Sample problems needing NDS for Wood Construction
Posted 11 October 2011 - 08:38 AM
I would like to use it in at least a couple problems before the exam. Has anyone come across any problems they can post or can point me in the right direction?
Posted 16 October 2011 - 09:36 PM
Problem 45.3 (11th ed)
A 4in x 4 in (nominal size) timber post is used to support a sign. The post's modulus of elasticity is 1.5x10^6 lbf/in^2. One end of the post is embedded in a deep concrete base. The other end supports a sign 9 ft above the ground. Neglect torsion and wind effects. What is the Euler load sign weight that will cause failure by buckling?
a- 2700 lbf
1) I = bh^3/12= (3.5)(3.5^3)/12= 12.51 in^4 (finished lumber size)
2) k = (I/A) ^ 1/2
k= (12.51/(3.5"x 3.5"))^1/2= 1.01 inches
3) The end restraint coefficient is C= 2.1 (NDS) <--- this line is quoted directly from Lindeburg's problem book. Does anyone know where to find this C=2.1 figure in NDS? (I obviously don't know how to use this reference) Any body have any pointers???
4) The slenderness ratio is:
L'/k= CL/k= (2.1)(9'x12)/1.01 = 224.6
There is note here: L/k is well above 100. (Note that most timber codes limit L/k to 50, so this would not be a permitted application).
5) Fe= (pi)^2 E I/ (L^2) = [(pi^2) (1.5 x 10^6 lbf/in^2) ( 12.51 in^4)] / [((2.1)(9'x12"))^2] = 3673 lbf
Answer is therefore b.
This problem is as close as I have found to what we are looking for... although it has much structural detail. But the question still remains in my mind... the one piece of info that came from NDS... I don't know where to find.
Anybody? End-restraint coefficient C = 2.1 (from NDS). This is a timber post.
I glanced to through the tables and a couple spots in NDS, but I had no luck.
Posted 13 December 2011 - 01:54 PM
There was one problem on the Construction PM session of the Oct 2011 exam that I wish I had it for. But my guestimate probably took less time than having to look it up.
I took the same test, and couldn't agree more. I just hope my thinking was logical at that point, it was fairly late in the day when I got around to that problem.
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