9.3.1 Beam Limitations
A wide range of beam sizes was tested with bolted brackets. The lightest beam size reported in the literature was a W16x40 (W410x60). The heaviest beam reported was a W36x210 (W920x313). In the W36x210 (W920x313) test, the specimen met the requirements, but subsequently experienced an unexpected nonductile failure of the bolts connecting the bracket to the column. The next heaviest beams reported to have met the requirements were W33x130 and W36x150 (W840x193 and W920x223). Based on the judgment of the CPRP, the maximum beam depth and weight was limited to match that of the W33x130 (W840x193). The maximum flange thickness was established to match a modest increase above that of the W36x150 (W920x223).
The limitation associated with minimum beam flange width is required to accommodate fillet weld attachment of the W-series bracket and to prevent beam flange tensile rupture when using the B-series bracket.
Bolted bracket connection test assemblies used configurations approximating beam spans between 24 and 30 ft (7.3 and 9.1 m). The beam span-to-depth ratios were in the range of 8 to 20. Given the degree to which most specimens significantly exceeded the requirement, it was judged reasonable to set the minimum span-to-depth ratio at 9 for both SMF and IMF systems.
As with other prequalified connections, beams supporting a concrete structural slab are not required to have a supplemental brace near the expected plastic hinge. If no floor slab is present, then a supplemental brace is required. The brace may not be located within the protected zone.
9.3.2 Column Limitations
Bolted bracket connection tests were performed with the brackets bolted to the column flange (i.e., strong-axis connections). In the absence of additional testing with brackets bolted to the column web (weak-axis connections), the prequalification is limited to column flange connections.
Test specimen wide-flange column sizes ranged from W12×65 to W27×281 (W310×97 to W690×418). Testing performed by Ricles et al. (2004) of deep-column RBS connections demonstrated that deep columns do not behave substantially different from W14 (W360) columns when a slab is present or when adequate lateral bracing is provided for the beam and/or column in the absence of a slab. Based on the similarity in performance to that of the RBS connection, the CBB is prequalified to include column sizes up to W36 (W920).
The behavior of a flanged cruciform column in CBB connections is expected to be similar to that of a rolled wide-flange shape. Therefore, flanged cruciform columns are prequalified, subject to the limitations imposed on rolled wide-flange shapes.
Two of the tests were successfully conducted using a built-up box column. In the first box column test, connections were made on two opposing column faces. Then, in the second test, a connection was made to the orthogonal face of the same column. These two tests were intended to prequalify a box column participating in orthogonal moment frames. The tested box column was 15 5/8 in. (400 mm) square (Adan and Gibb, 2009). Consequently, bolted bracket connections are prequalified for use with built-up box columns up to 16 in. (400 mm) square.
Based on both successful wide-flange and built-up box column testing, acceptable performance would also be expected for boxed wide-flange columns. Therefore, the use of boxed wide-flange columns is also prequalified. When moment connections are made only to the flanges of the wide-flange portion of the boxed wide flange, subject to the bracing limitations mentioned previously, the column may be as deep as a W36 (W920). When the boxed wide-flange column participates in orthogonal moment frames, neither the depth nor the width of the column is allowed to exceed 16 in. (400 mm), applying the same limit as a built-up box.
9.3.3 Bracket Limitations
The ASTM cast steel material specification used to manufacture the brackets is based on recommendations from the Steel Founders’ Society of America (SFSA).
The cast brackets are configured and proportioned to resist applied loads in accordance with the limit states outlined by Gross et al. (1999). These limit states include column flange local buckling; bolt prying action; combined bending and axial loading on the bracket; shear; and, additionally for the B-series, bolt bearing deformation and block shear rupture.
In tests representing new applications, the bracket column bolt holes were cast vertically short-slotted. The vertically slotted holes provide field installation tolerance. In tests representing a repair application, the holes were cast standard diameter. There has been no difference in connection performance using either type of cast hole (Adan and Gibb, 2009).