big box building lateral system

[bjb]

Most of the buildings I work on are much smaller than a big box store, and are often very different in other ways too. My question isn't specific for particular project, but just a general inquiry.

Is it more common to use shear walls fro the lateral force system or frame action between the roof framing and the columns?

 

[DaveAtkins]

In general, shear walls are the most efficient lateral force resisting system, because they are already there for other reasons (i.e., they are bearing walls, they enclose the building, etc.).

Braced frames would be the second most efficient lateral force resisting system, because they resist lateral forces through AXIAL loading in their members (and axially loaded members are more efficient than bending members).

Frame action is the least efficient way to resist lateral loads, but must be used if the other systems are unavailable.

DaveAtkins

 

[JAE]

For "big box" buildings such as warehouses, the roof height can run between 25' and 40'. Moment frames just won't work with that one-story height in an economic way.

Usually you see braced frames - X-braces or chevron braces.

If the building has tilt-up concrete walls, they can be utilized as shearwalls.

 

[bjb]

The kind of building that I'm thinking about is something like a WalMart, Home Depot, etc. Based on me looking at the roof framing I see that usually these buildings are divided with expansion joints, and often the bottom chord of the joists is extended to the column where it looks like it's been welded. With a 40 to 50 foot column spacing, I wonder if the designers are trying to use frame action at each column line by creating continuity between the joist and the tube column. Vulcraft has a book where they talk about this. If these were my buildings, I would try to use perimeter shear walls if possible.

JAE,

I'm not experienced with precast wall panels. If you have them on a job and want to use them as shear walls, do you indicate on the drawings what the required in-plane shear capacity of the panels is, or do wall panel manufacturers have catalogs with this value, similar to precast floor plank allowable load tables.

 

[UcfSE]

If you want a specialty engineer to design your wall panels (tilt panels), you should give them any loads they need to design the panels and connections if they are to be included. Of course, you can always design them yourself if you want. Big box buildings like grocery stores and Walmarts are nearly square in plan and have enormous masonry shearwalls. Because of the aspect ratio or the roof, the diaphragms usually work fine. Expansions joints can be detailed to allow shear transfer across the joint. I live in a low seismic area also, so maybe it isn't the same every where.

 

[JAE]

I'd agree with UcfSE - concrete wall panels can either be tilt-up (cast on site) or precast.

With the tilt panels, we usually design the wall and reinforcing, checking it for shear capacity, etc. but leave the erection embeds and any additional steel required due to erection up to a separate entity - usually a firm that prepares the shop drawings for the wall panels themselves.

For precast, you need to do preliminary design to ensure that the thickness you are looking at is appropriate for the applied shear, wind loads, etc., but the final design is by the precaster and based upon load criteria that you should supply.

 

[rholder98]

I was just in Wal-Mart, and happened to notice the bottom chords of the joist girders welded to the plate on the column. I don't like it, myself. I've seen older engineers do this as a standard detail, without intending to use the frame in the lateral system (not a good idea), so there's really no telling if this was the primary lateral system or not. I've never seen any Wal-Mart plans, so I don't know what system they typically use. I have, however, seen a lot of Home Depot plans, having worked on several. These are typically designed as noted above, with tilt walls used as shear walls. You would design the tilt walls for final, in-place loads, and anything required for lifting would be designed by the contractor's consultant, as UcfSE and JAE said.