Design Procedures

Design Procedures
The truss design is initiated by the builder or owner, or his designate; i.e. the general contractor or architect/engineer. The documentation must include: -the size of the building, -the building occupancy, -the shape and span of the truss, -where the truss will be supported, -the type of roof construction (finish, insulation, sheeting, ceiling type) -what the loads on the truss will be special requirements to be considered in truss design such as special loading and placement geometry defining parameters (pitches, heel heights, overhang and cantilever details)
For more details on the design responsibilities of the truss designer and the building designer consult the TPIC design procedures page iii.
Typically, the building designer or builder will contract with the truss fabricator, who will supply a truss layout and a structural design of each significant element of the roof system. The truss plate manufacturer's engineer usually reviews and seals the individual truss designs on behalf of the truss fabricator. In North America, designs are based on structural requirements from Building Codes using design standards referenced in Building Codes and approved material properties: -Structural analogues and methodology have been developed and standardized by National Associations such as TPIC in Canada and TPI in the United States who represent the manufacturers of metal plate connectors. -Lumber design values for use in Canada are published by Canadian Standards Association (CSA 086-Engineering Design in Wood). -Truss connector plates are proprietary and therefore come with different structural properties. Design values for truss plates are developed through tests and analyses in accordance with referenced standards. Approval of the design values is overseen by national certification organizations such as the Canadian Construction Materials Centre (CCMC). Preliminary discussion of a design with a truss fabricator may result in suggestions leading to the most efficient and the most cost effective design. Truss design is facilitated by the use of computer software that designs all members, connections and produces a design drawing for an engineer's approval and also shop drawings and cutting lists for manufacturing and quality control. The approval and acceptance process of truss design drawings depends on local requirements. In most jurisdictions, a professional engineer's stamp on the truss design drawing may be compulsory. In other cases alternate procedures may be acceptable.