Spring Curving Technical Information

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Material Specifications


Minimum Ridge Purlin Spacing For Spring Curved Ridges
Maximum Roof Slope Smartspan® BMT CGI Corrugated BMT CGI Curving BMT
0.42mm 0.48mm 0.42mm 0.48mm 0.60mm
1 in 20 (3°) 1400 1500      
1 in 15 (4°) 1500 1600      
1 in 12 (5°)   1700 1200 1300 1200
1 in 10 (6°)       1400 1300
1 in 8 (7°)         1400

Note: If oil canning in pans is considered acceptable, concealed fix decks such as Topdek® 700 can be spring curved over a ridge up to a maximum slope of 1 in 30 (2˚) providing the spacing between the ridge purlins are slightly less than Stratco’s recommended internal spans. Please refer to Spring Curving in the Stratco Technical Guide for further information.

Spring Curved Convex Roofing

Using the overall width plus the rise of a convex roof, the radius of curvature can be calculated using the equation shown in Figure 2. The side laps of convex roofs are to be sealed using a recommended sealant. This is required at the roof crest where the slope is less than the recommended minimum for each roofing profile. The length of roof to be sealed (shown as seal length ‘s’) can be calculated using the equation shown in Figure 2.


Recommended Radius For Convex Spring Curving
Sheet Profile BMT (mm) Min. Radius (m) Purlin Spacing at Min. Radius* (mm) Max. Radius† (m)
Smartspan® 0.42 20 1200 60
0.48 20 1400 60
CGI Corrugated 0.42 12 800 35
0.48 10 1000 35
CGI Curving 0.60 9 900 35

*For radii curvature greater than the recommended minimum, the purlin spacing can be increased. However, the purlin spacing should not exceed the recommended maximum for straight sheeting given in Stratco product literature.
†Maximum recommended radius to provide sufficient drainage near crest of curvature.

Note: Please refer to Spring Curving in the Stratco Technical Guide for further information.

Spring Curved Concave Roofing

Sheeting can also be spring curved to the minimum radii shown in
Table 3 to form a concave roof.



Recommended Radius For Concave Spring Curving
Sheet Profile Base Metal Thickness (mm) Minimum Radius (m) Purlin Spacing at Minimum Radius*(mm)
Topdek® 0.42 24 1000
0.48 26 1400
Smartspan® 0.42 18 1200
0.48 20 1400
Superdek® 0.42 20 1000
0.48 22 1200
CGI Corrugated 0.42 10 800
0.48 10 1000
CGI Curving 0.60 8 800
*For radii curvature greater than the recommended minimum, the purlin spacing can be increased. However, the purlin spacing should not exceed the recommended maximum for straight sheeting given in Stratco product literature.