Cantilevered Stacked Block Wall Design 2

[Boiler106]

I've been asked to provide preliminary footing/slab designs for 24 inch thick stacked concrete block walls similar to what you might see in a batch plant for material storage.

These solid concrete blocks get stacked like masonry but do not have vertical reinforcing nor positive attachments from course to course

I am looking for any seismic design resources for these walls using ASCE 7-16 15.6.8 Ground Supported Cantilever Walls or Fences. Specifically, I'm looking to determine the fundamental period.

Using equation 15.4-6 for the fundamental period, it would seem that fi and wi are the same values for a cantilevered wall. Is this correct?

I suppose i can use Ts=Sd1/Sds but these forces are very large even for SDC B.

My concern is that these walls never get designed and Im running a fool's errand to support them. Anyone's input is welcome.

 

[r13]

If the stacked wall isn't anchored to the footing/slab, then what effect it has during a seismic event, it will topple, isn't it?

 

[dhengr]

Boiler106:
They are gravity walls, acting under self weight, two or three blocks high, and they may move to some extent under and lateral loads EQ or impact and considering their own self weight. They are usually not stacked so high as to be a serious health and individual safety problem. Although, that doesn’t mean that they might not be a safety problem. They are usually cast from waste concrete from returning trucks and can have some sort of shear lugs, indentations and matching protrusions cast into their bearing surfaces to key them together.

 

[Boiler106]

@dhengr thanks for the info. the manufacturer wants to stack the blocks 15 ft high. "we've always done it this way"

@retired13 i think we're on the same page. i still have to come up with a prelim footing design, though

 

[MIStructE_IRE]

15ft high?!! Can we see a photo of this?

 

[HTURKAK]

You are responsible for the foundation design only ..is that true? In this case, you will design the foundation for vertical,
lateral, and rocking loading.


But the solid blocks stacked with mortar.. is this true ?

Although there are stone obelisks resisting to EQ for thousands of year and still standing,
If I were in your shoes, I would follow the code and provide steel ribbon reinf. both sides and anchor the ribbons to the foundation.

 

[Boiler106]

15ft high?!! Can we see a photo of this?

No, still in preliminary design but im told "they do these up to 35 ft tall all the time!"

You are responsible for the foundation design only ..is that true? In this case, you will design the foundation for vertical,
lateral, and rocking loading.

Yes, i would be responsible for all of that.

But the solid blocks stacked with mortar.. is this true ?

No, no mortar

Is anyone aware of a design methodology for this? I have a 33% base shear which gives me net tension (P/A-M/S) at just about any height. Maybe there are industry guidelines somewhere? Not sure where to look. This would help me in making my case that this wont work.

 

[dauwerda]

The NCMA has a design manual for this type of retaining wall. I don't know if it addresses seismic concerns or not, but it may be a good starting point. It can be found here:

https://ncma.org/resource/srw-design-manual/

 

[kissymoose]

I don't know if it addresses seismic concerns or not

It certainly does, in quite a bit of detail. Great reference

 

[r13]

I don't think you need to worry the seismic effect on the unbonded block in footing design, no matter it fails or not during earthquake, it will have negligible effect on the foundation. Just design for the normal use conditions, including weight, lateral pressure, snow, and wind, assuming monolithic block wall.