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General Description
Section 1
1-50
1.11 Cable Members
STAAD supports 2 types of analysis for cable members - linear
and non-linear.
1.11.1 Linearized Cable Members
Cable members may be specified by using the MEMBER CABLE
command. While specifying cable members, the initial tension in
the cable must be provided. The following paragraph explains how
cable stiffness is calculated.
See
s
ection 5.23,
5.37 &
1.18.2.5
The increase in length of a loaded cable is a combination of two
effects. The first component is the elastic stretch, and is governed
by the familiar spring relationship:
F
EA
L
==Kx where K
elastic
The second component of the lengthening is due to a change in
geometry (as a cable is pulled taut, sag is reduced). This
relationship can be described by
F
T
wL
=Kx but here K
sag
12
3
23
=
( 1.0 / cos
2
α )
where w = weight per unit length of cable
T = tension in cable
α = angle that the axis of the cable makes with a
horizontal plane (= 0, cable is horizontal; = 90,
cable is vertical).
Therefore, the "stiffness" of a cable depends on the initial installed
tension (or sag). These two effects may be combined as follows