The cheapness is in the build design used. It doesn't have much effect on functionality in most circumstances except in design limit states pertaining to corrosion resistance and other maintenance factors.
It is a very cheap build. That does NOT mean it works less well or withstands an explosion less well (actually this depends but not the intended purpose of design). It is not comparable to prestressed concrete sections and reinforced girder designs. Not comparable in cost and not comparable in longevity. But this is perhaps the point also. It is built in a and for a strategically important setting. That certainly weighs in on design decisions when they planned the bridge and settled on a design. At least it should.
So either the contractors just cheaped out for the sake of cheaping out (note that this does NOT have anything to do with blast resistance or planning for blast resistance as some fanboys would no doubt begin talking about now despite having no knowledge in this field). Or it could have been done intentionally to save money because they did a risk assessment and decided to go cheap because just in case the Ukrainians/NATO destroy it or whatever. Both designs have their advantages and disadvantages re utility and re replacing sections.
