Wood Columns Flashcards
In a free standing 4x10 wood column with no intermediate bracing, which is the cricital buckling axis: x-x or y-y
y-y
what k factor is usually used for wood compression members (columns)
1.0
What is the slenderness limit (l/d) given in the NDS for wood columns
50
What limits the upper end stress value for Euler equation
the crushing failure of the material
how is column instability accounted for in the NDS
by the column stability factor Cp
what are the characteristics of an ideal column
initially straight
homogeneous material
concentric loading
end conditions aligned
how is the critical load determined for a column that fails by crushing
P = F’c * A, where F’c is the factored allowable compressive stress and A is the cross sectional area
along which axis does column buckling occur when the unbraced length is the same for both axes?
the axis with the least moment of inertia, which also has the least radius of gyration
In a typical free standing column, what is generally the mode of failure?
buckling
What 18th century mathematician developed the column buckling formula?
Leonhard Euler
As columns are made more slender, will their critical buckling strength increase or decrease?
decrease
For columns with more than one slenderness ratio, which one controls buckling?
the larger
Which columns are more efficient in load carrying capacity to weight: more slender or less slender columns?
less slender columns (stubby).
The cross-section of a column shown below will buckle about which axis?
(Shown is the elevation of the column with pin ended supports top and bottom; no intermediate bracing; cross section of 4” x 3”)
y-y
When is the Euler Formula valid for determining buckling?
Only below the elastic limit of the material
In the given Euler curve, if point A represents the elastic limit of the material, what would be the failure mode for a column with a slenderness ratio at B?
Crushing
The two sections shown are each made using four 2x6 wood sections. What would be true for a long column?
A. Square Tube
B. I Beam
A would be stronger than B
The pole supported structure shown, is not braced against side-sway and is pin connected at the top, and fixed at the base. In determining a slenderness ratio, what value would you use for K?
2.0
What influences the slenderness ratio of a column?
- moment of inertia
- cross-sectional area
- end support conditions
- length of column between bracing
What will an eccentric load on a column cause?
A bending moment plus an axial load in the column
What are three ways to decrease a column’s slenderness ratio?
Decrease length (L)
Decrease fixity factor (K)
Increase cross sectional radius of gyration r
True or false: Lateral bracing will increase the slenderness ratio for a column?
False
Does the weak axis always fail before strong axis?
If the weak axis is sufficiently braced, the strong axis will fail first.
Determine the theoretical fixity factors, Ke for the following column cases: pin ended top and bottom pin ended top, fixed bottom fixed top and bottom free end top, fixed bottom
pin ended top and bottom 1.0 pin ended top, fixed bottom 0.7 fixed top and bottom 0.5 free end top, fixed bottom 2.0
For a 2x4 stud wall with compression members at 12” o.c., should the repetitive member factor, Cr be applied?
No, Cr does not apply to compression members.
