| Allowable
Stress Increase: A percentage increase in
the stress permitted in a member, based on the length of time that
the load causing the stress acts on the member. The shorter
the duration of the load, the higher the percent increase in
allowable stress.
Axial
Force: A push (compression) or pull (tension) acting
along the length of a member. Usually measured in pounds, kips
(1,000 lbs.) or tons (2,000 lbs.), or metric equivalent.
Axial
Stress: The axial force acting at a joint along the
length of a member divided by the cross-sectional area of the
member. Usually measured in pounds per square inch.
Bearing:
A structural support, usually a wall that occurs at the top
or bottom chord or between the end points of a roof or floor truss.
Bending
Moment: A measure of the bending effect on a member due
to forces acting perpendicular to the length of the
member. The bending moment at a given point along a
member equals the sum of all perpendicular forces, either to the
left or right of the point, times their corresponding distances from
the point.
Bending
Stress: The force per square inch of area acting at a
point along the length of a member, resulting from the bending
moment applied at that point. Usually measured in pounds per
square inch or metric equivalent.
Bottom
Chord: A horizontal or inclined (e.g. Scissors Truss)
member that establishes the lower edge of a truss, In a
conventional system, this is the ceiling joist.
Butt Cut:
Slight vertical cut at the outside edge of truss bottom
chord made to ensure uniform span and tight joints - usually 1/4
inch.
Camber:
An upward vertical displacement built into a truss bottom
chord to compensate for deflection due to dead load.
Cantilever:
Extension of the bottom chord beyond its support, exclusive
of overhang.
Check:
A lengthwise separation of wood fibers, usually extending
across the rings of annual growth, caused chiefly by strains
produced in seasoning.
Clear
Span: Horizontal distance between interior edges
of supports.
Combined
Stress: The combination of axial and bending
stresses acting on a member simultaneously, such as occurs in the
top chord (compression + bending) or bottom chord (tension +
bending) of a truss.
Concentrated
Load: Superimposed load centered at a given point
(e.g., roof-mounted air conditioner, furnace).
Connector
Plate: Pre-punched metal toothed connectors
located at the joints and splices of a truss and designed to hold
the forces which occur at those locations.
Cripple
Rafter: Infill rafter installed to continue the
roof line - fixed to valley board in valley construction.
Dead Load:
Any permanent load such as the weight of roofing, flooring,
sheathing, insulation or ceiling material, as well as the weight of
the truss itself.
Deflection:
Downward vertical movement of a truss (when in place) due to dead
and live loads.
Design
Loads: The dead and live loads which a truss is
engineered to support.
Engineer
Certified Drawing: A truss design where loading
requirements, lumber species, sizes, grades and connector plate
requirements are detailed and a certified engineer's seal is
affixed.
Girder
Truss: Usually a multiple-ply truss designed to carry
other trusses over an opening.
Heel: Point
on a truss at which the top and bottom chords intersect.
Heel Cut:
See Butt
Cut.
Jack
Rafter: Infill rafter installed to continue the
roof-line - fixed from wall plate to hip board in hip end
construction.
Joint:
See Panel
Point.
Lateral
Brace: A member placed and connected at
right angles to a chord or web member of a truss.
Level
Return: A lumber filler placed horizontally from
the end of an overhang to the outside wall to form a soffit.
Live Load:
Any loading which is not of a permanent nature (e.g., snow, wind).
Moisture
Content of Wood: The weight of the moisture
in wood expressed as a percentage of its ovendry weight.
Overall
Rise: Vertical distance from bottommost part of
the bottom chord to uppermost point on peak.
Overhang:
The extension of the top chord of a truss beyond the heel, measured
horizontally.
Panel:
The chord segment defined by two adjacent joints.
Panel
Length: The centerline distance between joints
measured horizontally.
Panel
Point: The point where a web or webs intersect a
chord.
Peak:
Point on truss where the sloped top chords meet.
Pitch:
Inches of vertical rise for each 12 inches of horizontal run.
Plumb Cut:
Top chord end cut to provide for vertical (plumb) installation to
fascia (face trim board).
Plumb
Rise: Vertical overall measurements at the end of
a truss where the top and bottom chords meet.
Purlin:
A horizontal member attached to and placed perpendicular to the
truss top chord to support the roofing.
Reaction:
Forces acting on a truss, through its support, that are equal but
opposite to the sum of the dead and live loads.
Ridge:
Line formed by truss apexes.
Rise:
Vertical distance from bottommost part of the bottom chord to inside
of the peak.
Scab:
Additional timber connected to a truss to effect a splice, extension
or general reinforcement.
Shop
Drawing: Detailed drawings of a roof truss or
roof framing showing critical dimensions such as span,
overhang,
cantilever,
slope,
etc.
Slope:
See Pitch.
Spacing:
Centerline distance between trusses - usually 24" O.C. (on
center).
Span:
Horizontal distance between outside edges of the supports.
Splice
Point: (Top & Bottom chord splice). The
point at which two chord members are joined together to form a
single member. It may occur at a panel point or between
panel points.
Square
Cut: End of top chord cut perpendicular to slope
of the member.
Symmetrical
Truss: Truss with the same configuration of
members and design loading occurring on each side of truss
centerline.
Top Chord:
An inclined or horizontal member that establishes the upper edge of
a truss - rafter in conventional frame.
Truss:
A pre-built component that functions as a structural support
member. A truss employs one or more triangles in its
construction.
Truss-Clip:
Metal component designed to provide structural connection of trusses
to wall plates to resist wind uplift forces.
Webs:
Members that join the top and bottom chords to form the triangular
patterns that give the truss strength.
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U.S.
Components, LLC Truss Terms