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59-470: A kunai ( 苦無 , kunai ) is a Japanese tool thought to be originally derived from the masonry trowel . The two widely recognized kinds are the short kunai (小苦無 shō- kunai ) and the big kunai (大苦無 dai-kunai ). Although a basic tool, the kunai , in the hands of a martial arts expert, could be used as a multi-functional weapon. The kunai is commonly associated with the ninja , who in folklore use them to climb walls. A Kunai normally had

118-407: A CMU wall having much greater lateral and tensile strength than unreinforced walls. "Architectural masonry is the evolvement of standard concrete masonry blocks into aesthetically pleasing concrete masonry units (CMUs)". CMUs can be manufactured to provide a variety of surface appearances. They can be colored during manufacturing or stained or painted after installation. They can be split as part of

177-671: A better bond with the concrete and reduce the risk of slippage. The most common type of rebar is carbon steel , typically consisting of hot-rolled round bars with deformation patterns embossed into its surface. Steel and concrete have similar coefficients of thermal expansion , so a concrete structural member reinforced with steel will experience minimal differential stress as the temperature changes. Other readily available types of rebar are manufactured of stainless steel , and composite bars made of glass fiber , carbon fiber , or basalt fiber . The carbon steel reinforcing bars may also be coated in zinc or an epoxy resin designed to resist

236-427: A darker color or an irregular shape. Others may use antique salvage bricks, or new bricks may be artificially aged by applying various surface treatments, such as tumbling. The attempts at rusticity of the late 20th century have been carried forward by masons specializing in a free, artistic style, where the courses are intentionally not straight, instead weaving to form more organic impressions. A crinkle-crankle wall

295-543: A device to reinforce arches, vaults , and cupolas . 2,500 meters of rebar was used in the 14th-century Château de Vincennes . During the 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov . The cast iron used for the rebar was of high quality, and there is no corrosion on the bars to this day. The carcass of

354-783: A leaf-shaped wrought blade in lengths ranging from 20 and 30 cm (7.9 and 11.8 in) and a handle with a ring on the pommel for attaching a rope. The attached rope allowed the kunai' s handle to be wrapped to function as a grip, or to be strapped to a stick as a makeshift spear ; to be tied to the body for concealment; to be used as an anchor or piton , and sometimes to be used as the Chinese rope dart . Contrary to popular belief, kunai were not designed to be used primarily as throwing weapons. Instead, kunai were primarily tools and, when used as weapons, were stabbing and thrusting implements. Varieties of kunai include short, long, narrow-bladed, saw-toothed, and wide-bladed. In some cases,

413-499: A limited ability to carry tensile loads. When rebar is added they are known as "reinforced masonry". A similar approach (of embedding rebar vertically in designed voids in engineered blocks) is also used in dry-laid landscape walls, at least pinning the lowest course in place into the earth, also employed securing the lowest course and/or deadmen in walls made of engineered concrete or wooden landscape ties. In unusual cases, steel reinforcement may be embedded and partially exposed, as in

472-575: A masonry wall is not entirely dependent on the bond between the building material and the mortar; the friction between the interlocking blocks of masonry is often strong enough to provide a great deal of strength on its own. The blocks sometimes have grooves or other surface features added to enhance this interlocking, and some dry set masonry structures forgo mortar altogether. Stone blocks used in masonry can be dressed or rough, though in both examples corners, door and window jambs, and similar areas are usually dressed. Stonemasonry utilizing dressed stones

531-508: A non-staggered bond. The wide selection of brick styles and types generally available in industrialized nations allow much variety in the appearance of the final product. In buildings built during the 1950s-1970s, a high degree of uniformity of brick and accuracy in masonry was typical. In the period since then this style was thought to be too sterile, so attempts were made to emulate older, rougher work. Some brick surfaces are made to look particularly rustic by including burnt bricks, which have

590-408: A permanent colored facing (typically composed of polyester resins, silica sand and various other chemicals) to a concrete masonry unit, providing a smooth impervious surface." Glass block or glass brick are blocks made from glass and provide a translucent to clear vision through the block. A masonry veneer wall consists of masonry units, usually clay-based bricks, installed on one or both sides of

649-715: A shuriken. As with ninjutsu , the exaggeration persistent in ninja myths played a large role in creating the popular culture image of kunai . In fictional depictions of ninjas, the kunai is commonly portrayed as a steel knife that is used for stabbing or particularly throwing, sometimes confused with the shuriken . The kunai was used in masonry to shape stonework. Turnbull, Stephen (2003). Ninja AD 1460–1650 . Osprey Publishing. ISBN   978-1-84176-525-9 . Masonry The common materials of masonry construction are bricks and building stone , rocks such as marble , granite , and limestone , cast stone , concrete blocks , glass blocks , and adobe . Masonry

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708-431: A structurally independent wall usually constructed of wood or masonry. In this context, the brick masonry is primarily decorative, not structural. The brick veneer is generally connected to the structural wall by brick ties (metal strips that are attached to the structural wall, as well as the mortar joints of the brick veneer). There is typically an air gap between the brick veneer and the structural wall. As clay-based brick

767-478: A wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They often are used as the structural core for veneered brick masonry or are used alone for the walls of factories, garages, and other industrial-style buildings where such appearance is acceptable or desirable. Such blocks often receive a stucco surface for decoration. Surface-bonding cement , which contains synthetic fibers for reinforcement,

826-418: Is a tension device added to concrete to form reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression , but has low tensile strength . Rebar usually consists of steel bars which significantly increase the tensile strength of the structure. Rebar surfaces feature a continuous series of ribs, lugs or indentations to promote

885-558: Is a brick wall that follows a serpentine path, rather than a straight line. This type of wall is more resistant to toppling than a straight wall; so much so that it may be made of a single wythe of unreinforced brick and so despite its longer length may be more economical than a straight wall. Blocks of cinder concrete ( cinder blocks or breezeblocks ), ordinary concrete ( concrete blocks ), or hollow tile are generically known as Concrete Masonry Units (CMUs). They usually are much larger than ordinary bricks and so are much faster to lay for

944-424: Is also used in high-corrosion environments. It is available in many forms, such as spirals for reinforcing columns, common rods, and meshes. Most commercially available rebar is made from unidirectional fibers set in a thermoset polymer resin and is often referred to as FRP. Some special construction such as research and manufacturing facilities with very sensitive electronics may require the use of reinforcement that

1003-424: Is approximated as (bar size/9)² square inches. For example, the area of #8 bar is (8/9)² = 0.79 square inches. Bar sizes larger than #8 follow the 1 ⁄ 8 -inch rule imperfectly and skip sizes #12–13, and #15–17 due to historical convention. In early concrete construction bars of one inch and larger were only available in square sections, and when large format deformed round bars became available around 1957,

1062-525: Is cast into it to carry the tensile loads . Most steel reinforcement is divided into primary and secondary reinforcement: Secondary applications include rebar embedded in masonry walls, which includes both bars placed horizontally in a mortar joint (every fourth or fifth course of block) or vertically (in the horizontal voids of cement blocks and cored bricks, which is then fixed in place with grout . Masonry structures held together with grout have similar properties to concrete – high compressive resistance but

1121-420: Is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can substantially affect the durability of the overall masonry construction. A person who constructs masonry is called a mason or bricklayer . These are both classified as construction trades . Masonry is one of the oldest building crafts in

1180-456: Is known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry . Both rubble and ashlar masonry can be laid in coursed rows of even height through the careful selection or cutting of stones, but a great deal of stone masonry is uncoursed. Solid brickwork is made of two or more wythes of bricks with the units running horizontally (called stretcher bricks) bound together with bricks running transverse to

1239-522: Is non-conductive to electricity, and medical imaging equipment rooms may require non-magnetic properties to avoid interference. FRP rebar, notably glass fibre types have low electrical conductivity and are non-magnetic which is commonly used for such needs. Stainless steel rebar with low magnetic permeability is available and is sometimes used to avoid magnetic interference issues. Reinforcing steel can also be displaced by impacts such as earthquakes , resulting in structural failure. The prime example of this

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1298-549: Is only as long as the wire they are composed of and if used in severe climates (such as shore-side in a salt water environment) must be made of appropriate corrosion-resistant wire. Most modern gabions are rectangular. Earlier gabions were often cylindrical wicker baskets, open at both ends, used usually for temporary, often military, construction. Similar work can be done with finer aggregates using cellular confinement . Masonry walls have an endothermic effect of its hydrates , as in chemically bound water , unbound moisture from

1357-717: Is sometimes used in this application and can impart extra strength to a block wall. Surface-bonding cement is often pre-colored and can be stained or painted thus resulting in a finished stucco-like surface. The primary structural advantage of concrete blocks in comparison to smaller clay-based bricks is that a CMU wall can be reinforced by filling the block voids with concrete with or without steel rebar . Generally, certain voids are designated for filling and reinforcement, particularly at corners, wall-ends, and openings while other voids are left empty. This increases wall strength and stability more economically than filling and reinforcing all voids. Typically, structures made of CMUs will have

1416-765: Is subject to the requirements of Australian Standards AS3600 (Concrete Structures) and AS/NZS4671 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing. The designation of reinforcement is defined in AS/NZS4671 using the following formats: Shape/ Section D- deformed ribbed bar, R- round / plain bar, I- deformed indented bar Ductility Class L- low ductility, N- normal ductility, E- seismic (Earthquake) ductility Standard grades (MPa) 250N, 300E, 500L, 500N, 500E Bars are typically abbreviated to simply 'N' (hot-rolled deformed bar), 'R' (hot-rolled round bar), 'RW' (cold-drawn ribbed wire) or 'W' (cold-drawn round wire), as

1475-718: Is the collapse of the Cypress Street Viaduct in Oakland, California as a result of the 1989 Loma Prieta earthquake , causing 42 fatalities. The shaking of the earthquake caused rebars to burst from the concrete and buckle . Updated building designs, including more circumferential rebar, can address this type of failure. US/Imperial bar sizes give the diameter in units of 1 ⁄ 8 inch (3.2 mm) for bar sizes #2 through #8, so that #8 = 8 ⁄ 8 inch = 1-inch (25 mm) diameter. There are no fractional bar sizes in this system. The "#" symbol indicates

1534-496: Is usually not completely waterproof, the structural wall will often have a water-resistant surface (usually tar paper ) and weep holes can be left at the base of the brick veneer to drain moisture that accumulates inside the air gap. Concrete blocks, real and cultured stones , and veneer adobe are sometimes used in a very similar veneer fashion. Most insulated buildings that use concrete block, brick, adobe, stone, veneers or some combination thereof feature interior insulation in

1593-477: The kunai and the Nishikori , a wide-bladed saw with a dagger-type handle, are difficult to distinguish. The kunai was originally used by peasants as a multi-purpose gardening tool and by workers of stone and masonry . The blade is made of soft iron and is left unsharpened because the edges are used to smash relatively soft materials such as plaster and wood, for digging holes, and for prying. Normally, only

1652-404: The number sign , and thus "#6" is read as "number six". The use of the "#" sign is customary for US sizes, but "No." is sometimes used instead. Within the trades rebar is known by a shorthand utilizing the bar diameter as descriptor, such as "four-bar" for bar that is four-eighths (or one-half) of an inch. The cross-sectional area of a bar, as given by πr ², works out to (bar size/9.027)², which

1711-657: The United States, made a significant contribution to the development of reinforcing bars in concrete construction. He invented twisted iron rebar, which he initially thought of while designing self-supporting sidewalks for the Masonic Hall in Stockton, California. His twisted rebar was, however, not initially appreciated and even ridiculed at the Technical Society of California, where members stated that

1770-413: The United States, who produced and tested reinforced concrete beams. Joseph Monier of France is one of the most notable figures for the invention and popularization of reinforced concrete. As a French gardener, Monier patented reinforced concrete flowerpots in 1867, before proceeding to build reinforced concrete water tanks and bridges. Ernest L. Ransome , an English engineer and architect who worked in

1829-486: The bar into place, while the second makes use of the high compressive strength of concrete. Common rebar is made of unfinished tempered steel, making it susceptible to rusting . Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover can compromise this guard through carbonation from the surface, and salt penetration . Too much concrete cover can cause bigger crack widths which also compromises

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1888-583: The bars and corrosion under the epoxy film have been reported. These epoxy-coated bars are used in over 70,000 bridge decks in the US, but this technology was slowly being phased out in favor of stainless steel rebar as of 2005 because of its poor performance. Requirements for deformations are found in US-standard product specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, and dictate lug spacing and height. Fibre-reinforced plastic rebar

1947-700: The beams at the columns. This type of failure manifested in the partial collapse of the Bixby Hotel in Long Beach, California and total collapse of the Eastman Kodak Building in Rochester, New York, both during construction in 1906. It was, however, concluded that both failures were the consequences of poor-quality labor. With the increase in demand of construction standardization, innovative reinforcing systems such as Kahn's were pushed to

2006-534: The concrete block, and the poured concrete if the hollow cores inside the blocks are filled. Masonry can withstand temperatures up to 1,000 °F (538 °C) and it can withstand direct exposure to fire for up to 4 hours. In addition to that, concrete masonry keeps fires contained to their room of origin 93% of the time. For those reasons, concrete and masonry units hold the highest flame spread index classification, Class A. Fire cuts can be used to increase safety and reduce fire damage to masonry buildings. From

2065-406: The concrete, it can still be pulled out of the concrete under high stresses, an occurrence that often accompanies a larger-scale collapse of the structure. To prevent such a failure, rebar is either deeply embedded into adjacent structural members (40–60 times the diameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking

2124-648: The cores remain unfilled. Filling some or all of the cores with concrete or concrete with steel reinforcement (typically rebar ) offers much greater tensile and lateral strength to structures. One problem with masonry walls is that they rely mainly on their weight to keep them in place; each block or brick is only loosely connected to the next via a thin layer of mortar. This is why they do not perform well in earthquakes, when entire buildings are shaken horizontally. Many collapses during earthquakes occur in buildings that have load-bearing masonry walls. Besides, heavier buildings having masonry suffer more damage. The strength of

2183-655: The effects of corrosion, especially when used in saltwater environments. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction. These alternative types tend to be more expensive or may have lesser mechanical properties and are thus more often used in specialty construction where their physical characteristics fulfill a specific performance requirement that carbon steel does not provide. Reinforcing bars in masonry construction have been used since antiquity , with Rome using iron or wooden rods in arch construction. Iron tie rods and anchor plates were later employed across Medieval Europe, as

2242-411: The form of fiberglass batts between wooden wall studs or in the form of rigid insulation boards covered with plaster or drywall . In most climates this insulation is much more effective on the exterior of the wall, allowing the building interior to take advantage of the aforementioned thermal mass of the masonry. This technique does, however, require some sort of weather-resistant exterior surface over

2301-405: The idea that Kahn's reinforcing system in concrete beams would act as a Warren truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest. Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in

2360-929: The industry manufactured them to provide the cross-sectional area equivalent of standard square bar sizes that were formerly used. The diameter of the equivalent large format round shape is rounded to the nearest 1 ⁄ 8 inch to provide the bar size. For example, #9 bar has a cross section of 1.00 square inch (6.5 cm ), and therefore a diameter of 1.128 inches (28.7 mm). #10, #11, #14, and #18 sizes correspond to 1 1 ⁄ 8 inch, 1 1 ⁄ 4 , 1 1 ⁄ 2 , and 2-inch square bars, respectively. Sizes smaller than #3 are no longer recognized as standard sizes. These are most commonly manufactured as plain round undeformed rod steel but can be made with deformations. Sizes smaller than #3 are typically referred to as "wire" products and not "bar" and specified by either their nominal diameter or wire gage number. #2 bars are often informally called "pencil rod" as they are about

2419-464: The insulation and, consequently, is generally more expensive. Gabions are baskets, usually now of zinc -protected steel ( galvanized steel ) that are filled with fractured stone of medium size. These will act as a single unit and are stacked with setbacks to form a revetment or retaining wall . They have the advantage of being well drained, flexible, and resistant to flood, water flow from above, frost damage, and soil flow. Their expected useful life

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2478-682: The local guard. As rust takes up greater volume than the steel from which it was formed, it causes severe internal pressure on the surrounding concrete, leading to cracking, spalling , and, ultimately, structural failure . This phenomenon is known as oxide jacking . This is a particular problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter, or in marine applications. Uncoated, corrosion-resistant low- carbon / chromium (microcomposite), silicon bronze , epoxy -coated, galvanized , or stainless steel rebars may be employed in these situations at greater initial expense, but significantly lower expense over

2537-457: The manufacturing process, giving the blocks a rough face replicating the appearance of natural stone, such as brownstone . CMUs may also be scored, ribbed, sandblasted, polished, striated (raked or brushed), include decorative aggregates, be allowed to slump in a controlled fashion during curing, or include several of these techniques in their manufacture to provide a decorative appearance. "Glazed concrete masonry units are manufactured by bonding

2596-446: The nominal bar diameter in millimeters, as an "alternate size" specification. Substituting a true metric size for a US/Imperial size is called a hard conversion , and sometimes results in the use of a physically different sized bar. bar size size (soft) Metric bar designations represent the nominal bar diameter in millimeters, rounded to the nearest 5 mm. bar size (kg/m) (mm) Area (mm ) Metric bar designations represent

2655-519: The nominal bar diameter in millimetres. Preferred bar sizes in Europe are specified to comply with Table 6 of the standard EN 10080 , although various national standards still remain in force (e.g. BS 4449 in the United Kingdom). In Switzerland some sizes are different from European standard. bar size density (kg/m) diameter (mm) area (mm ) Reinforcement for use in concrete construction

2714-424: The point of view of material modeling, masonry is a special material of extreme mechanical properties (with a very high ratio between strength in compression and in tension), so that the applied loads do not diffuse as they do in elastic bodies, but tend to percolate along lines of high stiffness. Rebar Rebar (short for reinforcing bar ), known when massed as reinforcing steel or steel reinforcement ,

2773-516: The qualification of “tentative” was removed when the updated standard ASTM A305-49 was issued in 1949. The requirements for deformations found in current specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, among others, are the same as those specified in ASTM A305-49. Concrete is a material that is very strong in compression , but relatively weak in tension . To compensate for this imbalance in concrete's behavior, rebar

2832-491: The same size as a pencil. When US/Imperial sized rebar are used in projects with metric units, the equivalent metric size is typically specified as the nominal diameter rounded to the nearest millimeter. These are not considered standard metric sizes, and thus is often referred to as a soft conversion or the "soft metric" size. The US/Imperial bar size system recognizes the use of true metric bar sizes (No. 10, 12, 16, 20, 25, 28, 32, 36, 40, 50 and 60 specifically) which indicates

2891-413: The service life of the project. Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with epoxy-coated rebar, because damage will reduce the long-term corrosion resistance of these bars. Even damaged epoxy-coated bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the epoxy coating from

2950-525: The side in favor of the concrete reinforcing systems seen today. Requirements for deformations on steel bar reinforcement were not standardized in US construction until about 1950. Modern requirements for deformations were established in "Tentative Specifications for the Deformations of Deformed Steel Bars for Concrete Reinforcement", ASTM A305-47T. Subsequently, changes were made that increased rib height and reduced rib spacing for certain bar sizes, and

3009-542: The steel tie bars that constrain and reinforce the masonry of Nevyansk Tower or ancient structures in Rome and the Vatican. Steel has a thermal expansion coefficient nearly equal to that of modern concrete . If this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different from the temperature of the setting. Although rebar has ribs that bind it mechanically to

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3068-730: The tension force present in modern thin, light, tall building systems. Masonry has both structural and non-structural applications. Structural applications include walls, columns, beams, foundations, load-bearing arches, and others. On the other hand, masonry is also used in non-structural applications such as fireplaces chimneys and veneer systems. Brick and concrete block are the most common types of masonry in use in industrialized nations and may be either load-bearing or non-load-bearing. Concrete blocks, especially those with hollow cores, offer various possibilities in masonry construction. They generally provide great compressive strength and are best suited to structures with light transverse loading when

3127-498: The tip is sharpened. Many ninja weapons were adapted from farming tools, not unlike those used by Shaolin monks in China. Since kunai were cheaply produced farming tools of proper size and weight and could be easily sharpened, they were readily available to be converted into simple weapons. As a weapon, the kunai is larger and heavier than a shuriken and with the grip could also be used in hand-to-hand combat more readily than

3186-410: The top course of blocks in the walls filled with concrete and tied together with steel reinforcement to form a bond beam. Bond beams are often a requirement of modern building codes and controls. Another type of steel reinforcement referred to as ladder-reinforcement , can also be embedded in horizontal mortar joints of concrete block walls. The introduction of steel reinforcement generally results in

3245-552: The tower was connected to its cast iron tented roof , crowned with one of the first known lightning rods . However, not until the mid-19th century, with the embedding of steel bars into concrete (thus producing modern reinforced concrete ), did rebar display its greatest strengths. Several people in Europe and North America developed reinforced concrete in the 1850s. These include Joseph-Louis Lambot of France, who built reinforced concrete boats in Paris (1854) and Thaddeus Hyatt of

3304-670: The twisting would weaken the iron. In 1889, Ransome worked on the West Coast mainly designing bridges. One of these, the Alvord Lake Bridge in San Francisco's Golden Gate Park, was the first reinforced concrete bridge built in the United States. He used twisted rebar in this structure. At the same time Ransome was inventing twisted steel rebar, C.A.P. Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and Julius Kahn

3363-597: The wall (called "header" bricks). Each row of bricks is known as a course. The pattern of headers and stretchers employed gives rise to different 'bonds' such as the common bond (with every sixth course composed of headers), the English bond, and the Flemish bond (with alternating stretcher and header bricks present on every course). Bonds can differ in strength and in insulating ability. Vertically staggered bonds tend to be somewhat stronger and less prone to major cracking than

3422-413: The world. The construction of Egyptian pyramids, Roman aqueducts, and medieval cathedrals are all examples of masonry. Early structures used the weight of the masonry itself to stabilize the structure against lateral movements. The types and techniques of masonry used evolved with architectural needs and cultural norms. Since mid-20th century, masonry has often featured steel-reinforced elements to help carry

3481-560: Was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902). Kahn predicted concrete beams with this reinforcing system would bend like a Warren truss , and also thought of this rebar as shear reinforcement. Kahn's reinforcing system was built in concrete beams, joists, and columns. The system was both praised and criticized by Kahn's engineering contemporaries: Turner voiced strong objections to this system as it could cause catastrophic failure to concrete structures. He rejected

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