Camber is the upward bending of structural members to compensate for their deflection under gravity (dead and live) loads. For flat roof systems, this is usually done to drain rainwater and prevent ponding (load due to rain), and to reduce the roof deflection. Camber can be achieved by increasing the length of the bottom layer members by a small amount in one direction to create a barrel shape or in both directions to form a shallow dome shape curvature. For members of spatial structures connected to each other through welding any type of camber can be accommodated as the joints can be placed at any desired elevation. Another common method of cambering a roof system is by changing the purlins’ elevation.
Barrel Shaped Camber for Spatial Structures
Dome Shaped Camber for Spatial Structures
The required camber for flat spatial structures has to satisfy two basic requirements:
The rise (camber) at the center in the supported layer has to be less than span/100.
The rise (camber) has to cancel out part of the maximum deflection.
For spatial structures with spans less than 100 ft carrying light to moderate live loads (less than 40 psf) cambering is not required.
The main disadvantage of cambering a flat spatial structure is that it loses the uniformity of standard elements which may cause difficulty with assembly and erection.
