TRUSS 2020.pptx

A truss is an assembly of members such as beams, connected by nodes, that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object"

1. STEEL ROOFS Presentation By- Ar. Roopa Chikkalgi 1

2. Use of trusses in buildings Trusses are used in a broad range of buildings, mainly where there is a requirement for very long spans, such as in airport terminals, aircraft hangers, sports stadium roofs, auditoriums and other leisure buildings. Trusses are also used to carry heavy loads and are sometimes used as transfer structures. The trusses are widely used to serve two main functions: To carry the roof load To provide horizontal stability. Robin Hood Airport, Doncaster Presentation By- Ar. Roopa Chikkalgi 2

3. There are numerous advantages to using steel trusses instead of traditional wood trusses but the main reasons are simplicity and strength. Some prefer to use the metal roof truss because the building of a structure is all about precision and metal has a more precise measurement than wood. Theses trusses are extremely simple to install. You never have to worry about them rotting or deteriorating from the weather. You also get more usable space inside your building. Wood trusses are less expensive truss per truss but they require you to install wood headers, the posts have to be closer together and you have more trusses to install. You generally have to protect the wood from the weather. Presentation By- Ar. Roopa Chikkalgi 3 WHY STEEL ROOF?

4. WHY STEEL ROOF? Prefabricated steel trusses offer a high-strength, light-weight roof system that can be installed quickly. In residential construction, wood trusses still dominate the industry, where additional strength is needed, or where greater free spans are required Steel roofs are preferred. Presentation By- Ar. Roopa Chikkalgi 4

5. Truss or  I beam For the same steel weight, it is possible to get better performance in terms of resistance and stiffness, with a truss than an  I beam . This difference is greater for long spans and/or heavy loads. The full use of this advantage is achievable if the height of the truss is not limited by criteria other than the structural efficiency, e.g. a limit on total height of the building. However,  fabrication  of a truss is generally more time consuming than for an  I beam , even considering that modern fabrication equipment is highly efficient. The balance between minimum weight and minimum cost depends on many conditions: the equipment of the  fabrication  factory, the local cost of manufacturing; the steel unit cost, etc. Trusses generally give an economic solution for spans over 20 m. An advantage of the truss design for roofs is that ducts and pipes that are required for operation of the buildings services can be installed through the truss web, i.e.  service integration . Aspects of truss design for roofs

6. General geometry For efficient structural performance, the ratio of span to truss depth should be chosen in the range 10 to 15. The architectural design of the building determines its external geometry and governs the slope(s) given to the top chord of the truss. The intended use of the internal space can lead either to the choice of a horizontal bottom chord, e.g. where conveyors must be hung under the chord, or to an inclined bottom chord, to allow maximum space to be provided. For an efficient layout of the truss members between the chords, the following is advisable: The inclination of the diagonal members in relation to the chords should be between 35° and 55° Point loads should only be applied at nodes The orientation of the diagonal members should be such that the longest members are subject to tension (the shorter ones being subject to compression).

7. Types of truss member sections     Bolted angles to form lightweight, long-span trusses (Image courtesy of Metsec plc) Many solutions are available. Choice of members depends on the magnitude of the internal forces, ease of connections between members, aesthetics and any necessity to connect prefabricated truss sections on site. When selecting members, the out-of-plane buckling resistance will be important, together with resistance under reversed loading, for example, uplift.             Typical element cross sections for light building trusses For smaller spans, tee sections are frequently used for chords, with  angles  used as internal members. The internal members may be bolted or welded to the tees. Back-to-back  angles  or  channels  may be used for longer spans or heavier loads, with a gusset plate used at nodes to connect the members. For large trusses and heavy loads, typically found in transfer trusses in buildings, members may be rolled sections; typically  UKC sections . Nodes are usually welded. Any necessary connections are completed with bolted splices within the length between nodes. For many exposed trusses,  hollow sections  are chosen for their structural efficiency and for aesthetic reasons. Nodes will generally be welded in the workshop. As part of the truss design, it is essential to verify the resistance of the joints (in accordance with BS EN 1993-1-8 [1] ) as the joint design may dominate member selection and final truss geometry. Members should be selected carefully to avoid expensive strengthening of trusses fabricated from  hollow sections .             Different types of steel section used in trusses

8. Advantages of Metal Roof Truss Structures Even though they are considered to be more expensive, metal roof trusses can span further than wood. Metal roof trusses can be manufactured to exact standards. They are much more lightweight and this allows for larger shipments. This reduces the time it takes to get to the project site. Metal roof trusses are fire resistant. They are compatible with almost all types of roofing systems. No insect infestations can occur. Chemical treatments are not necessary to maintain the trusses. 8. Metal roof trusses are recyclable and therefore environmentally friendly. 5 Presentation By- Ar. Roopa Chikkalgi

9. Presentation By- Ar. Roopa Chikkalgi 9 Disadvantages of Metal Roof Truss Structures Skilled labor is required to install metal roof trusses. They are not energy efficient since they allow more heat to escape from the structure. Metal roof trusses allow sound to be more easily transmitted. Temperature fluctuations allow them to move more. When the metal is cut, drilled, scratched or welded, rust can become a problem. The workers have a higher risk of electrocution when installing the metal roof trusses.

10. Different types of Wooden and Steel Roof Trusses : King Post Truss Queen Post Truss Howe Truss Pratt Truss Fan Truss North Light Roof Truss Quadrangular Roof Truss King Post Truss King Post Truss is a wooden truss. It can also be built of combination of wood and steel. It can be used for spans upto 8m. Presentation By- Ar. Roopa Chikkalgi 10

11. Queen Post Truss ss. Queen Post Truss is also a wooden tru It can be used for spans upto 10m. Howe Truss It is made of combination of wood and steel. The vertical members or tension members are made of steel. It can be used for spans from 6-30m. Presentation By- Ar. Roopa Chikkalgi 11

12. Pratt Truss Pratt Truss is made of steel. Vertical members are tension and diagonal members are compression. These are very economical form of roof trusses. It can be used for spans from 6-10m. Fan Truss It is made of steel. In Fan Trusses, top chords are divided into small lengths in order to provide supports for purlins •It can be used for spans from 10-15m. 9 Presentation By- Ar. Roopa Chikkalgi

13. Typical Steel Connections Steel Connections Many configurations are used for force transfer in connections. The configuration depends upon the type of connecting elements, nature and magnitude of the forces (and moments), available equipment, fabrication and erection considerations, cost, etc. Ri v e ts 14 Presentation By- Ar. Roopa Chikkalgi

14. Bo l ts Presentation By- Ar. Roopa Chikkalgi 15

15. TRUSS - INTRODUCTION A truss is a structure composed of members fastened together in such a way to resist change in shape and it is rigid structure. 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. Its purpose is to support a larger load or span a greater distance than any individual member from which the truss may be built Triangular unit

16. TRUSS – INTRODUCTION CONTINUE External forces and reactions to those forces are considered to act only at the nodes. Moments (torques) are explicitly excluded because, and only because, all the joints in a truss are treated as pin joint or hinge joint . Result in forces in the members which are either tensile or compressive forces. Node Tie strut

17. PLANE TRUSS VS SPACE TRUSS Plane Truss All member of truss and applied load lie in a same plane. In a simple truss, m = 2n - 3 where m is the total number of members and n is the number of joints. Space Truss An elementary space truss consists of 6 members connected at 4 joints to form a tetrahedron. In a simple space truss, m = 3n - 6 where m is the number of members and n is the number of joints.

18. ROOF TRUSS TERMINOLOGY

19. Gusset plate connections Gusset plates are usually either made from cold rolled or galvanized steel based upon their use. Gusset plates are used for various structures. Gusset plates are used to connect beams and columns together or to connect truss members. They can be either the only way of connecting the beam and columns or they can be used with bolts and welds. Presentation By- Ar. Roopa Chikkalgi 16

20. 21 Presentation By- Ar. Roopa Chikkalgi

21. 22 Presentation By- Ar. Roopa Chikkalgi

22. Types of connections          For all the types of member sections, it is possible to design either bolted or welded connections. Generally in steelwork construction,  bolted site splices  are preferred to  welded splices  for economy and speed of  erection . Where  bolted connections  are used, it is necessary to evaluate the consequences of 'slack' in connections. In order to reduce these consequences (typically, the increase of the deflections), pre-loaded assemblies to produce non-slip joints are recommended. Hollow sections  are typically connected by  welding  whilst  open sections  are connected by  bolting  or  welding , which will usually involve the use of gusset plates. Guidance on the  design of welded joints for Celsius®355 and Hybox®355  hollow sections is available from Tata Steel. Small trusses which can be  transported  whole from the fabrication factory to the site, can be entirely  welded . In the case of large roof trusses which cannot be  transported  whole, welded sub-assemblies are delivered to site and are either bolted or  welded  together on site. In light roof trusses, entirely bolted connections are less favoured than welded connections due to the requirement for gusset plates and their increased  fabrication costs .

23. Galvanized Steel Sheets (Plain and Corrugated) Galvanized iron (GI) sheets are steel sheets which are basically coated with zinc and include a range of hot dip galvanized and electro-galvanized steel sheets. Corrugated galvanised iron or steel is a building material composed of sheets of hot-dip galvanised mild steel, cold-rolled to produce a linear corrugated pattern in them. The corrugations increase the bending strength of the sheet in the direction perpendicular to the corrugations, but not parallel to them. Normally each sheet is manufactured longer in its strong direction. Presentation By- Ar. Roopa Chikkalgi 19

24. Galvanized Corrugated Steel Sheets Presentation By- Ar. Roopa Chikkalgi 20

25. FIXING ACCESSORIES J-Bolt J-bolt, also called hook bolt, is a bolt in the form of letter “J” used to fix roof-sheathing or wall sheathing to purlins and other structural members. Presentation By- Ar. Roopa Chikkalgi 21

26. INSTALLATION OF CORROGATED SHEETS Presentation By- Ar. Roopa Chikkalgi 22

27. TUBULAR TRUSS

28. Tubular Steel Truss are used for large span constructions such as factories, industry worksheds, shopping malls, huge exhibition centre, multiplexes etc. They are generally used for spans as large as 25-30m. TUBULAR STEEL TRUSS:- 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. 29 Presentation By- Ar. Roopa Chikkalgi

29. Steel Construction …….Building Construction Sem. IV

30. Contents….

31. 1 Northlight Truss …… & examples

32. North Light Truss North Light Truss are traditionally used in industrial buildings. They allow maximum benefit to be gained rom natural lighting by the use of glazing on the steeper pitch which generally faces the north or north-east to reduce solar heat gain. One of the oldest and economical methods of covering large areas is the north light truss and lattice girders system. This type of truss system is generally used where the floor spans exceeds 15m. Roof lights in the slopes of symmetrical pitch roofs which are generally set in east and west facing slopes may cause discomfort through overheating in summers and disrupt manufacturing activities by the glare from sunlight. To avoid these possibilities the north light roof is used.

33. Types of North Light Trusses Single bay North Light Truss Multiple bay North Light Truss

34. The whole of the south slope is covered with profiled sheets and the whole of the north facing slope with glass or clear or translucent plastic sheet. North light truss has an asymmetrical profile with a south facing slope at 17º or more to horizontal and the north facing slope at from 60º to vertical. Because of the steel pitch of the north facing slope the space inside the roof trusses of a north light roof is considerably greater than that of a symmetrical pitch roof of the same span.

35. 2 Monitor Roof …… & examples

36. Monitor Roof A monitor in architecture is a raised structure running along the ridge of a double-pitched roof, with its own roof running parallel with the main roof.  With flat or low pitched roof it is difficult to ensure a water tight system of roof glazing fixed in slope of the roof, hence monitor roof is used for natural lighting through roof. The monitor lights project above the roof with two upstand faces that may be sloping or vertical. Monitor roof can be constructed to provide natural or controlled ventilation.

37. Purpose: Natural Lighting Ventilation

38. 3 Skylights

39. Skylights Skylights are light transmitting fenestration (elements filling building envelope openings) forming all, or a portion of, the roof of a building's space for daylighting purposes. In general, a skylight allows approximately eight times as much light to enter the house as a comparably sized wall window. Purpose Natural Lighting Ventilation Heating/Cooling providing a visual connection to the outdoor environment to interior occupants.

40. Flashing to ensure waterproofing

41. Dormer Windows Clearstorey Windows