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ALLOWABLE UNIT
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. AXIAL FORCE – A push (compression) or
pull (tension) acting along the length of a member. Usually measured in pounds.
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.
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 right of the point, times their corresponding
distances from the point. Usually measured in inch-pounds.
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. |
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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 – Additional loading centered at a given point. An example is a crane
or hoist hanging from the bottom chord at a panel point.
DEAD LOAD – Any permanent
load such as the weight of the member itself, purlin, sheathing, roofing, ceiling, etc.
DEFLECTION – Downward
vertical movement of a truss due to dead and live loads.
LIVE LOAD – Any loading which
is not of a permanent nature such as snow, wind, movable concentrated loads, furniture,
etc.
REACTION – Forces acting on a
truss through its supports that are equal but opposite to the sum of the dead and live
load thereby holding the truss in a stable position.
STRESS DIAGRAM – Graphical
solution of axial forces as they interact within the members of a truss. |
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