Steel roof trusses are used for mainly for the Industrial buildings where free space requirement are essential for more working areas. The span of truss varies from 10’-0” to 300’-0” depending on the type of requirement and the available spaces.
The following steps should be considered when designing a truss:
Select the general layout of truss members and truss spacing.
Estimate external loads to be applied including self weight of truss, purlins and roof covering together with wind loads.
Determine critical (worst combination) loading. It is usual to consider Dead loads alone and then Dead and Imposed loads combined.
Analyze the frame work to find forces in all members.
Select material and section to produce in each member a stress value which does not exceed the permissible value. Particular care must be taken with compression members (struts) or members normally in tension but subject to stress reversal due to wind uplift.