Pond Boss

Well as you can see we decided to try cables to stabilize the end of the deck, it didn’t work….it’s still a diving board. The cable are ¼” SS rated at 7500 lbs ea. They have some stretch to them so that’s part of the problem.



The deck is solid out to the ladder, after that hang on.



I don’t like the location of the cables on the deck, going to move them to the outside so they are not in the way of the decking and hand rails.



This is my idea…move up to a ½ “ cable and then attach the ¼” cables underneath both corners of the deck out at the end of the deck, and then back to the pillars. Giving me upward and downward stability and being able to adjust as needed.

I dont think the move to 1/2 inch will work, you should triple the amount of cables not the diameter of the cable. That is one very cool, very ambitious home project

Well it's about time!

Jim, I like your modification idea. Even 1/4" high tensile steel is a bit stretchy. SS is simply not in the same league with HT as far as stretch. The 1/4" SS should be fine underneath to prevent bounce.

I would go with 1/2" HT, and de-grease, prime, and paint it with a good epoxy paint.

It would also help to pre-load your cable until the end of the wharf is lifted up 1/2" to 1".

Another alternative would be to brace it with a box beam, triangulated underneath the structure. Start it somewhere between the end and the ladder, and attach it at the base of the concrete forms. If you could bend the beam into a gentle arch, it would look fantastic.

The cables look super, BTW. Here's what came to mind when you first started your project: cable stays!

You guys must be Rocket Scientists in your spare time. WOW. And I though my 4x4 wooden pier was nice...

Very Nice Jim. It just makes you want to walk out there, dosnt it?

Jim your on the right track. A single larger cable will do the trick, dont be afraid to go to big. If you have a crane rental company near by, or a large GC, you might be able to get the cable for free, its changed off cranes alot, and really no use after. You have to get rid of all stretching.

Dont be afraid to step back a little with the attachment point, as in right before the platform. This will keep it in line with your steel columns and remove the load that is on an angel to the steel columns and lessen the angle of the cables so your steel columns dont have to hold as much weight.

As bobad said, you want to load them. Keep pulling them till you have raised it above or at least equal to the elevation of the concrete columns. Once you have done this, no cables under will be needed. You have to get the cables holding the same amount of weight that the concrete columns are holding divied by half. Once this is done, it will be like having concrete columns at the end.

With out knowing the weights, your vertical columns are now going to be the weak spot, as in crushing them when the cables are loaded. Quick example, lets say you have 4,000 lbs on the two concrete columns, that means you need 1,000 lbs of vertical force on the cables. If the cables were vertical, it would be easy, but your pulling at an angle, the more you lessen this angle, the less weight you are pulling lateral and more vertical. Example, you have 3,000 lbs of pull on the cable, 2,000 lbs is pulling lateral to get 1,000 lbs vertical, this will change continually all due to the angle of your cable. When your finished, this vertical load now is imposed on your steel columns. trying to crush them, your lateral load is taken up by the back cables, but keep in mind, they are imposing the same vertical force also. In the above example, your going to have 4,000 lbs total of vertical force on your two steel columns.

Jim,

Excellent advice from Winston.

1 thing I forgot to add: Any steel structure with a great span is going to bounce or sway a little. It's normal and harmless. It can take numerous stays or extremely large bracing to remove all of the movement, and you get diminishing returns. Just get it "comfortable", and accept a little bit of movement. It will remind everyone they are high up, and make them appreciate your fine structure.

PS: I hope you have pulleys or something smooth to prevent wear on your cables where they run on top of your towers.

Jim I noticed you said you were going to have hand rails. Why not make them from the same size tubing you are already using and make a truss out of them. This will not totally stiffen the structure as many have pointed out, but perhaps will be enough to live with. I recommend you use your backhoe to lift the end up and hold it while you fab the hand rail trusses. What ever distance it sags naturally down lift it that same amount uppered above level this will preload the structure and take out the sagging and the spring board effect.

The cable idea has too much play in it, and even if you get it right, they still move all the time, and in time, the problem will return. If you want it rock solid, you either need to create a very solid truss along the top, or brace it from below.

I like Rockytoppers idea, but don't know how big, or what size material you will need to make it work. Too small and you wont accomplish anything. Too big and you risk either making it too heavy for your cantelever, or you waste allot of money on material.

My first thought was to attach a beam, or support to the footing and 2/3rds out on your pier, to create a large brace. Basically support it from underneath.

Somewhere, you need to create some triangles to lock it all together. Either a very large one at the bottom, or allot of smaller ones on top.

Eddie

Sorry eddie and rocky, I have to disagree. Trusses are made light weight, and normaly end bearing, he has to offset the weight of the beam plus any other material or live load on top of that. Also they will not give any more lateral support than cable would since its going to be a thru-truss.

The cable if done right, there would not even be any bounce, considering the weigth of a person jumping (live load) will be a fraction of the actual tension on the cables, and it would never need adjusting if you use the proper size cable.

Keep in mind, the same load that would be needed on the cables, depending on the angle of the cable, the truss turns this load completly horizontal. This tension load now is transfered into the top rail.

I will agree with eddie on the point that if you had any beam left for the underside and did as he said, it would do the trick, but i dont beleive that was the "look" you were going for. How far you get the beam out will determine how much bounce you will have at the end.

Sorry, one other thing, the cables will need to be attatched to the columns independently, as I beleive you had done.

I thought of this after I left and it might help. A truss is good at transfering its load over the length of it. The problem in this case is its a point load at the end of the beam.

WOW! I say leave it alone and have the worlds biggest diving board!

Jersey I'm with you but with the spring that things got it will be cheaper on Jim to stiffen it up, other wise he's going to have to expand the pond to insure know one goes plum across and hits on the otherside.

What if you pile drove two I beams in the corners of the T then bolted the pier to the beams? Less material and more stable and you could have a more finished look. Of course I don't know what putting those beams in would entail but it seems as though you want to do it right. I say more pilings or beams driven. This would also add structure for fishing straight down.

The steel kickers from the base of the pillars to the end of the deck is one option, but it’s defeating my goal and it‘s ugly IMO. The goal is….try to make as much of the walk way and deck appear as if it’s floating in mid air.

Were going to try some big HT cable with a ½” positive camber and use the ¼” cables to suck it down to level.
Folks, I want to thank each one of you for your ideas and suggestion, I feel guilty because all I’ve done is pick your brains and feel like I haven’t contributed a darn thing to this site.

Why not a floating dock? Maybe a stupid question? Just seems like a lot of work to me. Our EZ docks are real popular here.

Jim,

I bet the 1/2" cables will turn the trick, provided the towers are rigid enough. You may not even need cables underneath. It would be a shame to add a lot of bracing and lose the clean look.

If you could stand or sit at the end of the deck, you would understand it. The man that dug my pond has been calling me crazy from the beginning of this project….well yesterday he walked out on the deck for the first time and he summed it up in four words..”wow, what a view”.

I think it's awsome like that!!! I wouldn't mind it bouncey. Actually, remember earlier someone talked about welding beads down the tops to counteract the forces and load the beams. How about that? The mini suspension bridge look is growing on me fast.

Jim, I just had a brain bubble. If the 1/2" cable doesn't do it, think about boxing in the outside of the I beams. It would be expensive, but would make them 2X or 3X more rigid.

Jim, here is some reading on this subject. the first is technical the second is in more laymen terms. You basically don't have enough section in your beam.

1. http://en.wikipedia.org/wiki/Cantilever

2. http://www.brantacan.co.uk/beam.htm

The following statement is from the second article

"The next two diagrams show the beneficial effect of doubling the thickness of the beam - the sag has been reduced to one eighth of the original value. But twice as much material has to be made, transported, and erected."
This is again your problem your beam doesn't have enough section.

There are many ways to solve this problem suspenion cables, truss beam, etc...
Bottom line is what kinda of look to you want? Golden gate bridge, or Frank Lloyd Wright fallen water cantilevered house. My biggest safety concern is How much concrete did you put into the ancor pad or block? If the beams were to fail they would simple yield and sag even worse but I don't thank anyone would be injured in that event. If the forces were to pull your ancor out of the ground it would be a different story and could happen in a manner of seconds.

Without doing a lot of calulations let me ask this.

First are you going to have hand rails as you stated?

If so, what size and gage tubing are you currently using?

Does the structure sway laterially side to side out on the end given that you have cross braced it?

If it is ridgid enough laterally then I summize that building a truss "hand rail on each side will fix your problem using the same material. As far as added weight concerns voiced by Eddie it appears from scaling the photo that there is about a 20% mechanical advantage in moment arm between the cantilvered end and the fixed end.

If you aren't going to want hand rails and want the walking the plank look then you could simple lift up the structure and slide 2 more of the same size beams underneath. Preload the structure as I've stated to pull the sag out and weld them together and your done. If you would have chosen taller beams to begin with you wouldn't have this problem. I'm still mostly concerned about the ancor I think that is you weakest link. I believe a cubic yard of concrete weighs about 4000 lbs, I hope you have enough mass to overcome the lever arm you have created. I'm not a structural engineer and don't claim tobe but I work with many and could easily get this analysised if I had too. Most of the places that sale I beams like the metal building fab places have a structural engineer that will help with determining and sizing the beam for your application. I would strongly recomend you consult one of them. generally if your buying their product they will work with you at no charge.

Good luck my friend.

The 1/2 cable will give you about 4,000 lbs each, i suspect it will be close.

Novice question.
What if you used chain (1/4" or 5/16") instead of cable?
Wouldn't it have less stretch?

It would work also but more expensive and not as strong. Cable wont stretch as long as you stay inside of its yeild strength or working load. As in the 1/4" cable at first, it says 7,500 lbs, but its yeild strength is only about a 1,000 lbs. Rule of thumb, in general, dia. x dia. x 8 = tons.

Was the idea that you didnt want anything in the pond supporting it? It seems, to me, that angle iron driven into the pond bed near the end and welded would stabilize it. Not a mechanical engineer so what am I missing?

Winston,
Your tip about free used cable from crane co’s was right on, it saved me $480.00...a big Thanks. BTW before anyone starts calling around trying to find some, you need to know something first…..e-mail me and I’ll give you a tip.

Were going with 5/8” HT cable