Shields have a "health" bar in blue, artillery (especially heavy) actually takes quite a large chunk out of the bar. However, any fire directed at something inside the shield causes loss on the bar. In theory you can put enough shields close enough together that you could protect something from a nuke, but anti nuke sites are better.
If a unit gets inside the field it bypasses the protection as it is "inside" the shield.
Hope this explains the shield story
i think even with plenty of shields it'll not work..a nuke will still take it out. flatten the entire area. no protection against nukes. except for anti-nukes. and sometimes even they can't stop it. it has happened a few times with me. but bunching several shield units together could make the target definitely more difficult to take out against other stuff.
[Edited by saurabhfzd, 4/30/2010 4:15:05 AM]