mtotheos
Structural
- Aug 4, 2023
- 1
I am designing a slab-mounted structural steel frame to support a new large 60" diameter exhaust duct inside an existing industrial facility over a 100' span, about 20 feet off of the finish floor. Nothing else will be attached to the new frame besides the duct.
The project site is Seismic Design Category C and the duct has an importance factor of 1.0. Looking at ASCE 7-16 Ch. 13, that would indicate the duct itself is exempt from the requirements of Ch. 13.
However, when it comes to designing the "pipe rack" type of frame that will support this duct, I am trying to understand what lateral forces to apply in the design. Would you design the frame per Ch. 15 - Nonbuilding Structures, and calculate out the seismic response coefficient (Cs) by selecting a structure type out of the tables in Ch. 15? Are we then applying that calculated Cs value to the self-weight of the structural frame AND the duct? Or since the duct was exempt are we not accounting for its seismic load being transferred into the frame?
Or since the duct is exempt and we are designing this frame solely to support the duct within an existing building, are we to just follow the basic requirement of Section 1.4.2 and analyze the structure for a minimum of 1% of total dead load in both lateral directions?
The way I have done it in the past, for something like this that utilizes significant structural steel framing (not just talking about supporting a duct with a piece of Unistrut) would be to calculate Cs for the structure per Ch. 15, and then accelerate all dead load on the structure (including the duct) by Cs.
The project site is Seismic Design Category C and the duct has an importance factor of 1.0. Looking at ASCE 7-16 Ch. 13, that would indicate the duct itself is exempt from the requirements of Ch. 13.
However, when it comes to designing the "pipe rack" type of frame that will support this duct, I am trying to understand what lateral forces to apply in the design. Would you design the frame per Ch. 15 - Nonbuilding Structures, and calculate out the seismic response coefficient (Cs) by selecting a structure type out of the tables in Ch. 15? Are we then applying that calculated Cs value to the self-weight of the structural frame AND the duct? Or since the duct was exempt are we not accounting for its seismic load being transferred into the frame?
Or since the duct is exempt and we are designing this frame solely to support the duct within an existing building, are we to just follow the basic requirement of Section 1.4.2 and analyze the structure for a minimum of 1% of total dead load in both lateral directions?
The way I have done it in the past, for something like this that utilizes significant structural steel framing (not just talking about supporting a duct with a piece of Unistrut) would be to calculate Cs for the structure per Ch. 15, and then accelerate all dead load on the structure (including the duct) by Cs.
