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TRIANGULATION STATIONS, SIGNALS, AND INSTRUMENT SUPPORTS
Figure 15-19.Bipod target. - 14070_363

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure  15-18.—Tripod  targets. well  guyed  and  plumbed  (fig.  15-18),  and  the  legs should   be   set   in   depressions   to   prevent   lateral movement. On uneven ground one leg may have to be shortened   or   dug   in   to   maintain   a   symmetrical appearance  from  all  directions.  Signal  cloth  wrapped around the tripod should be used only on low-order (fourth-order) work as it is almost impossible to make it symmetrical around the station. BIPOD  TARGET.—  Bipod  targets  are  more simply constructed than tripods but are less stable and must  be  strongly  guyed.  Figure  15-19  shows  a  standard surveying biped target. It is carried disassembled in a canvas case about 53 inches long. It can be assembled, erected, and plumbed by two men in 15 minutes. If this target must be left standing in the weather for any extended period, the rope guys should be replaced with wire and two more wire guys added to each end of the crossbar.  In  soft  ground  the  pointed  legs  will  sink unevenly because of wind action and rain; therefore, they should be set in holes bored in the end of wooden stakes driven flush or in a short piece of 2-inch by 4-inch lumber laid flat in a shallow hole. POLE TARGETS.— Pole targets  (fig.  15-20)  are seldom used because the station cannot be occupied while the target is in place. In certain cases, as when an unoccupied  station  must  be  sighted  and  cutting  of  lines of sight is difficult or impossible, a pole target that can be  seen  above  the  trees  maybe  erected  The  staff  may be constructed of 2-inch by 2-inch lumber or cut poles, varying from about 2 inches to 6 inches in diameter. The method  of  joining  sections  of  2-inch  by  2-inch  lumber and the construction of a panel target are shown in figure 15-20. The targets must be plumbed by manipulation of the guy wires. Special care must be taken when warped or crooked boards are used to construct pole targets, and they must be checked for eccentricity. 15-28







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