12 COLLAPSE OF TEXAS TOWER NO. 4 
The legs themselves, in the case of tower No. 4, consisted of an 
annular ring of steel he inch thick with a diameter of 121% feet. 
An inner ring or core of 8 feet in diameter extended from the base 
of the platform to 50 feet below the surface of the water and it was 
between those two annular rings of steel that cement was poured 
to provide greater rigidity. 
The pin-connected bracings of tower No. 4 were installed below 
water at depths of —25 feet, —75 feet, and —125 feet, the horizontal 
braces being affixed to the legs at those levels with the diagonal braces 
extending from the midpoint of each down to the legs and next lower 
horizontal brace. 
The footings beneath each leg were 25 feet in diameter, filled with 
cement, and sunk or embedded into the ocean floor to a depth of 18 
feet. 
For a graphic presentation of the underwater bracing system and 
footings for tower No. 4, there is reprinted (on p. 13) a rough sche- 
matic diagram approximating the “as built” drawings of the tower. 
(b) Design specifications.—Structural engineers use the term 
“static” and “dynamic” in differentiating between types of forces ap- 
plied to a structure. While there is some difficulty in precisely de- 
fining the differences between the two, the term “dynamic” is generally 
used ‘where the forces are instantaneously variable in either magnitude 
or direction, thus subjecting a structure to instantaneous fluctuations 
of force. Mr. Brewer, chief engineer of Brewer Engineering Labora- 
tories, Inc., used the analogy of a diver at the end of a diving board. 
If he remains still, his weight will exert a static force on the board. 
If he jumps up and down he will impart an impulsive dynamic loading 
to the board by which, although there is no change in his weight, he 
will exert stresses on the board some three or four times his inert 
static-weight stress. Although the sea is in constant, unrelenting 
random motion, in the design of the towers, merely the static force 
of a single breaking wave of 35 feet in height was taken as the basis 
for computing the stress exerted against the tower by the sea. In 
a motion study conducted by Mr. Brewer on tower No. 4, at a time 
when the upper braces on the A—B side were admittedly not func- 
tioning, he found that a series of waves 10 to 11 feet in height caused 
greater stress and greater movement of the platform than did waves 
of 30 feet in height. This was due to the peculiar spacing between 
10-foot waves, roughly the dimension of the tower, so that these waves 
could strike all three tower legs simultaneously. In the case of the 
30-foot wave, however, its peculiar spacing was such that only one 
such wave would strike one leg at a time and its force would have 
been appreciably dissipated prior to its contacting another leg; 1.e., 
the crest might strike one leg but by the time the wave had progressed 
through the dimension of the tower, its trough would strike the other 
leg. 
‘No model studies for the exposure to such hydrodynamic forces 
were conducted, on the grounds that— 
(1) It was impossible to duplicate the random nature of the 
sea waves in an artificial basin; and 
(2) The design engineers were told that a Reynold’s number, 
by which the miniature model is magnified thr ough mathemati- 
cal multiplication to the actual size of the tower itself, would not 
be applicable in this case. 
