This is probably the biggest brick torture I've seen, since my visit to LW Zwolle where the giant Ferry Wheel was twisting Technic beams like if they were made of butter...
Tristan Lostroh from Australia has made some strength tests with Technic Liftarms and Brick Beams, at Faculty of Engineering, University of South Queensland.
The tests were basically done for tension and transverse forces. A second category of tests also focused on strength of pin connections in liftarms. Aim was to find failure modes and damage extension.
This was the second test series and report of of this kind, made that Tristan and you can download it here.
You may find some interesting results, mostly expected and that LEGO Technic beams are quite resistant for the material they are made of and weight. Also you will learn about the most common failure modes, which eventually may guide you on your larger and stressful models.
Those with a Materials, Mechanical or Civil Engineering background will certain be able to extract more conclusions and eventually criticize the applied methods, sampling or whatsoever.
Some discussion on the first and second reports can be found at Eurobricks.