Chest and tris are complimentary muscles and are often times done on the same days, working your chest hits your tris a little and vice versa. The same can be said for back/bis. However, it is often a good idea to switch up your routine to create muscle confusion which can stimulate more growth.
No part of your routine should be the same for too long. Otherwise your muscles get accustomed to the lifts and you don't see much in the way of gains.
On a side note I'd look at giving shoulders their own day, unless your satisfied with your current shoulder development. Again that's just my opinion.
btw, UNC sucks! As a current NCSU student, it has to be said. (just kidding) Hope that helps out a little bit bro.