Sheila Marie V. Lapuag CE 521 December 6, 2011 BSCE-V Engr. Geffren Bernardo ARCH BRIDGES • An arch bridge is a bridge with abutments at each end shaped as a curved arch. • Arch bridges cannot bend, that is why they are made from many different types of materials such as masonry materials eg. Stone, brick etc. • An arched bridge channels the weight from above to the foundations below. • Arch bridges don't need additional supports or cables - they will stand on their own for a long time. Forces The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart. Instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the supports at each end. The weight is transferred to the supports at either end. These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out. The load at the top of the key stone makes each stone on the arch of the bridge press on the one next to it. This happens until the push is applied to the end supports or abutments which are embedded in the ground. HISTORY OF ARCH BRIDGES • Arch bridges are one of the oldest types of bridges and have been built for thousands of years. Arch bridges have great natural strength. • The Romans developed considerable skill in constructing arches and many of their structures remain intact today. However, they were not able to calculate the strength of their-arches although their knowledge of geometry inherited from the Greeks led them to adopt semicircular spans. • Their arches were constructed of stone made into the form of wedge shaped segments, or voussoirs, built up side by side on temporary timber supports until the top piece at the crown of the arch is pushed hom(keystone). • One of the most famous examples of their handiwork is the Pont du Gard aqueduct near Nîmes, France. Built before the birth of Christ, the bridge is held together by mortar only in its top tier; the stones in the rest of the structure stay together by the sheer force of their own weight. • Modern arch bridges are built of concrete. It is an effective way to transfer loads to the ground where foundation conditions are adequate to resist horizontal loads. • A large number of concrete arch bridges have been constructed in the 20th century in both in-situ reinforced concrete and precast concrete. • Today materials like steel and pre-stressed concrete have made it possible to build longer and more elegant arches, including a spectacular 1700 foot span in New River Gorge, West Virginia. (More typically, modern arch bridges span between 200-800 feet.) How arch bridges are built? The wooden form or template (in brown). The stone is built up on top of the form until the arch is complete, after when the form is knocked out or, sometimes, burnt away. For years, engineers used a technique called centering, in which a wooden form supported both spans until they locked together at the top. Before an arch can be built a wooden frame is built. This allows the stones to be put in position. The frame is removed after the stones are in position. A newer method today supports the spans using cables anchored to the ground on either side of the bridge. Skew Arch Bridge o A skew arch (also known as an oblique arch) is a method of construction that enables an arch bridge to span an obstacle at some angle other than a right angle. o This results in the faces of the arch not being perpendicular to its abutments and its plan view being a parallelogram, rather than the rectangle that is the plan view of a regular, or "square" arch. o In the case of a masonry skew arch, the construction requires precise stonecutting as none of the cuts form right angles but once the principles were fully understood in the early 19th century it became considerably easier and cheaper to build a skew arch of brick. The typical span length of arch bridges range from 40 to 150 meters. Advantages of an Arch Bridge . The arch is the strongest shape with the least amount of material known. The arch is also the only shape that can use single individual modules of materials, like brick and stone, and be used to span a distance that straight stone spans could never do. The weight of the story above resting on the top of the arch is transferred down each leg to the ground, instead of pressing on the lower story. The span uses the compressive strength of stone and gravity to allow it to bridge large expanses without the tensile limit presented by the material itself. Disadvantages . The disadvantage is the shape itself. It needs firm support from the sides. Can only be used where the ground is solid and stable. Parts of an Arch Bridge . arch Metal bow-shaped structure supporting the deck, whose load it transfers to the abutments. trussed arch Arched girder consisting of two chords joined by a triangulated network of struts. thrust Point at which the arch is supported by the abutment. lower chord Lower lengthwise steel girder forming the metal arch. deck Set of components making up the structure that carries the bridge’s traffic lanes. abutment Base of the pier; it supports the arch’s weight and thrust. pier Solid concrete construction acting as counterweight to the thrust of the arch against the abutment. column Sturdy component forming a vertical support. portal frame Part of the deck’s frame over firm ground, lying on columns. upper chord Upper lengthwise steel girder forming the metal arch. Did you know that … • An arch ten times as big in every way as another perfectly strong arch will behave completely differently to the smaller arch. The larger arch is, in fact, ten times weaker - or ten times more prone to stress - than the smaller one. This is because the weight of the larger arch goes up by a factor of ten cubed, since it depends on the number of cubic metres of material in the bridge. LIST OF LONGEST ARCH SPANS Sydney Harbour Bridge (Sydney, Australia) Length 1,149 m (3,770 ft) Span 503 m (1,650 ft) Arch construction – steel Completed – 1932 Bayonne Bridge (Kill Van Kull (New Jersey, New York)) Length 1,761 m (5,778 ft) Span 504 m (1,654 ft) Arch construction – steel Completed – 1931 New River Gorge Bridge (Fayetteville, West Virginia) Length 924 m (3,031 ft) Span 518 m (1,699 ft) Arch construction – steel Completed – 1977 Lupu Bridge (Shanghai, China) Length 3,900 m (12,800 ft) Span 550 m (1,800 ft) Arch construction – steel/concrete Completed – 2003 Chaotianmen Bridge (Chongqing, China) – Length 1,741 m (5,712 ft.) Span 552 m (1,811 ft.) Arch construction – steel Completed - 2009 In the Philippines ….. The San Juanico Bridge, part of the Pan- Philippine Highway, stretches from Samar to Leyte across the San Juanico Strait in the Philippines. Its longest length is a steel girder viaduct built on reinforced concrete piers, and its main span is of an arch-shaped truss design. With a total length of 2.16 kilometers (1.34 mi), it is the longest bridge in the Philippines spanning a body of seawater. It is considered one of the most beautifully-designed bridges in Philippines. The bridge has 43 spans and medium size boats can pass beneath its large main arch the top of which rises 41 meters above the sea. Construction commenced in 1969 over San Juanico Strait from Cabalawan, Tacloban City to the municipality of Santa Rita, Samar, with completion in 1973. Types and Classification of Arch Bridge Arches may be classified according to the following parameters: . Structural Articulation . Position of Deck Structural Articulation With regard to structural articulation the arch can be fixed or hinged. In the latter case either one, two or three hinges can be incorporated into the arch rib. While the fixed arch has three redundancies, the introduction of each hinge reduced the indeterminancy by one until, with three hinges, the arch is statically determinate and hence, theoretically, free of the problems of secondary stresses. Although a through arch is shown, but this applies to all type of arch bridges. The concept of the arch varies in relation to the way it absorbs and transfers the roadway’s weight to its support points. a. Three-hinged arch Arch with three roller joints: one at each support and one at the crown. This kind of arch is statically determinate. The thrusts on the abutments, and the bending moments and shearing forces on the arch itself, are not affected by small movement of one abutment relative to the other. This type of arch is therefore used when there is a possibility of unreal settlement of the abutments b. two-hinged arch Arch whose ends rest on an abutment attached by a roller joint. The two hinged arch uses hinged bearings which allow rotation. The only forces generated at the bearings are horizontal and vertical forces. This is perhaps the most commonly used variations for steel arches and is generally a very economical design. c. one-hinged arch Arch whose roller joints is at the crown. It is statically indeterminate to the second degree. It is rarely used because it has no distinct advantages.