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86-591: The Presidential Emergency Operations Center ( PEOC , PEE -ock ) is a bunker underneath the East Wing of the White House . It serves as a secure shelter and communications center for the president of the United States and others in case of an emergency. The first White House bunker was built during World War II to protect President Franklin D. Roosevelt in the event of an aerial attack on

172-410: A Scots word for "bench, seat" recorded 1758, alongside shortened bunk "sleeping berth". The word possibly has a Scandinavian origin: Old Swedish bunke means "boards used to protect the cargo of a ship". In the 19th century the word came to describe a coal store in a house, or below decks in a ship. It was also used for a sand-filled depression installed on a golf course as a hazard. In

258-589: A White House Fellowship , and other staff including Norman Mineta . President George W. Bush was visiting a school in Florida at the time of the attacks. Australian Prime Minister John Howard was incorrectly reported as being bundled into the PEOC but was actually in a bunker at the Australian Embassy. President Donald Trump retreated to the PEOC during the night of May 29, 2020, at the beginning of

344-476: A pillbox can be killed with flamethrowers . Complex, well-built and well-protected fortifications are often vulnerable to attacks on access points. If the exits to the surface can be closed off, those manning the facility can be trapped. The fortification can then be bypassed. Famous bunkers include the post-World War I Maginot Line on the French eastern border and Czechoslovak border fortifications mainly on

430-443: A "caul plate" or on a cylindrical structure referred to as a "mandrel". However, most fibre-reinforced plastic parts are created with a mould or "tool". Moulds can be concave female moulds, male moulds, or the mould can completely enclose the part with a top and bottom mould. The moulding processes of FRP plastics begins by placing the fibre preform on or in the mould. The fibre preform can be dry fibre, or fibre that already contains

516-474: A "preform" or "charge", of SMC , BMC is placed into mould cavity. The mould is closed and the material is formed & cured inside by pressure and heat. Compression moulding offers excellent detailing for geometric shapes ranging from pattern and relief detailing to complex curves and creative forms, to precision engineering all within a maximum curing time of 20 minutes. Individual sheets of prepreg material are laid-up and placed in an open mould. The material

602-468: A 'U' shape around the sides and bottom (tension) face of the beam. If all faces of a beam are accessible, the use of closed wraps is desirable as they provide the most strength enhancement. Closed wrapping involves applying FRP around the entire perimeter of the member, such that there are no free ends and the typical failure mode is rupture of the fibres. For all wrap configurations, the FRP can be applied along

688-465: A 500 m (1,600 ft) high building, an elevator would use 15% less electrical power than a steel-cabled version. As of June 2013, the product had passed all European Union and United States certification tests. FRP is used in designs that require a measure of strength or modulus of elasticity for which non-reinforced plastics and other material choices are ill-suited, either mechanically or economically. The primary design consideration for using FRP

774-502: A female-style mould along with a balloon-like bladder. The mould is closed and placed in a heated press. Finally, the bladder is pressurized forcing the layers of material against the mould walls. When the raw material (plastic block, rubber block, plastic sheet, or granules) contains reinforcing fibres, a compression moulded part qualifies as a fibre-reinforced plastic. More typically the plastic preform used in compression moulding does not contain reinforcing fibres. In compression moulding,

860-400: A final product with certain desired material and mechanical properties. Fibre-reinforced plastics are a category of composite plastics that specifically use fibre materials to mechanically enhance the strength and elasticity of plastics. The original plastic material without fibre reinforcement is known as the matrix or binding agent . The matrix is a tough but relatively weak plastic that

946-406: A great deal of gas, making it useful as an insulator, especially at high temperatures. A suitable resin for combining the "fibreglas" with a plastic to produce a composite material, was developed in 1936 by du Pont . The first ancestor of modern polyester resins is Cyanamid 's resin of 1942. Peroxide curing systems were used by then. With the combination of fibreglas and resin the gas content of

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1032-401: A house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with large cabinets. One common design approach uses fibre-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching. The overburden is designed to shield from radiation. To prevent the shelter from floating to the surface in high groundwater, some designs have

1118-448: A measured amount of resin called "prepreg". Dry fibres are "wetted" with resin either by hand or the resin is injected into a closed mould. The part is then cured, leaving the matrix and fibres in the shape created by the mould. Heat and/or pressure are sometimes used to cure the resin and improve the quality of the final part. The different methods of forming are listed below. Individual sheets of prepreg material are laid up and placed in

1204-560: A meeting of the American Chemical Society on 5 February 1909. The development of fibre-reinforced plastic for commercial use was being extensively researched in the 1930s. In the United Kingdom , considerable research was undertaken by pioneers such as Norman de Bruyne . It was particularly of interest to the aviation industry. Mass production of glass strands was discovered in 1932, when Games Slayter ,

1290-400: A narrow, 1–2-metre (3.5–6.5 ft), flexible tent of thin wood is placed in a deep trench, and then covered with cloth or plastic, and then covered with 1–2 m (3.5–6.5 feet) of tamped earth. A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from

1376-472: A researcher at Owens-Illinois accidentally directed a jet of compressed air at a stream of molten glass and produced fibres. A patent for this method of producing glass wool was first applied for in 1933. Owens joined with the Corning company in 1935 and the method was adapted by Owens Corning to produce its patented "fibreglas" (one "s") in 1936. Originally, fibreglas was a glass wool with fibres entrapping

1462-477: A significant aspect of this industry from the beginning. A polymer is generally manufactured by step-growth polymerization or addition polymerization . When one or more polymers are combined with various agents to enhance or in any way alter their material properties, the result is referred to as a plastic . Composite plastics refers to those types of plastics that result from bonding two or more homogeneous materials with different material properties to derive

1548-762: A single piece enhances the material and structural integrity of the product by reducing the requirements for joints, connections, and hardware. As a subset of plastic, FR plastics are liable to a number of the issues and concerns in plastic waste disposal and recycling. Plastics pose a particular challenge in recycling because they are derived from polymers and monomers that often cannot be separated and returned to their virgin states. For this reason not all plastics can be recycled for re-use, in fact some estimates claim only 20% to 30% of plastics can be recycled at all. Fibre-reinforced plastics and their matrices share these disposal and environmental concerns. Investigation of safe disposal methods has led to two main variations involving

1634-522: A skirt held down with the overburden. It may also serve the purpose of a safe room . Large bunkers are often bought by super rich individuals in case of political instability , and usually store or access large amounts of energy for use. They are sometimes refereed to as "luxury bunkers," and their locations are often documented. Munitions storage bunkers are designed to securely store explosive ordnance and contain any internal explosions. The most common configuration for high explosives storage

1720-463: A wet bath of resin and wound over a rotating steel mandrel in specific orientations. Parts are cured either room temperature or elevated temperatures. Mandrel is extracted, leaving a final geometric shape but can be left in some cases. Fibre bundles and slit fabrics are pulled through a wet bath of resin and formed into the rough part shape. Saturated material is extruded from a heated closed die curing while being continuously pulled through die. Some of

1806-707: Is a stub . You can help Misplaced Pages by expanding it . Bunker A bunker is a defensive military fortification designed to protect people and valued materials from falling bombs, artillery, or other attacks. Bunkers are almost always underground, in contrast to blockhouses which are mostly above ground. They were used extensively in World War I , World War II , and the Cold War for weapons facilities, command and control centers, and storage facilities. Bunkers can also be used as protection from tornadoes . Trench bunkers are small concrete structures, partly dug into

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1892-417: Is an unusually large number of bunkers because of a law requiring protective shelters to be constructed for all new buildings since 1963, as well as a number of bunkers built as part of its National Redoubt military defense plan. Some of Switzerland's bunkers have since become tourist attractions housing hotels and museums such as Sasso San Gottardo Museum. The Soviet Union maintained huge bunkers (one of

1978-504: Is anywhere from one to several hours. This precise control creates the exact laminate geometric forms needed to ensure strength and safety in the aerospace industry, but it is also slow and labour-intensive, meaning costs often confine it to the aerospace industry. Sheets of prepreg material are wrapped around a steel or aluminium mandrel. The prepreg material is compacted by nylon or polypropylene cello tape. Parts are typically batch cured by vacuum bagging and hanging in an oven. After cure,

2064-699: Is by far the most popular means to reinforce plastic and thus enjoys a wealth of production processes, some of which are applicable to aramid and carbon fibres as well owing to their shared fibrous qualities. Roving is a process where filaments are spun into larger diameter threads. These threads are then commonly used for woven reinforcing glass fabrics and mats, and in spray applications. Fibre fabrics ( glass cloth , etc.) are web-form fabric reinforcing material that has both warp and weft directions. Fibre mats are web-form non-woven mats of glass fibres. Mats are manufactured in cut dimensions with chopped fibres, or in continuous mats using continuous fibres. Chopped fibre glass

2150-404: Is covered with release film, bleeder/breather material and a vacuum bag . A vacuum is pulled on part and the entire mould is placed into an autoclave (heated pressure vessel). The part is cured with a continuous vacuum to extract entrapped gasses from laminate. This is a very common process in the aerospace industry because it affords precise control over moulding due to a long, slow cure cycle that

2236-445: Is credited with producing the first composite boat in 1937, but did not proceed further at the time due to the brittle nature of the plastic used. In 1939, Russia was reported to have constructed a passenger boat of plastic materials, and the United States a fuselage and wings of an aircraft. The first car to have a fibre-glass body was the 1946 Stout Scarab . Only one of this model was built. The Ford prototype of 1941 could have been

2322-437: Is reinforced by stronger stiffer reinforcing filaments or fibres. The extent that strength and elasticity are enhanced in a fibre-reinforced plastic depends on the mechanical properties of both the fibre and matrix, their volume relative to one another, and the fibre length and orientation within the matrix. Reinforcement of the matrix occurs by definition when the FRP material exhibits increased strength or elasticity relative to

2408-421: Is repaired, strengthening can be achieved through wet, hand lay-up of fibre sheets impregnated with epoxy resin, applied to the cleaned and prepared surfaces of the member. Two techniques are typically adopted for the strengthening of beams, depending on the strength enhancement desired: flexural strengthening or shear strengthening . In many cases it may be necessary to provide both strength enhancements. For

2494-434: Is the igloo shaped bunker. They are often built into a hillside in order to provide additional containment mass. A specialized version of the munitions bunker called a Gravel Gertie is designed to contain radioactive debris from an explosive accident while assembling or disassembling nuclear warheads . They are installed at all facilities in the United States and United Kingdom which do warhead assembly and disassembly,

2580-417: Is to ensure that the material is used economically and in a manner that takes advantage of its specific structural characteristics, but this is not always the case. The orientation of fibres creates a material weakness perpendicular to the fibres. Thus the use of fibre reinforcement and their orientation affects the strength, rigidity, elasticity and hence the functionality of the final product itself. Orienting

2666-414: Is under vacuum in resin transfer moulding . Resin is entirely pulled into cavity under vacuum in vacuum-assisted resin transfer moulding. This moulding process allows precise tolerances and detailed shaping, but can sometimes fail to fully saturate the fabric leading to weak spots in the final shape. FRP allows the alignment of the glass fibres of thermoplastics to suit specific design programs. Specifying

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2752-546: Is used in processes where lengths of glass threads are cut between 3 and 26 mm, threads are then used in plastics most commonly intended for moulding processes. Glass fibre short strands are short 0.2–0.3 mm strands of glass fibres that are used to reinforce thermoplastics most commonly for injection moulding. Carbon fibres are created when polyacrylonitrile fibres (PAN), Pitch resins, or Rayon are carbonized (through oxidation and thermal pyrolysis) at high temperatures. Through further processes of graphitizing or stretching,

2838-677: The East Wing of the White House serves as a secure shelter and communications center for the President of the United States in case of an emergency. 1. abmm.org : Australian Bunker And Military Museum 2. BunkerBlog : All about German fortifications 1933-1945 3. Bunkersite.com : About bunkers built by the Germans during 1933–1945 in the whole of Europe 4. German bunkers in Poland : Fortified Front Odra-Warta rivers, Boryszyn Loop Fiber-reinforced plastic FRPs are commonly used in

2924-805: The Far East the term was also applied to the earth and log positions built by the Japanese, the term appearing in a 1943 instruction manual issued by the British Indian Army and quickly gaining wide currency. By 1947 the word was familiar enough in English that Hugh Trevor-Roper in The Last Days of Hitler was describing Hitler's underground complex near the Reich Chancellery as "Hitler's own bunker" without quotes around

3010-731: The First World War the belligerents built underground shelters, called dugouts in English , while the Germans used the term Bunker . By the Second World War the term came to be used by the Germans to describe permanent structures both large ( blockhouses ), and small ( pillboxes ), and bombproof shelters both above ground (as in Hochbunker ) and below ground (such as the Führerbunker ). The military sense of

3096-486: The George Floyd protests . After his time in the bunker was reported in the news, Trump demanded that officials find and prosecute those responsible for the information getting to the press. Trump's Secretary of Defense, Mark Esper , described in his 2022 book that Trump stated the person who leaked his whereabouts "should be tried for treason and should be executed". This United States government–related article

3182-408: The beams , columns , and slabs of buildings and bridges. It is possible to increase the strength of structural members even after they have been severely damaged due to loading conditions. In the case of damaged reinforced concrete members, this would first require the repair of the member by removing loose debris and filling in cavities and cracks with mortar or epoxy resin . Once the member

3268-401: The deflection capacity and ductility. For the shear strengthening of a beam, the FRP is applied on the web (sides) of a member with fibres oriented transverse to the beam's longitudinal axis. Resisting of shear forces is achieved in a similar manner as internal steel stirrups , by bridging shear cracks that form under applied loading. FRP can be applied in several configurations, depending on

3354-658: The PEOC. Day to day, the PEOC is staffed around the clock by joint-service military officers and non-commissioned officers . During the September 11 attacks , a number of key personnel were evacuated from their offices in the White House to the PEOC. These included Vice President Dick Cheney , First Lady Laura Bush , Lynne Cheney , Condoleezza Rice , Mary Matalin , "Scooter" Libby , Joshua Bolten , Karen Hughes , Stephen Hadley , David Addington , Secret Service agents, U.S. Army major Mike Fenzel serving on

3440-444: The aerospace, automotive, marine, and construction industries. They are commonly found in ballistic armour and cylinders for self-contained breathing apparatuses . Bakelite was the first fibre-reinforced plastic. Leo Baekeland had originally set out to find a replacement for shellac (made from the excretion of lac bugs ). Chemists had begun to recognize that many natural resins and fibres were polymers, and Baekeland investigated

3526-403: The application of intense heat: in one binding agents are burned off - in the process recapturing some of the sunk material cost in the form of heat - and incombustible elements captured by filtration; in the other the incombustible material is burned in a cement kiln, the fibres becoming an integral part of the resulting cast material. In addition to concerns regarding safe disposal, the fact that

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3612-542: The blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation . A bunker's door must be at least as strong as the walls. In bunkers inhabited for prolonged periods, large amounts of ventilation or air conditioning must be provided. Bunkers can be destroyed with powerful explosives and bunker-busting warheads . The word bunker originates as

3698-452: The blast wave or a reflection cannot lift the edge. A bunker should have two doors. Door shafts may double as ventilation shafts to reduce digging. In bunkers inhabited for prolonged periods, large amounts of ventilation or air conditioning must be provided in order to prevent ill effects of heat. In bunkers designed for war-time use, manually operated ventilators must be provided because supplies of electricity or gas are unreliable. One of

3784-412: The cello and mandrel are removed leaving a hollow carbon tube. This process creates strong and robust hollow carbon tubes. Wet layup forming combines fibre reinforcement and the matrix as they are placed on the forming tool. Reinforcing fibre layers are placed in an open mould and then saturated with a wet resin by pouring it over the fabric and working it into the fabric. The mould is then left so that

3870-411: The end products of pultrusion are structural shapes, i.e. I beam, angle, channel and flat sheet. These materials can be used to create all sorts of fibreglass structures such as ladders, platforms, handrail systems tank, pipe and pump supports. Also called resin infusion . Fabrics are placed into a mould into which wet resin is then injected. Resin is typically pressurized and forced into a cavity which

3956-411: The exposed faces of the member and the degree of strengthening desired, this includes: side bonding, U-wraps (U-jackets), and closed wraps (complete wraps). Side bonding involves applying FRP to the sides of the beam only. It provides the least amount of shear strengthening due to failures caused by de-bonding from the concrete surface at the FRP free edges. For U-wraps, the FRP is applied continuously in

4042-886: The fibers together and transfers loads between them. FRP composites have a wide range of applications across various industries due to their unique combination of properties, including high strength-to-weight ratio, corrosion resistance, and design flexibility. A moulded polymer product is cheaper, faster, and easier to manufacture than a cast aluminium or steel product, and maintains similar and sometimes better tolerances and material strengths. Rudder of Airbus A310 Engine intake manifolds are made from glass-fibre-reinforced PA 66. Automotive gas and clutch pedals made from glass-fibre-reinforced PA 66 (DWP 12–13) Aluminium windows, doors and façades are thermally insulated by using thermal insulation plastics made of glass fibre reinforced polyamide. In 1977 Ensinger GmbH produced first insulation profile for window systems. FRP can be applied to strengthen

4128-444: The fibre for similar reasons. Finally, the matrix should be of a plastic that remains chemically and physically stable during and after the reinforcement and moulding processes. To be suitable as reinforcement material, fibre additives must increase the tensile strength and modulus of elasticity of the matrix and meet the following conditions; fibres must exceed critical fibre content; the strength and rigidity of fibres itself must exceed

4214-410: The fibre reinforcement for maximum adhesion within a suitable curing period. The matrix must also completely envelop the fibres to protect them from cuts and notches that would reduce their strength, and to transfer forces to the fibres. The fibres must also be kept separate from each other so that if failure occurs it is localized as much as possible, and if failure occurs the matrix must also debond from

4300-490: The fibres either unidirectionally, 2-dimensionally, or 3-dimensionally during production affects the strength, flexibility, and elasticity of the final product. Fibres oriented in the direction of applied forces display greater resistance to distortion from these forces, thus areas of a product that must withstand forces will be reinforced with fibres oriented parallel to the forces, and areas that require flexibility, such as natural hinges, will have fibres oriented perpendicular to

4386-484: The fibres parallel to expected forces. When forces are exerted perpendicular to the orientation of fibres, the strength and elasticity of the polymer is less than the matrix alone. In cast resin components made of glass reinforced polymers such as UP and EP, the orientation of fibres can be oriented in two-dimensional and three-dimensional weaves. This means that when forces are possibly perpendicular to one orientation, they are parallel to another orientation; this eliminates

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4472-559: The fibres strength or elasticity can be enhanced respectively. Carbon fibres are manufactured in diameters analogous to glass fibres with diameters ranging from 4 to 17 μm. These fibres wound into larger threads for transportation and further production processes. Further production processes include weaving or braiding into carbon fabrics, cloths and mats analogous to those described for glass that can then be used in actual reinforcements. Aramid fibres are most commonly known as Kevlar, Nomex and Technora. Aramids are generally prepared by

4558-485: The fibres themselves are difficult to remove from the matrix and preserve for re-use means FRP's amplify these challenges. FRP's are inherently difficult to separate into base materials, that is into fibre and matrix, and the matrix is difficult to separate into usable plastics, polymers, and monomers. These are all concerns for environmentally-informed design today. Plastics do often offer savings in energy and economic savings in comparison to other materials. In addition, with

4644-538: The first plane, a Vultee BT-15 , with a GFRP fuselage, designated the XBT-19, being flown in 1944. A significant development in the tooling for GFRP components had been made by Republic Aviation Corporation in 1943. Carbon fibre production began in the late 1950s and was used, though not widely in British industry until the early 1960s. Aramid fibres were being produced around this time also, appearing first under

4730-689: The first plastic car, but there is some uncertainty around the materials used as it was destroyed shortly afterwards. The first fibre-reinforced plastic plane was either the Fairchild F-46 , first flown on 12 May 1937, or the Californian built Bennett Plastic Plane. A fibreglass fuselage was used on a modified Vultee BT-13A designated the XBT-16 based at Wright Field in late 1942. In 1943, further experiments were undertaken building structural aircraft parts from composite materials resulting in

4816-442: The flexural strengthening of a beam, FRP sheets or plates are applied to the tension face of the member (the bottom face for a simply supported member with applied top loading or gravity loading). Principal tensile fibres are oriented parallel to the beam's longitudinal axis, similar to its internal flexural steel reinforcement. This increases the beam strength and its stiffness ( load required to cause unit deflection), but decreases

4902-459: The forces. Orienting the fibres in more dimensions avoids this either-or scenario and creates objects that seek to avoid any specific weakness due to the unidirectional orientation of fibres. The properties of strength, flexibility and elasticity can also be magnified or diminished through the geometric shape and design of the final product. For example, ensuring proper wall thickness and creating multifunctional geometric shapes that can be moulded as

4988-433: The ground. Many artillery installations, especially for coastal artillery , have historically been protected by extensive bunker systems. Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. When a house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with fiber-reinforced plastic shells. Bunkers deflect

5074-479: The important categories of fibre used in FRP. Global polymer production on the scale present today began in the mid 20th century, when low material and productions costs, new production technologies and new product categories, combined to make polymer production economical. The industry finally matured in the late 1970s, when world polymer production surpassed that of steel , making polymers the ubiquitous material that they are today. Fibre-reinforced plastics have been

5160-563: The largest being the Pantex plant in Amarillo, Texas , which has 12 Gravel Gerties. Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 21  kPa (3  psi ; 0.21  bar ) of overpressure , bunkers are regularly constructed to survive over 1,000 kPa (150 psi; 10 bar). This substantially decreases

5246-841: The largest individual pre-Cold War bunkers. The walls of the ' Batterie Todt ' gun installation in northern France were up to 3.5 metres (11 ft) thick, and an underground bunker was constructed for the V-3 cannon . Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. They were built mainly by nations like Germany during World War II to protect important industries from aerial bombardment . Industrial bunkers are also built for control rooms of dangerous activities, such as tests of rocket engines or explosive experiments. They are also built in order to perform dangerous experiments in them or to store radioactive or explosive goods. Such bunkers also exist on non-military facilities. When

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5332-506: The lateral expansion of the column, which can enhance confinement in a similar manner as spiral reinforcement does for the column core. In June 2013, KONE elevator company announced Ultrarope for use as a replacement for steel cables in elevators. It seals the carbon fibres in high-friction polymer . Unlike steel cable, Ultrarope was designed for buildings that require up to 1,000 m (3,300 ft) of lift. Steel elevators top out at 500 m (1,600 ft). The company estimated that in

5418-420: The length of the member as a continuous sheet or as discrete strips, having a predefined minimum width and spacing. Slabs may be strengthened by applying FRP strips at their bottom (tension) face. This will result in better flexural performance, since the tensile resistance of the slabs is supplemented by the tensile strength of FRP. In the case of beams and slabs, the effectiveness of FRP strengthening depends on

5504-513: The likelihood that a bomb (other than a bunker buster ) can harm the structure. The basic plan is to provide a structure that is very strong in physical compression . The most common purpose-built structure is a buried, steel reinforced concrete vault or arch . Most expedient blast shelters are civil engineering structures that contain large, buried tubes or pipes such as sewage or rapid transit tunnels. Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these,

5590-416: The material can be adapted to meet specific design requirements, such as cutting the tough material during manufacture. Fibre-reinforced plastics are best suited for any design program that demands weight savings, precision engineering, definite tolerances, and the simplification of parts in both production and operation.The fibers provide strength and stiffness to the material, while the polymer matrix holds

5676-455: The material was replaced by plastic. This reduced the insulation properties to values typical of the plastic, but now for the first time the composite showed great strength and promise as a structural and building material. Confusingly, many glass fibre composites continued to be called " fibreglass " (as a generic name) and the name was also used for the low-density glass wool product containing gas instead of plastic. Ray Greene of Owens Corning

5762-412: The matrix. Fibre preforms are often manufactured in sheets, continuous mats, or as continuous filaments for spray applications. The four major ways to manufacture the fibre preform is through the textile processing techniques of weaving , knitting , braiding and stitching . A rigid structure is usually used to establish the shape of FRP components. Parts can be laid up on a flat surface referred to as

5848-511: The most efficient manual ventilator designs is the Kearny Air Pump . Ventilation openings in a bunker must be protected by blast valves . A blast valve is closed by a shock wave, but otherwise remains open. One form of expedient blast valve is worn flat rubber tire treads nailed or bolted to frames strong enough to resist the maximum overpressure. Bunkers can be destroyed with powerful explosives and bunkerbusting warheads. The crew of

5934-466: The muzzle pointing upwards (e.g., mortars and anti-aircraft weapons). Many artillery installations, especially for coastal artillery , have historically been protected by extensive bunker systems. These usually housed the crews serving the weapons, protected the ammunition against counter-battery fire, and in numerous examples also protected the guns themselves, though this was usually a trade-off reducing their fields of fire. Artillery bunkers are some of

6020-473: The national capital of Washington, D.C. The present-day PEOC space has modern communications equipment including televisions and phones to coordinate with outside government entities. During a breach of White House security, including violations of the Washington, D.C. Air Defense Identification Zone (P-56 airspace), the president and other protectees are relocated to the executive briefing room, next to

6106-1003: The northern Czech border facing Germany (but to lesser extent all around), Fort Eben-Emael in Belgium, Alpine Wall on the north of Italy, World War II Führerbunker and in Italy, industrial Marnate's Bunker , the V-weapon installations in Germany ( Mittelwerk ) & France ( La Coupole , and the Blockhaus d'Éperlecques ) and the Cold War installations in the United States ( Cheyenne Mountain Complex , Site R , and The Greenbrier ), United Kingdom ( Burlington ), Sweden ( Boden Fortress ) and Canada ( Diefenbunker ). In Switzerland, there

6192-573: The orientation of reinforcing fibres can increase the strength and resistance to deformation of the polymer. Glass reinforced polymers are strongest and most resistive to deforming forces when the polymers fibres are parallel to the force being exerted, and are weakest when the fibres are perpendicular. Thus, this ability is at once both an advantage or a limitation depending on the context of use. Weak spots of perpendicular fibres can be used for natural hinges and connections, but can also lead to material failure when production processes fail to properly orient

6278-421: The performance of the resin chosen for bonding. This is particularly an issue for shear strengthening using side bonding or U-wraps. Columns are typically wrapped with FRP around their perimeter, as with closed or complete wrapping. This not only results in higher shear resistance, but more crucial for column design , it results in increased compressive strength under axial loading. The FRP wrap works by restraining

6364-400: The potential for weak spots in the polymer. Structural failure can occur in FRP materials when: A thermoset polymer matrix material, or engineering grade thermoplastic polymer matrix material, must meet certain requirements in order to first be suitable for FRPs and ensure a successful reinforcement of itself. The matrix must be able to properly saturate, and preferably bond chemically with

6450-408: The reaction between an amine group and a carboxylic acid halide group (aramid);. Commonly, this occurs when an aromatic polyamide is spun from a liquid concentration of sulphuric acid into a crystallized fibre. Fibres are then spun into larger threads in order to weave into large ropes or woven fabrics (aramid). Aramid fibres are manufactured with varying grades based on strength and rigidity, so that

6536-486: The reactions of phenol and formaldehyde. He first produced a soluble phenol-formaldehyde shellac called "Novolak" that never became a market success, then turned to developing a binder for asbestos which, at that time, was moulded with rubber. By controlling the pressure and temperature applied to phenol and formaldehyde , he found in 1905 he could produce his dreamed of hard mouldable material (the world's first synthetic plastic ): bakelite. He announced his invention at

6622-426: The resin will cure, usually at room temperature, though heat is sometimes used to ensure a proper cure. Sometimes a vacuum bag is used to compress a wet layup. Glass fibres are most commonly used for this process, the results are widely known as fibreglass , and is used to make common products like skis, canoes, kayaks and surf boards. Continuous strands of fibreglass are pushed through a hand-held gun that both chops

6708-661: The secondary uses of the very deeply dug Moscow Metro and Kyiv metro systems was as nuclear shelters). A number of facilities were constructed in China, such as Beijing 's Underground City and Underground Project 131 in Hubei ; in Albania , Enver Hoxha dotted the country with hundreds of thousands of bunkers . In the United States, the Presidential Emergency Operations Center underneath

6794-430: The strands and combines them with a catalysed resin such as polyester. The impregnated chopped glass is shot onto the mould surface in whatever thickness and design the human operator thinks is appropriate. This process is good for large production runs at economical cost, but produces geometric shapes with less strength than other moulding processes and has poor dimensional tolerance. Machines pull fibre bundles through

6880-439: The strength and elasticity of the matrix alone. FRP involves two distinct processes, the first is the process whereby the fibrous material is manufactured and formed, the second is the process whereby fibrous materials are bonded with the matrix during moulding. Reinforcing Fibre is manufactured in both two-dimensional and three-dimensional orientations: Fibre preforms are how the fibres are manufactured before being bonded to

6966-828: The strength and rigidity of the matrix alone; and there must be optimum bonding between fibres and matrix "Fibreglass reinforced plastics" or FRPs (commonly referred to simply as fibreglass ) use textile grade glass fibres . These textile fibres are different from other forms of glass fibres used to deliberately trap air, for insulating applications (see glass wool ). Textile glass fibres begin as varying combinations of SiO 2 , Al 2 O 3 , B 2 O 3 , CaO, or MgO in powder form. These mixtures are then heated through direct melting to temperatures around 1300 degrees Celsius, after which dies are used to extrude filaments of glass fibre in diameter ranging from 9 to 17 μm. These filaments are then wound into larger threads and spun onto bobbins for transportation and further processing. Glass fibre

7052-425: The trade name Nomex by DuPont . Today, each of these fibres is used widely in industry for any applications that require plastics with specific strength or elastic qualities. Glass fibres are the most common across all industries, although carbon-fibre and carbon-fibre-aramid composites are widely found in aerospace, automotive and sporting good applications. These three ( glass , carbon, and aramid ) continue to be

7138-409: The walls and floors. Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation . Usually, these features are easy to provide. The overburden ( soil ) and structure provide substantial radiation shielding, and the negative pressure is usually only 1 ⁄ 3 of the overpressure. The doors must be at least as strong as

7224-407: The walls. The usual design is now starting to incorporate vault doors . To reduce the weight, the door is normally constructed of steel, with a fitted steel lintel and frame. Very thick wood also serves and is more resistant to heat because it chars rather than melts. If the door is on the surface and will be exposed to the blast wave, the edge of the door is normally counter-sunk in the frame so that

7310-408: The word bunker. This type of bunker is a small concrete structure, partly dug into the ground, which is usually a part of a trench system. Such bunkers give the defending soldiers better protection than the open trench and also include top protection against aerial attack. They also provide shelter against the weather. Some bunkers may have partially open tops to allow weapons to be discharged with

7396-657: The word was imported into English during World War II, at first in reference to specifically German dug-outs; according to the Oxford English Dictionary , the sense of "military dug-out; a reinforced concrete shelter" is first recorded on 13 October 1939, in "A Nazi field gun hidden in a cemented 'bunker' on the Western front". All the early references to its usage in the Oxford English Dictionary are to German fortifications. However, in

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