1. DESIGN OF TRUSS ROOF Chapter 7
University of Engineering & Technology, Taxila
Prof Dr Z. A. Siddiqi

2. Design of Corrugated Sheet
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3. GALVANIZED IRON (G.I) CORRUGATED ROOFING SHEETS
Standard Designation
Nominal pitch in mm x Nominal depth in mm
Following two sheets are commonly used.
65 x 13 G.I. Corrugated Sheet
75 x 20 G.I. Corrugated Sheet
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6. 300 mm
Length = L
One Panel
Pitch = P
End lap = E
Side lap= s
Width = W

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16. DESIGN OF CORRUGATED SHEET
Use Design Aids for the related definitions and data.
Allowable stress design (ASD) is used here as for the purlin design.
Dead plus live load combination seems to be critical for the sheet design and hence wind combinations are not considered.
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17. End lap should be exactly on the purlin (Figures 7.16 and 7.17).
Accordingly, the length of sheet panel (L) is corresponding to 1,2 or 3 times the inclined panel length plus the required end lap.
The resulting dimension may be rounded to upper 0.25m length.
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18. Correct Incorrect End Lap Over Purlins End Lap Within Purlins
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Figure Correct Position of End Lap

19. Correct
Incorrect
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Figure Correct Placement of Overlap Within End Lap

20. If the required length of sheet corresponding to single panel length is more than 4.0m or if the available section modulus does not satisfy the flexural criterion, extra purlins may be placed between the two panel points. If one purlin is used at center of a panel length, the span of the sheet reduces to p/2. However, the top chord of the truss must be checked for the combined action of compression and bending moment.
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21. Consider unit width of slab (1 m) and design this strip as a beam.
Similarly, purlin design must also be made using spacing of purlins equal to the modified c/c distance between the purlins.
Total load on the sheet = dead load of roofing + insulation live load (N/m2)
Consider unit width of slab (1 m) and design this strip as a beam.
Load per unit length of roof strip, w (N/m), is calculated as follows:
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22. W = load per unit roof area x 1 m width
= load per unit roof area, magnitude-wise only, in N/m units (only applicable for a roof and not for a beam)
Assume the sheet to be simply supported over the purlins. Even if it is continuous, the maximum bending moment will nearly be the same.
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23. (Sx) req =
Select gage of sheet from 1st column of the corresponding table in Design Aids for properties of the corrugated sheets.
Actual self weight of roofing = value from Col.4 of the properties table x 1.35
  ≤ 1.2 x assumed weight OK
If self-weight is significantly greater, revise the sheet as well as the purlin design.
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24. Note: The 35% increase in the above expression is for more area of the inclined sheet due to slopping roof and the overlap.
Calculate the deflection due to live load (∆max) and check against the allowable value (∆a).
(∆max) < ∆a OK
Calculate the number of sheet panels required for 100 m2 of roof area (N100) using the expression given earlier. It is better to use the actual length of the panel before rounding.
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25. The inclined roof area on one side.
The total length of building may be represented by Nt x S, where Nt is the number of spaces between the trusses.
The inclined roof area on one side.
The number of sheets on one side.
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26. Total number of sheets = 2 x N1
Decide spacing of bolts in end and side laps such that bolts are only applied at the crests.
 Summarize the design results as under:
Final Results For Corrugated Roof Sheet Design:
Gage of sheet
Standard designation
Sheet panel size
Bolt spacing in the two directions
Number of sheets required
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27. Example 7.3 Design a 75x 20 G. I. corrugated sheet for a truss roof having the following data. Also calculate the number of sheets required. Assumed dead load of roofing = 16 kg/m2 Insulation not attached to the sheet Total miscellaneous load = 5 kg/m2 Live load = 60 kg/m2 = 300 P = 2.5 m S = 5.5 m Number of truss panels = 8 Total number of trusses = 9 Sheet Projection beyond center of the truss support = 300 mm
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28. Solution: w = [16 + 60 + 1/3 (5)] x 9.81 = 762 N/m2
= 762 N/m for 1m wide strip
L1 = P/ cos + E
= 2.5 / cos
= m
L2 = 2 x 2.5 / cos
= m
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29. Solution: L = 3.25 m Mmax = w p2 / 8 = 762 x (2.5)2 / 8 = 596 N – m
(Sx)req = =
= mm3
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30. Trial sheet gage: 22 gage, I= 4.23 x 104 mm4
Self-weight of roofing = 1.35 x 77.6
= 105 N/m2 < 1.2 x 16 x 9.81 N/m Ok
wL = 60 kg/m = 0.60 N/mm
∆max = 0.01 x WLP4/EI
= 0.01 x 0.60 x (2500)4 / (200,000 x 4.23 x 104)
= mm
∆a = span / 90
= 2500 / 90 = 28 mm
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31. ∆max < ∆a OK
N100 = = = 60
A = =
= m2
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32. Total number of sheet panels = 2 x 314 = 628 Final Results
Gage of G.I. corrugated sheet = 22 gage
Standard Designation = 75 x 20
Sheet panel size = 0.7 x 3.25 m
Total number of sheet panels = 628
J-bolts at a spacing of 219 mm within the end laps and ordinary bolts at a spacing of 300 mm along the side laps.
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33. Design Corrugated Sheet for your truss using your own data
A s s i g n m e n t
Design Corrugated Sheet for your truss using your own data
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