I2.1 Protected Zone
Stress concentrations could lead to fracture in regions of high plastic strain; therefore, there is a prohibition on placement of attachments in the protected zone. Following is a discussion of exceptions to this prohibition and other considerations.
Arc spot welds (puddle welds) associated with the attachment of steel deck to structural steel do not produce high stress concentrations. Research has shown that the performance of full-scale moment connection specimens with arc spot welds in a pattern typical of deck attachment was unaffected by the arc spot welds (Toellner et al., 2015). In addition, a series of tests conducted on full-scale moment connection specimens with 0.177-in.- (4.5-mm-) diameter, full-tip, knurled shank, power-actuated fasteners applied in a pattern typical of deck attachment or grid patterns with 1 in. (25 mm) edge distance and 2 in. (50 mm) spacing satisfied special moment frame (SMF) qualification criteria (Toellner et al., 2015). Negligible differences were found in the cyclic load-displacement envelope (backbone), energy dissipation, and strength degradation prior to fracture as compared to specimens with no fasteners. For these reasons, arc spot welds and power actuated fasteners up to 0.18 in. (4.6 mm) diameter are allowed for deck attachment.
While welds and power-actuated fasteners used to attach deck in typical patterns are permitted, such attachments are prohibited when used for other applications. In other applications, the attachments could be installed by tradespersons who are not subject to the same quality control (QC) and quality assurance (QA) standards that are required for structural steel. The prohibition reflects potential lack of control and inspection to ensure that attachments are provided consistent with the conditions of the testing (Toellner et al., 2015).
The exception in the Provisions permits the engineer of record to designate or approve attachments within the protected zone. Fastening or welding close to, or at, a component edge or with close spacing should not be allowed. Appropriate QC and QA should be required for any attachments within the protected zone.
Erection aids and attachments to meet safety requirements may be necessary in the protected zone. If erection aids or other attachments are required to be placed within the protected zone, good welding practices, including proper preheat, should be used. It may be necessary to remove the erection aid or attachment after ward, and the surfaces of the protected zone may need to be further smoothed by grinding to remove any notch effects. In these and other such cases, the protected zone must be repaired. All such repairs must be approved by the engineer of record to ensure that severe stress concentrations would not cause a fracture during a seismic event.
I2.2 Bolted Joints
The default installation requirements for high-strength bolts in the Specification is to the snug-tightened condition. In Section D2.2, the default condition for bolted connections in the SFRS is pretensioned bolts with faying surfaces of Class A slip coefficient or higher.
I2.3 Welded Joints
These Provisions make reference to AWS D1.8/D1.8M (AWS, 2021) for welded connection details.
Because the selection and proper use of welding filler metals is critical to achieving the necessary levels of strength, notch toughness, and quality, the review and approval of welding procedure specifications is required. The engineer of record may use outside consultants to review these documents, if needed.
Welds are sometimes specified for the full length of a connection. Weld tabs are used to permit the starts and stops of the weld passes to be placed outside the weld region itself, allowing for removal of the start and stop conditions and their associated discontinuities. Because the end of the weld, after tab removal, is an outside surface that needs to be notch-free, proper removal methods and subsequent finishing is necessary.
At continuity plates, the end of the continuity plate to column flange weld near the column flange tip permits the use of a full weld tab, and removal is generally efficient if properly detailed. It is permitted to allow 1/4 in. (6 mm) of weld tab material to remain at the outboard end of the continuity plate-to-column weld ends because the strain demand placed on this weld is considerably less than that of a beam-to-column flange weld, and the probability of significant weld discontinuities with the distance permitted is small. Also, complete weld tab removal at beam-to-column joints is required to facilitate magnetic particle testing required by Section J7.2f, but such testing is not required for continuity plate welds. At the opposite end of the continuity plate to column flange weld, near the column radius, weld tabs are not generally desirable and may not be practicable because of clip size and -area concerns. Weld tabs at this location, if used, should not be removed because the removal process has the potential to cause more harm than good.