PROJECT: Western Flyer Crane repair (Allied Sysetms crane)
ENGINEER: J.Erickson: M.Brown
UNITS:
REFERENCE:
Roark's Formulas for Stress and Strain  6th edition
Mechanical Engineering Design: Shigley 5th ed.

Title: Static & Dynamic analysis

PROPERTIES & ASSUMPTIONS:

Boom extension 
Rectangular Tube

For each Gusset, compute the Inertia:  

parallel Axis Th.

For 4ea Gussets there are 8 welds.  Therefore the total Inertia of the Gussets is:

Maximum Weld Stress @ end of Gusset:  

Looks like we can't get over 4 here
but we feel there is plenty of safety factor anyhow.
Below: Jon took a look at trying to plug weld to the existing verticals to see if we gained anything
 (not much)
Calc Inertia for each Plug Weld:  

parallel axis th.  

For 4 plug welds there are 8 weld sides: