SteelPE
Structural
- Mar 9, 2006
- 2,747
I have a question regarding the design of cold formed light gauge metal girt systems.
All of my projects to date have been covered by the IBC code system. I design mostly structures 3 stories or less in height. I design 2-3 warehouses per year. Sometimes these building have corrugated metal siding other times insulated metal panel (IMP). These systems often required cold formed girts placed at regular intervals to support the panel system (anywhere from 5’-0” o.c. to 7’-6” o.c.).
The girt systems are governed by the AISI spec (which I find to be a very difficult spec to get through). When designing these girt systems, I am typically confronted with unbraced length difficulties with regards to lateral torsional buckling (LTB). I know the AISI has some exceptions listed towards to the back when it comes to LTB and the corrugated metal siding. However, when I am tasked with designing IMP systems, I typically default to installing some type of LTB bracing on the girt (at the 1/2, 1/3 or 1/4 span points). My detail is a lt gauge strap that loops over the girt and is attached to the inside face of the metal panel (not the best system). We call these girt straps. We have designed the IMP systems this way for the past 10 years and occasionally have some slight push back from the clients.
This week I had one client, a steel fabricator/metal siding installer, completely blow up at the installation of these girt straps. He is complaining that these straps are cutting into his profit margin (which I DGAF about). He is looking to eliminate the straps… I told him no.... explosion.
The question I have is in regards to the design of these system.
Is it the correct approach to assume that IMP systems do not brace the metal panel the same way corrugated panel does?
Is there a better way to increase the strength of these systems without having to install the straps?
All of my projects to date have been covered by the IBC code system. I design mostly structures 3 stories or less in height. I design 2-3 warehouses per year. Sometimes these building have corrugated metal siding other times insulated metal panel (IMP). These systems often required cold formed girts placed at regular intervals to support the panel system (anywhere from 5’-0” o.c. to 7’-6” o.c.).
The girt systems are governed by the AISI spec (which I find to be a very difficult spec to get through). When designing these girt systems, I am typically confronted with unbraced length difficulties with regards to lateral torsional buckling (LTB). I know the AISI has some exceptions listed towards to the back when it comes to LTB and the corrugated metal siding. However, when I am tasked with designing IMP systems, I typically default to installing some type of LTB bracing on the girt (at the 1/2, 1/3 or 1/4 span points). My detail is a lt gauge strap that loops over the girt and is attached to the inside face of the metal panel (not the best system). We call these girt straps. We have designed the IMP systems this way for the past 10 years and occasionally have some slight push back from the clients.
This week I had one client, a steel fabricator/metal siding installer, completely blow up at the installation of these girt straps. He is complaining that these straps are cutting into his profit margin (which I DGAF about). He is looking to eliminate the straps… I told him no.... explosion.
The question I have is in regards to the design of these system.
Is it the correct approach to assume that IMP systems do not brace the metal panel the same way corrugated panel does?
Is there a better way to increase the strength of these systems without having to install the straps?
