The unbraced frame shown below has all members oriented for bending about strong axis. All the beams are $W1835$ and all the columns are $W1279.$

$a=16ft$

$b=16ft$

$c=20ft$

$d=13ft$

"pin connection"

Find:

Determine the effective length of column $AB,$ assume $P_u=900$ kips and use ${}_b.($Hint: use ${}_b$ from AISC table $4-13)(10$ points$)$

Determine the effective length of column $CH,$ ignore ${}_b.(8$ points$)$

Determine the effective length of column EF$,$ ignore ${}_b.(8$ points$)$