often characterized by the maximum or mldspan sag s, the support reaction forces, the natural frequen- 

 cies, and the mode shapes with respect to the equilibrium position. It should be noted that the SLAK 

 code is three-dimensional and permits applied loads in the z-direction and computes the out-of-plane or 

 sway modes of the cable. Additional information concerning the code itself, the numerical method, 

 and the required input data is available from NRL. 



B.5. Inclined Slack Cable Comparisons. This section compares numerical, theoretical, and experi- 

 mental results for inclined slack cables. The purposes of the comparisons are twofold. First, an 

 attempt is made to account for some discrepancies between the experimental data and the theoretical 

 predictions at moderate sag-to-span ratios. Second, and more important, the extension of the linear 

 theory to inclined slack cables (B7) is tested against the finite element code calculations so that 

 engineering limits for the simple extension can be determined. The slack cable problem is defined in 

 the preceding pages where descriptions of the theory and the finite element code are given. This sec- 

 tion deals only with comparisons and with an analysis of the results. 



The discrepancy just mentioned is illustrated in Fig. B6. For sag-to-span rations s/l greater than 

 0.02 the experimental data no longer follow the theoretical prediction. Earlier attempts to identify the 

 mode shape (s) in these instances were frustrated by the complex construction of the DAS cable speci- 

 men near its ends. It is in these segments of the cable that additional loops in the mode shape are 

 known to form during and after the "modal cross-over". The complex construction can also directly 

 influence the dynamics by abrupt changes in the mass per unit length, by abrupt changes in the cable 

 stiffness and by a number of lesser effects. Neither the theory nor the finite-element code provides for 

 cable stiffness and it was felt that this might be the largest source of error because of the relatively large 

 amount of local curvature required by the forming loops as compared to the significant stiffness of the 

 cable segment and of its aluminum terminations. 



An important feature of the simplified inclined cable analysis is that all frequencies should col- 

 lapse onto a single curve if the span and the sag are measured in the appropriate inclined coordinates 



130 



