k Factor Calculation

Find the “K X-X” (i.e. bending about the x-x axis) factor for the W12x106 Column using the Figure 2 on Page 3-5 of the AISC/ASD ninth edition.

Figure 1: 3D View of the structure

Figure 2: Plan view of frame structure Given: W30x116: Ix = 4930 in4 W12x106: Ix = 933 in4

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Solution: G at Base = 10 (assume supported but not rigidly connected)

IC

G=

∑L

C

I ∑ LY Y

933in =

4930in

30 ft

11 ft + 4930in

= 0.258 ≈ 0.26 30 ft

Connect points GA=10 and GB=0.26 (for x-x) (Bending about x-x)

Figure 3: Alignment chart for effective length of columns in continuous frames – Sideways Uninhibited

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1. Click on Design->Steel control tab on your left hand side. 2. Make sure that the code is set to AISC ASD in the Data Area. Select the column for which the KZ has to be determined. Click the Define Parameters button in the data area. 3. Select the KZ option in the Design Parameters dialog box and press the calculate button.

Figure 4: AISC ASD KZ Calculator in STAAD.pro.

Figure 5: AISC ASD KZ Calculator in STAAD.pro. 4. Press the No button for the KFactor dialog box that will appear. Press the Assign button to assign the KZ to the selected column.

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STAAD SPACE START JOB INFORMATION ENGINEER DATE 03-Jan-07 END JOB INFORMATION INPUT WIDTH 79 UNIT FEET KIP JOINT COORDINATES 1 0 11 0; 2 30 11 0; 3 60 11 0; 4 60 0 0; 5 30 0 0; 6 0 0 0; MEMBER INCIDENCES 1 1 2; 2 2 3; 3 3 4; 4 5 2; 5 6 1; DEFINE MATERIAL START ISOTROPIC STEEL E 4.176e+006 POISSON 0.3 DENSITY 0.489024 ALPHA 6.5e-006 DAMP 0.03 END DEFINE MATERIAL MEMBER PROPERTY AMERICAN 3 TO 5 TABLE ST W12X106 1 2 TABLE ST W30X116 CONSTANTS MATERIAL STEEL ALL SUPPORTS 4 TO 6 PINNED PARAMETER 1 CODE AISC KZ 1.73315 MEMB 4 FINISH

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