RESEARCH TOPIC.

Bracing Tytpes of bracings to use:

• Long span trusses are braced securely at the end of the building. Shorter trusses can be
  supported laterally by a single gable end brace. The ground braces should be located directly in
  line with all rows of top chord continuous lateral bracing, otherwise the top chord of the first truss
  can bend sideways and allow the trusses to shift, putting a substantial strain on all connections
  of the bracing system. Scabs should not be nailed to the end of the building to brace the first
  truss. These scabs can break off or pull out, thus allowing a total collapse.
  Cross-bracing subsequent trusses to prevent buckling
  As trusses are continuously set in place, sufficient temporary bracing is applied to hold the trusses plumb, in alignment and secure untill permanent bracing, decking and/or sheathing can be installed. Temporary bracing should not be less than 38 × 89 mm lumber and should be as long as possible. The use of short spacer pieces of lumber between adjacent trusses is not considered a means of bracing. Temporary bracing should be nailed with two 3-1/2" double headed nails at every intersection with the braced members. The practice of removing bracing to adjust spacing of trusses as sheathing is applied can cause trusses to topple if a key connection is removed at the wrong time. Therefore, exact spacing of trusses should be maintained as temporary bracing is applied. Cross bracing should be installed as soon as the first few trusses are in place, in the vertical plane, between trusses, together with continuous lateral braces fastened to the top and bottom chords to prevent the trusses from toppling.
   Temporary bracing of top-chord plane
  Truss top chords are very susceptible to lateral buckling before they are braced or sheathed.
  Continuous lateral bracing should be installed within 150 mm of the ridge line or centre line and at
  approximately 2.4 to 3 m intervals between the ridge line of sloped trusses or centre line of flat
  trusses and the eaves. Diagonals, set at 45° between the lateral bracing, form the required
  stability of the top chord. On longer span trusses, lateral bracing and diagonals may require
  closer spacing. If possible the continuous lateral bracing should be located on the underside of
  the top chord so that it does not have to be removed as sheathing is applied. This will ensure that
  the trusses are held securely during installation of the decking. Bracing lumber should be no less
  than 38 × 89 mm by 3.05 m long.
  Temporary bracing of web member plane
  Temporary bracing of the web member plane is usually installed at the same location specified on
  the engineering plan for permanent bracing. Permanent lateral web bracing should be called out
  on the truss design to reduce the buckling length of the individual web members. The bracing can
  form part of the temporary and permanent web bracing system. Sets of diagonal bracing should
  not be spaced more than 6 m apart (clear space between end of one set of braces and start of
  another set).
   Temporary bracing of bottom chord plane
  To hold the proper spacing of the bottom chord, continuous lateral bracing at no greater than 2.4
  to 3 m on centre along truss length is used for the full length of the building, secured to the
  bottom chord. Diagonal bracing at 45° between laterals will stabilize this bracing system. The
  bracing is usually left in place to become part of the permanent bracing system. Once the
  temporary bracing is properly installed, permanent bracing and decking can be installed.
  Concentrated loads from sheathing or roofing material should not be placed on trusses. These
  loads should be spread evenly over a large area to prevent overloading of any one truss. A limit of
  eight sheets of plywood should be placed on any pair of trusses and should be located adjacent
  to the supports.
   Permanent bracing of top chord plane (large buildings)
  If plywood floor or roof sheathing is properly applied with staggered joints and adequate nailing,
  a continuous diaphragm action is developed to resist lateral movement at the top chord, and
  additional bracing in the plane is generally not required. Some metal roofing materials may act as
  a diaphragm when properly lapped and nailed, but selection and use of these materials is at the
  discretion of the building designer. If purlins are used, spaced not to exceed the buckling length at
  the top chord, diagonal bracing should be applied to the underside of the top chord to prevent
  lateral shifting of the purlins. The diagonal bracing should be installed on both sides of the ridge
  line in all end bays. If the building exceeds 18 m in length, this bracing should be repeated at intervals not exceeding 6 m.
   Permanent lateral bracing to web member or bottom chord plane (all buildings)
  
  Permanent bracing in web and bottom chord planes is usually applied as temporary bracing
  (Steps 4 and 5). Lateral bracing of compression web members is a typical method to prevent
  buckling. The method used to anchor the lateral bracing must be specified by the designer.
  Bottom chord bracing helps to maintain truss spacing, also can resist buckling caused by stress
  reversal. Multiple-bearing or cantilevered trusses can result in compressive forces in bottom chords.