10.3.1 Beam Limitations
Minimum beam depth is controlled by the collar dimensions and is 18 in. (450 mm). Maximum beam depth is controlled by strong-column/weak-beam considerations and is limited to 30 in. (750 mm) for practical purposes. The flange width and thickness requirements are limited by the ability of the collar flange to accommodate the beam flange weld and also by the strength of the bolts. A key ConXL requirement for allowable beam sections is limiting the force delivered by the beam to the bolts connecting the collar flange/beam to the collar corner assemblies/column so as to not overcome the pretension load applied to the bolts. This requirement is covered in detail in Section 10.7.
ConXL connections have been successfully tested without reduced beam section reductions in flange width and are qualified for use without such reductions. However, RBS cuts in beam flanges can be a convenient way to achieve strong column weak beam limitations without increasing column weight.
Lateral bracing of beams is in accordance with the AISC Seismic Provisions. During the biaxial moment connection tests, the test beams (W30x108 with 50% RBS, W21x55 with 50% RBS) were not braced at the RBS and were braced at the beam ends, 10 ft (3 m) from the column center.
All moment-connected beams are required to meet seismic compaction requirements of the AISC Seismic Provisions, if RBS beams are used, the width-to-thickness ratio is taken within its reduced flange width as permitted for RBS connections [Section 5.3.1(6)].
10.3.2 Column Limitations
The key requirement for ConXL moment columns is a square sectional dimension of 16 in. (400 mm). Section type (built-up box or HSS) can vary, as can steel strength and wall thickness. All columns used in ConXL moment connections are concrete-filled with either normal or lightweight concrete, having minimum compressive strength of 3,000 psi (21 MPa). Columns are typically filled with concrete at the job site after erection and bolting is complete. The concrete is pumped to the top of column and allowed to free-fall the full height of column, using the column as a tremie. There are no obstructions, stiffener plates, etc., within the column; thus, the column is similar to a tremie-pipe allowing the concrete an unobstructed path to its placement with excellent consolidation (Suprenant, 2001).
Two biaxial beam-column tests (Tests 2111 and 2113, Table C-10.1) were performed with built-up box section columns fabricated using PJP groove welds to join the box section flange and web plates as illustrated in Figure 10.5. In each case, the column marginally met biaxial strong-column/weak-beam requirements, and some limited yielding of column flanges was observed in later stages of the tests. Both tests reached total rotation demands of 0.047 rad without failure or noticeable loss of load carrying ability. In addition, a single cantilever column test (Test 1120) was conducted to evaluate the inelastic behavior of box columns with PJP groove welds. In this test, a 16 in. square built-up box column with -in.- (31-mm-) thick plates joined using a PJP groove weld size of in. (24 mm) was subjected to uniaxial ramped cyclic loading in a cantilever condition, while maintaining an applied axial load of 640 kips (2,800 kN) [approximately 9 ksi (62 MPa) axial stress]. The specimen was loaded to six cycles of displacement each to story drift ratios of 0.00375, 0.005, and 0.0075; four cycles at 0.010 rad; and two cycles each at 0.015, 0.020, 0.030, and 0.045 rad. Initial yielding was observed to occur at displacements of 0.0075 rad. Minor bowing of the flange plates occurred at 0.045 rad. The test was terminated without failure and while still exhibiting positive strain hardening after loading to two cycles at 0.045 rad. No evidence of distress to the PJP welds in any of these tests was observed.
10.3.3 Collar Limitations
Appendix B describes the forged steel material specification used to manufacture the collars. The forging process produces an initial collar (blank collar) slightly larger than the final overall dimensions. The collar is then machined to their manufacturing dimensions within the required tolerances.