Wood Columns

Question 1

In a free standing 4x10 wood column with no intermediate bracing, which is the cricital buckling axis: x-x or y-y

Answer 1

y-y

Question 2

what k factor is usually used for wood compression members (columns)

Answer 2

1.0

Question 3

What is the slenderness limit (l/d) given in the NDS for wood columns

Answer 3

50

Question 4

What limits the upper end stress value for Euler equation

Answer 4

the crushing failure of the material

Question 5

how is column instability accounted for in the NDS

Answer 5

by the column stability factor Cp

Question 6

what are the characteristics of an ideal column

Answer 6

initially straight
homogeneous material
concentric loading
end conditions aligned

Question 7

how is the critical load determined for a column that fails by crushing

Answer 7

P = F’c * A, where F’c is the factored allowable compressive stress and A is the cross sectional area

Question 8

along which axis does column buckling occur when the unbraced length is the same for both axes?

Answer 8

the axis with the least moment of inertia, which also has the least radius of gyration

Question 9

In a typical free standing column, what is generally the mode of failure?

Answer 9

buckling

Question 10

What 18th century mathematician developed the column buckling formula?

Answer 10

Leonhard Euler

Question 11

As columns are made more slender, will their critical buckling strength increase or decrease?

Answer 11

decrease

Question 12

For columns with more than one slenderness ratio, which one controls buckling?

Answer 12

the larger

Question 13

Which columns are more efficient in load carrying capacity to weight: more slender or less slender columns?

Answer 13

less slender columns (stubby).

Question 14

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”)

Answer 14

y-y

Question 15

When is the Euler Formula valid for determining buckling?

Answer 15

Only below the elastic limit of the material

Question 16

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?

Answer 16

Crushing

Question 17

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

Answer 17

A would be stronger than B

Question 18

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?

Answer 18

2.0

Question 19

What influences the slenderness ratio of a column?

Answer 19

• moment of inertia
• cross-sectional area
• end support conditions
• length of column between bracing

Question 20

What will an eccentric load on a column cause?

Answer 20

A bending moment plus an axial load in the column

Question 21

What are three ways to decrease a column’s slenderness ratio?

Answer 21

Decrease length (L)
Decrease fixity factor (K)
Increase cross sectional radius of gyration r

Question 22

True or false: Lateral bracing will increase the slenderness ratio for a column?

Answer 22

False

Question 23

Does the weak axis always fail before strong axis?

Answer 23

If the weak axis is sufficiently braced, the strong axis will fail first.

Question 24

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

Answer 24

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

Question 25

For a 2x4 stud wall with compression members at 12” o.c., should the repetitive member factor, Cr be applied?

Answer 25

No, Cr does not apply to compression members.