Glossary of Terms

 
 

AXIAL FORCE

A push (compression) or pull (tension) acting along the length of a member. Usually measured in pound, kips (1000 lb), tons (2,000 lb) or the metric equivalents.

 

AXIAL STRESS

The axial force acting at a point along the length of a member, divided by the cross sectional area of the member (usually measured in pounds per square inch).

 

BEAM POCKET

A void deliberately set into the top of a wall to allow a beam or floor truss to bear on the wall.

 

BEARING

A structural support, usually a wall, that occurs at the top or bottom chord or between the end points of 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, whether 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, usually carrying combined tension and bending stresses.

 

BUILDING COMPNENT

A preassembled part usually fabricated in a manufacturing plant for use in the construction of a building.

 

BUILT-UP BEAM

A single member composed of two wood members having the same thickness but not necessarily the same depth, which provides greater load carrying capability as well as lower deflection, e.g., garage door, stairwell and fireplace headers.

 

BUTT CUT

Slight vertical cut at outside edge of truss bottom chord made to insure uniform nominal span and tight joints. Usually ¼ inch.

 

 CAMBER

An upward vertical displacement built into a truss bottom chord to compensate for deflection due to dead load.

 

CANT

Slight pitch on flat trusses

 

CANTILEVER

The part of the truss that extends beyond its support, exclusive of overhang.

 

CENTER BEARING

Truss with structural support at center of truss span as well as at the heel points.

 

CHASE OPENING

An open panel in a floor truss for the purpose of running utilities through it, such as heating and air conditioning ducts.

 

CLEAR SPAN

Horizontal distance between interior edges of supports.

 

COMBINED STRESS

The combination of axial and bending stress acting on a member simultaneously, such as occurs in the top chord (compression and bending) or bottom chord (tension and bending) of a truss.

 

CONCENTRATED LOAD

Superimposed load centered at a given point, e.g., roof mounted air conditioners.

 

DEAD LOAD

Any permanent load such as the weight of the truss itself, purlins, sheathing, roofing and ceiling.

 

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 designed to support.

 

DUAL PITCH TRUSS

A truss that has two different pitches on its top chord.

 

DURATION OF LOAD 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 the allowable stress.

 

FASCIA

Trim board applied to ends overhang.

 

HEEL

Point on truss at which the top and bottom chords intersect.

 

HEEL CUT

See Butt Cut.

 

LATERAL RESTRAINT

A structural member (typically lumber or metal) installed at right angles to a chord or web member of a truss to reduce the laterally unsupported length of the truss member.  The Lateral Restraint must be properly braced to prevent lateral deformation and/or buckling of the truss member to which it is attached due to laterally imposed loads on, and/or the accumulation of buckling forces within, the truss member, respectively.

 

LET TAILS RUN<:p>

Top chord not cut off to specific overhang length but extended to maximum length provided by lumber used in top chord.
 

LEVEL RETURN

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, such as snow, wind and temporary construction loads.

 

NOMINAL SPAN

Horizontal distance between outside edges of the supports.

 

OVERALL TRUSS HEIGHT

Vertical distance from bottom-most part of the truss to upper-most point of the peak.

 

OVERHANG

The extension of the top chord of a truss beyond the bearing support.

                                                                                                           

OVER SPAN

See Cantilever.

 

PANEL

The chord segment defined by two adjacent joints.

 

PANEL LENGTH

The center line distance between joints measured along the chords.

 

PANEL POINT

The point of intersection where a web (or webs) meet a chord.

 

PEAK

Point on truss where the sloped top chords meet.
 

PITCH

Inches of vertical rise for each twelve inches of horizontal run.

 

PLUMB CUT
Top chord end cut to provide for vertical (plumb) installation of fascia.

 

PURLIN

A horizontal member attached to and placed perpendicular to the truss top chord for supporting the roofing: i.e., corrugated roofing or plywood and shingles.

 

QUARTER POINT

Point on triangular, Fink, Howe truss where the webs connect to the top chord.

 

REACTION

Forces acting on a truss through its support that are equal but opposite to the sum of the dead and live loads.

 

SEALED BUILDING DRAWINGS

Drawings prepared, checked, and/or approved by and having the seal of a registered professional architect or engineer.

 

SHORT TERM INCREASE

Increase allowed for design loads of short duration

 

SHORT TERM LOADING

Live loads of a short duration, such as wind and snow loads.

 

SLOPE

See Pitch.


SPLICE POINT
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.

 

SPLIT TRUSS
Trusses used where fireplace intersects the truss span, parallel or perpendicular to the truss in the middle or inside of the house. A split truss can be defined also as a stub truss if it is longer than one-half the span or as a monopitch truss if less than one-half the span.

 

SQUARE CUT

End of top chord cut perpendicular to the slope of member.

 

SYMMETERICAL TRUSS

Truss with the same configuration of member occurring on each side of truss centerline.

 

THIRD POINT
Point on triangular, Fink truss where the webs connect to the bottom chord.

 

TOP  CHORD

An inclined or horizontal member that establishes the upper edge of a truss.

 

TRUSS
An engineered, pre-built structural component, assembled from wood members and metal connector plates, and designed to carry superimposed dead and live loads. The truss members form a rigid, plane, structural component and are usually assembled such that the members form triangles.

 

WEBS
Members that join the top and bottom chords to form the triangular patterns that give truss action, usually carrying tension or compression stresses.

 

WEDGE RETURN
See Level Return.

 

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Phone: (813) 972-1135

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6904 Parke East Blvd Tampa Florida 33610
Phone: 813-972-1135  Fax: 813-971-6117  Email: TPA-Information@mii.com