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Truss Terminology

To assist you in understanding the technical terms used in the truss industry, we have compiled the following descriptions and illustrations that may come in handy:

A:


  • Apex - The highest point on a truss.

B:


  • Barge - Trim along the edge of roofing at a gable end. Slopes at the roof pitch
  • Batten - Roofing battens or ceiling battens. Usually timber members fixed at right angles to the truss chords to support roof tiles or ceiling material. Also provides lateral restraint to the truss.
  • Bearing/Support point - Point at which the truss is supported. A truss must have two or more supports located at truss panel points.
  • Bottom Chord - Truss member forming the bottom edge of a truss.

C:


  • Camber - Vertical displacement built into a truss to compensate for the downward movement expected when the truss is fully loaded.
  • Cantilever - That part of a truss that projects beyond an external main support, not including top chord extensions or overhangs
  • Chord - The truss members forming the top and bottom edges of the truss.
  • Clear Span - Horizontal distance between inner edges of supports.
  • Concentrated Load - A load applied at a specific position. eg. load applied by an intersecting truss.
  • Connector (or Connector plate) - Light gauge steel plate with teeth projecting from one face. When pressed into intersecting timber members the plate connects the members in a rigid joint.
  • Creep - Movement resulting from long term application of load to a timber member.

D:


  • Dead Load - Permanent loads due to the weight of materials and truss self weight.
  • Deflection - Vertical and horizontal movement in a truss due to the applied load.
  • Design Loads - The various loads that a truss is designed to support.
  • Distributed Load - Loads spread evenly along truss member.

F:


  • Fascia - Trim along the edge of the eaves.

G:


  • Gable Truss - Standard triangular shaped truss.
  • Girder Truss - Truss designed to support one or more trusses.

H:


  • Heel Joint - The joint on a truss where the top and bottom chords meet.
  • Heel Point - The position on a truss where the bottom edge of the bottom chord meets the top chord.  Used for setting up production jigs.
  • Hip - Intersection of two roof surfaces over an external corner of a building.
  • Hip Roof - Roof constructed with rafters or trusses pitched over all perimeter walls.

K:


  • King Post - Vertical web at the centre of a gable truss, or the vertical web at the end of a half gable truss.

L:


  • Lateral Brace - Bracing restraint applied at right angles to web or chord to prevent buckling.
  • Longitudinal Tie - Bracing restraint applied at right angles to web or chord to prevent buckling.
  • Live Load - Temporary load due to traffic, construction, maintenance, etc.

O:


  • Overall Length - Length of truss excluding overhangs.
  • Overhang - Extension of top chord beyond support.  Provision of eaves on gable trusses.

N:


  • Nominal Span - The horizontal distance between supports of a truss.

P:


  • Panel-point - The point where several truss members meet to form a joint.
  • Panel-point Splice - Splice joint in a chord coinciding with web intersection.
  • Pitch - Angular slope of truss chord measured in degrees.
  • Purlin - Roofing purlins.  Usually timber members fixed at right angles to the truss chords t support roof sheeting.  Also provides lateral restraint to truss.  Similar to battens except more widely spaced.

R:


  • Rafter - A roof members supporting roofing battens or roofing purlins in conventional construction.  Rafters employ only the bending strength of the timber.  A roof truss may also be called a trussed rafter.
  • Ridge - The highest point on a gable roof.

S:


  • Span - The horizontal distance between the outer edges of the truss supports.
  • Span Carried - The span of standard trusses that are supported by a girder truss.
  • Stress Grade - Strength classification of timber.  Based on species, seasoning and frequency of defects such as knots and sloping grain.  Alternatively based on actual mechanical testing of each piece.
  • Station - The position of a truss measured from the outside face of the end wall.  Usually used to describe the position of truncated Girder and Standard trusses in a Hip End.

T:


  • Top Chord - Truss member forming to edge of truss.
  • Truss - Trussed rafter.  Triangulated, self supporting framework of chords and webs that supports applied loads by a combination of the bending strength of the chords and the axial compressive and tensile strength of the chords and webs.

V:


  • Valley - Intersection to two roof surfaces over an internal corner of a building.
  • Verge - Roof overhang at a gable end.
  • Verge Rafter - Rafter projecting from gable end to support verge.

W:


  • Waling Plate - Timber member bolted to the face of a truss to support intersecting rafters or trusses.  May also be used to support intersecting battens or purlins.
  • Web - The internal members of a truss.  Usually only subject to axial loads due to truss action.
  • Wind Load - Load applied to the roof by the wind.
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