COLLAPSE OF TEXAS TOWER NO. 4 247 



Mr. EuTLEDGE. Yes, sir ; all of the towers were so subjected. 

 Mr. Kendall. Why was only a static force analysis made in de- 

 signing the towers ? 



STATIC rOECE ANALYSIS COMPARED TO DYNAMIC FORCE ANALYSIS IN 



DESIGN 



Mr. KuTLEDGE. Sir, the analysis was based on dynamic loading. 

 The forces acting on the tower were computed from dynamic forces 

 of waves and wind exerted on the tower, using the maximum combina- 

 tion of forces produced by the design wind and wave, which was the 

 design wave hitting two of the legs with maximum force, and with 

 a portion of that w^ave or another wave acting on the third leg with 

 a force corresponding to the position of the wave. 



These forces, which are dynamic forces, were translated into stresses 

 in the structure on the basis of static analysis for an instantaneous 

 condition of the dynamic force. 



Mr. Kendall. Are you saying now that you made a dynamic force 

 analysis, as well as a static force analysis ? 



Mr. Kutledge. The term "dynamic force analysis," I believe, is 

 somewhat misleading. We computed the spring constants and the 

 natural frequencies of these towers to compare them with the fre- 

 quency of application of wave forces. But I am not sure of what you 

 mean by a dynamic force analysis. 



Mr. Kendall. Well, state for the record what the difference is be- 

 tween a dynamic force analysis and a static force analysis, basically. 



Mr. Kutledge. I still am not clear. We use dynamics to get the 

 loads, the forces acting on the structure. From there on one has to 

 compute the stresses on the basis of a static analysis. The dynamics 

 is to compute the natural frequency of the structure. 



Mr. Kendall. I believe, Mr. Brewer, in testifying before the com- 

 mittee, if I understood him correctly, testified that waves of 10 to 12 

 feet in height caused a greater stress than waves of 30 feet in height. 

 I believe he so stated in his report. 



Isn't that an example of why dynamic forces should have been 

 calculated ? 



Mr. Kutledge. The condition that Mr. Brewer was describing in 

 his report was for small waves that create very small stresses, where 

 the wave length is equal to the distance from one pair of legs to the 

 third leg, so that the crest of the wave hits — the crest of two waves 

 hit all three legs at the same time. 



This condition creates stresses which are far below the stresses 

 that are used for the actual design analyses, because the waves are 

 smaller. 



He is comparing this condition of 10- to 12-foot waves with 28-foot 

 waves, or 30-foot waves. But our design analyses were for 60-foot 

 waves of this type, or for 35-foot breaking waves. 



Senator Saltonstall. What was that last statement again, please? 



Mr. Kutledge. His comparison is for 10- to 12-foot waves versus 28- 

 to 30-foot waves, from his measurement. His stresses, then, are in 

 the order of 2,000 to 2,500 pounds per square inch. Our design 

 analyses are based on 60-foot greenwater waves, or 35-foot breaking 

 waves, which create stresses in the order of 20,000 pounds per square 



