Single story commercial 50 x110 rectangle.
Single story commercial 50 x110 rectangle.
(OP)
What are some creative choices for handling the lateral load in a single story commerical wood frame structure that is 50 by 110 feet? We are considering a clear span using 50' open web trusses every 24 inches. We wish to keep the space as open as possible but some posts in the center are acceptable. We are in San Francisco. The 50' front of the building is a complete glass storefront.






RE: Single story commercial 50 x110 rectangle.
DaveAtkins
RE: Single story commercial 50 x110 rectangle.
RE: Single story commercial 50 x110 rectangle.
DaveAtkins
RE: Single story commercial 50 x110 rectangle.
But because of its length and its location in San Francisco what are the choices for handling the rest of the lateral load economically. The front of the building can be a rigid steel frame and the back of the building can be a sheer wall. Will the length of the building require further lateral support and if so how can it be handled economically. I'm trying to avoid using more rigid steel frames spanning the entire 50 feet.
RE: Single story commercial 50 x110 rectangle.
DaveAtkins
RE: Single story commercial 50 x110 rectangle.
Note: My architect consulted his strutural engineer and was told there would need to be a rigig frame in the front of the building spaning 50 feet across above the storefronts. He also mentioned that there would need to be additional rigid frames located approximately at 25, 75, and 100 feet along the length of the building to hadle the lateral load. The very back of the building will be a sheer wall and will not need a rigid frame. I'm looking for alternatives to the rigid frames spanning 50 feet at the 25, 50, and 75 foot locations. I've heard of strong walls,for example.
RE: Single story commercial 50 x110 rectangle.
A diaphram is a flat sturctural unit acting like a deep, thin beam. The term is usually applied to roofs and floors designed to withstand lateral loads. Diaphrmas are commonly created by installing wood structural panels over roof or floor supports.
Can the 50 foot by 110 building be designed with a diaphram so as not to require any additional rigid frames for lateral support? (50 is the store front with a rigid frame, and 110 is the length, and a solid 50 foot rear shear wall)
RE: Single story commercial 50 x110 rectangle.
DaveAtkins
RE: Single story commercial 50 x110 rectangle.
A strong wall is another name for a simpson shear wall, which is just a wood/steel shear wall used in wood buildings. If you have an open storefront, this won't work, and so the rigid frame is required.
RE: Single story commercial 50 x110 rectangle.
I disagree with you. One could design a roof system with in-plane braces to transfer the lateral shear between the rigid frames & to the shear wall. This may or may not be an economical way to resist the lateral loads but it could be done.
Regards,
chichuck
RE: Single story commercial 50 x110 rectangle.
RE: Single story commercial 50 x110 rectangle.
Furthermore, since the two 110 foot walls would be sheer walls along the entire length I was under the impression that this would handle the lateral load of the length of the building (110 feet)
RE: Single story commercial 50 x110 rectangle.
DaveAtkins
RE: Single story commercial 50 x110 rectangle.
Let me try to understand your last posting.
If the building is a rectangle 50x110 with the 50 being the front of the building and the front is facing north and there is a westerly wind, then the wind hits the 110 foot long sheer wall and the wind load is carried to the ground and roof diaphragm by the wall.
Now, it seems intuitive to me that the wind is trying to knock the wall down and the rigid frame on the front (50")and the sheer wall on the rear (50") and the diaphragm between them are what will stop the forces of the wind.
With the diaphram on the roof and sheer walls on 3 sides and a rigid frame on the fourth side we have a very strong box. I still don't intuitively see why additional rigid frames are needed. The diaphragm on the roof seems like a sheer wall built horizontally and it doesn't seem like it would flex much. It would remain a rectangle whether there are westerly winds or north winds. If there are westerly winds the front rigid frame and the rear sheer wall should stop the 110 foot wall from being pushed, raised, or toppled over. Its hard to break a box.
What am I missing? I'd like to understand for purely scientific interest. Obviously, an engeener will have to design the final structure according to local codes.
RE: Single story commercial 50 x110 rectangle.
Let's say you come up with a given required diaphragm strength to support your building and stabilize it. If the material you want to use will not be able to supply that strength, you will have two choices: change to a stronger material or reduce the demand on the diaphragm. Adding additional walls or frames in the interior region of the building would serve to reduce the diaphragm's internal forces and potentially make a material work that wouldn't otherwise. The other option would be to switch to a stronger diaphragm material, such as a steel deck in stead of plywood, or to use a stronger connection, such as having blocking under all the plywood joints and lots and lots of extra nails.
Basically, wind load will hit a wall and travel to the roof diaphragm for the upper part of the wall, and to the slab or foundation directly for the lower portion of the wall. All of this load will then travel through the diaphragm to either a shear wall or a frame. Those in turn will carry the load to the ground. That's not to say there aren't alternate methods of designing your load path but it's probably cheaper than most if not all to build. Besides finding all of these forces and strengths, you also have to check how all of these components will cooperate with each other, and if they will actually behave as assumed. It's fine to assume, for instance, that a frame will share load evenly with a shear wall, but will it actually do so? These are some of the things we check, or should check when necessary.
RE: Single story commercial 50 x110 rectangle.
Do you roof over a steel deck just like a plywood one? What is the preferred or typical roofing material over a steel deck? Can modified bitumen membrane be used?
Can a steel deck be installed over open wood trusses set at 24 inch intervals?
Can 1 1/4" plywood decking with plenty of nails and blocks ever be as strong as a steel deck?
RE: Single story commercial 50 x110 rectangle.
Vulcraft Steel Deck Catalog (pdf file)
I also don't recall ever seeing any values for 1.25" plywood deck. Almost all the diaphragm strength values we use are based on testing. What that means is you get the most bang for your buck so to speak since with testing you know for sure just how much a material and fastener configuration can handle. What it also means is that if what you want to do isn't tested you have to go down to the next lowest size that is tested.
There is, however, some over lap in the strengths of steel and wood deck. The best wood deck will not be as strong as the best wood deck, but if you have enough money you could probably get a wood deck to achieve strength comparable to a steel deck in terms of diaphragm shear values. Now that doesn't mean you need to worry about having to have a steel deck. My post above was intended to give very general information about how some simple buildings may work. Whether you can use wood deck will be governed by your actual building and location and will be up to your professional engineer.
These questions would be best directed toward the professional structural engineer whom you hire in the end, but I'm sure most people here don't mind helping someone learn a bit.
RE: Single story commercial 50 x110 rectangle.
dominic