Internal Structural Support

"I intend to provide as much structural support internally as possible." --- I'm afraid I'm missing something:

support internally to the 3" steel pipes?...to the floating dock?... to the adjacent stationary/roofed dock?...

What portion of the post did not display here for me? Or what am I missing?

Guest,

The 3" galv. pipes are driven into the ground (river bed). Rectangular closed brackets located at two points on the covered (thus the roof) floating dock are placed around the pipes such that the dock can move vertically with the change in depth of water while remaining in position. The only way to access the open ends at the tops of the pipes will be when the water rises to a point where I can stand on the roof.

The issue with the pipe support is that over time the pipes will degrade to a point they will no longer hold the dock in place. I'm trying to postpone the inevitable.

Hope this helps. I'll see what I can do about a photo.

I'll be interested to hear the suggestions on this (particularly from those with experience of any significant duration). According to NACE (Nat'l Ass'n of Corrosion Engineers Intn'l) galvanizing is not recommended for anything but atmosheric service ... especially not immersion service (due to limited "throw" distance of protective current) and because zinc is amphoteric, most certainly not for contact with cementitious materials. I would think that the better choice would have been 'pointed' carbon steel pipes (grout-filled and capped), with a decent coating system and appropriate replaceable anodes just above the mudline. (Some replaceable pvc sleeves in the area where the enclosed brackets travel would minimize re-coating intervals.)

Wishing you success, enjoyment, and environmental-friendliness...(!)

Thanks ndt-tom, good comments.

It was interesting to note the total lack of zinc remaining on the lower, more continually immersed sections of pipe and associated degree of corrosion. I have just finished the wire brush, OSPHO and cold galvanize (uh oh) job on the exposed surfaces. I had considered your suggestion of pvc pipe as a wear barrier but decided it was of more value to me to be able to see the structural member.

I am looking towards grouting the pipes and would like to provide structural support at the same time, especially at the mud line as you called it and above. I have thought of using short sections of pipe (say 5 ') screwed together and inserted into the 3" and used to inject grout. The reason for the short sections is my desire not to be standing on a slanted roof over the river holding a 21' stick of pipe vertically by the end. What I would like to do is inject grout from the top through the pipe assembly to the bottom and back through the annular space to the top leaving the smaller pipe as a large piece of re-bar of sorts. The problem here may be the discharge head of the grout pump.

Dear Contributor,

I must say I needed the photograph to understand your problem. It woulod seem to me from past marine experience ( in harbours where the tidal range is approx. 8 meters ) that you may have been incorrectly advised.

The pipes you are using would probably have no lateral stability with any form of flooding current and the surface wear that you have or anticipate could be hard to overcome.

Rather than pipes I suggest that you would be better equipped by having four solid concrete anchors of suitable size.These would be lowered with care onto the mud level. A wire rope ( I would suggest stainless steel) would be fixed on the side( or underside) of your covered landing at each corner . Each wire (one per corner)would be threaded through a simple solid steel block attached to each concrete block anchors prior to its lowering in place . The return of each of these wires could come to the top (near the eve)of the outside of the corner posts of your covered landing . Again another wire rope block would externally receive the end of this "anchor wire rope " . There , a lenght of pipe (say 4" or 6 " diameter )filled with concrete to make it heavy ( as a permanent counterweight) would keep each of the anchor wires : tight - and I might add, keep the landing always in position.

I have used this system previously. It works very well and requires absolutely minimal maintenace. Unless there is a very strong current (which you can overcome by the sizing of ; anchors and counterweights, it will keep your landing absolutely steady . As well may I suggest, with somewhat better looks then the present unsupported pipes that stick like a "sore- thumb" behid what must be a very peacefull and enjoyable retreat. Best wishes,

Labor.

"Unique" approach, that is... sort of a combination between "tension-legs" (as opposed to rigid legs) on an offshore platform, in unison with the anchor wires.

The only problem might be the amount of depth available for built-in "slack" in the wires, to account for worst-case floodwater heights. (If sufficient, I can envision custom welded SS eye-bolts ~eyes-on-bottom~ weights allowed to hang straight down, with the anchor-pillars out-and-away from the corners a bit.)

On the other hand, I disagree with the "unfeasability" of the post concept. At:

http://www.popsci.com/popsci/science/185c893302839010vgnvcm1000004eecbccdrcrd/6.html
(scroll down to "Specs" paragraph...) this exact concept is described, and in use.

Certainly some modifications [reinforcement, and substitution of the galvanizing ~ especially the cold galv, which will probably / actually be worse than nothing at all!] are called for.

Whilest all is currently working, you might seek a local civil engineer familiar with the waters and bed-geology, and ask his opinion. I know that holes can be bored for such posts, and concrete-pour filled around them (carbon steel embedded in cement is afforded a degree of passivity, and CP can be added for further longevity).

The pic looks great ~ enjoy it all you can... don't make it more work than you can tolerate!

Work,

My wife insists that I could be placed in a straight jacket, locked in an empty concrete room and still find something to work on. Drives her nuts.

There is still time on the cold galv. spray while the river is low and I am still off the road. I'm open to suggestions. I would also appreciate your take on the OSPHO treatment. I feel the need top provide some form of protection as the carbon steel is beginning to pit. By the way it is a fresh water system as I suspect you were aware.

Thanks

Pepper

..."locked in an empty concrete room..." Jokes abound, in (this) world of commercial diving, particularly jabbing their notoriety; e.g., "Put a diver in a room with 3 steel (bearing) balls, and when you let him out, he will have stolen one, lost one, and will deny that the third ever existed!"

I assume that your comment about "time on the cold galv. spray while the river is low" means you could PWB it off & re-do...(?) Hmmm. "Where-to-start"...?

How about the OSPHO (?); The phosphoric-acid based "rust converters" (there are numerous) are good products with many applications where they are useful additions to ongoing corrosion maintenance programs¹. In a scenario where submersion is going to take place: #1~ galvanizing is bad ("Period"). #2~ Believe-it-or-not, TSA (Thermal Sprayed Aluminum) IS a viable option. #3~ in fresh water, zinc anodes don't work as well as aluminum or magnesium because it will readily passivate (chlorides in seawater help to maintain activity level of zinc on Petro-platforms, etc).

#4~ re: that superscript '1', above: OSPHO treatment is probably NOT as important a step as testing for, and removing any and all traces of salts from the surface before coating (on your project, probably with a good marine epoxy product topcoated with a urethane for UV resistance... epoxies chalk in sunlight, without the topcoat). Even after a surface is sand (or grit, slag, garnet, or other media) blasted, it should be tested for salts (which can be driven-into/embedded into the profile). Chlor*Rid is one of the finer products for eliminating surface-residue salts, which are hygroscopic, and thus would draw moisture through the coating (even the BEST!) and into those salts on the surface, producing osmotic blisters and subsequent delaminations etc.

NACE has a great training program for Marine Coatings. There's a wealth of knowledge on how to do things right the first time. The high-tech polymer coatings being produced nowadays are capable of incredible performance and longevity, *IF* applied properly to a properly-prepared surface. Sadly, about 2-1/2% of today's "self-proclaimed-experienced-applicators" have actually learned what they need to know ... and then APPLY that learning correctly!

Many aphorisms exist in the field of coatings, including: "Sometimes NO coating is better than having a poor coating." Whereas some SS's (particularly in chloride environments) suffer failure by pitting mechanism, Carbon steels tend to exhibit slow, uniform corrosion. A poorly-coated C steel, however, may be encouraged to pit! Your singular best defense (for your posts) is, without reservation, cathodic protection below the waterline and a superior-grade tidal/flood/splash-zone coating.

Praise be to Him, from whom all knowledge comes...

Guest,

I agree. Had I a hand in the design and construction of the dock it would have been different including the location. It has however performed much better than one might have expected. The dock has been within 6 feet of the top of the pipes without failure and the structure itself has withstood three major tropical storms. But as they say here the river takes everything eventually.

Thanks for the information on your anchoring / station keeping system. My problem appears to be that the height of my structure is less than the potential rise / fall of the river. At low water as in the picture the shoreward side of the dock actually rest on the bottom while the other side is over 20 ft. deep. I will effectively have only 8 ft. of rise available on one side which is substantially less than what we can anticipate here. Tell me if I am missing something.

Thanks again for you comment.

Pepper

Dear Pepper,

I do not want for my comments to be patronising but please may I quote what one my Professors kept repeating to us. This was : what the Greek Philosopher had written " There are no problems . Only : solutions in disguise"

Your indications of the quite unequal mud- depths can be overcome in a number of ways :

1- The simpler one is having (on the shore side,( at each corner of the landing, and somewhat like you presently have : two pipe uprights). These would serve as masts(bolted on the existing corner posts from the deck upwards) to give more lenght of wire to the counterweights.(Again they would have a steel block at the top)Thus you would accomodate the difference in mud-level depth.

2-The other solution would be having blocks that have double sheaves which would take up the greater lenght of wire. This however is a bit more complicated but can easily be adapted to your system.( FYI if you have ever noticed the tensionning systems used for electric train 's overhead wiring along the tracks you can note that constant , permanent : tensionning is achieved by the above method.

Perhaps above will overcome the poor professional application of surface coatings .Believe me for them to be effective and long lasting they need at the very least an electric or air " needle- gun " surface preparation or better still : sand or grit blasting . To do this properly where the landing is situated I wish you luck !. May I instead suggest that the KIS system, above , may be the best. Good luck and enjoy the landing it looks very inviting !

Keep us advised.

Labor

Dear Guest,

Thanks again for your input. A mentor once told me to "search for the elegant solution". You have been far from patronizing. I appreciate both you and ndt-tom taking time to respond to the thread and I have learned from both of you.

Guest,

Picture as promised. Note the two pipes rising behind the structure. Upstream is to your left. Hope this helps and look forward to your comments.

Pepper