified either as parts of a bridge superstructure or as parts of a bridge substructure. 1. SUPERSTRUCTURE: The superstructure consists of the components that actually span the obstacle the bridge is intended to cross and includes the following  Bridge deck  Structural members  Parapets (bridge railings), handrails, sidewalk, lighting and some drainage features. 2. SUBSTRUCTURE: The substructure consists of all of the parts that support the superstructure. The main components are abutments or end-bents, piers or interior bents, footings, and piling. Abutments support the extreme ends of the bridge and confine the approach embankment, allowing the embankment to be built up to grade with the planned bridge deck. Fig.1.Superstructure&Supstructure
  3. 3. Bridges Construction  Page | 2 Girder bridges are the simplest bridge type in structure and consist of steel beams shaped to an I- section or box section, called a plate girder bridge or a box girder bridge, respectively. Girder bridges are comprised of deck slabs, on which vehicles and people pass, and of main girders supporting the deck slabs. Deck slabs include RC deck slabs, steel deck slabs, composite deck slabs, and PC deck slabs. Bridges where the deck slabs and the main girders work together to resist loads are called composite girder bridges, and bridges designed to resist loads with the main girders only are called non-composite girder bridges. In general, effective spans of about 25 to 150 meters are applied.  There are three main types of girder bridge: 1. Box girders: are often used in the construction of roadway flyovers and elevated bridges for light rail transport. Box girders are more expensive than I-beams and not as easy to build. However, they do have some important advantages. For example, box girders are better suited to handling twisting forces. As such, they are ideal for the construction of curved bridges. Box girders are also more effective than I-beams over longer spans. Box girders are more suitable for larger spans and wider decks. Economy and aesthetics further lead to the evolution of cantilevers in top flanges and inclined webs in external cells of box girder, As the span and the width increase, the beams and bottom slabs are to be tied to keep the geometry which in turn leads to evolution of box girder. It can be used for spans up to 150m depending upon the construction methods. Box girder bridges may be cast in place using false work supports, removed after completion, or in sections in case of a segmental bridge. It may also be prefabricated in a fabrication yard, then transported and installed using cranes. Another method of box girder bridge construction is the incremental launching. Under this method, gantry cranes are often used to place new segments onto the completed portions of the bridge until the bridge superstructure is completed. Fig.2. Cantilever Construction Method for Box Girder Bridge Fig.3. Incremental Lunching Box Girder Construction Method
  4. 4. Bridges Construction  Page | 3 Specifications  It can cover a range of spans from 25m up to the largest non-suspended concrete decks built; of the order of 300m.  Single box girders may also carry decks up to 30m wide  Single cell box girder cast-in-situ is used for spans from 40m to 270m. Benefits  It is an economical and an aesthetic solution for the over crossings, under crossings, grade separation structures and viaducts found in the modern highway system.  Interiors of box girder bridges can be used to accommodate service such as gas pipes, water mains etc.  The maintenance of box girder is easier; interior space is directly accessible without the use of scaffolding.  It has high structural efficiency Fig.4.Box girder 2. Concrete girder: is made of pre-stressed concrete in an I-beam shape. The concrete is also reinforced with steel rods. This combination is particularly effective in bridge construction. “The concrete withstands the forces of compression well and the steel rods embedded within resist the forces of tension. Fig.5. PS Concrete girder
  5. 5. Bridges Construction  Page | 4 1. I-beam girders: are among the most commonly used girders in bridge construction. I-beam girders are made from rolled steel, and bridges constructed using I-beams are often called rolled steel girder bridges. I-beam girder bridges are economical, simple to design and relatively straight forward to build, making them a good option in most cases. However, according to About Civil.com, “if the bridge contains any curves, the beams become subject to twisting forces, also known as torque." I-beams, therefore, are best used to construct bridges that do not have any significant curves. Fig.6. Rolled beam steel  There are Three Types of Loads Considered in RC girder Bridges Construction specially and all types of bridges generally: 1. Dead Load: The dead load of a bridge is the bridge itself -- all the parts and materials that are used in the construction of the bridge. This includes the foundation, beams, cement, cables, steel or anything else that comprises the parts of the bridge. It's called a dead load because it doesn't move. It may breathe with the seasons or sway with the wind, but those movements are almost imperceptible. 2. Live Load: A live load is the moving weight the bridge will hold, such as traffic. It is based on traffic patterns that include the number of cars, trucks and other vehicles that will travel across it at any given time. Certain variables, such as snow, may be calculated into the total live weight for a more accurate estimate. The heaviest possible weight in the most extreme conditions is also a factor despite the rarity of such an occurrence. 3. Dynamic Load: Dynamic loads are outside forces that cannot be accurately measured such as wind, vibration and extreme weather. These factors need to be considered in the construction of a bridge to build "breathing" room into the structure. This breathing room allows the bridge to move or adjust to the dynamic loads without collapsing or permanently shifting. As solid as a bridge may seem, it still has the ability to sway when a strong wind is present. o When building a bridge, there are other types of loads that need to be considered that are specific to the terrain in which the foundation will be laid. Environmental factors and weather patterns are also considered when calculating load-bearing needs. The load expectation of a bridge will determine the best design for strength and to ensure its longevity, whether the bridge is to span over large bodies of water or between rising mountaintops.
  6. 6. Bridges Construction  Page | 5 o Slab and girder bridges are used when the economical span limit of solid slab bridges is exceeded. For simply supported spans, this limit is generally found to be nearly 10 meters and for continuous or balanced cantilever type structures, this limit is 20 to 25 meters, The deck slab of a slab and Girder Bridge spans transversely over the girders which run longitudinally spanning between abutment or pier supports. The spacing of the girders depends on the number of girders to be provided in the deck which again is related to the cost of materials, shuttering, staging etc. o Closer beam spacing means lesser thickness of deck slab and consequently savings in concrete and steel in deck slab but since the number of beams is more in that case, this increases the quantity of concrete, shuttering and reinforcement for girders and for longer spans where bearings are required, the number of bearings, therefore, the most economical arrangement of bridge deck varies from place to place depending on the cost of materials, shuttering, staging etc., in that locality. It has been observed that three beams deck is generally found economical than two, four or five beams deck having a carriageway for two lanes. The girder spacing’s in such cases are usually between 2.25 to 2.75 meters. CONCLISION Girder Bridge is a one type of structure bridges types, this type called also Beam Bridge consist of horizontal beam transfer loading for the slab bridge to its piers and columns, this type used in short and medium spans, and its suitable from the economic way, he construction of a beam bridge is the simplest of all types of bridges. The design of a beam bridge should be such that it does not bend under load. For this, the top surface of this bridge is compressed and the bottom surface is under tension, thus helping the beam remain in a straight line. REFRENCES https://erkrishneelram.wordpress.com/2015/01/21/what-is-a-girder-bridge/ https://careertrend.com/list-7223578-types-girder-bridges.html https://erkrishneelram.wordpress.com/2015/03/08/basic-bridge-terms/ STRUCTURAL DESIGN OF REINFORCED CONCRETE BRIDGES Collection by: Skumar http://www.yourarticlelibrary.com/bridge-construction/design-of-slab-and-girder-bridges-with- diagram/93648 https://theconstructor.org/structures/construction-box-girder-bridge/2166/

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