Computerization has brought significant advantages with regard to making changes to
drawings. Before CAD, moving a gridline some distance to the north required redrawing
every sheet that had a plan view of the columns on that grid. CAD saved time, because with
CAD every plan sheet could be opened and one half of the building could simply be cut and
pasted into the new position. Of course, moving the columns required adjusting the beams,
the elevations, perhaps even some details, and it was easy to forget to tie everything back
together again or to miss that an associated section or detail had now been changed. If there
were multiple stories, simply opening every drawing required a significant amount of time.
With a parametric relational modeler present in the BIM software, the relationship of the
columns to the grids can be locked, at which point, when the grids are moved, all linked
elements are automatically extended. Sections and the outline of details are automatically
updated, because they are merely views of the 3D building model.
This parametric relationship between building objects potentially offers significant time
savings, although it should be noted that human nature dictates that the easier it is to make
changes, the more changes will be demanded (closer to deadlines!) by the rest of the design
team. As BIM becomes more prevalent, it may become even more important to regulate and
limit project changes. Just because changing the model is easy, does not mean changes
should be frequent, as engineers still must perform design calculations for every iteration, as
highlighted in the next section.