ARS97
Structural
- Feb 24, 2010
- 160
I have an interesting problem. It's something that I haven't dealt with before, but perhaps some people on here who typically deal with commercial wood designs can steer me in the right direction. It's a bit longwinded, but here goes.
First off, my specialty is industrial steel structures. I have done only a very few wood-related designs in my career, and they were pretty basic.
A local volunteer fire department is building an addition. This new addition is roughly 70' x 65' in plan and is a typical gable roof with 18' eave height and 3:12 roof slope. It's a pretty decent size structure. This building has two (2) elevated levels besides the ground floor (slab) where the fire trucks are stored. The first elevated level is for offices, which is supported by wood floor trusses, and a 100 psf live load is being used. The second elevated floor is smaller, located within the wood roof trusses, and is used for minor storage (20 psf LL).
Early on, before I became involved, some people within the fire department procured the services of an architect, who began the "layout" this building. Originally this building was to be wood framed, so the architect got a local wood truss supplier involved. The wood truss supplier "designed" some floor & roof trusses along the way (which only supported some gravity loads), but they limited their design to only those wood items. They did not handle the supporting wood walls, roof rafters, or any other part of the building. (The architect was going to take care of that somehow.) In their design, they assumed a few steel beams with posts that hold up their floor trusses on the first elevated floor.
Since some "minor" steel design was neededm the fire department & architect called the company I work for and ask if we can size a few steel beams and columns for them. Sure, no problem. Once I get involved however, I raise the same question that any structural guy would - what about lateral loads and stability? Who was handling that? This building layout, as large as it was, had no interior shearwalls. Instead, the plywood floor diaphram would have to transmit all the load out to the exterior walls. However, they're not going to provide much help since the large garage doors blow right through them and there's nothing there to act as a shearwall.
At this point, the architect wisely decides that they need to appoint a structural EOR for the project. Long story short, I recommend going with an interior steel frame on the lower level (basically a knee-brace frame), which supports (both vertically and laterally) the wood floor & roof system above.
The plan was to have the wood truss supplier design the individual floor and roof trusses (PE stamped) and I would handle the rest, including the incidental wood walls and roof rafters in the upper area.
Here's the problem - the structural frame of this building is a mix between an upper level wood frame and a lower level steel frame. You can't simply separate the two (2) systems....they act together and need to be analyzed as such. The only person involved in this process who is able to perform an overall frame analysis and determine the forces within both frames is a structural engineer (me). The truss supplier is off to the races already "designing" these trusses, but the question is, with what loads? So.....how do I best convey the internal loading requirements for the wood floor & roof trusses to the truss supplier? Are we talking basic stick diagrams with max tension/compression loadings, or what?
This has been a real headache. Any help or guidance would be really appreciated.
First off, my specialty is industrial steel structures. I have done only a very few wood-related designs in my career, and they were pretty basic.
A local volunteer fire department is building an addition. This new addition is roughly 70' x 65' in plan and is a typical gable roof with 18' eave height and 3:12 roof slope. It's a pretty decent size structure. This building has two (2) elevated levels besides the ground floor (slab) where the fire trucks are stored. The first elevated level is for offices, which is supported by wood floor trusses, and a 100 psf live load is being used. The second elevated floor is smaller, located within the wood roof trusses, and is used for minor storage (20 psf LL).
Early on, before I became involved, some people within the fire department procured the services of an architect, who began the "layout" this building. Originally this building was to be wood framed, so the architect got a local wood truss supplier involved. The wood truss supplier "designed" some floor & roof trusses along the way (which only supported some gravity loads), but they limited their design to only those wood items. They did not handle the supporting wood walls, roof rafters, or any other part of the building. (The architect was going to take care of that somehow.) In their design, they assumed a few steel beams with posts that hold up their floor trusses on the first elevated floor.
Since some "minor" steel design was neededm the fire department & architect called the company I work for and ask if we can size a few steel beams and columns for them. Sure, no problem. Once I get involved however, I raise the same question that any structural guy would - what about lateral loads and stability? Who was handling that? This building layout, as large as it was, had no interior shearwalls. Instead, the plywood floor diaphram would have to transmit all the load out to the exterior walls. However, they're not going to provide much help since the large garage doors blow right through them and there's nothing there to act as a shearwall.
At this point, the architect wisely decides that they need to appoint a structural EOR for the project. Long story short, I recommend going with an interior steel frame on the lower level (basically a knee-brace frame), which supports (both vertically and laterally) the wood floor & roof system above.
The plan was to have the wood truss supplier design the individual floor and roof trusses (PE stamped) and I would handle the rest, including the incidental wood walls and roof rafters in the upper area.
Here's the problem - the structural frame of this building is a mix between an upper level wood frame and a lower level steel frame. You can't simply separate the two (2) systems....they act together and need to be analyzed as such. The only person involved in this process who is able to perform an overall frame analysis and determine the forces within both frames is a structural engineer (me). The truss supplier is off to the races already "designing" these trusses, but the question is, with what loads? So.....how do I best convey the internal loading requirements for the wood floor & roof trusses to the truss supplier? Are we talking basic stick diagrams with max tension/compression loadings, or what?
This has been a real headache. Any help or guidance would be really appreciated.