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Polymers for Heavy Engineering. Silicones , or polysiloxanes. Silicones , or polysiloxanes , are inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl , ethyl , and phenyl .
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Silicones, or polysiloxanes • Silicones, or polysiloxanes, are inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl, ethyl, and phenyl. • These materials consist of an inorganic silicon-oxygen backbone (...-Si-O-Si-O-Si-O-...) with organic side groups attached to the silicon atoms, which are four-coordinate.
Silicones, or polysiloxanes • In some cases organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions. • They can vary in consistency from liquid to gel to rubber to hard plastic. The most common type is linear polydimethylsiloxane or PDMS
Silicones, or polysiloxanes • Service temperature to about 260C • Good chemical resistance, low water absorption, good electrical properties, & available in flame retardant grade • In the plumbing and automotive fields, silicone grease is often used as a lubricant. In plumbing, the grease is typically applied to O-rings in faucets and valves.
In the automotive field, silicone grease is typically used as a lubricant for brake components since it is stable at high temperatures, is not water-soluble
Epoxy • Epoxy or polyepoxide is a thermosettingepoxidepolymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or "hardener" • The family of epoxy resin includes epichlorohydrin with bisphenol-A (range from low viscosity liquids to high molecular weight solids).
Epoxy • Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" • These high performance adhesives are used in the construction of aircraft, automobiles, bicycles, golf clubs, skis, snow boards, and other applications where high strength bonds are required. • In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than when cured at room temperature.
Epoxy • Novolacs are another important class that offer higher thermal properties and improved chemical resistance • The cycloaliphatics types important for the applications requiring high resistance to wheatering
Epoxies typically are not used in the outer layer of a boat because they are deteriorated by exposure to UV light • In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. Typical fiber reinforcements include glass, carbon, Kevlar, and boron.
INTRODUCTION 1.0 Introduction Bearings - structural joints that are installed between a structure and its foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.
HOW THE BEARING WORKS Figure: Base-Isolated and Fixed-Base Buildings • A base isolated structure is supported by a series of bearing pads which are placed between the building and the building's foundation
2.0 How The Bearing work? As a result of an earthquake, the ground beneath each building begins to move. Each building responds with movement which tends toward the right. The building's displacement in the direction opposite the ground motion is actually due to inertia.
2.0 How The Bearing work? In addition to displacing toward the right, the un-isolated building is also shown to be changing its shape-from a rectangle to a parallelogram. –deforming The primary cause of earthquake damage to buildings is the deformation which the building undergoes as a result of the inertial forces acting upon it.
2.0 How The Bearing work? The base-isolated building retains its original, rectangular shape. It is the elastomeric bearings supporting the building that are deformed. It implies the inertial forces acting on the base-isolated building have been reduced.
ELASTOMERIC BEARINGS Fig: Basic structure of rubber bearing 3.0 Elastomeric Bearings Consist of thin rubber sheets bonded onto thin steel plates and combined with an energy dissipation mechanism. The rubber sheets are vulcanized and bonded to the thin steel plates under pressure and heat. it is designed in such a way that bearing is very stiff and strong in vertical direction, but flexible in horizontal direction. Thick mounting steel plates are bonded to the bottom and top surfaces allowing the isolator to be firmly connected to the foundation below and the superstructure above.
TYPES OF ELASTOMERIC1. LEAD RUBBER BEARINGS (LRB) • lead inserted as center core of bearing dissipates the energy of earthquake while the rubber, reinforced with steel plates, provide stability, supports structure and isolate vibration. • LRB provide initial rigidity, due to the high elastic stiffness of lead, which is essential for minor lateral loads. 4.0 Types Of Elastomeric Bearing a bigger laminated bearing manufactured from layers of low-damping natural rubber sandwiched together with layers of steel and a lead cylinder plug firmly fitted in a hole at its center to deform in pure shear.
2. HIGH DAMPING RUBBER BEARING (HDRB) • Consists of thin layers of high damping rubber sandwiched between steel plates. • High-damping rubber is filled rubber compound with inherent damping properties due to the addition of special fillers, such as carbon and resins. The addition of fillers increases the inherent damping properties of rubber without affecting its mechanical properties. • When shear stresses are applied to high-damping rubber, a sliding of molecules generates frictional heat which is a mechanism of energy dissipation. 4.0 Types Of Elastomeric Bearing
3. Hybrid type: Lead High-damping Rubber Bearing (LHDRB) • Consist of layers of high-damping rubber sandwiched between steel plates and a smaller diameter lead cylinder plug firmly fitted in a hole at its center. • LHDRB has both an initial rigidity, due to the presence of the lead plug, and a continuous energy dissipation mechanism, due to the damping properties of the high-damping rubber. 4.0 Types Of Elastomeric Bearing
Requirements for Rubber Bearings 5.0 Requirements • Mechanical and damping properties of the bearing must remain constant over the whole life of the structure • Ability to return to its original configuration and dimensions when unloaded • Elastomeric bearings must be strong and stiff for vertical loadings and flexible under shear stresses • The base isolator must support the vertical load of the structure with a large safety factor. • The sheer stiffness of the isolator must be low enough to attenuate the majority of the frequency components in an earthquake on that site.
5.0 Requirements • The isolator must be stiff enough vertically to power significantly amplification of any vertical component in the earthquake. • During an earthquake, the building will move sideways on the isolators. At the extremes of the movements, the bearing must continue to support the vertical load of the structure. • The damping in the isolators must be sufficient to prevent a build- up of amplitude in the structure during an earthquake. • Motion of the structure during high winds should not be sufficient to disturb the occupants. • The isolator should provide a restoring force so the building will always return to its original rest position.
BEARING MATERIALS 6.0 Raw Materials Natural Rubber and Polychloroprene Ethylene Propylene Rubber as a promising alternative to Natural Rubber and Polychloroprene will be consider as the raw material for earthquake bearing elastomer.
