A simple suspension bridge (also rope bridge, swing bridge (in New Zealand), suspended bridge, hanging bridge and catenary bridge) is a primitive type of bridge in which the deck of the bridge lies on two parallel load-bearing cables that are anchored at either end. They have no towers or piers. The cables follow a shallow downward catenary arc which moves in response to dynamic loads on the bridge deck.
The arc of the deck and its large movement under load make such bridges unsuitable for vehicular traffic. Simple suspension bridges are restricted in their use to foot traffic. For safety, they are built with stout handrail cables, supported on short piers at each end, and running parallel to the load-bearing cables. Sometime these may be the primary load-bearing element, with the deck suspended below. Simple suspension bridges are considered the most efficient and sustainable design in rural regions, especially for river crossings that lie in non-floodplain topography such as gorges.
In some contexts the term "simple suspension bridge" refers not to this type of bridge but rather to a suspended-deck bridge that is "simple" in that its deck is not stiffened.[1][2] Although simple suspension bridges and "simple" suspended deck bridges are similar in many respects, they differ in their physics. On a simple suspension bridge, the main cables (or chains) follow a hyperbolic curve, the catenary. This is because the main cables are free hanging. In contrast, on a suspended deck bridge (whether "simple" or not) the main cables follow a parabolic curve. This is because the main cables are tied at uniform intervals to the bridge deck below (see suspension bridge curve).
A stressed ribbon bridge also has one or more catenary curves and a deck laid on the main cables. Unlike a simple suspension bridge however, a stressed ribbon bridge has a stiff deck, usually due to the addition of compression elements (concrete slabs) laid over the main cables. This stiffness allows the bridge to be much heavier, wider, and more stable.
The earliest reference to suspension bridges appear in Han dynasty records on the travels of Chinese diplomatic missions to the countries on the western and southern fringe of the Himalaya, namely the Hindukush range in Afghanistan, and the lands of Gandhara and Gilgit.[8] These were simple suspension bridges of three or more cables made from vines, where people walked directly on the ropes to cross. Later, they also used decking made from planks resting on two cables.[8]
1952, suspension bridge over Cuanana river, Yosondua, Oaxaca, Mexico.
Development of wire cable suspension bridges dates to the temporary simple suspension bridge at Annonay built by Marc Seguin and his brothers in 1822. It spanned only 18 m.[7] However, simple suspension bridge designs were made largely obsolete by the 19th century invention and patent of the suspended deck bridge by James Finley.[9] A late 18th century English painting of a bridge in Srinagar[citation needed], then part of the Garhwal Kingdom, anticipates the invention of the suspended deck bridge. This unusual bridge, built on a floodplain, had suspended deck ramps used to access a simple suspension bridge supported from towers.
Materials
This type of bridge is known as a rope bridge due to its historical construction from rope. Inca rope bridges still are formed from native materials, chiefly rope, in some areas of South America. These rope bridges must be renewed periodically owing to the limited lifetime of the materials, and rope components are made by families as contributions to a community endeavor.
Simple suspension bridges, for use by pedestrians and livestock, are still constructed, based on the ancient Inca rope bridge but using wire rope and sometimes steel or aluminium grid decking, rather than wood.
In modern bridges, materials used instead of (fiber) rope include wire rope, chain, and special-purpose articulated steel beams.
Living bridges
In the northeast Indian state of Meghalaya, Khasi and Jaintia[10] tribal people have created living root bridges, which are a form of tree shaping. Here, simple suspension bridges are made by training the roots of the Ficus elastica species of banyan tree across watercourses.[11] There are examples with a span of over 170 feet (52 m).[12] They are naturally self-renewing and self-strengthening as the component roots grow thicker and some are thought to be more than 500 years old.[13][14][15]
In the Iya Valley of Japan, bridges have been constructed using wisteria vines. To build such a bridge, these vines were planted on opposite sides of a river and woven together when they grew long enough to span the gap. The addition of planks produced a serviceable bridge.[16][17]
Design
In a simple suspension bridge the deck lies on the main cablesIn a suspended deck bridge the deck is carried below the main cables by vertical "suspenders"Comparison of a catenary (black dotted curve) and a parabola (red solid curve) with the same span and sag. The catenary represents the profile of a simple suspension bridge, or the cable of a suspended-deck suspension bridge on which its deck and hangers have negligible mass compared to its cable. The parabola represents the profile of the cable of a suspended-deck suspension bridge on which its cable and hangers have negligible mass compared to its deck.
The very lightest bridges of this type consist of a single footrope and nothing more. These are tightropes and slacklines, and require skill to use. More commonly, the footrope is accompanied by one or two handrail ropes, connected at intervals by vertical side ropes. This style is used by mountaineers and is employed extensively in New Zealand on lesser backcountry walking tracks where examples are referred to as 'three wire bridges'. A slightly heavier variation has two ropes supporting a deck, and two handrail ropes. Handrails are necessary because these bridges are prone to oscillate side to side and end to end. Rarely, the footrope (or footrope plus handrails) is combined with an overhead rope similar to a zip-line or cableway.
In some cases, such as the Capilano Suspension Bridge, the primary supports form the handrails with the deck suspended below them. This makes for more motion side-to-side in the deck than when the primary supports are at deck level, but less motion in the handrails.
Disadvantages connected with simple suspension bridges are very great. The location of the deck is limited, massive anchorages and piers generally are required, and loading produces transient deformation of the deck.[18] Solutions to these problems led to a wide variety of methods of stiffening the deck,[18][19] resulting in several other types of suspension bridge. These include a stressed ribbon bridge, which is closely related to a simple suspension bridge but has a stiffened deck suitable for vehicle traffic.
A very light bridge, constructed with cables under high tension, may approach a suspended deck bridge in the nearly horizontal grade of its deck.
The bridge may be stiffened by the addition of cables that do not bear the primary structural or live loads and so may be relatively light. These also add stability in wind. An example is the 220-meter-long (720ft) bridge across the river Drac at Lac de Monteynard-Avignonet: this bridge has stabilizing cables below and to the side of the deck.
To reduce twisting motion in response to users a bridge may employ vertical drop cables from each side at the center of the bridge, anchored to the ground below.
Use
The lightest of these bridges, without decking, are suitable for use only by pedestrians. Light bridges with decking, and sufficient tension that crossing the bridge does not approach climbing, may be used also by pack horses (and other animals), equestrians, and bicycle riders. To walk a lighter bridge of this type at a reasonable pace requires a particular gliding step, as the more normal walking step will induce traveling waves that can cause the traveler to pitch (uncomfortably) up and down or side-to-side. The exception is a stabilized bridge, which may be quite stable.
Simple suspension bridges have applications in outdoor recreation. They are a popular choice for tree-top trails[20] and, where the terrain is suitable, for stream crossings.[21] They may be designed without stabilizing so that the free movement of the bridge provides a more interesting experience for the user.[21]
In French, a rudimentary simple suspension bridge is known by one of three names, depending on its form: pont himalayen ("Himalayan bridge": a single footrope and handrails on both sides, usually without a deck); pont de singe ("monkey bridge: a footrope with overhead rope); and tyrolienne ("Tyrolean": a zip-line).[22] Zip-lines can be traversed by hanging below, or walked (by individuals with exceptional balance). A more developed version of the pont himalayen, provided with a deck between a pair of main cables, is known as a passerellehimalayenne (French, "Himalayan footbridge").[23] Examples of this type include two bridges at Lac de Monteynard-Avignonet in the French Alps; these bridges are exceptionally long, for bridges of this type.
In physics and geometry, a catenary is the curve that an idealized hanging chain or cable assumes under its own weight when supported only at its ends in a uniform gravitational field.
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
A cable-stayed bridge has one or more towers, from which cables support the bridge deck. A distinctive feature are the cables or stays, which run directly from the tower to the deck, normally forming a fan-like pattern or a series of parallel lines. This is in contrast to the modern suspension bridge, where the cables supporting the deck are suspended vertically from the main cable, anchored at both ends of the bridge and running between the towers. The cable-stayed bridge is optimal for spans longer than cantilever bridges and shorter than suspension bridges. This is the range within which cantilever bridges would rapidly grow heavier, and suspension bridge cabling would be more costly.
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side, and partially into a vertical load on the arch supports. A viaduct may be made from a series of arches, although other more economical structures are typically used today.
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similarly constructed cord, string, and twine.
Inca rope bridges are simple suspension bridges over canyons, gorges and rivers (pongos) constructed by the Inca Empire. The bridges were an integral part of the Inca road system and exemplify Inca innovation in engineering. Bridges of this type were useful since the Inca people did not use wheeled transport – traffic was limited to pedestrians and livestock – and they were frequently used by chasqui runners delivering messages throughout the Inca Empire.
A suspension bridge supports its structural load with cables, ropes, or chains anchored at each end. Cables on the earliest suspension bridges were anchored in the ground; some modern suspension bridges anchor the cables to the ends of the bridge itself. Earliest suspension bridges had no towers or piers but the majority of larger modern suspension bridges have them. All of the 14 longest bridges in the world are suspension bridges.
A fly system, or theatrical rigging system, is a system of ropes, pulleys, counterweights and related devices within a theater that enables a stage crew to fly (hoist) quickly, quietly and safely components such as curtains, lights, scenery, stage effects and, sometimes, people. Systems are typically designed to fly components between clear view of the audience and out of view, into the large space, the fly loft, above the stage.
Each yard on a square or gaff rigged sailing ship is equipped with a footrope for sailors to stand on while setting or stowing the sails.
Hampden Bridge is a heritage-listed single-span suspension bridge that carries Moss Vale Road (B73) across the Kangaroo River, in Kangaroo Valley, in the City of Shoalhaven local government area of New South Wales, Australia. The bridge was designed by Ernest de Burgh and built by Loveridge and Hudson. The property is owned by Transport for NSW. It was added to the New South Wales State Heritage Register on 2 August 2019.
Wire rope is composed of as few as two solid, metal wires twisted into a helix that forms a composite rope, in a pattern known as laid rope. Larger diameter wire rope consists of multiple strands of such laid rope in a pattern known as cable laid. Manufactured using an industrial machine known as a strander, the wires are fed through a series of barrels and spun into their final composite orientation.
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch(es) are borne as tension by a chord tying the arch ends rather than by the ground or the bridge foundations. This strengthened chord may be the deck structure itself or consist of separate, independent tie-rods.
Inca technology includes devices, technologies and construction methods used by the Inca people of western South America, including the methods Inca engineers used to construct the cities and road network of the Inca Empire.
A catenary arch is a type of architectural arch that follows an inverted catenary curve. The catenary curve has been employed in buildings since ancient times. It forms an underlying principle to the overall system of vaults and buttresses in stone vaulted Gothic cathedrals and in Renaissance domes. It is not a parabolic arch.
The Lac de Monteynard-Avignonet is an artificial water reservoir for the Électricité de France (EDF) power station on the river Drac. It belongs to the department of Isère. It is bounded by the canyons of the Drac and Ebron.
Xerxes' pontoon bridges were constructed in 480 BC during the second Persian invasion of Greece upon the order of Xerxes I of Persia for the purpose of Xerxes' army to traverse the Hellespont from Asia into Thrace, then also controlled by Persia.
The Térénez bridge is a cable-stayed bridge, located between Landévennec and Rosnoën, Finistère, France.
The Dodhara Chandani Bridge, commonly known as Mahakali Bridge is a suspension bridge for pedestrians and at this point only about 1452.5 m long over Mahakali River in the far west of Nepal.
Highline179 is located near Reutte on the Bavarian–Austrian Border, it extends at an altitude of 114 meters (374 ft) above the Ehrenberg castle and connects the Ehrenberg ruins with Fort Claudia. The location of the bridge was chosen so that it would have a span of 403 meters (1,322 ft).
A suspended structure is a structure which is supported by cables coming from beams or trusses which sit atop a concrete center column or core. The design allows the walls, roof and cantilevered floors to be supported entirely by cables and a center column.
↑ Calladine, C. R. (2015-04-13), "An amateur's contribution to the design of Telford's Menai Suspension Bridge: a commentary on Gilbert (1826) 'On the mathematical theory of suspension bridges'", Philosophical Transactions of the Royal Society A, 373 (2039): 20140346, Bibcode:2015RSPTA.37340346C, doi:10.1098/rsta.2014.0346, PMC4360092, PMID25750153
1 2 Henry Taylor Bovey (1882). Applied Mechanics. Vol.2. Montreal: Printed by John Lovell & Son for the Office of the Minister of Agriculture, Canada. p.150. pages 85-90
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