STRUCTURAL ELEMENTS Structural elements
Structural elements :They are used in structural analysis to convert a complex structureinto simple elements. Within a structure, an element cannot be broken (decomposed) into different parts (e.g., beam or column). Structural elements can be linear, surfaces or volumes.
DIFFERENT TYPES OF STRUCTURAL ELEMENTS:
In Linear elements we have different types of elements.They are:
Rod-it is cylindercial shaped bar,with curvilinear shapes
Beam-it is may be the form of cylindercial (or) rectangular shape which bears loads
Struts-this are used in automobiles for shock absortion
Wire ropes-it is a cylindercial shaped sturcutre which is flxiblieSurface elements:
In Surface elements we have different types of elements.They are:
1) Concrete slab-it is a horizontal slab of steel reinforced concrete.generally it has a thickness range would vary from 4 inch to 20 inch
2) Deck-it is a surface of a bridge and is one superstructure of bridge. It may be an integral part of the bridge
3) HYPERLINK “https://en.wikipedia.org/wiki/Shear_wall” o “” shear panel –it is a structural system composed of braced panels to counter the effect of lateral load acting on
DIFFERENT TYPES OF MATERIALS USED IN STRUCTURAL ELEMENTS:
Cast iron is a brittle form of iron which is weaker in tension than in compression. It has a relatively low melting point, good fluidity, castability, excellent machinability and wear resistance. Though almost entirely replaced by steel in building structures, cast irons have become an engineering material with a wide range of applications, including pipes, machine and car parts.
Cast iron retains high strength in fires, despite its low melting point. It is usually around 95% iron, with between 2.1% and 4% carbon and between 1% and 3% silicon. It does not corrode as easily as steel.
Steel is an iron alloy with controlled level of carbon (between 0.0 and 1.7% carbon).
Steel is used extremely widely in all types of structures, due to its relatively low cost, high strength-to-weight ratio and speed of construction.
Steel is a ductile material, which will behave elastically until it reaches yield (point 2 on the stress–strain curve), when it becomes plastic and will fail in a ductile manner (large strains, or extensions, before fracture at point 3 on the curve). Steel is equally strong in tension and compression.
Steel is weak in fires, and must be protected in most buildings. Despite its high strength to weight ratio, steel buildings have as much thermal mass as similar concrete buildings.
The elastic modulus of steel is approximately 205 HYPERLINK “https://en.wikipedia.org/wiki/GPa” o “GPa” GPa.
Steel is very prone to corrosion (rust).
Stainless steel HYPERLINK “https://en.wikipedia.org/w/index.php?title=Structural_material&action=edit§ion=5” o “Edit section: Stainless steel” edit
Stainless steel is an iron-carbon alloy with a minimum of 10.5% chromium content. There are different types of stainless steel, containing different proportions of iron, carbon, molybdenum, nickel. It has similar structural properties to steel, although its strength varies significantly.
It is rarely used for primary structure, and more for architectural finishes and building cladding.
It is highly resistant to corrosion and staining.
Reinforced concrete is concrete in which steel reinforcement bars (“rebars”), plates or fibers have been incorporated to strengthen a material that would otherwise be brittle. In industrialised countries, nearly all concrete used in construction is reinforced concrete. Due to its weakness in tension capacity, concrete will fail suddenly and in brittle manner under flexural (bending) or tensile force unless adequately reinforced with steel.
Prestressed concrete is a method for overcoming the concrete’s natural weakness in tension.12 It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would otherwise experience due to a bending load
AluminiumAluminium is a soft, lightweight, malleable metal. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, and extruded.
Corrosion resistance is excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.
Aluminium is used in some building structures (mainly in facades) and very widely in aircraft engineering because of its good strength to weight ratio. It is a relatively expensive material.
In aircraft it is gradually being replaced by carbon composite materials.
They provide extremely good strength to weight ratios, but are also very expensive. The manufacturing processes, which are often extrusion, do not currently provide the economical flexibility that concrete or steel provide. The most commonly used in structural applications are glass-reinforced plastics.
Masonry is very strong in compression but cannot carry tension (because the mortar between bricks or blocks is unable to carry tension). Because it cannot carry structural tension, it also cannot carry bending, so masonry walls become unstable at relatively small heights. High masonry structures require stabilisation against lateral loads from buttresses (as with the flying buttresses seen in many European medieval churches) or from HYPERLINK “https://en.wikipedia.org/wiki/Windpost” o “Windpost” windposts.
Since the widespread use of concrete, stone is rarely used as a primary structural material, often only appearing as a cladding, because of its cost and the high skills needed to produce it. Brick and concrete blockwork have taken its place.
Masonry, like concrete, has good sound insulation properties and high thermal mass, but is generally less energy intensive to produce. It is just as energy intensive as concrete to transport.
Timber is the oldest of structural materials, and though mainly supplanted by steel, masonry and concrete, it is still used in a significant number of buildings. The properties of timber are non-linear and very variable, depending on the quality, treatment of wood, and type of wood supplied. The design of wooden structures is based strongly on empirical evidence.
Wood is strong in tension and compression, but can be weak in bending due to its fibrous structure. Wood is relatively good in fire as it chars, which provides the wood in the centre of the element with some protection and allows the structure to retain some strength for a reasonable length of time.