mastruc
Structural
- Sep 30, 2013
- 15
Afternoon, all:
I've got a question on a design process that I'm trying to put together for what feels like a simple situation, but my experience with foundations like this is limited. We're going to be surface-mounting an 8' chain-link fence on a continuous concrete curb, 12" wide. The curb will, in places, effectively serve as a very short sheet-pile, retaining about 12" of granular backfill at maximum. We're making the assumption that the client may put signage or windblocking of some sort on the fence, so the lateral loads I'm estimating are fairly significant (~130 lb/ft of fence for this preliminary design.) My gut says that the post spacing should be close enough to treat the wind-loading as a line-load in that fashion, for the sake of curb/soil interaction.
The question I have is, what's a reasonable way to model this thing? My first thought was to shoehorn the situation into the "standard" way of designing a sheetpile by simulating the wind-force as a low-density "soil" that's 12 feet in height to get the resultant in the right place (that is to say, 4' above the top-of-curb.) But since the textbook way of solving for the embedment depth (based on resisting active soil pressure alone) is based off of the geometry of the loads (see pg 23 of this design process: the depths that result are unrealistically large.
My second thought (and this is a worse thought) was to use IBC's equation for nonconstrained posts (section 1807.3.2.1) and treat the curb like a series of adjacent 12"x12" post footings. Although IBC doesn't specify a minimum spacing between post foundations, this doesn't strike me as in the spirit of the code -- for one thing, it seems to make sense that this equation was derived assuming a bulb of passive soil resistance that an immediately neighboring "post" would encroach on, giving an overall non-conservative result.
I discussed this briefly with a structural in the office who also hasn't run into this particular situation. In trying to track down a tried-and-true method online, I'm coming up dry. Any thoughts?
I've got a question on a design process that I'm trying to put together for what feels like a simple situation, but my experience with foundations like this is limited. We're going to be surface-mounting an 8' chain-link fence on a continuous concrete curb, 12" wide. The curb will, in places, effectively serve as a very short sheet-pile, retaining about 12" of granular backfill at maximum. We're making the assumption that the client may put signage or windblocking of some sort on the fence, so the lateral loads I'm estimating are fairly significant (~130 lb/ft of fence for this preliminary design.) My gut says that the post spacing should be close enough to treat the wind-loading as a line-load in that fashion, for the sake of curb/soil interaction.
The question I have is, what's a reasonable way to model this thing? My first thought was to shoehorn the situation into the "standard" way of designing a sheetpile by simulating the wind-force as a low-density "soil" that's 12 feet in height to get the resultant in the right place (that is to say, 4' above the top-of-curb.) But since the textbook way of solving for the embedment depth (based on resisting active soil pressure alone) is based off of the geometry of the loads (see pg 23 of this design process: the depths that result are unrealistically large.
My second thought (and this is a worse thought) was to use IBC's equation for nonconstrained posts (section 1807.3.2.1) and treat the curb like a series of adjacent 12"x12" post footings. Although IBC doesn't specify a minimum spacing between post foundations, this doesn't strike me as in the spirit of the code -- for one thing, it seems to make sense that this equation was derived assuming a bulb of passive soil resistance that an immediately neighboring "post" would encroach on, giving an overall non-conservative result.
I discussed this briefly with a structural in the office who also hasn't run into this particular situation. In trying to track down a tried-and-true method online, I'm coming up dry. Any thoughts?
![[idea]](/data/assets/smilies/idea.gif "[idea] [idea]")
![[r2d2]](/data/assets/smilies/r2d2.gif "[r2d2] [r2d2]")
