Trusses are designed as individual components to resist the in-plane stresses resulting from the loads applied in the same in-plane direction. To resist out of plane forces, adequate bracing/restraint is required. In absence of designed temporary and permanent bracing plans, BCSI (Building Component Safety Information) is the industry bracing guideline that framers must follow.
Lateral Bracing/Restraint keeps the compression members of the truss from out of plane buckling due to applied loads shown on the Truss Design Drawing. Per ANSI/TPI 1 (National Design Standard for Metal Plate Connected Wood Truss Construction), it is the responsibility of the truss designer to provide required permanent individual truss member restraint location.
Bracing on the truss design drawing is denoted by the symbol “x in a box”. Truss design drawings show the bracing to be located on a side of the member needing bracing/restraint. The actual application of the bracing, whether on the top edge of the member or on the bottom edge of the member, is not important. What is critical is the specific location (i.e., midpoint of the web member) of the bracing/restraint and the number of rows. If the brace/restraint cannot physically be placed on the side of the member as the drawings show, then place it on the member at the same location except attach it to the opposite edge as shown below. [For all images, See PDF or View in Full Issue.]
In some instances, interior webs or end verticals are braced by attaching approved sheathing to their edge such as the collar tie of an attic truss. When this is done, it should no longer be required to attach continuous lateral bracing in addition to the sheathing to the same member as shown.
Truss top and bottom chord members shall be braced/restrained. If top and bottom chords are not sheathed, the truss design drawing shows the maximum unbraced length of the chords. Please note web-to-chord and chord-to-chord connections are always considered braced at those connections due to the continuous lateral bracing of the chords, web-to-web connections aren’t considered braced without the addition of a joint brace. Joint braces are not always feasible and are sometimes overlooked in the field. Care should be taken when designing web-to-web connections to ensure that buckling potential of webs will be resisted appropriately. The image shows an example of this scenario.
For additional information, or if you have questions, please contact the MiTek Engineering department.