Frequently turbulence is circular in motion. So one wingtip is in
the up air, the other is in the down air. It's usually incorrect to
think of turbulence just being an upsurge or downsurge of air. It is in
all directions. This is why Va, although a good idea, does NOT really
GUARANTEE no structural damage. Slowing down helps, but since you can
be hit with oncoming air that almost instantly raises your airspeed (as
well as violently moving the plane up or down), it IS possible to get
structural damage in extreme turbulence even if you are flying at or
below Va.