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In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole ("eye") at each end for fixing to other components. Eyebars are used in structures such as bridges, in settings in which only tension, and never compression, is applied. Also referred to as "pin- and eyebar construction" in instances where pins are being used. [1]
A closed eyebar will typically have a rectangular cross section of constant thickness throughout its length and a constant width for all but the ends. The ends will transition to a wider part that is terminated by a rounded end. In the center of this end will be a hole which will receive a cylindrical pin, which may have provision to accept one or more nuts or bolts. If of round cross section the bar will typically be end-forged to create a head, which is then flatted by additional forging. The head may then be machined to a precise thickness and flatness. An alternative method for using round bar is to form a loop and to forge-weld (hammer weld) or electrically weld the free end to the main bar. [2]
Open eyebars are not used in the cable anchorages of modern wire-cable suspension bridges. This does not allow the wires to be looped over the eye, rather than requiring threading through a closed eye.
The bars may be fabricated with pin holes that are slightly undersized. If so, these are then reamed in the field. This field reaming ensures that stresses will be uniformly distributed among the several bars forming the truss element or the chain link. Corrosion resistant treatment in the form of grease, white or red lead oil paste, or other water-excluding material may be added at the time of the assembly.
Eyebars are used in portions of pin-jointed trusses where it can be established by engineering procedures that the bar will not be imposed with any stress other than tension under all expected conditions. Eyebars are used to supplement roof truss framing supports made of wood or metal. They are placed as the struts for the truss, located next to the king joist.
Eyebar links have long been used in suspension bridges with a number of eyebar links combed together to form a highly redundant structure. This use of eyebar places it in a chain linkage that is holding a load based on tension rather than compression. However, more modern low-redundancy chain link suspension spans fell into general disfavor as a result of the collapse of the Silver Bridge in 1967, which led to the deaths of 46 people.
(The current method of suspension bridge design is to use multiple strands of drawn wire to form substantial cables.) [3]
Eyebars may be cast, forged, or cut from rolled plate. If round stock is used the eyes will usually be forged. Heat treatment (heating and rapid cooling) will result in a fine-grained microscopic crystal structure, enhancing the strength of the bar. Excessive hardness may induce brittleness, which should be avoided. The pins used to join bars will also be heat treated, usually to a degree of hardness exceeding that of the bars so that they will not shear under high stress.
Original eyebars were formed from "piling" [2] thin iron metal on top of one another and forging it together in a furnace. Once together the piece was heated and hammered into a U shape over a die. To create the eye the heated bent iron was hammered into itself closing the gap and creating the eye shape. [2] This method created a quick and efficient way to create the bar, however would not structurally stay together after a certain point due to the piling method being ill heated or being defective.
Piling was superseded by casting, wherein the eye and the bar are cast together in the same mold, creating a more sound piece with less area for the bond to break apart.
Newer methods of steel cutting such as laser / plasma / and water-jetting allow the production of steel items such as eyebars from prefabricated steel plates:
A strong laser is used to accurately cut a programmed design from steel. This method is quick and reduces waste, but also requires additional sanding and finishing before use.
Oxygen gas is funneled past an electrode creates an arc, which can be channeled down into steel allowing the metal to be cut. This method for cutting only works on conductive metals.
Similar to the laser, water-jet cutting utilizes a cutting machine but uses for the force of water to cut through the steel. Using water creates smoothed near finished cuts lowering production time.
Eyebars were created during the early 1900s where the cost of steel was high. The creation of the eyebar provided a simple solution to lessening the amount of steel needed in a bridge. Using a pin and eye method less stress would theoretically be placed on the joining members. [4]
Issues occur for the following reasons:
A bar may not be made properly due to bad casting, if steel, or not being hammered properly, if iron. This error is evident in points where the head has snapped off from the bar or the head has cracked across from a pin hole to the exterior side. [2]
Eye bars when placed as supports in bridges are not layered enough. Consider the catastrophe of Silver Bridge, this was an instance where only 2 eyebars were paired together as supports in the chain. It was more common practice to use 4 eye bars pinned together in the instance where one eyebar failed 3 more would be able to split the load rather than just the single eyebar left. In the case of Silver bridge the remaining eye bar also broke which caused the bridge to collapse. [5]
Like all metal, steel wears down over time. As a result, the steel pins in the eyes become loose and lose tension, which in turn compromises the integrity of the structure.
Due to the technological advancements in creating eyebars, iron and old cast method of steel eyebars are less common. These older bridges however still need to be maintained and reviewed. Researchers like Dewey Walls Jr. of the Union Pacific Railroad have compiled resources on how to review, identify compromised locations and how to properly repair the area. [4]
| Name | ID | Date | Significance |
|---|---|---|---|
| Three Sisters Bridges | HAER PA-490-A | 1926 | Example of Large Eyebar Suspension Bridge |
| Brooklyn Bridge | HAER NY-18 | 1883 | Once largest spanning bridge in the world, has eyebar anchors |
| Dresden (Ohio) Suspension Bridge | HAER OH-93 | 1914 | One of the few examples of Eyebar Suspension Bridge |
A forge is a type of hearth used for heating metals, or the workplace (smithy) where such a hearth is located. The forge is used by the smith to heat a piece of metal to a temperature at which it becomes easier to shape by forging, or to the point at which work hardening no longer occurs. The metal is transported to and from the forge using tongs, which are also used to hold the workpiece on the smithy's anvil while the smith works it with a hammer. Sometimes, such as when hardening steel or cooling the work so that it may be handled with bare hands, the workpiece is transported to the slack tub, which rapidly cools the workpiece in a large body of water. However, depending on the metal type, it may require an oil quench or a salt brine instead; many metals require more than plain water hardening. The slack tub also provides water to control the fire in the forge.
A knife is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced by the Oldowan tools. Originally made of wood, bone, and stone, over the centuries, in step with improvements in both metallurgy and manufacturing, knife blades have been made from copper, bronze, iron, steel, ceramic, and titanium. Most modern knives have either fixed or folding blades; blade patterns and styles vary by maker and country of origin.
In woodworking and construction, a nail is a small object made of metal which is used as a fastener, as a peg to hang something, or sometimes as a decoration. Generally, nails have a sharp point on one end and a flattened head on the other, but headless nails are available. Nails are made in a great variety of forms for specialized purposes. The most common is a wire nail. Other types of nails include pins, tacks, brads, spikes, and cleats.
Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often mistakenly called Damascus steel, blades forged in this manner often display bands of slightly different patterning along their entire length. These bands can be highlighted for cosmetic purposes by proper polishing or acid etching. Pattern welding was an outgrowth of laminated or piled steel, a similar technique used to combine steels of different carbon contents, providing a desired mix of hardness and toughness. Although modern steelmaking processes negate the need to blend different steels, pattern welded steel is still used by custom knifemakers for the cosmetic effects it produces.
Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent welding using chemicals to melt materials being bonded without heat, and solid-state welding processes which bond without melting, such as pressure, cold welding, and diffusion bonding.
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.
Wrought iron is an iron alloy with a very low carbon content in contrast to that of cast iron. It is a semi-fused mass of iron with fibrous slag inclusions, which give it a wood-like "grain" that is visible when it is etched, rusted, or bent to failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily forge welded, but is more difficult to weld electrically.
A blacksmith is a metalsmith who creates objects primarily from wrought iron or steel, but sometimes from other metals, by forging the metal, using tools to hammer, bend, and cut. Blacksmiths produce objects such as gates, grilles, railings, light fixtures, furniture, sculpture, tools, agricultural implements, decorative and religious items, cooking utensils, and weapons. There was a historical distinction between the heavy work of the blacksmith and the more delicate operations of a whitesmith, who usually worked in gold, silver, pewter, or the finishing steps of fine steel. The place where a blacksmith works is variously called a smithy, a forge, or a blacksmith's shop.
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer or a die. Forging is often classified according to the temperature at which it is performed: cold forging, warm forging, or hot forging. For the latter two, the metal is heated, usually in a forge. Forged parts can range in weight from less than a kilogram to hundreds of metric tons. Forging has been done by smiths for millennia; the traditional products were kitchenware, hardware, hand tools, edged weapons, cymbals, and jewellery.
Metalworking is the process of shaping and reshaping metals in order to create useful objects, parts, assemblies, and large scale structures. As a term, it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges, down to precise engine parts and delicate jewelry.
An anvil is a metalworking tool consisting of a large block of metal, with a flattened top surface, upon which another object is struck.
Forge welding (FOW), also called fire welding, is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. The process, although challenging, has been a method of joining metals used since ancient times and is a staple of traditional blacksmithing. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical welding and gas welding methods during the Industrial Revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process.
A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements, usually forming triangular units. The connected elements, typically straight, may be stressed from tension, compression, or sometimes both in response to dynamic loads. There are several types of truss bridges, including some with simple designs that were among the first bridges designed in the 19th and early 20th centuries. A truss bridge is economical to construct primarily because it uses materials efficiently.
Metal fabrication is the creation of metal structures by cutting, bending and assembling processes. It is a value-added process involving the creation of machines, parts, and structures from various raw materials.
Sword making, historically, has been the work of specialized smiths or metalworkers called bladesmiths or swordsmiths. Swords have been made of different materials over the centuries, with a variety of tools and techniques. While there are many criteria for evaluating a sword, generally the four key criteria are hardness, strength, flexibility and balance. Early swords were made of copper, which bends easily. Bronze swords were stronger; by varying the amount of tin in the alloy, a smith could make various parts of the sword harder or tougher to suit the demands of combat service. The Roman gladius was an early example of swords forged from blooms of steel.
Bladesmithing is the art of making knives, swords, daggers and other blades using a forge, hammer, anvil, and other smithing tools. Bladesmiths employ a variety of metalworking techniques similar to those used by blacksmiths, as well as woodworking for knife and sword handles, and often leatherworking for sheaths. Bladesmithing is an art that is thousands of years old and found in cultures as diverse as China, Japan, India, Germany, Korea, the Middle East, Spain and the British Isles. As with any art shrouded in history, there are myths and misconceptions about the process. While traditionally bladesmithing referred to the manufacture of any blade by any means, the majority of contemporary craftsmen referred to as bladesmiths are those who primarily manufacture blades by means of using a forge to shape the blade as opposed to knifemakers who form blades by use of the stock removal method, although there is some overlap between both crafts.
Japanese swordsmithing is the labour-intensive bladesmithing process developed in Japan beginning in the sixth century for forging traditionally made bladed weapons (nihonto) including katana, wakizashi, tantō, yari, naginata, nagamaki, tachi, nodachi, ōdachi, kodachi, and ya (arrow).
A Howe truss is a truss bridge consisting of chords, verticals, and diagonals whose vertical members are in tension and whose diagonal members are in compression. The Howe truss was invented by William Howe in 1840, and was widely used as a bridge in the mid to late 1800s.
An ironworker is a tradesman who works in the iron-working industry. Ironworkers assemble the structural framework in accordance with engineered drawings and install the metal support pieces for new buildings. They also repair and renovate old structures using reinforced concrete and steel. Ironworkers may work on factories, steel mills, and utility plants.
The Silver Bridge was an eyebar-chain suspension bridge built in 1928 which carried U.S. Route 35 over the Ohio River, connecting Point Pleasant, West Virginia, and Gallipolis, Ohio. Officially named the Point Pleasant Bridge, it was popularly known as the Silver Bridge for the color of its aluminum paint.