ROOF TRUSS.pptx

TRUSS TYPES

1. Trusses Introduction Trusses are rigid structures made up of two-force members, which are objects with exactly two forces/connections. Trusses are commonly found in the frame of a roof and the sides of a bridge. Trusses are triangular frame works, consisting of axially loaded members They are more efficient in resisting external loads as the cross section of all the members are nearly uniformly stressed They are Extensively used for Larger Spans

2. Pitched Roof Trusses Most common types of roof trusses. Top chord is provided with a slope in order to facilitate natural drainage of rainwater and clearance of dust/snow accumulation . The typical span to maximum depth ratios of pitched roof trusses are in the range of 4 to 8M , the larger ratio being economical in longer spans.

3. Applications Trusses are used in Roofs of Single Story Industrial Buildings. Long Span Floors and Roofs Of Multistory Buildings, to resist gravity loads . Trusses are also used in Walls and Horizontal Planes of Industrial Buildings to resist Lateral Loads and to provide Lateral Stability .

4. Analysis of Trusses Truss members are regarded as being pinned joints. They are assumed to be joined together so as to transfer only the axial forces and not moments and shears from one member to the adjacent members The loads are assumed to be acting only at the nodes of the trusses. The trusses may be provided over • a single span, simply supported over the two end supports, in which case they are usually statically determinate. • Such trusses can be analyzed manually by – method of joints – method of sections. • Computer programs are also available for the analysis of trusses.

5. Parts of a Truss A truss is composed of: Joints Members External forces (reaction forces and applied forces).  

6. A  two force member  is a body that has forces (and only forces, no moments ) acting on it in only two locations. In order to have a two force member in static equilibrium , the net force at each location must be equal, opposite, and collinear. This will result in all two force members being in either tension or compression.

7. Components of Roof Truss

8. Roof Truss Advantages Roof trusses can save on-site costs . Less labor requirement . Faster shell completion time. Greater flexibility in locating plumbing, duct work, and electrical wiring Floor plan freedom in locating interior partitions often without additional support required Fewer pieces to handle and reduced installation time Reduced HVAC, plumbing, and electrical subcontractor time on job No column pads to pour, no steel beams and posts to place Job site material pilferage and cutting waste reduced Roof Truss Disadvantages Roof trusses have a series of supporting members that limit the use of attic space . Large trusses require a crane

9. Types of Roof Trusses

10. Types of Roof Truss Pitched roof trusses Parallel chord trusses Trapezoidal trusses

11. The typical span to maximum depth ratios of pitched roof trusses are in the range of 4 to 8m, the larger ratio being economical in longer spans. These trusses have a greater depth at the mid-span . Due to this even though the overall bending effect is larger at mid-span, the chord member and web member stresses are smaller closer to the mid-span and larger closer to the supports. Most common types of roof trusses Top chord is provided with a slope in order to facilitate natural drainage of rainwater and clearance of dust /snow dust/snow accumulation. Pitched Roof Trusses

12. Pratt Truss (6-30m) In Pratt trusses web members are arranged in such a way that under gravity load the longer diagonal members are under tension and the shorter vertical members experience compression. This allows for efficient design, since the short members are under compression. However, the wind uplift may cause reversal of stresses in these members and nullify this benefit.

13. The converse of the Pratt is the Howe truss . This is commonly used in light roofing so that the longer diagonals experience tension under reversal of stresses due to wind load. Howe Truss (6-10m)

14. Fink trusses are used for longer spans having high pitch roof. The web members in such truss are subdivided divided to obtain shorter members Fink Trusses(up to 10m)

15. Fan trusses are used when the rafter members of the roof trusses have to be subdivided into odd number of panels Fan Trusses (10-15m)

16. Mansard Trusses(20-30m) Mansard trusses are variation of fink trusses, which have shorter leading diagonals even in very long span trusses, unlike the fink and fan type trusses. The Mansard trusses can be used in the span ranges of 12 m to 30 m.

17. When to use a roof truss: Roof trusses are characterised by an economic use of construction materials (timber, steel). Composed of individual lightweight pieces, a truss can also provide considerable advantage in transport and assembly as compared to conventional roof structures. On the other hand, trusses are more labour-intensive and require connection devices. However, if a greater number of identical trusses can be manufactured, then considerable economies of scale can be achieved.The structural height of a truss is usually larger than the height of similar structures using solid beams. For roofs, however, this is usually no disadvantage as roofs must often - depending on roof cover material used - be higher at the ridge and lower at the eaves to facilitate roof drainage and ensure water tightness. While the use of steel for roof structures almost invariably calls for a truss, it is with timber structures where the truss has strong competitors. These are the purlin and the rafter roofs.

18. Materials for Roofing

19. Fastenings for Sheeting

20. Side lap Corrugated Sheet Flat Cum Corrugated Sheets