No, TrashMan is technically right in this case. The reason why girdered structures are used is because they weigh much less and can therefore better support their own weight as well as other load.
However, solid pipe IS stronger than a hollow tube of same material and diameter. So yes, a solid chunk of metal
would be stronger than girder structure. But, in space the weight is nonexistant (as it depends on gravity, although inertial mass is still present and can cause some pretty interesting structural strength requirements if you want the ship to be capable of turning fast or being able to accelerate rapidly). In fact, structural strength in traditional engineering sense has little relevance to ships that spend their entire lives in space, like the Orions or Colossus.
However, how are you going to pull that off? Weld enough girders together to form a solid hull? The amount of building materials increases drastically. Structurally it's not
that much stronger, and even though you might get some better armour plating as a result, the maneuverability and acceleration of the ship decrease linearly as the mass increases.
A girder-like skeleton structure with internal hull makes sense, especially if you consider that more than likely Colossus was rushed into service when the Shivans made themselves a threat again. The timing of Colossus to enter service when it did always seemed a bit conspicuous to me, except if you assume that the GTVA chose to push it into service partially incomplete.
Explains the lacking turrets as well.
