Important Question And Problems With Answer: Roof Trusses And Industrial Buildings

Important Question And Problems With Answer: Roof Trusses And Industrial Buildings

1.       Name the types of roofing systems.          

          Flat roofing consists of either RCC construction or RSJ slab construction Sloping roofing                

2.       Where the steel roof trusses are used?                

          Industrial buildings, workshop buildings, storage godowns, warehouse and even for residential   buildings,  school  buildings,   offices  where  the  construction        work  is to  be completed in a short duration of time.       

3.       Mention the advantages of a roof truss.              

          Its mid-span depth is the greatest specially where bending moment in the span is the maximum Great economy.               

          Sloping faces of trusses facilitate in easy drainage of rainwater.     

4.       What is the factor that is considered in the roof truss and why?     

          The factor, which is considered in the roof truss, is pitch, it is defined as the ratio of the          span  length  to  the  depth      of  the  truss,  is  governed  by  the   roofing material  and other requirements such as ventilation and light.

5.       How the trusses are classified according to the pitch?

          Small pitch - span depth ratio is more than 12 m

          Medium pitch       - span depth ratio is between 5m to 12 m

          Large pitch - span depth ratio is 5 or less.

8.       What is gantry girder and what are the forces that are acting on it?

          A gantry girder, having no lateral support in its length, has to withstand vertical loads from the weight of the crane, hook load and impact and horizontal loads from crane surge. 

9.       What is meant by purlins?     

          Purlins are structural members which are supported on the principal rafter, and which run transverse to the trusses. The span of the purlins is equal to the center-to- center spacing of the  trusses.  The       purlins  support  the roof  covering  either  directly or  through  common rafters.  They   are  usually  made  of  either  an  angle  section  or a     channel  section  and  are therefore subjected to unsymmetrical bending.

10.     Why the bracings are provided?

Bracing  is  required  to  resist  horizontal  loading  in  pin-jointed  buildings, including roof trusses.  Bracing of roof trusses  and supporting  columns  provide          still rigid  structure.  When wind blows normal to the inclined surface of the trusses,       it is efficiently  resisted  by  all  the  members  of  the  truss  and  the  wind  forces  are transferred to the supports at the ends of the truss.

11. Name the most common roof covering materials.

Slates          Glass

Tiles  Corrugated aluminium sheets 

Lead  Galvanized corrugated iron sheets (G.I. sheets)  

sheets          Asbestos cement sheets (A.C. sheets)        

Zinc           

sheets                  

13. Mention some of the requirements of a good joint.

The line of thrust should pass through the C.G of the rivet group and the riv ets should be symmetrically arranged about this line.

For a tensio n member, the rivets should be so arranged that the area of the member joined is not reduced more than necessary.

The numbe r and the diameter of rivets should be suffici ent to develop the maximum stresses induced in all the members at the connection. Members s hould be straight and bolts used to draw th em together before the rivets are driven.

14.     What are the cond itions that to be satisfied for the end supports?

The size of  base plate should be sufficient  so that the bearing

pressure does not exceed the permissible value.

Anchor bol ts should be provided at one end to accomm odate the thermal expansion of the truss.

The lines of forces in rafter, bottom tie and vertical end reaction meet at a point.

15. Where the gantry girders are used?

Gantry        girders  or  crane  girders  carry  hand  operated  or  electric  over head  cranes  in ind ustrial  buildings  such  as  factories,  worksh ops,  steel  works etc.,  to  lift  heavy  materials, equipment etc., to carry them fro m one location to the other, within the building.

17. What is drag force?

This  is  caused  due  to  the  starting  and  stopping  of  the  crane  bridge moving  over  the  crane  rails  as  the  crane  m0oves  longitudinally,  i.e.  in  the direction of gantry girders.

18. What is the permissible deflection where the electrically overhead cranes operated over 500kN?

The  maximum  vertical  deflection  for  crane  girder,  under  dead  and imposed  loads shall not exceed L/1000, where L is the span of the crane runway girder.

19. Define shoe angle.

It is a supporting  angle provided  at the junction  of the top and bottom chords  of  a truss.  The  reaction  of  the  truss  is  transferred   to  the  supports through the shoe angle. It is supported on the base plate.

20. What is panel point?These are the prominent points along the principal rafter, at which various members (i.e. ties and struts) meet. The distance of the principal rafter between any two panel point is termed as panel.

This  is  caused  due  to  the  starting  and  stopping  of  the  crane  bridge  moving  over  the crane rails as the crane m0oves longitudinally, i.e. in the direction of gantry girders.

18. What     is       the   permissible   deflection    where          the     electrically   overhead   cranes operated    over 500kN?                                              

The maximum      vertical        deflection    for crane     girder,         under dead and imposed