Problems with Six Minute Solutions - Structural

[Mike1144]

Question #5 involves the wind force on a 50ft high by 20ft diameter circular concrete water tank. I had very little trouble following the procedures in the ASCE 7-02 code. I did have quite a bit of trouble figuring out what the tank actually looked like. I initialy thought it was a 50ft high cylinder, 20ft in diameter. Turns out its a 20ft diameter sphere, with its top 50ft above the ground. Did anyone else have this kinda problem with the six minute solution book?

Side note, do they make spherical concrete water tanks 30ft off the ground?

 

[DVINNY]

I guess for the problems sake, you just have to assume they do.

The center of gravity of the tank will just have a higher elevation, other than that, what changes?

 

[Mike1144]

I would have found roughly the same wind pressure, but the question asked for total force. The projected area on the 20ft diameter sphere = 314 ft^2. The projected area on a 50ft x 20ft cylinder would be 1000ft^2. This would greatly effect the total force.

 

[rdbse]

The water tank should actually be a water tower (tank on a tall column). Think of a giant lollipop.

 

[Mike1144]

The water tank should actually be a water tower (tank on a tall column). Think of a giant lollipop.

The question was, and I quote... "A circular 50 ft high, 20 ft diameter water tank...."

The solution is clearly for the "lollipop" tank. But I feel the above description is more suited to a cylindrical storage vessel.

 

[rdbse]

I have worked through the problems and I found the same wording errors.

The author should include more diagrams and provide clearer problems statements. Also, the solutions include lots of assumptions.

I still found the book useful as a refresher. Work the problems first, then look up the solutions. Don't be discouraged if you only get half correct on your first try.

 

[rdbse]

Author: Christine Subasic from Penn State