Midterm (2) (1)
- 1. CONSTRUCTION AND MATERIALS I (ARC 106) LECTURERS: DR.VEDIA AKANSU DR.UMRAN DUMAN DR.FATEMAHTAVASOLI IBTIHAL AL HINDWAN 20192954 MID TERM ASSIGNMENT
- 2. LARGE SPAN STRUCTURE 1.INTRODUCTION 2.DEFINITION 3.COMMON STRUCTURALSYSTEMS 4. LARGE SPAN BUILDING 5.CONCLUSION CONTENTS
- 3. INTRODUCTION TO LARGE SPAN STRUCTURE WHAT IS A SPAN? Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge. A span can be closed by a solid beam or by a rope. The first kind is used for bridges, the second one for power lines, overhead telecommunication lines, some type of antennas or for aerial tramways. Example of a span is shown in Fig 1. Fig 1
- 4. DEFINITION OF LARGE SPAN STRUCTURE • Large-span structures traditionally appear as long even strip, for example, in bridges, portal rigid frames, and large-span arenas. With respect to these structures, vertical load is the control load. Uncommon consideration should be paid to deliberate plan of level foundation with regards to the calculated plan of large-span structure. In particular, the power bearing limit of vertical load and the control upon vertical dislodging will be improved with the goal that the structure has adequate quality and solidness to oppose vertical load as a whole. • Structures with span larger than 15-20 meters are regarded to as Long Span Structures. For Such structures span is unable to be achieved with ordinary Reinforced Cement Concrete (R.C.C.) construction. Generally long spans result in; 1. Flexible 2. column-free internal spaces 3. reduces substructure costs and time to erect the structure.
- 5. Large span structures create unobstructed column free spaces greater than 30m (100 feet) for a variety of functions VisibilityFlexibility Manufacturingfacilities Large Scale Storage StadiumsAircraft hangars
- 6. Common structural systems for large span structures A.Long span beam B.Long span truss C.Tensilestructures D.Foldedplates E.Shell structure F.PortalFrames 1. Parallel beam approach 2. Composite beams with web openings 3. Cellular composite beams 4. Tapered girders 5. Haunched composite beams 1. Prass truss 2. Waren truss 3. North light truss 4. Saw tooth truss 5. Fink truss 6. Tubular steel truss 1. Linear tensile structure a.Suspension bridges b.Cable stayed beams c. Cable truss 2. 3D tensile structure a. 3D cable trusses b. Tensegrity structures c. Bicycle wheel 3. Surface-Stressed tensile structure a.Fabric structure b.Prestressed membrane c.Pneumatically stressed membrane d.Grid shell 1. Folded plate surfaces structures 2. Folded plate frames structures 3. Spatial folded plate structures 1. Thin shell structure 2. Folded shell structure 3. Barrel shell structure 4. Timber shell structure 5. Lattice and grid shell structure 6. Hypar and concrete shell structure 1. Duo pitch portal frame 2. Curved portal frame 3. Portal with crane
- 7. A. Long span beams The use of long span beams realizes an extent of points of interest, includingversatile, area free inward spaces, reduced foundationcosts, and diminished steel erection times. Many long span beams are likewise very much adjusted to encourage the combination of administrationswithout expanding the overall floor depth. Example of long span is shown in Fig 1 Types of long span beams include 1. Parallel beam approach 2. Composite beams with web openings 3. Cellular compositebeams 4. Tapered girders 5. Haunched composite beams Fig 1
- 8. 1. Parallel beam approach • The parallel beam approachis effective for spans up to around 14 m. Floor grids comprise two layers of fully continuousbeams runningin orthogonaldirections. Services runningin either direction can be integrated within these two layers, so that services passing in any direction can be accommodated within the structuralfloor depth. Afurther benefit is that, being fully continuous, the depth of the beams themselves is reduced without incurring the expense and complexity of rigid, full strength connections.This is shown in Fig 1.1 and Fig 1.2 Fig 1.1 Fig 1.2
- 9. 2. Composite beams with web openings • Web openings are typically formed in beams to allow services to pass through the beam. This enables the structural and service zones to occupy the same space, thereby reducing the effective overall depth of floor construction for a given spanning capability. Openings may also be formed for aesthetic reasons, for instance with cambered beams used to support a roof. Composite beams with web openings have been shown to be a cost effective solution for spans in the range 10 to 16 m. • A particular type of composite beam with web openings is the so- called cellular beams, which is formed in a specific way. The alternative way of forming the web openings is simply to cut them into the plate used to form the web of a plate girder, or into the web of a rolled section.Example shown in Fig 2.1. The most appropriate solution to adopt depends on the size, shape and regularity of the openings, or more commercial drivers such as the method used by a preferred supplier. Beams with web openings present no disadvantages in terms of erection and familiarity as they are much the same as a 'standard' solid web beam. • The design of beams with web openings must recognize the fact that the openings introduce a number of potential failure modes not found in solid web beams. Around the openings the beam behaves as a Vierendeel girder, and web post buckling may govern design Large openings may require stiffening to avoid instability (buckling) of the web posts. Visual shown in Fig 2.2 Fig 2.1 Fig 2.2
- 10. 3. Cellular composite beams • Cellularbeams are a form of beam with multiple regular web openings, formed by splitting two rolled sections longitudinally, to form two Tee sections as shown in Fig 3.1 The two Tees, which may not come from the same donorsection are then welded togetherto form an I-section with web openings which have a characteristicshape (normally, but not necessarily, circular). The process used to form cellularbeams enables the bottomhalf of the final beam to be formed from a heavier donor section than the top half - in otherwords the bottom flange can be significantly bigger than the top flange. This makes sense when, as is often the case, the beams are to act compositely and thereforea concreteflange effectively replaces the uppersteel flange in the final state (the upper steel flange only needs to be big enough to meet constructionneeds and serve as a platformfor the shear studs).Different examples are shown in Fig 3.2 Fig 3.1 Fig 3.2
- 11. 4. Tapered girders • Tapered girders can be a cost effective solution in the span range 10 m to 20 m. They are anothersolutionthat allows services to be accommodated within the structuralfloor zone. The depth of the girder increases towards mid-span, where applied moments are greatest, and thereby facilitating hanging services under the shallowerregions near the beam supports. It is also possible to form web openings in tapered girders in regions of low shear, towards mid-span. These provide more optionsfor service integration. Understanding of tapered girders can be reached in Fig 4.1 and Fig 4.2 Fig 4.1 Fig 4.2
- 12. 5. Haunched composite beams • Haunches maybe added at the ends of a composite beam to provide moment continuity as shown in fig 5.1. The stiffness and strengthof the connections mean that the rest of the span can be shallower (the bending moment diagram is 'lifted' and the effective stiffness of the beam substantiallyincreased), and services passed under it. In buildings where the services are likely to need frequent replacement (for examplein hospitals ), hanging the services under the beams rather than passing them through holes in the webs, or through a truss, can be advantageous. Spans in excess of 20 m can readily be achieved. Haunched composite beam is well explained in fig 5.2 Fig 5.1 Fig 5.2
- 13. B. Long span trusses • A roof truss is a structure that incorporates one or numerous triangular units that incorporate straight slender members with their ends connected by means of nodes as shown in fig 1 Trusses are very widely used to serve two main functions: 1. To carry the roof load: - Gravity loads (self-weight, roofing and equipment, either on the roof or hung to the structure, snow loads) Actions due to the wind (including uplift due to negative pressure). 2. To provide horizontal stability: - Wind girders at roof level, or at intermediate levels if required - Vertical bracing in the side walls and/or in the gables. Types of long span trusses 1. Prass Truss 2. Warren Truss 3. North Light Truss 4. Saw Tooth Truss 5. Fink Truss 6. Tubular Steel Truss Fig 1
- 14. 1. Prass Truss • A Pratt truss includes vertical members and diagonals that slope down towards the center, the oppositeof the howe truss as shown in fig 1.1 .The interior diagonals are undertension under balanced loadingand vertical elements under compression. If pure tension elements are used in the diagonals (such as eyebars ) then crossing elements may be needed near the centerto accept concentratedlive loads as they traverse the span. It can be subdivided, creating Y- and K-shaped patterns. Example of prass truss is shown in fig 1.2 • This truss is practical for use with spans up to 250 feet (76 m) and was a common configuration for railroad bridges as truss bridges moved from wood to metal. They are staticallydetermine bridges, which lend themselves well to long spans. Fig 1.1 Fig 1.2
- 15. It is possible to add secondary members in Pratt truss to: • Create intermediate support points for applied loads • Limit the buckling length of members in compression (although in a 2D truss, the buckling length is only modified in one axis).
- 16. 2. Warren Truss The Warren truss consists of longitudinal members joined only by angled cross- members, forming alternately inverted equilateraltriangle-shaped spaces along its length, ensuring that no individual strut, beam, or tie is subject to bendingor torsional straining forces, but only to tension or compression as shown in fig 2.1. Loads on the diagonals alternatebetween compression and tension (approachingthe center), with no vertical elements, while elements near the centermust support both tension and compression in response to live loads. This configuration combines strength with economy of materials and can therefore be relatively light. The girders being of equal length, it is ideal for use in prefabricated modularbridges. It is an improvement over the Neville truss which uses a spacing configuration of isosceles triangles. A good example of warren truss is shown in fig 2.1 Fig 2.1 Fig 2.2
- 17. 3. North Light Truss • North light trusses are traditionally used for short spans in industrial workshop-type buildings as shown in fig 3.1. They allow maximum benefit to be gained from natural lighting by the use of glazing on the steeper pitch which generally faces north or north-east to reduce solar gain. On the steeper sloping portion of the truss, it is typical to have a truss running perpendicular to the plane of the North Light truss, to provide large column-free spaces. It is shown in fig 3.2 • The use of north lights to increase natural daylighting can reduce the operational carbon emissions of buildings although their impact should be explored using dynamic thermal modelling. Although north lights reduce the requirement for artificial lighting and can reduce the risk of overheating, by increasing the volume of the building they can also increase the demand for space heating. Fig 3.1 Fig 3.2
- 18. 4. Saw Tooth Truss • A saw-tooth roof is a roof comprising a series of ridges with dual pitches either side as shown in fig 4.1. The steeper surfaces are glazed and face away from the equatorto shield workers and machinery from direct sunlight. This kind of roof admits natural light into a deep plan buildingor factory as shown in fig 4.2 Fig 4.1 Fig 4.2
- 19. 5. Fink Truss • A fink roof truss is traditionallythe most commonly used truss type, providing a simple, adaptableand cost efficient roofing solution. • The “fink” is a basic webbed truss design that provides the most economical roof solution. • The web members form a ‘W’ as shown in fig 5.1 to provide a high strength structure with good load- carrying capacity. The roof load is transmitted entirely to support on the wallplates. • The fink truss can also be used as a support for other trusses by doublingor trebling the number of plies, i.e. in a “hip” roof. • Due to its design flexibility, the fink truss is the most frequentlyused truss in roof design. With a large variety of spans up to 14 metres and pitch range from 10° to 60°, the finks truss offers a cost effective and versatile roof solution. Example is shown in fig 5.2. Fig 5.1 Fig 5.2
- 20. 6. Tubular Steel Truss TubularSteel Truss are used for large span constructionssuch as factories, industry worksheds, shoppingmalls, huge exhibition centre, multiplexes etc. Example in fig 6.1 They are generally used for spans as large as 25-30m. ADVANTAGES OF TUBULAR STEEL ROOF TRUSSES:- •30% to 40% less surface area than that of an equivalent rolled steel shape. Therefore, the cost of maintenance, cost of painting or protective coatings reduce considerably. •The moisture and dirt do not collect on the smooth external surface of the tubes. Therefore, the possibility of corrosion also reduces. •The ends of tubes are sealed. As a result of this, the interior surface is not subjected to corrosion. The interior surface do not need any protective treatment. •They have more torsional resistance than other section of the equal weight. Fig 6.1 Fig 6.2
- 21. ADVANTAGES OF TRUSSES • Trusses consume a lot less material compared to beams to span the same length and transfer moderate to heavy loads. However, the labour requirement for fabrication and erection of trusses is higher and hence the relative economy is dictated by different factors. In India these considerations are likely to favor the trusses even more because of the lower labour cost. In order to fully utilize the economy of the trusses the designers should ascertain the following: a) Method of fabrication and erection to be followed, facility for shop fabrication available, transportation restrictions, field assembly facilities. b) Preferred practices and past experience. c) Availability of materials and sections to be used in fabrication. d) Erection technique to be followed and erection stresses. e) Method of connection preferred by the contractor and client (bolting, welding or riveting). f) Choice of as rolled or fabricated sections. g) Simple design with maximum repetition and minimum inventory of material.
- 22. C. Tensile structure A tensile structure is a structure elements carrying only tension and no compression or bending.Atensile membrane structure is most often used as a roof, as they can economically and attractively span large distances. These type of structure is commonly found in sports facilities, warehousing and storage buildings, and exhibition venues Types of Tensile Structures 1. Linear Tensile Structures 2. Three-dimensional Tensile Structures 3. Surface-Stressed Tensile Structures
- 23. Types of Tensile Structure 1. Linear Tensile Structures Linear tensile structures are the structure in which the all the member are in linear tensile forces. This linear members are supported by the compression members , but the major loads are carried out by tensile members. Common example of these structure is cable suspended bridges. The main pillars acts as compression members, but the whole load is carried out by the cables which are in tension. Linear tensile structures are further classified into following types, • Suspension bridges • Cable-stayed beams or trusses • Cable trusses Suspension bridge Cable stayed bridge Cable truss
- 24. 2. Three-Dimensional Tensile Structures Three-dimensional tensile structures, is a compilation of elements that are primarily in tension, with the compression being transferred to a central mast and down into the ground. The most common occurrenceof three-dimensionaltension can be seen at sports arenas and usually serve as roofs for these structures. Three-dimensional tensile structuresare further classified into following types, • 3D cable trusses • Tensegrity structures • Bicycle wheel (can be used as a roof in a horizontalorientation) Bicycle Wheel 3D Cable truss Tensegrity structures
- 25. 3. Surface-Stressed Tensile Structures Surface-stressed tensile structuresare same as other2 tensile structure, but the surface members are tension bearing members. Fabric tensile structuresare the great examples of Surface-stressed tensile structures, where the vertical pillars hold the special designed fabric which is in tension. Surface-Stressed tensile structures are further classified into following types • Fabric structure • Prestressed membranes • Pneumaticallystressed membranes • Grid shell Fabric Structure Prestressed membranes Pneumaticallystressed membranes Grid shell
- 26. D. Folded plates Folded platesare assemblies of flat plates rigidly connected together along their edges in such a way that the structural system capableof carrying loadswithout the need for additionalsupportingbeams along mutual edges. Example is shown in fig 1 Types of Folded Structure Based on geometric shape folded structurescan be divided into: 1. Folded platesurfaces structuresfig 1.1 2. Folded plateframes structuresfig 1.2 3. Spatial folded platestructuresfig 1.3 Fig 1.1 Fig 1.2 Fig 1.3 Fig 1
- 27. The Principle of Folding The structural characteristics of folding structures depend on- • The pattern of the folding. • Their geometrical basic shape. • Its material. • The connection of the different folding planes. • The design of the bearings. Structural Behavior of Folding Structural Condition Of Folding Structures. Load Distribution process • At first, the external forces are transferred to the shorter edge of one folding element. • There, the reaction as an axial force is divided between the adjacent elements. • Then the forces transferred to the bearings.
- 28. Application of folded structures As a roof structure As a floor structure As a wall structure As steel sheet pile
- 29. Advantages and Disadvantages of folded plates Advantages • Very light form of construction. To span 30 m shell thickness required is 60 mm only. • The use of concreteas a building material reduces both materials cost and a construction cost. • Longer span can be provided. • Flat shapes by choosing certain arched shapes. • Estheticallyit looks good over otherforms of construction Disadvantages • Shutteringis difficult. • Greater accuracy in formwork is required. • Good laborand supervision necessary. • Rise of roof may be a disadvantage.
- 30. E. Shell structure • A shell structure is a light weight construction using shell elements. These elements are usually curved and are assembled to large structures • It covers large floor spaces with economical use of materials of construction • The thickness of shells range from 75 mm to 150 mm • Shell roofs are generally adopted for hangers, sport auditoriums, exhibition halls, industrial buildings, operas as shown in fig 1 and a variety of other large span structures where uninterrupted floor space is required • Its efficiency is based on its curvature (single or double), which allows a multiplicity of alternative stress paths and gives the optimum form for transmission of many different load type Types of shell structures: 1. Thin shell structure 2. Folded shell structure 3. Barrel shell structure 4. Timber shell structure 5. Lattice and grid shell structures 6. Hypar and concrete shell structures Fig 1
- 31. 1.Thin shell structure • Thin shell structures are light weight constructions using shell elements • A thin shell is defined as a shell with a thickness which is very small compared to its other dimensions and in which deformations are not large compared to thickness • These elements are typically curved and are assembled to large structures. • Membrane action in a shell is primarily caused by in-plane forced (plane stress), though there may be secondaryforces resulting from flexural • Though the ideal thin shell must be capable of developing both tension and compression 2.Folded shellstructure • The folded plates are the typical two- element construction • North light is achieved in this roof structure by truss elements cast in the plates • The edge plates are small because they are supported by columns. Thin shell structure Folded shell structure
- 32. 3.Barrel shell structure • The barrel shell is a series of very thin arches that share their compressive strengths with one another. • This relationship of compressive forces allow for the barrel shell to support very large amounts of weight as long as the weight is distributed proportionally. • Barrel shells with a consistent thickness are very weak against the concentrated loads. The barrel shell is formed like the arch that transfer the compressive loads to the ground. • Barrel shells can be used in a variety of different applications. 4.Timber shell structure • The timber shell structure consists of wooden planks to form the ribs. • These planks are approximately 3 x 16 cm, and several interlocked layers are used to form each rib. • These planks are screwed together, usually no glue is used. Each layer of planks is continuous in one direction. • Filler boards are installed between these planks Barrel shell structure Timber shell structure
- 33. 5.Lattice and grid shell structure • Grid shell structures are structures made of grid or lattice forms, set into a double curve. • Grid shell structures can be made from almost any material, as long as the material can be set into a nearly even grid and can be bent enough to achieve a double curve. • Most of the materials used for grid shell structures are wood and steel. 6.Hypar and concrete shells • Concrete shells were brought into the post- classical by Heinz Isler. • There is little further reinforcement required for the 7 cm, thick shells, and they have no measurable deflection. Lattice and grid shell structure Hypar and concrete shells
- 34. Advantages and Disadvantages of Shell Structures Advantages • Thickness is small relative to other dimensions. • Considerablereduction in the self-weight of the structure. • Attraction of elegant simplicity of curved shell forms that utilize the natural strength and stiffness of shell form with great economy in the use of material. • Continuityand Curvature – The essential ingredients of a shell structure. Disadvantages • More expensive than a part framed structure, cost of labor, the constructionof centering of shell is very high. • While rigidity and strength are in many cases desirable attributesof shell structures, there are some important difficulties that occur precisely on account of unavoidablerigidity. • A tiny weakness or imperfection on the covering can cause the whole structureto fall.
- 35. F. Portal Frames Portal frames are a type of structuralframe, that, in their simplest form, are characterized by a beam (or rafter) supported at either end by columns, however, the joints between the beam and columns are 'rigid' so that the bendingmoment in the beam is transferred to the columns. Portal Frames are generally used for single story constructionas shown in fig 1.1 which require a large unobstructedfloor space. Portal frames are made in a variety of shapes and sizes. They are usually made from steel, but can also be made from concreteor timber. The portal structureis designed in such a way that it has no intermediate columns as shown in fig 1.2, as a result large open areas can easily be created within the structure. Fig 1.1 Fig 1.2
- 36. Types of portal frames 1. Duo pitch portal frame Fig 1 2. Curved portal frame Fig 2 3. Portal with crane Fig 3 Fig 1 Fig 2 Fig 3
- 37. Application of portal frames as roofs and walls • A high percentage of roofs are covered with composite profile metal sheets with a colored external skin. • These composite sheets have approximately 50mm of insulation sandwiched between two thin metal sheets or aluminum sheets. Coated steel is lowest in cost but limited in life due to the durability of the finish. Aluminum develops its own protective film. Profile sheets are quick to erect, dismantle and repair. • Galvanized steel purlins span between the steel rafters. • Wall panels.
- 38. Advantages and Disadvantages of Portal Frames Advantages • Speed and ease of erection • Buildingcan be quickly closed in and made water tight. • Framework prefabricated in a workshop and not affected by weather. • Site works such as drainage, roads etc, can be carried out until framework is ready for erection. • No weather hold up during erecting the framework. • Connectedtogetherin factories by welding and site connectionsshould be bolted. Disadvantages Although steel is incombustibleit has a poorresistance to fire as it bends easily when hot. Subject to corrosion
- 39. Example of a large span building Beijing Daxing InternationalAirport • The phoenix-shaped Beijing Daxing InternationalAirport has become a new iconic building in the Chinese capital. • Designed by Zaha Hadid Architects, ADP Ingenierie and Beijing Institute of Architectural Design (BIAD), the terminal building has a total GFA of over 700,000m² and is designed to have a maximum capacity of 100 million passengers every year, relieving pressure on the Beijing Capital International Airport. • The new airport is also designed to be a super transportation hub for Beijing – beneath the terminal building there will be three underground railway stations with a total area of 200,000m² for five railway lines to allow easy transfer for passengers to various means of transportation. • In realizing this second international airport for Beijing, Arup was appointed as the fire engineering consultant by the Beijing Institute of Architectural Design, and later to carry out peer review and value engineering for the steel roof structure by the Beijing New Airport Construction Headquarters.
- 40. Optimizing the roof structure • The roof of the terminal building is a large-span and complex hyperboloid steel grid structurecovering over 350,000m²and containingmore than 170,000 steel members. It is supportedby giant C-shape columns seamlessly connectingwith the roof curvature. • Arup engineers, with the help of in-house developed software, studied the structuralconfiguration, loading, vertical support system reactions and the structural deflection and displacement. Atotal of 420 load combinationswere considered and 38 different cross section sizes were employed in the superstructure.Our analysis revealed that therewas roomfor design optimization. • With extensive experience in long span steel structuresand structuraldesign optimization, Arup proposed various strategies for the different zones of the terminal to improve the roof truss patternsand reduce unnecessarystructural depth and member sizing.
- 41. CONCLUSION • All the structuresdiscussed above have their own advantages and disadvantages. Therefore it is very important that the constructionfirm of the different large span structuresis able to tackle all the issues by considering the different elements of large span structuressuch as design, installationand materials and consider which structuralsystems is suitablefor the large span structurerequired to be constructed. • You tubevideo link https://www.youtube.com/watch?v=U7iqjVyVqtE&t=194s
- 42. THANK YOU