Cable stayed bridge thesis
General Design of Cable Stayed-Bridges The main structural elements of a cable stayed bridges are the bridge deck, piers, towers and the stays. The deck supports the loads and transfers them to the stays and to the piers through bending and compression. The stays transfer the forces to the towers, which transmit them by compression to the foundations Figure 1. Figure 1 — Behavior of a cable stayed bridge. The suspension system is usually one of two main types, with the stays anchored to the top of the tower Fan or the anchors are distributed along the length of the tower Semi-Fan and Harp.
This system directly affects the level of axial load and the elastic support given to the deck and to the tower.
Share this link with a friend: Copied! Other Related Materials pages. Optimum size, position and number of cables in cable. Such a cable-stay arrangement is very unsymmetrical about the pylon and special pylon arrangement is necessary. A finite element model ofthe bridge is generated using finite element package SAP The static non-linear analysis under dead load is essential as a first step for the non-linear seismic analysis.
Nonlinear static analysis under the action of static loads i. The behavior of composite girder cable stayed bridges under static loads is highly nonlinear. The role of dynamic forces in cable stayed supported bridges is very important more than for any other type of bridge. Such forces can even determine the very feasibility of the project. The vibrations due to wind, traffic and seismic activity can result in inconvenience to users.
These physiological effects are generally very subjective experiences. If vibrations become large, damage can occur too. Analysis of all these dynamic phenomena, including seismic effects, calls for prior knowledge of the free vibration characteristics frequencies and vibration modes of the structure and accordinglya free vibrationanalysis has been conducted for the cable-stayed bridge. In general cable stayed bridges are regarded as structures on which vibrations due to earthquake have little effect as they rest on a limited number of point supports abutments, piers, pylons which absorb different displacements during seismic action.
Over past 40 years, rapid developments have been made on modern cable stayed bridge. With main span length increasing , more shallow and slender stiffness girders used in modern cable stayed bridge, the safety of whole bridge under service loading and environmental dynamic loading such as impact , wind and earthquake loadings , presents increasingly important concern in design , construction and service.
In the present study, the failure of cable stayed bridge across Chambal River Kota will be discussed. The causes of its collapse and detail study of the cable stayed bridge cross Chambal River will be done. The static and dynamic modeling of cable stayed bridge is also done. At the end, the measure to repair and rehabilitation cable stayed is discussed. It is a matter of pleasure for me to express my deep feelings of gratitude and sincere thanks to my guide Dr. Shrimali Head, Department of Structural Engineering as his inspiring guidance, ever enthusiasm and parental care have been invaluable assets throughout my dissertation work.
His constant encouragement and valuable suggestion for my improvement have been of great help in preparing this report. Iam also especially thankful to Dr. Bharti Associated Professor, Department of Structural Engineering for providing me constant inspiration, enthusiasm, cooperation and valuable suggestion for my dissertation work. Iam thankful to Mr. Iam also thankful of all the faculty members of my Department for their invaluable guidance and encouraging me during my work. Cost comparison among various repair strategies 4. Burst and damaged protective tape 4. PE sheathing split not providing protection, and wire is corroded.
Bridge is a structure providing passage over an obstacle without closing the way beneath.
The required passage may be for a road , a railway, pedestrian, a canal or a pipeline. The obstacle to be crossed may be a river, a road, railway or a valley.
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There are two classes of cable-stayed bridges: Harp design, cables are made nearly parallel by attaching them to various points on the tower so that height of attachment of each cable on the tower is similar to the distance from tower along the roadway to its lower attachment. Where as in fan design, the cables all connect to or pass over the top of the tower. Compared to other bridge the cable-stayed is optimal for span longer than typically seen in cantilever bridges, and shorter than typically requiring a suspension bridge.
This is range in which cantilever spans would rapidly grow heavier if having long length and in which suspension cabling is not economical, were the span is to be shortened. Engineers introduced the concept of cable stayed bridge very early on, at the same time as they began developing suspension bridge; however , with the early collapse of cable supported bridges built over the river Tweed Europe and Saale Germany , at the beginning of the 19th century, the idea was abandoned. A lot of bridges had been destroyed during World War II, it was necessary to rebuild those after the war.
At this period of time, steel was less in amount and new bridge had to be constructed with minimum weight. With the aim of providing economy in material and cost, engineers have gone back to the concept of cable stayed bridge. The Stromsund Bridge in Sweden may be accepted as the first modern cable stayed bridge Gimsing The Donzere-Mondragon Bridge in France was the first modern cable-stayed bridge.
The towers were short and the cables were less than 45 degrees they impart more horizontal force than vertical support. Texas, bridge was the first US cable stayed bridge. The bridge was in service for nine years before that was done and the original deck design was clearly not intended to have any vertical stiffness on its own.
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A multiple-tower cable-stayed bridge looks like suspension bridge, but it is very different in principle and method of construction. In the suspension bridge, a large cable is made up by "spinning" small diameter wires between two towers, and at each end to anchorages into the ground or to a massive structure. These cables form the primary load-bearing structure for bridge deck. Before the deck is installed, the cables are under tension from only their own weight.
Smaller cables or rods are then suspended from the main cable, and used to support the load of the bridge deck, which is lifted in a sections and attached to the suspender cables. When this is done the tension in the cables increases, as it does with the live load of vehicles or persons crossing the bridge. The tensions on the cables are to be transferred to the earth by the anchorages, which are sometimes difficult to construct due to poor soil conditions. While in the cable-stayed bridge, the towers is the primary load-bearing structure.
A cantilever approach is often used for support of the bridge deck near the towers, but mainly areas further from them are supported by cables running directly to the towers. This has the disadvantage, compared to the suspension bridge, that the cables pull to sides as opposed to directly up, requiring the bridge deck to be stronger to resist the resulting horizontal compression loads; but has the advantage of not requiring firm anchorages to resist a horizontal pull of the cables, as in the suspension bridge.
All static horizontal forces are balanced so that the supporting tower does not tend to tilt or slide, needing only to resist such forces from the live loads.
Design optimization of cable-stayed bridges
This bridge form can be as easily built with a single tower, as with a pair of towers. However, a suspension bridge is usually built only with a pair of towers. A side-spar cable-stayed bridge uses a central tower supported from only one side. This is not significantly different in structure from a conventional cable-stayed bridge. Figure 1. A Cable-stayed bridges with more than three spans involves significantly more challenges in designs than two -span or three-span structures.
In two-span or three-span bridge, the loads from the main spans are normally anchored back near the end abutments by stays in the end spans. For more spans, this isn't the case, and the bridge structure is less stiff overall. This can create difficulties both in the design of the deck and the pylons.
Examples of multiple span structures where this is the case are Ting Kau Bridge, where additional 'cross-bracing' stays are used to stabilize the pylons; Millau Viaduct and Mezcala Bridge, where twin-legged towers are used; and General Rafael Urdaneta Bridge, where very stiff multi-legged frame towers were adopted.
It is the only bridge in the world that has 2 curved tracks supported by a single concrete mass. The extradosed bridge is a cable-stayed bridge but with a more substantial bridge deck that being more in terms of stiffness and stronger allows the cables to be omitted close to the tower and for the towers to be lower in proportion to the span.
This system carries the strands within the stays from bridge deck to bridge deck, as a continuous element, eliminating anchorages in the pylons. Each epoxy-coated steel strand is carried inside the cradle in a one-inch steel tube. Each strand acts independently, allowing for removal and replacement of individual strands. A bridge deck or roadbed is the roadway, or the pedestrian walkway, surface of a bridge. It is not to be confused with any deck of a ship.
The deck may be of concrete, which in turn may be covered with asphalt concrete or other pavement. The concrete deck may be an integral part of the bridge structure T-beam structure or it may be supported with I-beams or steel girders floor beams. The deck may also be of wood, or open steel grating.
Pylon Shape Analysis of Cable-Stayed Bridges
An orthotropic bridge or deck is one whose deck typically comprises a structural steel deck plate stiffened either longitudinally or transversely, or in both directions. This allows the deck both to directly bear vehicular loads and to contribute to the bridge structure's overall load-bearing behavior. The orthotropic deck may be integral with or supported on a grid of deck framing members such as floor beams and girders. The same is also true for concrete slab in a composite girder bridge, but the steel orthotropic deck is considerably lighter, and therefore allows longer span bridges to be more efficiently designed.
The stiffening elements can serve several functions simultaneously. They enhance the bending resistance of the plate to allow it to carry local wheel loads and distribute those loads to main girders. They also increase the total cross-sectional area of steel in the plate, which can increase its contribution to the overall bending capacity of the deck. The stiffeners increase the resistance of the plate to buckling.