Optimal Ratios of Cuttinq Edae Length to Anchor Width 



Purpose . The nrevious section addressed increasina the lateral load 

 canacitv of a deadweight by increasinn the cuttinq edqe lenqth. Cuttinn 

 edoe lengths are limited in practice; however, by two factors. One of 

 these factors, aqqravation of the overturning nroblem was treated earlier. 

 The other, implementation of cutting edqe penetration, piaces' 

 efficiencv/cost limitations on the cuttinq edqe lenqths and section thick- 

 nesses. Lenatheninq the cuttinq edqes increases the lateral load and the 

 effective moment arm actinq to bend the cutting edge at its noint of 

 attachment to the anchor base (see Fioure 41). To develop the increased 

 bendinq moment and shear capacity in the cutting edqe, the structural 

 section must be increased (thickened). The cuttinq edqe of qreater 

 thickness and length reouires a qreater force, obtained from the HeaH- 

 weiqht submerged weiaht, to accomplish complete embedment. The increased 

 costs of the greater structural section in the lonqer cuttinq edqe and 

 the increased costs for materials, construction, and handling of the 

 heavier deadweiqht both imoose an upper limit on the practical lenqth of 

 cuttino edge to be used. 



This report section approaches the subject of optimal Z/R ratios 

 from an idealized standpoint. It assumes that minimum cost is directly 

 related to the minimum deadweight mass reauired to embed a cutting edqe 

 design sufficient to resist the desion lateral load. Clarification of 

 this statement is left to the discussion of results for this section. 



Structural Design of Cuttinq Edges . 



1. Procedure . The cutting edges were desiqned to resist the 

 pressure of a passive wedge as the cuttinq edge is moved laterally without 

 rotation. The pressure distribution on the cutting edge wall was assumed 

 triannular. Then the force resultant acting on the wall could be taken 

 to operate at the two-thirds point (see Figure 41). The force ner unit 

 width of anchor block R D ^ was obtained from the earlier presented passive 

 wedqe data. The force times the moment arm yields the bendinq moment to 

 be resisted at the juncture of cuttinq edge and deadweiqht block: 



M ] = R ] (2/3 Z) (18) 



P n 



This analysis is conservative, but justified because it is simple. The 

 analysis is conservative because the cuttinq edges would normally be 

 arranged in a qrid pattern beneath the deadweiqht and would interact. 

 Those cutting edqes oriented parallel to the mooring line direction would 

 act as shear walls assisting in transferring the mooring load to the 

 perpendicular oriented set of cutting edges and thereby reducing the 

 bending moment in that perpendicular set. 



83 

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