Most tilt up towers seems to be built from round tubing. My question is why? Cost, strength, weight, etc. Thanks
Well, you hit them all or, almost all. Square tubing would also have a more interesting structural calculation as it does not have truly symmetrical properties as does a round tube.
By weight, round tubing is a very interesting structural material. It does have a few problems in fitting joints for the casual builder. You will notice many large cell towers have round tubing 'corners' and angle iron keeping those members in location. Such construction lowers fitting costs, avoids the problems with almost sealed tubes rusting and is fast to assemble in the field.
Designs are also dictated by many related costs. Among them are fabrication, material and erection. Large towers are sometimes all angle or angle and flat. Angle 'corners' and either angle or strap bracing is very cheap to fabricate. All of the bolt holes can be punched. This is much cheaper than welding or drilling holes. Sometimes the material and labor costs are cheaper to build larger is less than those to build more materially efficient.
Much of this will be dictated by accountants rather than by engineers. An engineer will 'build' several towers of different designs to the same load specification. From there, the design goes to an estimator who may also engage someone who may actually know how to build the product with the equipment and labor skills available. There may also be a time and scheduling problem that overrides other considerations.
It all becomes a balancing act.
Ron
