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Handyman: Foot bridge design

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Mvule
Arua
Uganda
(Zone 11)

August 20, 2012
7:41 AM

Post #9247483

I would like to have a fairly broad foot bridge over a small stream in the center of our property. It should be tasteful but also practical as it will be a significant feature. We are here northern Uganda. Does anyone know of a website that gives ideas of how to design and build such bridges.

Also how durable would I expect untreated Mahogany to be is I used it to build the bridge with it. We get plenty of rain in season. I cant think of any other timber that might be durable and yet is available here. I could combine it with metallic tubing for the verticals perhaps.

Thanks
velveteena
Seattle, WA

August 21, 2012
4:19 PM

Post #9249371

What sort of wood is used locally that seems to hold up? Is mahogany native to Uganda? I thought it was from S. America, but maybe more from the Indies. My understanding is that it is not an easily renewable tree. Having never been to Uganda I am curious about the existence of lumber yards. In any case, there MUST be carpenters! Find out where they get their supplies. I know lots of wood in Africa gets burned up for fuel---does the actual timber come from overseas?
velveteena
Seattle, WA

August 21, 2012
4:23 PM

Post #9249379

Maybe you'll be needing to use metal cable for your span. This can be tightened so it doesn't get that swaying effect. How wide is the stream? If I were building here at home I'd be using cedar, but anything you use will be fairly costly unless you can salvage some old steel or wooden beams.
Mvule
Arua
Uganda
(Zone 11)

August 21, 2012
8:40 PM

Post #9249595

Thanks velveteena. All wood is grown locally. Locally been either here in Uganda, from Congo (border about 5 miles from here) or Sudan (about 50 miles from here) I know that teak was planted commercially in Sudan in the 50/60s and is now been cut down a quite a rate. But most of it goes for export. Mahogany is a local tree I think and is also planted (I have planted some myself). We have lots of Eucalyptus and also some pine, both planted. But now you have encouraged me to go and ask more questions and find out more.

The span of the bridge would be about 10-15m. Most of the time the stream is about a meter across but in the rains it floods periodically. I have not thought of using metal cable. I am not sure where I would get that from.
Doug9345
Durhamville, NY
(Zone 5b)

August 22, 2012
7:27 AM

Post #9249874

How high above the ground would it have to be? Also when you say flood, does the water just spread out or is there also a current with it. Basically as the structure gets longer, higher and the conditions under it become poorer( wetter, softer, or fast flowing water) the more critical the design is to be safe and last. At the minimum your are going to need to get someone involved that has done a couple of similar ones before. If you could find one that is build in very similar circumstances then you could copy it. The trick is to make sure the circumstances are actual similar.

If this is going to be what amounts to a board walk over a part time swamp, Then I think you may be able to figure it out on your own. The trick is to over build and over secure things.

If it is any higher than maybe 1.5 meters above the land it is going over or there is a strong current when the area is flooded then I think you need experienced help. I was going to say civil engineer, but I don't know what your situation is where you are. What the cost to hire an civil engineer as opposed to your resources.
Mvule
Arua
Uganda
(Zone 11)

August 23, 2012
6:53 AM

Post #9251028

We have an existing bridge made up from Eucalyptus logs and scrap timber that we found a round it has served quite well but a bit scrappy and some timber is beginning to rot. I just went and measured it out it is about 28 paces long and roughly 1.2-1.5 m high from the swampy bit. When it floods there is quite a current and a lot of debris gets swept down. But the bridge has held firm unlike our previous attempts which we would have to retrieve from down stream!

So what I would like to do is have something that would be more aesthetically pleasing with an arch perhapse. This would become a focal point for the property. Getting a engineer is beyond our finances though I am happy to ask lots of advise!

The foot bridges I have seen a round have been quite plain and uninspiring. Hence coming to Dave's Garden!
Doug9345
Durhamville, NY
(Zone 5b)

August 23, 2012
7:14 PM

Post #9251721

Ok, from experience you have a pretty good Idea how to make it strong enough. now you just have to figure out how to make it pretty. If you can post a picture maybe you'll get so suggestions.
velveteena
Seattle, WA

August 23, 2012
8:22 PM

Post #9251808

This is SO exciting, Mvule, and I realize just how ignorant I am about so much, and Africa in particular. I have never seen a mahogany tree before, but I sleep in a mahogany bed and eat off a mahogany dining table. Just exactly how much is a pace? Feet and inches or metric??? Metal cable can be quite pricey here, but is often used when you want strength in a material that will "disappear", or blend in. I'm thinking the artistic bits might be on either end where you secure your boards or logs. Do you want it to be the same style as your house? Maybe you could lay some attractive stone or pavers in a path leading to the bridge, and use same to form a platform for your bridge. You might even want to build some steps up to it. This will be so fun to see. Can you possibly post a picture?
Mvule
Arua
Uganda
(Zone 11)

August 24, 2012
11:42 PM

Post #9252877

Here are some shots of the bridge we have with my son for scale! The Eucalyptus we used have put in for about 5 years. The uprights are still strong but I don't know for how much long they will last. but the other vertical slats and handrails are rotting now.

Thumbnail by Mvule   Thumbnail by Mvule   Thumbnail by Mvule   Thumbnail by Mvule   Thumbnail by Mvule
Click an image for an enlarged view.

Doug9345
Durhamville, NY
(Zone 5b)

August 25, 2012
8:16 AM

Post #9253114

Here are my thoughts that maybe someone can add to.

The bridge isn't badly designed. It has stood there for five years which I figure is good for a wooden structure in contact with the ground in a hot climate.

The structure would have looked better with the deck boards cut to the same length and arranged in some pattern with their varying widths.

It would also have looked better with more detail paid to the joinery.

Here is one proposal I have. Use masonry for the post/ pillars. Masonry can be concrete; mortared brick, concrete block or stone. You can put a decorative facing on it of stone or stucco if the material you use is not that attractive.

Use shorter log segments, or beams between the pillars to do two things. One is to build a segmented curve to make the bridge more visually appealing. The current one has a more or less flat run with a sharp drop off at the end. I'm impressed that you have two 25m(?) logs, but that also means that they have twists in them that the deck follows and detracts from the appearance. Do what ever tool work is necessary so that the deck lies flat and even on the support timbers. Pay a lot of attention to how timbers are joined. It makes a big difference in how things appear.

If the decking boards vary in width, place them in some kind of pattern. For example if you have an even number of each, you could lay them wide, narrow, wide, narrow. You could also put all the narrow ones at the ends of the bridge and the wide ones in the middle.
Cut them to all the same length.

I'm just throwing ideas out there. I don't know what materials are available to you on
the budget you have. I'm just going by what you have already used. I have also attached a drawing to show what I'm trying to say. It's not quite in proportion but gives you the idea.

Thumbnail by Doug9345
Click the image for an enlarged view.

Mvule
Arua
Uganda
(Zone 11)

August 30, 2012
6:42 AM

Post #9259105

Thank you for your ideas. The bridge was put together in a hurry by some guys that came to visit. We cut down some Eucalyptus to for the bridge. Hence the long rough cut timber. Then we gathered scrap timber from the buildings we were putting up for the slats.

Thinking about your suggestions I like the cladding on concrete pillars it would then become quite a feature rather than an eye sore! Also the way of getting a curve on the bridge. How would the timber be secured to the pillar? Would we bolt it? It needs to be able to be replaced if the bridge timber rots in 10 years or so.

Thanks for all the help! Tomorrow is my last day of free access to Dave's Garden :-(
Doug9345
Durhamville, NY
(Zone 5b)

August 30, 2012
8:32 AM

Post #9259210

First we can continue the discussion in Home repairs and maintenance which is free or I think you can still dmail me and we can go back and forth there. I have one exchange that's been going on for a couple of years.

There are several way to fasten the timber to the pillars. I have things I need to do right now, but I'll get back to you this evening, which will be the wee hours in the morning where you are.

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