Under floor frames of CH-47 Chinook were investigated, and topology optimized by Boeing and NCDMM (link). Possibility of using monolithic “one-piece machining” structures, which is an increasing trend in aviation and topology optimization of such structures were studied. Ramp downs in the ribs were utilized as can be seen from the photo below, which permits further weight reductions. 
It is stated that %15 weight reduction was obtained as an average of all 4 cases studied. 3 profiles, namely T, I and + were studied, where I profile did not have connected edges, which does not seem to be ideal.