Page 20 - Pipeline Rules of Thumb Handbook

General Information 7

Stress in guy wires

Guys are wire ropes or strands used to hold a vertical approximated by measuring the deflection at the center of
structure in position against an overturning force. The most the span from the chord drawn from the guy anchorage to
common types of guyed structures are stacks, derricks, masts the point of support on the structure. A good average figure
for draglines, reversible tramways and radio transmission to use for erection tension of guys is 20% of the maximum
towers. working tension of the guy.
As a general rule, stresses in guys from temperature This discussion outlines the method for determining
changes are neglected, but in structures such as radio masts the stresses in guys. One of the first considerations is the
this is an important feature and must be subject to special location of the guy anchorages. The anchorages should be
analysis. so located that the angle a, between the horizontal plane
The number of guys used for any particular installation and the guy line, is the same for all guys (to equalize erec-
is contingent on several variable factors such as type of struc- tion tensions). Angle a, in good practice, seldom exceeds
ture, space available, contour of the ground, etc., and is not 45 degrees with 30 degrees being commonly used. The
a part of this discussion. tension in the guys decreases as angle a becomes less. The
It is desirable to space guys uniformly whenever possible. direct load on the structure is also less with smaller value of
This equalizes the pull, P, on each guy insofar as possible, a.
particularly against forces which change in direction, as when To find the maximum extra tension, T, that will be applied
a derrick boom swings in its circle. to any single guy by the force, F; first, determine the pull, P,
It is also desirable to equalize the erection tensions on the which is the amount required along the guys, in the same ver-
guys. When no external force is acting on the structure, the tical plane as the force to resist the horizontal component of
tension in each guy should be the same. A “Tension Indica- the force. This pull is entirely independent of the number of
tor” is sometimes used to determine the tension in guys. If guys. Assume that the following are known:
this instrument is not available, the tension can be very closely

Figure 1