Deadman Holdfast

A DEADMAN provides the best form of anchorage for heavy loads. It consists of a log, a steel beam, a steel pipe, or a similar object buried in the ground with the guy connected to it at its center. (See fig. 6-5.) Because it is buried, the deadman is suitable for use as a permanent anchorage. When installing a permanent deadman anchorage, you should put a turnbuckle in the guy near the ground to permit slackening or tightening the guy when necessary.

In digging the hole in which to bury the deadman, make sure it is deep enough for good bearing on solid ground. The less earth you disturb in digging, the better the bearing surface will be. As shown in figure 6-5, you should undercut the bank in the direction toward the guy at an angle of about 15 from the vertical. To increase the bearing surface, drive stakes into the bank at several points over the deadman.

A narrow, inclined trench for the guy has to be cut through the bank and should lead to the center of the deadman. At the outlet of the trench, place a short beam or log on the ground under the guy (fig. 6-5). In securing the guy to the center of the deadman, see that the standing part (the part on which the pull occurs) leads from the bottom of the log deadman. Thus, if the wire rope clips slip under strain, the standing part will rotate the log in a counterclockwise direction, causing the log to dig into the trench rather than roll up

Figure 6-5.\Log deadman.

and out. See that the running end of the guy is secured properly to the standing part.

Steel-Picket Holdfast

The STEEL-PICKET holdfast shown in figure 6-6 consists of steel box plates with nine holes drilled through each and a steel eye welded on the end for attaching the guy. When installing this holdfast, it is important that you drive steel pickets through the holes in such a manner that will cause them to clinch in the ground. You will find the steel-picket holdfast especially useful for anchoring horizontal lines, such as the anchor cable on a pontoon bridge. The use of two or more of the units in combination will provide a stronger anchorage than a single unit.

Figure 6-4.\Rock holdfast.

Figure 6-6.\Steel-picket holdfast.

GIN POLE

The GIN POLE is a rig constructed from a single pole, square timber, or steel beam. It stands almost vertically and is supported by guys. Loads of medium weight can be lifted from 10 to 50 feet (3 to 16 meters) by a block and tackle supported on the gin pole. The hauling part of the tackle leads through a snatch block at the base of the pole to the source of power.

The timber gin pole should not be longer than 60 times its minimum thickness because of the tendency to buckle under compression. If the pole is too short and you have to splice two together, place the sections so that the end of one touches the end of the other. This is called BUTT SPLICING. Join the sections together by bolting wooden scabs or metal plates onto them. Sometimes large spikes are used to fasten the wooden scabs. When there is a tendency on the part of a spliced pole to buckle, fasten an additional set of guys at the splice.

Guy lines, incidentally, may be either wire rope or fiber line, although wire rope is usually preferred because of its strength and resistance to corrosion and weathering. Generally, four guys are considered a minimum with 90 angles between guys. If the pole or spar supported by the guys is long and slender, it may be advisable to provide support at several points on the pole in a tiered effect.

Guy lines should be anchored a considerable distance from the base of the gin pole. The recommended minimum distance from the base of the gin pole to the anchorage of the guy line is twice the height of the pole.

The angle of the pole is especially important in the matter of stress. For instance, if the pole is vertical, the stress on each after guy is practically zero. But, when the angle between the guy and the ground is 45, the stress on each guy is almost one half of the total load. That is why you have to use a guy that will stand stress of at least one half of the load.

The weakest point in the gin pole assembly is most likely to be the after guy. If you study figure 6-7, you will see that as the gin pole is slacked outward, distance (b) becomes less and distance (a) becomes greater. After the pole has reached a certain angle, (a) becomes greater than (b), and from then on, the guy has a strain on it greater than the weight. This increases so rapidly as the pole approaches the horizontal that the amount of strain is theoretically almost infinite when the pole is lying nearly flat. Obviously, then,

Figure 6-7.\Stress on after guy and gin pole.

the nearer the gin pole is to the vertical, the less the stress on the after guy, and the pole cannot be lowered far off the perpendicular without setting up dangerous stresses.

The formula for finding the thrust on the pole itself is rather complicated and involves a value that is difficult to determine without the use of trigonometry. You can easily see that in the vertical position, the pole would be supporting a thrust equal to, but no greater than, the weight. As the pole is slacked outward, the thrust on it, like the stress on the guy, increases, reaching fantastic proportions when the pole gets beyond a certain angle.

About the best thing you can do, then, is to remember that a gin pole cannot be slacked to more than a few degrees off the vertical before it begins to take a heavy strain.