Are rectangular towel bars more likely to suffer bending damage than round towel bars?
Answers:
Most towel bar rods are brass tubing - either square or round. The inexpensive units are a particularly thin gauge of brass. Brass is a fairly soft metal (made mostly from copper); the engineers compensate for the weakness by making the diameter of the rod bigger. When you see a thick rod in the lower priced units, beware.
Some towel bars are steel, which is stronger than brass but are usually the cheapest pieces out there because steel does not take the plating as nicely - you can see the difference.
The best bet is to spend a little more money and buy something nice to safeguard against bending. The models at the home centers can typically be pretty bad, but I have noticed some nice designs at Lowe's lately. I have done alot of work with bathroom renovation, and here are a few recommendations for nice designs.
Other answers:
my rectangular one is damaged from a towel
my rectangular one is damaged from a towel
Ever wondered why most bicycles are built of round tubing? Or why backhoes uses square tubing for the main boom? Of course, there are reasons for everything and tradeoffs to be made.
The table below summarizes some of the choices we're faced with when looking at Towel racks. I've taken the liberty of avoiding any discussion of material (aluminum, steel, titanium, etc.) - we'll leave that to another question. I've specified 2 geometric cases for our consideration. We want to compare the relative merits of square versus round tubing for towel bars. Assume the material, tube length, applied load, and end support conditions are the same. If you compare bending a 1/2" square tube to a 1/2" diameter tube there are a few ways to do it.
[A note of explanation: "Normalizing" means to divide some value by some other value so that everything is on the same playing field, so to speak. In the cases below, we'll want to evaluate the stiffness relative to the weight, so we'll divide the Moment of Inertia by the Cross Sectional Area. The stiffer a towel rack is the more resistance it has to buckling under load. The stiffer or larger value of stiffness is better. This is OK since we've assumed that the tube material is the same in all cases, therefore the Moment of Inertia is representative of the stiffness and the area representative of the weight all other things being equal.
case # case 1 case 2
tube type square round
dimension 1/2.000 1/2.000
wall thick 0.125 0.125
Area, A 0.9375 0.7363
% wt of sq 100% 78.5% comparing square tubing to round
Moment, I 0.5518 0.3250
% I of sq 100% 58.9%
normalized I 0.5885 0.4414 Larger is better
% nor I of sq 100% 75.0%
The areas are indicative of weight (wt = area * length * density).
Case 1 vs 2: The round tube of same outer dimension and wall thickness will weigh less than a square tube (less material means less cost to manufacture). And, it is much less stiff (based on the moment).5885 square tube vs 0.4414, though not as much if the moment is normalized by the cross-sectional area.
Formulas used: D = OD, d = ID
Area of round tube = PI/4 (D^2 - d^2)
Area of square tube = (D^2 -d^2)
Moment of inertia, round tube = (PI/64)*(D^4 - d^4)
Moment of inertia, square tube = (1/12)*(D^4 - d^4)
where PI = 3.14215927
Summary: If you want a light but stiff structure, use as little material as possible (thin wall thickness), but place it as far to the outside of the envelope as possible (maximize the outer dimension). The square tubing will provide greater local buckling failure resistance because it has more material and a larger outside distance from its center. If you use a round tube one must use a larger diameter tube in order to be as strong as a square tube all else being equal.
Yes
When you bead metal you casue damage. Also round shapes are stronger by nature. Why do you think they make arches round