Concrete-framed, multi-story buildings with post-tensioned floors and reinforced-masonry infill make up a large portion of new construction work. Of course, we encounter all of the same issues on just about every building. However, as of late, the one that rears its head all too often is the matter of "construction tolerance" or "Whoa, what happened here? I can't work with this mess." That means that the masonry doesn't line up with the floors, which don't line up with the frame, which doesn't line up with the established building lines-everything is so far out of alignment, that windows and doors, etc., cannot be installed and the building cannot be clad without major field modifications. There have been instances where the top of the floor had to be chipped out because the sliding glass doors wouldn't fit between floors. Gosh, I wish I could show you a couple hundred wonderful pictures from our files.
The International Building Code tells us that "Masonry, except masonry veneer, shall be constructed within the tolerances specified in American Concrete Institute 530.1/ASCE 6/TMS 602. ACI's Specification for Masonry Structures gives us the erection tolerances for masonry. However, in the construction process, the masonry infill comes last; first comes the poured concrete frame, etc., and then the post-tensioned floors and then the masonry. So, first things first, let us look at the code requirements for concrete construction tolerances. Houston, we have a problem.
Although Chapter 19 of the IBC's 2000, 2003 and 2006 versions include ACI Section 318, "Building Code Requirements for Structural Concrete" by reference, there is no mention of "tolerances" except for rebar placement. However, Section 1906, "Formwork, Embedment Pipes and Construction Joints, Paragraph 1.1-General," says that, "Forms shall result in a final structure that conforms to shapes, lines, and dimensions of the members as required by the construction documents." Please note the verbiage, namely "construction documents."
ACI 117-90, "Standard Specifications for Tolerances for Concrete Construction and Materials," addresses tolerances for concrete construction, such as vertical alignment, lateral alignment, level alignment-the list goes on. However, ACI 117-90 is a reference standard only, which means that it is not a part of the building code and is therefore not mandatory. To become mandatory, as the foreword (F2) to the document suggests, ACI 117-90, with project specific modifications, must be made a part of the construction documents. So, the conclusion is that the code addresses masonry tolerances but unless the designers include project specific concrete tolerances in the project documents, there are no concrete tolerances to follow, so to speak.
So, why are these newly constructed building skeletons so far out of whack and what's being done to prevent it from happening? Well here are a few reasons: