physics behind residential framing

[wolfwatcher667]

hey, Im in a carpentry class in highschool and am researching the physics behind all the parts of framing. Studs, floor joists, rafters, cripple studs, ect... I apalogize, I didnt know where to ask, but any help is apreciated. I find this interesting and do realise that I may not find all the answers here. Just hoping. If you know of any reliable resources that will tell me of the physics behind all the parts, that would be apreciated also. Thank you all for your time, and I look foward to hearing more about the topic.

[Cole]

Not sure of what you are asking us?

[Joe Bartok]

By physics do you mean basic engineering? For example, studs behave like columns, joists behave like beams? The physical properties of the wood such as modulus of elasticity, weight or allowable stresses? How these properties interact with loads imposed under different conditions?

[Rich]

I guess this is why you're taking the class :)
The pieces of framing are pretty simple in and of themselves - they act compression, tension, shear, and deflection. Reasons for the above reactions are caused by weight of the structure, wind, snow, earthquakes, etc.

[wolfwatcher667]

I guess Im asking not for the physics behind the wood itself, but why the pieces are put together the way they are, what is the framing members purpose and how does it fulfill its purpose. So I guess the physics behind each members purpose really. Why are the King studs placed on the side of each door, and window to, right? How do the cripple studs under the window, or above the door, also headers, help? ect... Get what I mean? Thanks for your replies, and yep, lol, that would be my purpose of taking the class. Need to learn these things or you wont make it far right, lol.

[Rich]

Ok - let's start with a wall stud. It's main purpose is for weight bearing - roof, wall, etc. A trimmer is for bearing the weight of headers. Headers are for bearing the weight across openings. King studs help hold the hinge points together between trimmers, cripples, and headers. Cripples are to allow attachment of materials - keeping with the same spacing layout as the wall studs (above headers) - below windows they are 2 fold - one for attaching the sheathing and for bearing the weight of the window itself. Top plates (typically double) to bear the weight of the roof trusses/rafters that don't line up with wall studs below. Sheathing is used to give shear resistance to the structure - this can (in some cases) be replaced by let in framing material or metal straps.

[Dex]

Just a general statement that might help you visualize the purpose of framing materials.

Framing (structural) members in a building are made to transfer the weight of any materials above it to the foundation (eventually).

That's a real rough definition, but it might help you a bit.

[Cole]

Welcome to the forum, Dex.

[Joe Bartok]

It would be nice if there was a website for beginners with clear, simple, not-too-technical images and text.
This is the best I've come up with so far.
http://www.cwc.ca/applications/light_framing/index.php

[wolfwatcher667]

Hey, thanks everyone, I really apreciate your help on this.

[wolfwatcher667]

Hey Im guessing the floor joists and perimeter beam is for holding the weight of all the walls and the roof, right? Is there any other reason except to walk on? And bridging, what is the point of bridging? It goes between each floor joist, is it just to support the joists? Thanks again for your time, I apreciate it.

[Rich]

Joists do not necessarily hold the weight of the roof - it may in some cases but not in a general sense - it's really only to walk on.
The perimeter rim joist is to help transfer roof loads to the foundation - it doesn't really hold it. Without the foundation the rim joist would be useless in holding much weight at all.
Bridging is more useful than just to stabilize the joist - it can also help share some of the weight between joists - making a diaphraghm if you will.

[Sweep]

The purpose of bridging or blocking is to limit the lateral movement of the bottom of the joist (ie twisting) when loaded. The primary result is to reduce deflection or bounce of the floor. Bridging is usually considered x-bracing with metal straps and blocking is usually considered solid wood between the joists although construction terminology differs by region. In my opinion, if the joists are sized properly for deflection (instead of the minimum sizes in code tables) or if there is a strapped ceiling below the joists, the bridging is not very important for normal spans.