- Some builders may choose to conventionally frame a valley (i.e., over-frame) instead of using valley set truss frames.
- Requirements in the IRC and the ANSI/AF&PA WFCM-2001 indicate it is not acceptable to bear the ends of valley rafters on top of roof sheathing without structural framing below.
- Valley rafters must be adequately connected at their supports to resist lateral and uplift forces caused by gravity and wind loads.
- If knee braces are shown, the trusses must be designed for them using the loads provided by the RDP.
- In the Midwest knee braces are used in many post frame buildings for which an RDP is neither required nor involved.
- This rapidly forces the Truss Designer into the position of designing building elements that ought to be specified by the person responsible for the overall building design.
- The relatively short spans and light end reactions associated with most jack trusses makes toe-nailing an efficient and effective attachment method.
- An open end jack truss (see Figure 1) meeting the same design parameters would perform in a similar manner as a rafter and ceiling joist and generate comparable reactions. The top chord and bottom chord of the jack truss should correspond to the rafter and ceiling joist tables provided in the code. For these situations, the nail connections specified by the code are also applicable to jack trusses.
- Deferred submittals are permitted by the model IRC code.
- The building official, at his or her discretion, may or may not require the submission of TDDs at the time the permit for the structure is requested.
- Without the diagonal brace, the only thing the lateral member(s) ensures is that the webs to which they are attached will be-have as a unit and buckle together in the same direction if and/or when the buckling load is reached.
- The single diagonal brace and web reinforcement options satisfy the need for bracing individual trusses and truss members, but not the stability bracing of the entire building system.
- BCSI-B3 Web Member Permanent Bra-cing/Web Reinforcement provides indus-try recommendations and methods for restraining web members against buckling.
- BCSI-B2 provides temporary bracing guidance for trusses spaced up to 24 inches on-center.
- BCSI-B10 offers temporary bracing guidance for wide on-center trusses such as those used in post frame buildings.
- Truss Designers note on Truss Design Drawings that truss top chords must be laterally braced by the roof sheathing to prevent the top chord from buckling.
- When purlins are specified, check with the Truss Designer to determine the maximum unbraced length of the top chord between purlins to avoid top chord buckling.
- Placing nails through metal connector plates into wood members is allowed.
- The 2001 National Design Specifica-tion® for Wood Construction lists design values for common wire, box or sinker nails for single shear connections with up to 20 gauge ASTM A653, Grade 33 steel side plates.
- Many contractors see wall girders as an ideal solution because costly beams and field framing are eliminated.
- Wall girders must meet the provisions for wall construction in the IBC or IRC.
- The primary issue that must be considered is out-of-plane bending when some or all of a wall girder is exposed to wind pressure.
- No matter which approach is chosen with wall girders, it must account for all the applied loads, connections and permanent bracing.
- As wall panels gain popularity, questions pertaining to sealed engineering requirements have increased.
- Can walls built in the shop rely on the prescriptive provisions of the building code?
- In the future, it is possible that component manufacturers will be responsible for providing sealed design drawings for their wall panel designs.
- Generally, wall girders cannot be used in second story framing because it is nearly impossible to brace the compression top chord of a girder when it is placed in a wall.
- The top chord(s) of girder trusses can experience very high compressive forces, which can cause the chord to buckle out of plane.
