Basement – Why did they hammer nails in half way and bent them over to secure supports

If I'm reading this right(and looking at the final picture), the beam itself is sagging. It may have reached an equilibrium point, and simply jacking up an reattaching it will fix it. But you'll still have a bowed beam.

My inclination is, a properly built beam should be able to span that distance and hold the weight without sagging. I have smaller, longer glulams spanning my basement, supporting two stories. But maybe someone who knows a bit more about structural engineering will chime in.

If you want to create one yourself, I would use like 3 2x12's laminated vertically. Boards are much stronger vertically oriented than horizontally. Think floor joists or door/window headers.

Nah - most of the strength is in shear, and joist hanger nails are nice and fat so they have good shear strength.

also, yanking them is likely to be harder than you think.

The actual nailing schedule seems to be here:

http://www.strongtie.com/products/connectors/H.asp

That suggests that 10d are one size larger than you should use in a model H1Z hanger (since that's the one you pictured and you did not give a model, I have to assume that's the model you have.) The specs call for 8dx1-1/2 (joist hanger) and 8d (standard 2-1/2") - if you are forcing 10d in there they might end up weaker due to surface damage.

The table appears to include a column for "uplift with 8dx1-1/2" implying that installing them with joist hanger nails everywhere is not unheard of. It changes the uplift from 585 to 455 pounds (per hanger) on the H1 size hanger (Z is a coating suffix) (those values are for "DF/SP" presuambly douglas fir and similar quality spruce - for "SPF/HF" the difference is only 400 lbs .vs. 370 lbs.