Ignoramus6193 wrote:
....
Lag bolts are 5" long, 5/16 in diameter, there is four of them,
screwed into those 2x12 and 2x10s.

In which direction?

This is for pulling, not lifting.

Same problem -- load isn't as great, but it's still a safety issue if it
pulls out while somebody is behind the ramp.

It's not at all an optimal design choice and it would seem essentially
trivial to make the lags machine bolts, ideally w/ the plate also on the
back side.

Note the pulling resistance of lags is only slightly over the weight
from the calculator posted which provides essentially a safety factor of
1.0 -- again an indication you're under-designed.

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