Peer-to-Peer Standards Exchange

Section 12.2.5.6.1b of ASCE 7-10 thought ASCE 7-22 states that steel ordinary moment frames assigned to seismic design category D and E are permitted within light frame construction up to a heigh of 35' where neither the roof dead load nor the dead load of any floor above the base exceeds 35 psf. I often run into the same two questions regarding this section:

1. What is intended to be included in the 35 psf limit specified in the section and what are the differences between this floor dead load and the dead loads within the effective seismic  weight specified in ASCE 7 12.7.2?
2. When determining whether a building qualifies as light-frame construction, are the framing members of the floor (bar joists, beams, etc.) intended to be considered or is the note referring to just the steel ordinary moment frame and it's framing?

That section of ASCE 7 is intended to permit the use of ordinary steel moment frames in typical low-rise residential construction, commonly composed of repetitively framed wood stud or cold formed steel stud walls.  It is not uncommon in such construction to use moment frames as the lateral support along walls with large window and door openings, and at the fronts of garages.  OMF is permitted because the reality is that it is very difficult to provide the lateral torsional bracing required for IMF and SMF beams, per AISC 341, with the light frame diaphragms.  Thus, OMF's were permitted, as a matter of practicality and with the understanding that loading on such frames would likely not reach yield levels, as the frame design is controlled by deflection and the damping in such structures is higher than the assumed 5%.  So think - single family home, 3-story apartment buidling/townhouse or similar construction.  Note that in the time since this provision was introduced, Simpson Strong-Tie brought their Stong Frame to market providing a practical SMF alternative for this construction type.

Section 12.2.5.6.1b of ASCE 7-10 thought ASCE 7-22 states that steel ordinary moment frames assigned to seismic design category D and E are permitted within light frame construction up to a heigh of 35' where neither the roof dead load nor the dead load of any floor above the base exceeds 35 psf. I often run into the same two questions regarding this section:

1. What is intended to be included in the 35 psf limit specified in the section and what are the differences between this floor dead load and the dead loads within the effective seismic  weight specified in ASCE 7 12.7.2?
2. When determining whether a building qualifies as light-frame construction, are the framing members of the floor (bar joists, beams, etc.) intended to be considered or is the note referring to just the steel ordinary moment frame and it's framing?

Thank you, Ronald! In addition to low rise residential construction, would pre-engineered metal buildings with single skin panel and cold-form girts and purlins as their cladding also fall into this light frame construction?

That section of ASCE 7 is intended to permit the use of ordinary steel moment frames in typical low-rise residential construction, commonly composed of repetitively framed wood stud or cold formed steel stud walls.  It is not uncommon in such construction to use moment frames as the lateral support along walls with large window and door openings, and at the fronts of garages.  OMF is permitted because the reality is that it is very difficult to provide the lateral torsional bracing required for IMF and SMF beams, per AISC 341, with the light frame diaphragms.  Thus, OMF's were permitted, as a matter of practicality and with the understanding that loading on such frames would likely not reach yield levels, as the frame design is controlled by deflection and the damping in such structures is higher than the assumed 5%.  So think - single family home, 3-story apartment buidling/townhouse or similar construction.  Note that in the time since this provision was introduced, Simpson Strong-Tie brought their Stong Frame to market providing a practical SMF alternative for this construction type.

Section 12.2.5.6.1b of ASCE 7-10 thought ASCE 7-22 states that steel ordinary moment frames assigned to seismic design category D and E are permitted within light frame construction up to a heigh of 35' where neither the roof dead load nor the dead load of any floor above the base exceeds 35 psf. I often run into the same two questions regarding this section:

1. What is intended to be included in the 35 psf limit specified in the section and what are the differences between this floor dead load and the dead loads within the effective seismic  weight specified in ASCE 7 12.7.2?
2. When determining whether a building qualifies as light-frame construction, are the framing members of the floor (bar joists, beams, etc.) intended to be considered or is the note referring to just the steel ordinary moment frame and it's framing?