194 COLLAPSE OF TEXAS TOWER NO. 4^ 



Now, that could be the resuh of a number of things. This is not to 

 say that the tower bracing was not there. 



As I think you will see, if the pins are loose and have a certain 

 amount of clearance, the bracing can still be intact structurally, but 

 the tower can nonetheless move back and forth until these clearances 

 between the pin and the bracing are actually taken up by the excur- 

 sion of the tower : and, of course, we have no way of knowing what the 

 conditions were underneath the water except that the tower bracing 

 was ineffective within the degree of motion that we measured, which 

 was approximately plus or minus 3 inches. 



Mr. French. You also found a degree of rotation before the pins 

 would fetch up, did you not? 



Mr. Brewer. Yes. It is a complex motion. The tower is not only 

 going back and forth in a random manner, but it is also rotating in 

 a random manner, and the mechanics of it are such that it probably 

 never repeats itself, because it is a combination of translation and 

 rotation that is set in motion primarily by the waves bearing against 

 the three legs, and the waves themselves are a very random structure, 

 so that the tower never does the same thing twice. 



So we took quite a lot of statistical data and made plots and tables 

 from the data that we recorded. 



Mr. French. What were the maximum weather conditions which 

 you encountered during your study ? 



MAXIMUM weather CONDITIONS ENCOUNTERED DURING MOTION STUDY 



Mr. Brewer. The maximum — the condition that created the — well, 

 the maximum sea state that we recorded was 30 feet — ^^that was a wave 

 30 feet in height — and in conjunction with that, I believe it was a 

 55-knot wind — yes, 65-knot wind and a 30-foot wave. That was the 

 greatest sea state and air state we measured simultaneously. 



There were other conditions where we had less waves, that is, waA'es 

 would not be as high, and the wind would be of a higher velocity. 



Mr. French. Under what sea conditions did you find you experi- 

 enced the maximum translation of the platform ? 



Mr. Brewer. Curiously enough, this recorded waves of approxi- 

 mately 10 to 12 feet in height. These waves set the tower into greater 

 motion than those of a larger height. 



It rather corroborated the experience of the tower personnel who 

 had told me that it seemed to them that sometimes the tower would 

 move or appear to move more with a small sea state than it did on a 

 veiy high sea state, and for a while we thought this might be due 

 to the pins taking up. That is, on very large waves, perhaps, the 

 tower moved to the point where the pins took up, and therefore it was 

 more rigid, but subsequently we came to the conclusion that the 

 small waves have just the right spacing so that they can strike all three 

 legs simultaneously and, as a consequence, impart more energy into 

 the tower than a single, big wave that hits only one leg at a*^ time. 

 This is our belief. 



Mr. French. Well, you are aware of the fact, are you not, sir, 

 that merely a static force analysis was made for the computation of 

 design. Would you kindly define the difference between "static" and 

 "dynamic." 



