How do you augment garage trusses to help a loft?

Are they attic trusses?.You can easily get more trusses and shorten the space between them

Yes... surround them with steel

With a high garage ceiling on the first floor, Id insert a glue laminate (GLU_LAM) wooden beam. Its a guge piece of PLYWOOD that's about 15" by 5" in cross section and is made in 10 ft increments of length. The glu lam would ride parallel with the roof axis and the trusses would lay on top and a a floor would lie atop the trusses. "Attic trusses" have "knee wall" on each end of the acute angle of the triangle base .
Id also, if the building has a span of >20 ft, put in two or three metal upright posts to support the glu lam and trusses. The glu-lam will have to be supported on each building end by a stack of support uprights that carry the weight to the foundation

I'm glad you asked that farmer.

I thought he was talking about hernia trusses.

goodness, they must really be uncomfortable. What kind of wood are they made of?

Usually hardwood. They work best for supporting your swinging sirloin, aka illinois rolled roast.

your Baltimore Bollocks

First, what kind of storage, ie. how much weight spread over what area?

The easiest thing to do is ask your truss supplier. They can tell you exactly what the bottom chords can support. I'd say that that design load wouldn't be a figure too much higher than the dead load imposed by the "warm" side ceiling covering, eg. drywall/sheetrock and the "cold" side insulation.

Unless someone specifically asks for attic trusses meant to carry a 2nd floor/attic storage, truss manufacturers don't just make them extra strong for potentials. They have to bid them for the purpose intended or they would never have their quotes accepted.

Right in the middle of the garage door opening.

Maybe you should stick to misleading students on geological issues, Farmer.