Term paper of Advanced mechanics of solids
Topic Write a report on rolled steel shapes used in structure making
Today there is a very much need of good structural materials as now the requirement of the people is increasing in terms of strength durability and weight So this demands for better shapes in the building materials and thus we are making better shapes to suit our demands.
There are different types of shapes which are used in structure making. Many of which are rolled steel shapes.
So I am going to present certain shapes generally used nowadays in structure making.
Rolled steel shapes used in structure making
Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties. Structural steel shape, size, composition, strength, storage, etc, is regulated in most industrialized countries.
Structural steel members, such as I-beams, have high second moments of area, which allow them to be very stiff in respect to their cross-sectional area.
Common structural shapes
In most developed countries, the shapes available are set out in published standards, although a number of specialist and proprietary cross sections are also available.
- I-beam (I-shaped cross-section - in Britain these include Universal Beams (UB) and Universal Columns (UC); in Europe it includes the IPE, HE, HL, HD and other sections; in the US it includes Wide Flange (WF) and H sections)
- Z-Shape (half a flange in opposite directions)
- HSS-Shape (Hollow structural section also known as SHS (structural hollow section) and including square, rectangular, circular (pipe) and elliptical cross sections)
- Angle (L-shaped cross-section)
- Channel ( [-shaped cross-section)
- Tee (T-shaped cross-section)
- Rail profile (asymmetrical I-beam)
- Railway rail
- Vignoles rail
- Flanged T rail
- Grooved rail
- Bar, a piece of metal, rectangular cross sectioned (flat) and long, but not so wide so as to be called a sheet.
- Rod, a round or square and long piece of metal or wood, see also rebar and dowel.
- Plate, sheet metal thicker than 6 mm or 1/4 in.
- Open web steel joist
A joist, in architecture and engineering, is one of the horizontal supporting members that run from wall to wall, wall to beam, or beam to beam to support a ceiling, roof, or floor. It may be made of wood, steel, or concrete. Typically, a beam is bigger than, and is thus distinguished from, a joist. Joists are often supported by beams and are usually repetitive.
The wider the span between the supporting structures, the deeper the joist will need to be if it is not to deflect under load. Lateral support also increases its strength. There are approved formulas for calculating the depth required and reducing the depth as needed; however, a rule of thumb for calculating the depth of a wooden floor joist for a residential property is half the span in feet plus two inches; for example, the joist depth required for a 14-foot span is 9 inches. Many steel joist manufacturers supply load tables in order to allow designers to select the proper joist sizes for their projects.
Engineered wood products such as I-joists gain strength from the depth of the floor or the height of each joist. A common saying in the industry is that deeper is cheaper, referring to the lower-quality cost-effective joists 14 inches and above.
HSS(Hollow steel shapes)
A hollow structural section (HSS) is a type of metal profile with a hollow tubular cross section. In some countries they are referred to instead as a structural hollow section (SHS).
Most HSS are of circular or rectangular section, although other shapes are available, such as elliptical. HSS is only comprised from structural steel per code.
HSS is sometimes mistakenly referenced as hollow structural steel. Rectangular HSS are also called tube steel or structural tubing. Circular HSS are sometimes mistakenly called steel pipe though true steel pipe is actually dimensioned and classed differently than HSS. The corners of HSS are heavily rounded, or chamfered, at radii approximately twice the wall thickness. The wall thickness is uniform around the section.
In the UK, the terms are circular and rectangular hollow section (CHS and RHS). However, the dimensions and tolerances differ slightly from HSS.
Use in structures
HSS, especially rectangular sections, are commonly used in welded steel frames where members experience loading in multiple directions. Square and circular HSS have very efficient shapes for this multiple-axis loading as they have uniform geometric and thus uniform strength characteristics along two or more cross-sectional axes; this makes them good choices for columns. They also have excellent resistance to torsion.
HSS can also be used as beams, although wide flange or I-beam shapes are in many cases a more efficient structural shape for this application. However, the HSS has superior resistance to lateral torsional buckling.
The flat square surfaces of rectangular HSS can ease construction, and they are sometimes preferred for architectural aesthetics in exposed structures, although elliptical HSS are becoming more popular in exposed structures for the same aesthetic reasons.
HSS is commonly available in mild steel, such as A500 grade B.
Square HSS is made the same way as pipe. During the manufacturing process flat steel plate is gradually changed in shape to become round where the edges are presented ready to weld. The edges are then welded together to form the mother tube. During the manufacturing process the mother tube goes through a series of shaping stands and cold forms the round HSS (mother tube) into the final round, square, or rectangular shape. Most American manufacturers adhere to the ASTM A500 standard, while Canadian manufacturers follow both ASTM A500 and CSA G40.21. European hollow sections are generally in accordance with the EN 10210 standard.
Application of HSS
HSS is often filled with concrete to improve fire rating, as well as robustness. When this is done, the product is referred to as a lolly column but lally column is the preferred spelling, since it got its name from the Lally Column Company. For example, barriers around parking areas, bollards, made of HSS are often filled, to at least bumper height, with concrete. This is an inexpensive (when replacement costs are factored in) way of adding compressive strength to the bollard, which helps prevent unsightly denting and bending.
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in forces in the members which are either tensile or compressive forces. Moments (torsional forces) are explicitly excluded because, and only because, all the joints in a truss are treated as revolutes.
A planar truss is one where all the members and nodes lie within a two dimensional plane, while a space truss has members and nodes extending into three dimensions.
Characteristics of trusses
A truss is composed of triangles because of the structural stability of that shape and design. A triangle is the simplest geometric figure that will not change shape when the lengths of the sides are fixed. In comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape.
Planar roof trusses
The simplest form of a truss is one single triangle. This type of truss is seen in a framed roof consisting of rafters and a ceiling joist. Because of the stability of this shape and the methods of analysis used to calculate the forces within it, a truss composed entirely of triangles is known as a simple truss.
A planar truss lies in a single plane. Planar trusses are typically used in parallel to form roofs and bridges.
The depth of a truss, or the height between the upper and lower chords, is what makes it an efficient structural form. A solid girder or beam of equal strength would have substantial weight and material cost as compared to a truss. For a given span length, a deeper truss will require less material in the chords and greater material in the verticals and diagonals. An optimum depth of the truss will maximize the efficiency.
Space frame truss
A space frame truss is a three-dimensional framework of members pinned at their ends. A tetrahedron shape is the simplest space truss, consisting of six members which meet at four joints. Large planar structures may be composed from tetrahedrons with common edges and they are also employed in the base structures of large free-standing power line pylons
A large timber Howe truss in a commercial building
There are two basic types of truss:
The pitched truss, or common truss, is characterized by its triangular shape. It is most often used for roof construction. Some common trusses are named according to their web configuration. The chord size and web configuration are determined by span, load and spacing.
The parallel chord truss, or flat truss, gets its name from its parallel top and bottom chords. It is often used for floor construction.
A combination of the two is a truncated truss, used in hip roof construction. A metal plate-connected wood truss is a roof or floor truss whose wood members are connected with metal connector plates.
The Pratt truss was patented in 1844 by two Boston railway engineers; Caleb Pratt and his son Thomas Willis Pratt. The design uses vertical beams for compression and horizontal beams to respond to tension. What is remarkable about this style is that it remained popular even as wood gave way to iron, and even still as iron gave way to steel.
The Southern Pacific Railroad bridge in Tempe, Arizona is a 69 meter (420 foot) long truss bridge built in 1912. The structure is composed of nine Pratt truss spans of varying lengths. The bridge is still in use today.
Bow string roof truss
Named for its shape, thousands of bow strings were used during World War II for aircraft hangars and other military buildings.
King post & Queen Post Truss
One of the simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support.
The queen post truss, sometimes queenpost or queenspost, is similar to a king post truss in that the outer supports are angled towards the center of the structure. The primary difference is the horizontal extension at the centre which relies on beam action to provide mechanical stability. This truss style is only suitable for relatively short spans.
The Waterville Bridge in Swatara State Park in Pennsylvania is a lenticular truss
Lenticular trusses, patented in 1878 by William Douglas, have the top and bottom chords of the truss arched, forming a lens shape.
Lattice truss bridge
American architect Ithiel Town designed Town's Lattice Truss as an alternative to heavy-timber bridges. His design, patented in 1820 and 1835, uses easy-to-handle planks arranged diagonally with short spaces in between them.
A Vierendeel bridge; note the lack of diagonal elements in the primary structure and the way bending loads are carried between elements
The Vierendeel truss is a truss where the members are not triangulated but form rectangular openings, and is a frame with fixed joints that are capable of transferring and resisting bending moments. Regular trusses comprise members that are commonly assumed to have pinned joints with the implication that no moments exist at the jointed ends. This style of truss was named after the Belgian engineer Arthur Vierendeel, who developed the design in 1896. Its use for bridges is rare due to higher costs compared to a triangulated truss.
The utility of this type of truss in buildings is that a large amount of the exterior envelope remains unobstructed and can be used for fenestration and door openings. This is preferable to a braced frame system, which would leave some areas obstructed by the diagonal braces.
The City of Glendale, California notably has three Vierendeel truss bridges, the Geneva Street bridge, the Kenilworth Avenue bridge, and the Glenoaks Boulevard bridge, all built in 1937. All three bridges are 95 feet in span, accommodating two lanes of traffic. They were built as part of the Verdugo Flood Control Project, the U.S. Army Corps of Engineers first project after passage of the 1936 Flood Control Act.
I-beams (also known as H-beams, W-beams (for "wide flange"), rolled steel joist (RSJ), or double-T (especially in Polish, Spanish and German)) are beams with an I- or H-shaped cross-section. The horizontal elements are flanges, while the vertical element is the web. The Euler-Bernoulli beam equation shows that this is a very efficient form for carrying both bending and shear in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying torsion, for which hollow structural sections are often preferred.
There are two standard I-beam forms:
- Rolled I-beam, formed by hot rolling, cold rolling or extrusion (depending on material).
- Plate girder, formed by welding (or occasionally bolting or riveting) plates.
I-beams are commonly made of structural steel but may also be formed from aluminium or other materials. A common type of I-beam is the rolled steel joist (RSJ) - sometimes incorrectly rendered as reinforced steel joist. British and European standards also specify Universal Beams (UBs) and Universal Columns (UCs). These sections have parallel flanges, as opposed to the varying thickness of RSJ flanges. UCs have equal or near-equal width and depth, while UBs are significantly deeper than they are wide.
I-beams engineered from wood with fiberboard and/or laminated veneer lumber are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden joists. However there has been some concern as to their rapid loss of strength in a fire if unprotected.
I-beams are widely used in the construction industry and are available in a variety of standard sizes. Tables are available to allow easy selection of a suitable steel I-beam size for a given applied load. I-beams may be used both as beams and as columns.
I-beams may be used both on their own, or acting compositely with another material, typically concrete. Design may be governed by any of the following criteria:
- deflection - the stiffness of the I-beam will be chosen to minimise deformation
- vibration - the stiffness and mass are chosen to prevent unacceptable vibrations, particularly in settings sensitive to vibrations, such as offices and libraries
- bending failure by yielding - where the stress in the cross section exceeds the yield stress
- bending failure by lateral torsional buckling - where a flange in compression tends to buckle sideways or the entire cross-section buckles torsionally
- bending failure by local buckling - where the flange or web is so slender as to buckle locally
- local yield - caused by concentrated loads, such as at the beam's point of support
- shear failure - where the web fails. Slender webs will fail by buckling, rippling in a phenomenon termed tension field action, but shear failure is also resisted by the stiffness of the flanges
- buckling or yielding of components - for example, of stiffeners used to provide stability to the I-beam's web
A girder is a support beam used in construction. Girders often have an I beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams. A girder is commonly used many times in the building of bridges, and planes.
The Warren type girder combines strength with economy of materials and can therefore be relatively light. Patented in 1848 by its designers James Warren and Willoughby Theobald Monzani, its structure consists of longitudinal members joined only by angled cross-members, forming alternately inverted equilateral triangle-shaped spaces along its length, ensuring that no individual strut, beam, or tie is subject to bending or torsional straining forces, but only to tension or compression. It is an improvement over the Neville truss which uses a spacing configuration of isosceles triangles.