It was certainly not constructed in memory of Nelson. It is merely on the same site as the Nelson Pillar which as anfieldman says was blown up by the IRA in 1966. If it represents anything, it would be an abstract concept - probably some guff like "a confident, thrusting Ireland within Europe". My favourite nickname for it is "the Stiffy by the Liffey".
It took ages to be erected, during which time, a gigantic crane stood near Clery's department. When it was finally taken down, some wag said "I can see Clery's now, the crane is gone".