Acm Unit 2
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This document provides information on various structural elements used in construction including beams, slabs, arches, vaults, trusses, frames, and domes. It describes the basic components, characteristics, types, and applications of each element. For example, it states that a beam is an element that resists bending forces, a slab is a horizontal surface element reinforced with steel bars, an arch distributes vertical loads into sideways forces through wedge-shaped blocks, and a dome is a curved ceiling structure similar to a hemisphere. The document also provides diagrams to illustrate different structural configurations.
![roof angle at the top, not ideal undersnow, for instance. Cross-tie, peak-tie and bell are other types of bow
dome, more appropriate for regions with lots of rainfall or snow.
Trusses
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 structuralstability 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.[1] In
comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape.
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 bottomchords.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 connectorplates.
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.[3] 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
Vaults
A Vault (] The parts of a vault exert a thrust that require a counter resistance.When vaults are built
underground,the ground gives all the resistance required. However, when the vault is built above ground,
various replacements are employed to supply the needed resistance.An example are the thicker walls used
in the case of barrel or continuous vaults.Buttresses are used to supply resistance when intersecting vaults](https://image.slidesharecdn.com/unit2-180611110119/85/Acm-Unit-2-5-320.jpg)
Acm Unit 2
- 1. Beams A beam is a structuralelement that is capable of withstanding load primarily by resisting bending.The bending force induced into the material of the beam as a result of the external loads, own weight and external reactions to these loads is called a bending moment. Internally, beams experience compressive, tensile and shear stresses as a result of the loads applied to them Above the supports,the beamis exposed to shear stress.There are some reinforced concrete beams that are entirely in compression. These beams are known as prestressed concrete beams, and are fabricated to produce a compression more than the expected tension underloading conditions Slabs A concrete slab is a common structural element of modern buildings. Horizontal slabs of steelreinforced concrete, typically between 10 and 50 centimetres thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving. In many domestic and industrial buildings a thick concrete slab, supported on foundations or directly on the sub soil, is used to construct the ground floor of a building. In high rises buildings andskyscrapers,thinner, pre-cast concrete slabs are slung between the steel frames to form the floors and ceilings on each level. For a suspended slab,there are a number of designs to improve the strength-to-weight ratio. In all cases the top surface remains flat, and the underside is modulated: Corrugated, usually where the concrete is poured into a corrugated steel tray. This improves strength and prevents the slab bending under its own weight. The corrugations run across the short dimension, from side to side. A ribbed slab, giving considerable extra strength on one direction. A waffle slab, giving added strength in both directions. Reinforcement design A one way slab has structural strength in shortest direction. A two way slab has structural strength in two directions ARCHES: The arch may be said to have originated with the idea of placing a considerable number of blocks in a concentric arrangement. The wedge-shaped blocks, called voussoirs,hold each other firmly in place and prevent each other from slipping. The voussoirs at the top, or crown, of the arch convert the downward pressure into lateral (sideways) pressure,or thrust,which is transmitted from the uppervoussoirs down around the opening and finally into the ground through the wall or pier on which the arch rests.Not only can considerable distances be spanned in this way, but arches can carry a much heavier load than a horizontal lintel. The arch is, however, not without its peculiar weakness. The lateral thrust is strongest at the haunches of the arch (the part midways between the crown and the springing). The keystone, and the other voussoirs at the crown, presses out against the voussoirs at the haunches,which may buckle and allow the crown to fall if they are not properly buttressed.The lateral thrust at the haunches can be counteracted by the thrust of arches placed to either side, as in an arcade, but,unless the arcade is circular, the lateral thrust of the arches at the end must finally be counteracted by the sheer mass of an abutment.
- 2. Typesofarches: Arches are constructed in four basic shapes that frame and support doors,windows, porches, and other wall openings: Flat arch Triangular arch Round arch Pointed arch Flat arch: An arch having a horizontal intrados with voussoirs radiating from a centre below, often built with a slight camber to allow settling is called a flat or jack arch. French arch: A flat arch with voussoirs inclined to the same angle at each side of the centre. The mortar joints do not,therefore, radiate to a common centre. Not, technically, a proper arch, and of weak form. Triangular arch: It is a primitive form of arch consisting of two stones laid diagonally to support each other over an opening. Hence, the span is limited by the size of the available material.
- 3. VAULTS: A vault is a ceiling of brick, stone,or concrete built in the principle of the arch. A tunnel vault, or barrel vault, is a tunnel-like, semi-cylindrical extension of an arch, which may be thought ofas an unbroken series of arches pressed together,one behind the other. It cannot be lighted except at the ends without being structurally weakened, because,as in an arch, continuous abutment must be applied to absorb the thrust carried down along the haunches to the walls supporting it. However, arches may be introduced in the supporting walls and transverse ribs may be inserted in the vault to concentrate thrust at a few strongly buttressed points,thereby permitting a reduction of weight and thrust in the segments of vaulting between the ribs. If a barrel vault is intersected at right angles by anotherbarrel vault of the same size, a cross vault, or groin vault, is formed. This is a very efficient form of vaulting allowing full illumination from the sides. Groin vaults also allow a great saving in material and labour over the simple barrel vault; thrust is concentrated along the groins (the four diagonal edges formed along the points where the barrel vaults intersect), so the vault need only be abutted at its four corners. Barrel or Tunnel Vault Groin Vault (from above)
- 4. Groin Vault (from below) Types of vaults: Barrel Vault:A barrel vault is the simplest of the vaults and is the base design for many vaults that have a more intricate design.It consists ofan on-going series of semi-circular arches. One is directly behind another, causing it to look like a half of a barrel. In some instances,it is described as resembling a tunnel. Groin Vault:A groin vault is created by two barrel vaults intersecting at right angles. The arches of groin vaults are round or pointed.It is also known as a cross vault. Rib Vault:A vault reinforced by masonry ribs is known as a rib vault. When this type of vault has two masonry ribs dividing it into four sections,it is called a quadripartite rib vault. A vault divided by three masonry ribs that make six sections is called a sexpartite rib vault. DOMES: Domes are curved architectonic structures with no angles or corners, similar to the upper half of a sphere. Despite their apparent fragility, domes are strong structures and have been used in buildings since ancient times, according to PBS Online. In Europe, the earliest domes were made of stone.The Roman Pantheon, built almost 2,000 years ago,is a good example of early dome engineering. Indigenous peoples in Ethiopia and otherplaces have used curved bows to create their huts,creating a primitive yet effective dome TYPES OF DOMES: Geodesic Dome: The geodesic dome was invented in the 1950s by American engineer and architect Buckminster Fuller, according to PBS Online. This type of dome is structured on triangles and other geometric shapes instead of the arches. The Epcot Centre in Orlando, the Caspary Auditorium in New York and the Eden Project in England are examples of geodesic domes. Monolithic Dome: The monolithic dome is made of one solid piece of material. Its construction begins with a circular concrete foundation,where a canvas "air form" is attached to the slab. The canvas is then inflated using special fans, thus forming the shape of the dome. After that, the interior is covered with a layer of polyurethane foam insulation . A steelbar is enclosed in the foam to give support to the dome. Finally, a special mix of concrete is spread over the interior of the building, reports the Architecture Week website. Bow Dome: The bow dome is made of wood bows, which can be substituted by aluminium, and canvas.This type of dome is rather archaic, yet efficient. It represents the first habitation built by humans, according to website Simply Different. There are different types of bow domes, which depend on how the bow is placed. Half sphere or unibow is the most common, but has some disadvantages,which include the almost horizontal
- 5. roof angle at the top, not ideal undersnow, for instance. Cross-tie, peak-tie and bell are other types of bow dome, more appropriate for regions with lots of rainfall or snow. Trusses 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 structuralstability 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.[1] In comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape. 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 bottomchords.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 connectorplates. 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.[3] 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 Vaults A Vault (] The parts of a vault exert a thrust that require a counter resistance.When vaults are built underground,the ground gives all the resistance required. However, when the vault is built above ground, various replacements are employed to supply the needed resistance.An example are the thicker walls used in the case of barrel or continuous vaults.Buttresses are used to supply resistance when intersecting vaults
- 6. are employed.French. voute, Italian. volta,) is an architectural term for an arched form used to provide a space with a ceiling or roof The simplest kind of vault is the barrel vault (also called a wagon or tunnelvault) which is generally semicircular in shape.The barrel vault is a continuous arch,the length being greater than its diameter. As in building an arch, a temporary support is needed while rings of voussoirs are constructed and the rings placed in position. Until the topmost voussoir,the keystone,is positioned the vault is not self- supporting. Portal frames Portal frame construction is a method of building and designing simple structures,primarily using steel or steel-reinforced precast concretealthough they can also be constructed using laminated timber such as glulam. The connections between the columns and the rafters are designed to be moment-resistant, i.e. they can carry bending forces. Because of these very strong and rigid joints some of the bending moment in the rafters is transferred to the columns. This means that the size of the rafters can be reduced or the span can be increased for the same size rafters. This makes portal frames a very efficient construction technique to use for wide span buildings. Portal frame construction is therefore typically seen in warehouses,barns and other places where large, open spaces are required at low cost and a pitched roof is acceptable. Generally portal frames are used for single story buildings but they can be used for low rise buildings with several floors where they can be economic if the floors do not span right across the building (in these circumstances a skeleton frame, with internal columns, would be a more economic choice). A typical configuration might be where there is office space built against one wall of a warehouse. Portal frames can be clad with all sorts of material but the most popular solution, for reasons of economy and speed,is some form of lightweight insulated metal cladding with cavity masonry work to the bottom 2m of the wall to provide security and impact resistance. The lightweight cladding would be carried on sheeting rails spanning between the columns of the portal frames. Space frames A space frame is a truss-like, lightweight rigid structure constructed from interlocking struts in a geometric pattern. Space frames usually utilize a multidirectional span,and are often used to accomplish long spans with few supports.They derive their strength from the inherent rigidity of the triangular frame; flexing loads (bending moments) are transmitted as tension and compression loads along the length of each strut. Space frames are double layered grids, excellent in appearance with large column free spaces.All type of elegant shape could be made by these systems using variety of grids. Two-way actions of space frames provide both economy and enormous spanning capability. Larger portable stages and lighting gantries are also frequently built from space frames and octet trusses APPLICATION Space frame is used for commercial and industrial buildings, auditoriums, airport hangers,sport stadium, sky lights, mosque, lighting towers, petrol pumps, canopies,exhibition hall, atrium, toll naka, LPG bottling plants. SALIENT FEATURES 1) Enormous Spanning Capability.2) Light Weight 3) High Aesthetics 4) High Resale Value 5) Higher Safety Factor 6) Extension With Additional Unit . Configuration of space frame build systems: • Generally square inverted pyramid modules connected at the top and bottom layers provide the most commonly used Space Frame structures
- 7. • Pipes, spherical node, cone, bolt and sleeve are the common components • There are various types of connection nodes patented by various companies in the world. Two popular nodes are solid spherical nodes per Mero systemGermany and hollow spherical node per Unibat • Polycarbonate sheets,fiberglass reinforced plastic sheets or glazing used for covering, to provide aesthetically beautiful sky light systems . However, colour-coated steel sheets.aluminium sheets and asbestos sheets are also used • Latticed Space Frame Structures,particularly for roofs are similar to two-way concrete slab or flat plates. These latticed structures,single layer or double layer, include 3-dimensional Space Grid Structures, Domes, Barrel Vaults, Hyperbolic Parabloid Shell Structures,etc. Applications: Malls, Food courts,Transport terminals, Schools, Pools, Arenas, Entertainment, Hospitals, Hotels, Corporate & Commercial Buildings, Convention centers Benefits: Minimum structure weight Long clear spans &cantilevers Accommodates concentrated loads Suits irregular supports orplan geometry Variable depth for roof drainage is built in Pre-assembly allows project acceleration Pre-finished to avoid site painting & inspection All service lines can run through frame Frame can be a feature without ceiling Simple modification or dis-assembly for re-use Rigid frames structures � Rigid frame structures are built at the site which may or may not be poured monolithically. � Rigid frame structures provide more stability. � Rigid frame structures resist rotations more effectively Advantages Rigid frame structures feature positive and negative bending moments throughout the structure due to interaction of walls, beams and slabs. Braced frame structures resist Braced frame structures resist lateral forces by the bracing action of diagonal members. � Braced frame structures are used toresist sideway forces. � Buildings are braced by inserting diagonal structural members into the rectangular areas of a structural frame. Advantages To stabilize the frame against earthquakes and strong winds. Lateral forces are resisted by axial actions of bracing and columns. More efficient than a rigid frame. Portal structural frames . � It resembles like a door. Multi-story, multi-bay portal frames are commonly used for commercial and industrial construction. � The members are usually made up of curved laminates and the members are thickened in the region of the knee or eaves joint to allow for the large moment.
- 8. Advantages ofFrames: Optimum use of floor space. � Easy construction. � Rapid construction. � Economical for high rise buildings. � Erected by steel and/or reinforced concrete Disadvantages � Generally, frames are flexible structures and lateral deflections control the design process for buildings with greater than about 4 stories.The concrete frames are 8 times stiffer than steel frames of the same strength. � Span lengths are limited when using normal reinforced concrete (generally less than about 13 m, but up to about 15 m).