HSS Column weepholes 1

[penpal97]

I have an outdoor 30' tall canopy made of a HSS members, architecturally exposed steel. There is a welded cap plate on the columns, and the welded base plates are embedded in 2' of concrete (architectural curb). Do you usually put a vent hole in the column?

I am afraid that the column will eventually rust somewhere (cause these things always do eventually) and then water will get into the HSS. I am thinking of adding a weephole at the base, but not sure how to drain the inside of a column embedded in concrete. Thoughts?

 

[hokie66]

Hot dip galvanize the column, which will provide protection inside and out. Then let the architect paint it as he pleases.

 

[swearingen]

If you hot-dip, you'll certainly need a weephole to stop it from exploding during galvanizing. Once the weephole is covered up, I wouldn't worry about it.


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

 

[asixth]

vent holes are provided for any hollow section that is galvanised. Waterproofing does become an issue. As swearingen mentioned, cover them up or make sure water cannot ingress into the section. Additional, the inside of the tube is galvanised.

 

[bigmig]

I live in an area that experiences a temperature swing in a single day that goes from 10 degrees to 80 degrees. We have come across this problem also. The cold air in the steel tube condensates when the afternoon air hits it. The steel expands (characterized by gun shot like pops), and eventually the bases erode away. We also see concrete that overlaps steel, or steel embedded in concrete, experiencing problems. The steel expands at a different rate than the concrete so the concrete distintegrates. Freeze thaw with water infiltration does the rest. Weep holes are very common.

In regards to all of you talking about galvanized columns, I have never seen a galvanized tube column, which leads me to assume that 1) they are expensive and your architect will laugh in your face 2) weep holes do just fine.

We buried some steel piles in the ground the other day without galvanic protection (pipe pile foundation support). The calcs said the pipe walls would last 80 years. So yes, they do corrode, but no, you will not be around when it finally does. If this is a concern use concrete.

 

[hokie66]

bigmig,

You should get around a bit more. Galvanized tube columns are common, and where I am, the architects insist on galvanizing for external columns.

Steel piles are a different issue. They either depend on extra thickness for a long term corrosion allowance, or galvanic protection if in an aggressive soil environment. Appearance is not an issue.

 

[penpal97]

OK, so vent holes would allow the air inside the column to expand/contract as temperature goes up and down, but would also allow water to drip in. I think the vent hole is a must because I do not want my occupants scared they are under attack on a daily basis. I will have to galvanize the inside of the tube, cap plate, and base plate.

Do I need a weephole near the base? (note the weephole could act as the vent hole) How do I drain the water from inside the column through the weephole? I can't put the weephole at the bottom of the column because of the concrete curb, and a weephole above the curb will not have anything to direct the water thru the weephole.

 

[hokie66]

With a tube fabricated with base plate and cap plate and then galvanized, you will automatically have holes near the top and bottom provided by the galvanizer to allow the molten zinc to drain and prevent pressurization of the tube. The hole near the top may be useful as your vent hole, but at the bottom, you could provide a further vent for the purpose you noted, although I have never known that to be a problem. You could always grout below the hole so any moisture in the column is directed out at your required level.