Glossary

Axial Force - A push (compression) or pull (tension) acting along the length of a member.  Usually measured in pounds (lbs).

Axial Stress - The axial force acting along the length of a member, divided by the cross-sectional area of the member. Usually measured in pounds per square inch (psi).

Bearing - Structural support of a truss, usually walls, hangers or post.

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 the given point along a member equals the sum of all perpendicular forces, either to the left or the right of the point, times their corresponding distances from the point. Usually measured in inch-pounds.

Bending Stress - The force per square inch acting at a point along the length of of a member, resulting from the bending moment applied at that point. Usually measured in pounds per square inch (psi).

Bottom Chord -   A horizontal or inclined (scissors truss) member that establishes the lower edge of a truss, usually carrying combined tension and bending stresses.

Built-Up Beam - A single unit composed of two or more wood members having the same thickness but not necessarily the same depth, which provides a greater load carrying capacity as well as greater resistance to deflection.

Butt-Cut - Slight vertical cut at outside end truss bottom chord made to insure uniform nominal span and tight joints.

Usually 1/4 inch.

Camber - An upward vertical displacement built into a truss to offset deflection due to dead load.

Cantilever -The part of a structural member that extends beyond its support.           To see the picture click here.

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 - An additional load centered at a given point. An example is a crane or hoist hanging from the bottom at a panel point or mechanical equipment supported by the top chord.

Dead Load - Permanent loads that are constantly  on the truss, ie: the weight of the truss itself, purlins, sheathing, roofing, ceiling, ect.

Deflection - Downward or horizontal displacement of of a truss due to loads.

Diaphragm - A large, thin structural element that acts as a horizontal beam to resist lateral forces on a building.

Drag Strut - Typically a horizontal member, such as a truss or beam, that transfers shear from a diaphragm to a shear wall.

Duration Of Load Factor - An adjustment in the allowable stress in a wood member, based on the duration of the load causing the stress . The shorter the time duration of the load, the higher the percentage increase in allowable stress.

Heel - Point on a truss at which the top and bottom chord intersect at the end of a truss with a sloping top chord.

Lateral Bracing - A member installed and connected at right angles to a chord or web member of a truss to resist lateral movement.

Level Return - Lumber filler placed horizontally from the end of an overhang to the outside wall to form soffit framing.

Live Load - Any load which is not of permanent nature, such as snow, wind, seismic, movable concentrated loads, furniture, ect. Live loads are generally of short duration.

Nominal Span - Horizontal distance between outside edges of the Outermost Supports.

Overhang - The extension of the top chord (usually) or bottom chord of a truss beyond the support.   Click here to see an overhang

Panel - The chord segment defined by two successive joints.

Panel Length - The centerline distance between joints measured along the chord.

Panel Point - The centerline of the point of intersection in a joint where a web(s) meets a chord.

Peak - Point on a truss where the sloped top chords meet.

Plumb Cut - Top chord cut that is plumb to the building foor line provided for vertical installation of a fascia.

Purlin - A horizontal member in a roof perpendicular to the truss top chord used to support the decking.

Reaction - Forces acting on a truss through its supports that are equal but opposite to the sum of the dead and live loads,

Shearwall - A wall element that acts as a large vertical beam, cantilevered from the foundation to resist lateral forces on the building.

Slope (Pitch) - The inches of vertical rise in 12 inches of horizontal run for inclined members, generally expressed as 3/12, 4/12 etc.

Span - Length of bottom chord including cantilevers

Splice Point (Top or Bottom Chord Splice) - The point at which two chord members are joined together to form a single member.

Square Cut - A cut perpendicular to the slope of the member at its end.

Top Chord - An inclined or horizontal member that establishes the upper edge of a truss, usually carrying combined compression and bending stresses.

Truss - A pre-built component that functions as a structural support member. A truss employs one or more triangles in its construction. Click Here to see the main types.

Vibration - The term associated with the serviceability of a floor. If the occupant feels the (loot respond to walking or other input, it may be referred to as vibration or response to load.

Webs - Members that join the top and bottom chords to form the triangular patterns that give truss action, usually carrying tension or compression stresses (no bending).

TrussTek, INC. 64679 Highway 2 Bonners Ferry, ID 83805 (208) 267 7471