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.
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.
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.
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.
Truss – A pre-built component that functions as a structural support member. A truss employs one or more triangles in its construction.
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).