The strength and movement of timber varies in its three dimensions. I want to know these dimentions.?
Answers:
Wood will change size as it's moisture content changes... usually, this change is more obvious in the width, and depth measurements of a piece.
Picture it like this...the 'woodgrain' is like a million little tubes...when the wood is 'dry' these tubes shrink, but when there is moisture, these tubes swell up, to carry the moisture...that is what they did when the tree was alive, and they still act that same way.
So, while there may be a minimal change in length (in the direction of the woodgrain), the larger change will be in the measurment 'around' the woodgrain. How much change in size will be determined by moisture content, and original dimension of the lumber. What kind of wood will also affect how much it changes...typically, hardwoods will change less, than soft woods. (Hardwoods would be species like, oak, maple, walnut...softwoods would be pine, fir, redwood. The term "hardwood", or "softwood" has nothing to do with the hardness of the wood itself...but rather, what kind of tree it is. Some "hardwood" species, are actually fairly soft, and easy to work with, poplar, for instance.)
Wood is also affected by temperature. The colder it is, the more it will shrink. (Steel on the other hand, expands when cold)
As to the strength of the timber tho, this is usually not affected by the moisture content. Here in the US, wood is typically kiln dried to 6 - 8% moisture content. That's drier than most locations in the US. This makes the wood fairly stable... it may expand just a bit, but you don't have to worry about it shrinking to a size smaller than you started with.
Moisture change in a piece of wood can also cause changes in the wood shape... bowing, cupping etc. Building construction is usually concerned more with bowing, and furniture construction has to be concerned with the cupping too. So, furniture construction is usually more selective about the moisture content than say, home construction. (While working at a furniture manufacturer, I once received a truckload of lumber, during the rain, and the driver had failed to cover it with a tarp...he had them, he just didnt take the time to do it... I measured the moisture content, before unloading it,and it was topping 20%... I sent the entire load back).
Loadbearing strength of a piece of timber, is strongest along its larger dimensions. Let's take a 2x6-8ft for instance. The 2 inch dimension will be the weakest. If you were to lay the board flat, so that the 2" is the load bearing side (like a shelf), it is the weakest. Turn that board up, so that the 6" side is running up, and you can carry a much larger weight load. This is why all floor studs and rafters, are placed in this direction. Now, if you stand the stud on its end, you can stack even more weight on top...altho, it is a much smaller area to stack on, lol.
You can make timber stronger, by 'doubling' it, that is, adding another piece of timber to it. This is usual, when spanning large areas, or needing to carry more load. Adding a strip of plywood between the two pieces of timber makes it even stronger, and more stable (less prone to bowing).
Ok, how much change can you expect in size in a timber? that depends, again, on the size of the timber to begin with, moisture change, and the species of wood too... some wood is more susceptible to moisture change than others. Hardwoods, for instance, will change less in dimension, than the softer woods. Using that same 2x6 - 8ft length I mentioned earlier, let's assume it is a piece of fir (most joists are fir, or pine)... assuming the wood got 'sopping wet', you might see it grow 1/16th inch in length, and add up to an 1/8inch in the other two dimensions. If this were oak, the measurement change would be in thirty-seconds of an inch, not sixteenths, or eigths.
Now... what to do if your wood has gotten wet?
Wood will usually change it's moisture content about 1% per day, assuming you keep it out of the rain, lol... So... If you have a bundle of floor joists, or wall studs for instance that have gotten rained on... You need to restack the timber, so that it will dry out. Lay out a large sheet of plastic on the ground (Im assuming this is outside), lay some ties ontop of this. Stack your first layer down on these ties, leaving about 3/4" between the boards. Then on top of this layer, put some sticks across, at least 1/2" thick, and lay down another layer. Do this, till you have all the wood stacked. This will leave plenty of room around each piece of wood, allowing it to dry out. Keep it covered when it is raining, of course, or you defeat your purpose, lol. There are some other 'tricks of the trade' that can be used to dry it even faster...adding a fan to blow into the end of the stack, using black plastic to cover it, to raise the temp on sunny days, etc. (by the way, that plastic sheet on the ground is to keep out the moisture that comes up from the earth, in the form 'dew' every morning...you'd be surprised just how much moisture comes up from the ground overnight!)
Anyone who works with wood on a regular basis, should own a moisture meter. Even home contractors, tho most don't. (they assume their supplier has kept the wood dry for them, not always the case). Lignomat has a series of good hand held moisture meters, and they don't cost a whole lot. Ive used these, and the types that you had to drive the pins deep into the wood... while the ones that drive the pins deep are slightly more accurate...I'd stick with the Lignomats ;)
I hope this covered what you were looking for. :)
Other answers:
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Width, Length, & Thickness.