When supported by a wall or beam, the bottom flange of BCI or AJS joists shall be nailed to the support with two 8d (BCI) or 10d (AJS) nails (one on each side of the web). In addition, some types of joist hangers also require flange nailing (see corresponding hanger literature).
Reaction design values are determined by full-size tests on wood I-joists in accordance with ASTM D 5005, Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists. An additional factor of safety is applied to the reaction value beyond what is normally applied to other wood design properties. This factor takes into account “..normal construction tolerances which may reduce specified bearing length, minor damage to joist ends during installation…” (ASTM D 5055 section X6.2.2). Thus, minor splitting due to flange nailing is expected and accounted for in the reaction design value.
Boise Cascade EWP Engineering has conducted specific testing on flange nailing and corresponding splitting. From this testing, splitting that does not exceed a maximum length of 3" measured from the inside face of the support does not reduce the reaction capacity of the joist. For splits that exceed 3" up to 12", the joist shall be reinforced as shown below:
For Splits that Exceed 12"
The joist shall be headered off to the adjacent joist if those joists are structurally adequate to support the additional load. Please refer to the following table for uniformly loaded (no point loads besides the header) floor joists; joists may only be headered off if the spans are equal to or less than the values listed.
Splitting in Top Flanges at Bearing
Splitting may occur in the top flanges from the use of larger nails or angled nailing of the rimboard-to-flange end connection. Since the stress in the top flange at end bearings is minimal, such splitting does not significantly affect the joist’s strength capacity.