DESIGN OF LAMINATES 6-151 



P a = 0.5 x 1 = 0.5 (6.54a) 



C a = 15. ii5 from Fig. 6-46 



k 



15.1.5 



s 3 x 0.863 



0.86 x 10 6 

 0.86 x 10 6 



1 



11 = 5.99 



qcr 



= 5.99 x 0.86xl0 6 x 0.50 2 = 322 5 ps i < 10100 psi (Table 5-14) 



loo 



C. Plates Loaded Laterally 



The mathematical solution of flat plates with lateral loads is much more complex and 

 time consuming than for flat plates in edge compression. The problem is further complicated 

 because of deflection considerations. When the deflection of the plate is equal to or less 

 than one-half the thickness of the plate, the loads are assumed transmitted mainly by bending 

 stresses. When the deflection exceeds one-half the thickness of the plate, direct stresses 

 are developed and these stresses must then be considered. Consequently for plates with 

 large deflections the loads are carried by both direct stresses and flexural stresses and a 

 new approach to the problem is necessary. 



Therefore, to properly analyze plates under lateral loads, it is necessary that the 

 following criteria be specified: 



1 . Boundary Conditions 



a. Simply supported edges 



b. Clamped edges 



c. Combinations of above 



2. Loading Conditions 



a. Uniformly distributed load 



b. Concentrated loads 



c. Variable loads 



d. Edge moments 



e. Combinations of above 



3. Plate Material 



a. Isotropic 



b. Orthotropic 



4. Deflection Limitation 



a. Plates with small deflections equal to or 

 less than one-half the thickness. 



b. Plates with deflections greater than 

 one-half the thickness. 



March (18) has developed procedures by which plywood plates under uniform or concen- 

 trated loads may be analyzed. Since most fiberglass laminates are orthotropic the approach 

 established by March will be used but the results are subject to verification by future tests. 



