When beams are unbraced, a multi-ply beam has much lower Moment capacity than a single ply beam of the same dimension. (For example: Double 1-3/4" vs. single 3-1/2".)
BC Calc® software defaults to Unbraced (or braced at supports) resulting in a more conservative design that may differ from published literature (for example: Eastern Specifier Guide).
A lack of beam bracing along the span length may cause lateral movement and buckling failure. Multi-ply beams, even when properly fastened, will deflect laterally much greater (5+ times) than solid beams of the same width. Thus, Bending capacity is reduced significantly more than solid beams for unbraced applications.
When comparing BC Calc output with published literature, it is important to read the general installation notes and footnotes below the span chart. The chart is based on a list of assumptions that must be complied with to be accurate. Bracing is one assumption that directly impacts multi-ply beams.
The Installation Notes specifically state that, "Continuous lateral support of top of beam shall be provided (side or top bearing framing)." The footnote below the Floor Load Tables includes this stipulation that, "Table values assume that lateral support is provided at each support and continuously along the top edge and applicable compression edges of the beam." Design conditions in BC Calc need to match criteria in the span tables to make a valid comparison.
Using BC Calc may allow a design that exceeds the published charts. From the footnotes:
"This table was designed to apply to a broad range of applications. It may be possible to exceed the limitations of this table by analyzing a specific application with BC Calc® software."