shaking steering wheel

[Qian Qian <qqian@pppl.gov>]

Somehow remember someone post a similar question but didn't follow
the thread. Here is my question:
Is it normal that the steering wheel shakes on a bumpy or uneven highway
at high speed? 
I began to realize this problem when I had several long distance trips
on highways recently. Since it's power steering, I would think any
vibration from front wheels should be absorbed somewhere before it
reaches the steering whe. the shaking steering wheel could indicate
some failure parts. Any idea from net wisdoms?
Regards!

Qian 85' 4000s