Harmon L. Roberts Urban Systems Project Office IV.-D-l-b. RECTENNA - STRUCTURAL SUPPORT AND GROUND PREPARATION The support structure for the rectenna concept defined in Section IV.D.(1)a. has been preliminarily designed for the purpose of estimating the materials required and costing the rectenna structure. The preliminary design selected is a very simple structural concept and no attempt has been made to optimize the structure as to concept, weight or cost. The basic concept used is to divide the rectenna into a number of equal sections normal to the beam. Using a rationale that any point in the rectenna could require maintenance during the life of the rectenna, the spacing between sections was set at 6.4m to allow entrance of maintenance vehicles. This width corresponds to a Houston, Texas location which requires a 36° elevation from the horizontal. With a spacing of 6.4m, the face width of the sections is 15m. After selecting the section face width, a loads criteria was determined. Again, these loads are selected without optimization. With the location selected as the Houston area, ice and snow loads were determined to be negligible and wind loads were set at 100 mph for winter and 130 mph for fall. Because of the high wind load, the dead load of the dipoles and structure is negligible. Using some rationalization of the load, the selected load used to size the structure is 31.6 1b/ft^ on the surface of the rectenna section. Allowable stresses used for the structural design are based on ASCE recommendations for aluminum and AISC specifications for structural steel. The structure concept shown in Figure IV.D.(l).b-l has been sized for the loads and allowable stresses discussed above. All members were sized using aluminum structural shapes and steel structural shapes. Concrete footings were placed at each support point as shown in Figure IV.D.(1) b.-l. The total weight for the concept is 0.62 million tons of aluminum or 1.38 million tons of steel and 1.289 million footings at 1.3 tons each. The cost of structural materials, construction labor and site preparation, based on 1975 cost indexes, for the rectenna is $125/kW for a 5 GW system using all aluminum structure and $155/kW using all steel structure. Other studies have indicated a cost range for this purpose from $100/kW to $490/kW.
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