Truss Bridge Kit
What Is Wood Wet Rot And How To Prevent And Cure It?
Compared with dry rot, wet rot is hardly a problem ! It is basically the timber decaying naturally in the presence of high levels of moisture. There is almost always a structural defect causing the problem, it may be that the wall adjacent to the timber is suffering from damp, or water collecting on the timber. Any structural problem must be tackled at the same time as the timber is treated otherwise the problem is likely to reoccur. The problem may just be damaged paint finish on the timber allowing the actual wood to absorb excessive moisture. Damage is normally limited to the timber although the original structural problem may also cause other areas to be affected by damp (such as plaster or just decorations).
What to look for:
Check vulnerable areas of timber, such as window and door frames, for signs of rot. The bottom of frames is more susceptible to rot where water can collect or the wall/floor is suffering from damp. If the paint finish is damaged, this can increase the risk of wet rot. However, although the paint may look sound, the timber underneath may be rotting from the back. You will often see a professional builder push a thin bladed knife into painted timber frames, the blade should stop after a very short distance; if it goes in upto the handle, it is a almost certainly a sign of rot behind the paint. Timber suffering from wet rot will feel spongy (even through a coat of paint) and look darker than the surrounding timber. When dry, the timber will easily crack and crumble into fine particles. Timber in the roof can also be at risk especially where there is roof damage allowing rainwater to run onto the roof timbers.
Wet Rot Prevention:
Ensure that all external timber frames are adequately painted to protect the timber from frontal ingress of water.
Be aware of any damp walls and address the problem, it could be a missing/damaged damp proof course (dpc), a bridged dpc or a bridged cavity. If necessary seek expert advice as the symptom may be just a sign of a bigger problem.
Make sure that any soil and other debris is cleared away from around the bottom of timber frames. Check the roof space for the ingress of water, you may not see daylight through a hole in the roof, the water could be running down the underfelt behind the tiles onto timber some distance away from the hole. When it is raining, go into the roof with a torch, the shining of water on a timber or felt normally stand out very easily.
Other favoured places for wet rot are under the kitchen sink, bath, shower, washing basins, toilet and behind the washing machine etc.; all areas where a small leak from either a water supply or drain could go unnoticed for a long time but where timber could become saturated with water.
Wet Rot Treatment:
First of all treat any structural problem, there is no point in repairing the damage to the timber if it is going to reappear.
If wet rot occurs in structural timbers (such as roof trusses, floor joists), expert advice should be sought as the implication for structural integrity must be established.
In other areas, the rotten timbers should be removed and replaced; if the damaged area is fairly small, it can be cut away and a new piece of timber joined to that remaining. If the damage is confined to a very small area, an epoxy based repair kit can be used to fill the damaged area once it has been cut back to sound timber and the new surface of the wood treated with a suitable primer. Preservative tablets are available which are inserted into the timber adjacent to the repaired area to protect the timber 'from within'. If there is any doubt that the structural problem has been eliminated, the new and adjoining timber should be treated with a proprietary wet rot treatment before redecorating.
After repair, external timbers should be protected with adequate coats of paint or some other suitable timber treatment/preservative.Visit the Woodworking Plans Website pages for more wood and woodworking articles.
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Can anyone tell me where the force is going?
?Hi i am doing a project about building bridges and i wonder if you guys can tell how the force is going if you put a weight on a truss bridge. I wonder if you could show me with arrows where the force goes.
Here is a picture of the bridge i want you show! 
http://lib.store.yahoo.net/lib/discoverthis/truss-bridge-building-kit-b.gif
Thx in advantage and have a nice day!
The forces on a truss are usually planar.
http://en.wikipedia.org/wiki/Truss
Take a look at this
http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/e/e8/Bridges_65.png&imgrefurl=http://commons.wikimedia.org/wiki/File:Bridges_65.png&usg=__oSvD0IrqTnbVIKrxgKeunBGrHF8=&h=336&w=852&sz=5&hl=en&start=14&um=1&tbnid=YPk_bFq-A0sHYM:&tbnh=57&tbnw=145&prev=/images%3Fq%3DForces%2Bon%2Ba%2Bbridge%2Btruss%26hl%3Den%26client%3Dfirefox-a%26channel%3Ds%26rls%3Dorg.mozilla:en-US:official%26sa%3DN%26um%3D1
In absence of horizontal loading due to wind, all forces are either normal (y coordinates) or along the connecting girders. There is (virtually) no rotational force at the truss connections.
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