with the nodes at either end of the plate; instead, the entire mass of each plate is accounted 

 for as a lumped mass located at a point midway between the ends of the plate. 



To take advantage of symmetry (if it exists) of the cross section about the y-axis, the 

 next step is to double the terms: 



S M; S MY; S MY^; 2 MZ^ 

 and to set to zero the terms: 



2MZ; 2 MYZ 



In either case (symmetry or nonsymmetry), the final step is the use of the following 

 equations to determine the mass, the location of the center of gravity, and the moments of 

 inertia about the center of gravity: 



MASS = SM 



Y-CG = SMY-rS M 



Z-CG = SMZ -rS M 



I-YY = SMY2 -(Y-CG)2 SM 



I-YZ = SMYZ - (Y-CG) (Z-CG) SM 



I-ZZ = SMZ2 -(Z-CG)2 IM 



I-MX =(I-YY) + (I-ZZ) 



The final term represents the polar moment of inertia of the weight of the section about a 

 longitudinal axis. 



Data required as input for the inertia calculations include items describing the por- 

 tions due to structural items (these are necessary for the flexibility calculations and need 

 not be duplicated) and the items describing the portions due to nonstructural members. The 

 following FORTRAN symbols are used for these latter terms: 



FORTRAN 



Symbol 



Symbol in 

 above equations 



FORTRAN 



Symbol 



Symbol in 

 above equations 



IW 



m 



WYZ 



yzm 



NW 



max. value of m 



WZZ 



K.m 



W 



M^ 



RHO 



P 



YW,ZW 



Vm' ^m 



AD 



Ci 



WYY 



I 



yym 



DX 



Ax 



For ether FORTRAN symbols refer to Table lb and to Figure 4b. 



It is, of course, necessary that these inputs be in consistent units. For example, if 

 SCALE = 1.0 (no mixed units), the following may be used: 



80 



