Wednesday, September 23, 2009


So, here is a little review outline I came up with ...


1. Stability

1) Internal
2) External
3) Global

2. External Stability

1) Sliding
2) Overturning
3) Bearing

Typical min FOS values …

Sliding … 1.5
Overturning 1.5
Flexible Systems 2.0
Rigid Systems 3.0

* Remember in the FOS calcs … keep the overturning effects and gravity (righting) effects separated … don’t use `net’ values.

3. Bearing Pressures

* Make sure you are clear on this `middle third’ thing. Remember, soils cannot take negative pressures.

… f = P/A +/- M/S

And if your resultant is not in the middle third, you better make some adjustments until it is!

4. Loads

1) Dead loads
2) Wind loads
3) Snow loads
4) Lateral soil pressure loads
5) Load combinations

5. Dead loads

*Make sure you are all over this stuff. If I bring in a piece of `Material X’ and a tape measure and a bathroom scale, can you determine specific weight, weight per linear foot, weight per square foot, and so on.

*Make sure you can deal with tributary width, area, etc.

* Make sure you can take material weights, say, in a roof plane, and translate them to a `footprint’ weight.

*Also, remember that `truss’ problem we did? … where we determined the weight of the timber truss, and then I asked how much do they contribute to the roof dead load (footprint) value, spaced 8 ft o.c.? …

… f = W / area = 1000 lb or so / (8 ft o.c. x 24 ft wide) = about 5 psf added …

* And it would be a good idea to have that one handout of `weights of construction materials’ or whatever it’s called, at your fingertips, unless you have found a better list (to have at your fingertips).

6. Wind loads

* You need to have some grip on the terminology …

MWFRS … versus … C&C

7. Snow Loads

* Have the snow load `lesson’ from the course Schedule printed off … so if I gave you some information dealing with `Exposure Category’, exposed or sheltered, heated or cold, slippery unobstructed or not, and slope, importance, and a value for ground snow load / ft of elevation (like 0.033 psf/ft), you could sort through the equations

… pf = 0.7 Ce Ct I pg … and … ps = Cs pf


… come up with a design roof snow load.

8. Load Combinations

* Make sure you understand that foundation calc we did, with the gravity loads D, S, and L coming down, and how we combined the loads to look at soil pressure … and how we came in later and added the (overturning) effect of wind … and also how we were allowed to increase the allowable soil pressure in resisting load combinations including wind.

9. Anything that I emailed you, or emphasized or directed you to on the blog … you should probably consider important.

10. Anything that I wrote on the board, and especially underlined … you should consider (real) important.

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