The subject of beam splicing occasionally comes up via the question “Are supports required at splice points?” This is typically asked because a beam has already been installed with ‘splices’ located in the span of the member and not over a support pier/column. See example in Figure 1 below.
Fig. 1: Unacceptable Beam Splice
For example, a 3 ply built up beam was specified to span 16′ total across 3 piers spaced 8′ apart. The framer had 12′ long material, so used 3 full length pieces and one piece cut into 4′ lengths with the short pieces staggered in the beam assembly as shown in Figure 2 below. The black segments represent the 12′ material while the blue represents the 4′ cut lengths.
The International Residential Code (IRC) provides guidance in section R502.6 where it states the ends of each beam shall have bearing. For the example above, the ends of the beam are supported but the ends of the individual plies aren’t.
Keep in mind that the ‘splice’ represents a break in the continuity of that individual ply. The break means there is no shear transfer or bending capacity in the ply at that location. Looking again at Figure 2, there is a continuity break in one ply for the left span and two plies for the right span. If 3 plies are truly required for strength, the right side is essentially a single ply when considering the splices/breaks. The performance of the installed beam will not be equivalent to a continuous (unspliced) 3 ply member.
While a ‘spliced’ design is possible, there are no rules of thumb or code guidance for the framer. The potential to induce cross grain tension into the adjacent plies via the connectors is significant. This condition should only be specified by a design professional.
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