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

Design of Corrugated Sheet 11/29/2018

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 11/29/2018

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300 mm Length = L One Panel Pitch = P End lap = E Side lap= s Width = W

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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. 11/29/2018

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. 11/29/2018

Correct Incorrect End Lap Over Purlins End Lap Within Purlins 11/29/2018 Figure 7.16. Correct Position of End Lap

Correct Incorrect 11/29/2018 Figure 7.17. Correct Placement of Overlap Within End Lap

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. 11/29/2018

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: 11/29/2018

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. 11/29/2018

(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. 11/29/2018

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. 11/29/2018

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. 11/29/2018

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 11/29/2018

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 11/29/2018

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 300 + 0.2 = 3.087 m L2 = 2 x 2.5 / cos 300 + 0.2 = 5.974 m 11/29/2018

Solution: L = 3.25 m Mmax = w p2 / 8 = 762 x (2.5)2 / 8 = 596 N – m (Sx)req = =   = 3.98 103 mm3 11/29/2018

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/m2 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) = 27.70 mm ∆a = span / 90 = 2500 / 90 = 28 mm 11/29/2018

∆max < ∆a OK N100 = = = 60 A = =   = 523.3 m2 11/29/2018

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. 11/29/2018

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 11/29/2018