COLLAPSE OF TEXAS TOV/ER NO. 4 197 



Senator Saltonstall. And what you are saying is that these 10- to 

 12-foot waves would be right in time with the movement, so that it 

 would cause a greater stress ? 



Mr. Brewer. No. I wanted to draw a distinction, that the reason 

 that the smaller waves caused more force was because they are just 

 the right spacing, so that they hit all three legs at once. Therefore, 

 you have three times as much force. 

 Senator Saltonstall. I see. 



Mr. Brewer. And a single wave hitting one leg, as very roughly 

 you could have one very large wave, if you only struck one leg, and 

 it is down by the time it gets here to the other leg, you really, in 

 effect, are only creating a load on one leg. 



Senator Saltonstall. What you are saying about the three legs 

 would be like the man out at the end of a diving board keeping in 

 time with the up and down motion of the board. 



Mr. Brewer. Well, that would be the resonant case, tmiing case. 



Let me see if I can think of a better analogy. If you can imagine 

 waves of just the right height so that one was hitting here and an- 

 other one hitting here simultaneously, that is the condition I was 

 speaking of ; whereas, with both the larger wave and the smaller wave, 

 that won't happen. One would be up here [mdicating] and down here 

 on this leg. 



You see, it takes a unique spacing of the waves to hit all the legs at 

 the same time, and a wave, to do that for this tower, the wave height 

 must be about 12 feet ; 10 or 12 feet. 



Senator Saltonstall. I understand. 



Mr. Brewer. If it is a bigger wave, it has a longer period, and it 

 does not do it, later it doesn't do it, and that is not the tuning. 



Now, a tuning case, and we have no evidence of this, a tuning case 

 would be if the waves hit a leg at the right frequency of the tower so 

 that each time the tower went back another wave hit it ; that is the re- 

 sonant case, the third condition. 



The tower w^as designed on the condition of one enormous wave 

 striking the leg, which is a static case. 



Now, the static case is usually the less force. But again you have 

 to look into the mechanics of the structure to decide whether a dynamic 

 case is worse than the static case. 



If you have a very short impulse on a tower that dosen't do nearly 

 as much as one that is on for a longer time. 



This has to be done by analysis and, as Mr. French has suggested, a 

 dynamic analysis of the tower might have revealed, under the case 

 that we found, that the loads would be higher. 



But this was already recognized as a bad condition, this very low 

 natural frequency, and they were making efforts to stop it, to 

 tighten up, to increase its natural frequency. 



Had it been done then, the dynamic loads would not be as great. 

 But this is something that I couldn't say without actually looking into 

 it, and that was not our job. 



We were not asked to do that, and we had not done it, so I am speak 

 ing now on the basis of opinion. 



Senator Stennis. 



Senator Stennis. All right. 



Is there anything further. Senator Saltonstall ? 



