Nope. Some cities have their rough bits, but those are never places you'd want to go anyway. Are there any parts you're particularly worried about?
Actually Singapore is so safe that we may forget about the danger in many parts of US, especially in some areas of big cities.
There are places you may want to go and the places themselves are okay, but the surrounding areas are not that safe.
A few examples I know of and I have been to.
1) LA, University of Southern California
2) Philadelphia, University of Pennsylvania
3) Troy, up state New York, Rensselaer Polytechnic Institute (okay the whole Troy is not a good place, except RPI).
I always feel not that safe in big cities in US, including LA, Cleveland, Chicago and Houston. On the other hand, no such fear in Nagoya Japan and Shanghai China. But of course there are good places in these big cities as well. So one needs to be cautious and carry out research first before going.
On the other hand, there are very nice and very safe small cities and small towns in US, even in decaying city like Cleveland. Many small cities in Southern California are very nice, for example Irvine California.