Anchorage of Vietnam Memorial Wall

[shacked]

I am providing the design and foundation details for a Vietnam Memorial wall for the City I live in in Southern California.(high seismic zone)

This is a 5300Lb granite wall with two 1.25" dia holes placed in the bottom for anchorage. See attached sketch.

I am designing this per ASCE 7-16 section 15 under non bldg structures not similar to buildings. I am using an R value of 1.25 and since the Sds is 1.036 the resultant seismic rxn is pretty large.

My concern is that the two holes that are provided for anchorage would crack the granite wall in the event of the design seismic event. Actually since I am using load combinations per 2.4.5 my DL is reduced to 0.45D and with the uplift force at each A.B. of 10.5kips I do not see a way to anchor this wall section.

Any comments or thoughts would be highly appreciated.
Thanks

 

[oldrunner]

where's the sketch?

 

[Flotsam7018]

Why 0.45D? Should only consider 0.6D, but even that for these situations is likely not applicable in my opinion.

If the entire system is solely this granite wall, than the dead load and the seismic weight are one in the same thus negating any consideration of reduced dead load as your seismic loads would be proportionally reduced. However, I don't believe there is an exception currently provided in ASCE 7 for these cases.

 

[driftLimiter]

Perhaps 0.6-0.2Sds = 0.45. I have seen people determine that the 0.6 D LC is not applicable for systems like this. The thinking is that you know the weight with pretty high confidence and your aware that it would need to be present during an EQ. 0.6D LC is covering uncertainty of weights from different materials over a large area. Still would like to see a sketch ID how 5300 lb component is generating 10.5 k uplift on multiple anchor bolts, sounds like you have a heinous amount of eccentricity. Anyway to reconfigure the AB locations??

 

[shacked]

Sorry Here is the attachment.

Thanks for the reminder about the purpose of the DL reduction. Yes, I applied the 0.6DL to resist the uplift and it reduces to 8.8kips.

Two 1.25" dia holes x 10" deep are provided. I have never worked with Granite before, but I guess if I have the mechanical properties then take a factor of safety of what....

 

[phamENG]

but even that for these situations is likely not applicable in my opinion.

So would you use an overturning factor of safety for the foundation of 1.0?

Using 0.6D is absolutely appropriate here - that reduction has very little to do with variable dead load (I've never designed a building where I thought there might be anything close to a 40% misunderstanding of the dead load)...it's primarily about maintaining traditional factors of safety using a single set of load combinations. That's been intensely debated before - lots of threads on it in the search.

Any chance you can have the wall embedded partially in the ground? Even if you ignore any fixity from embedding it (which I would if it's only 8 inches or so), you could conceal some angles spaced at 2'0" o/c down each face with through bolts. That'll decrease your overall tension demand by increasing your moment arm on the anchors, and decreasing your spacing will further decrease each one.

 

[Flotsam7018]

From my understanding the 0.6DL cases do simply stem from considering a 10% overestimation of the dead loads with a 1.5 FOS baked in, i.e. 0.9/1.5 = 0.6.

But regardless of that interpretation, if the dead load can be known with near 100% accuracy - such as anchoring a piece of equipment with a specified weight from the manufacturer directly to the foundation - the seismic load will be directly proportional to the weight of the equipment, and therefore I see no value in considering reduced dead load combinations for such circumstances. I would simply consider the 1.0DL+0.7E load combination with a 1.5 FOS.

 

[dvd]

Are you providing engineering for the actual granite memorial, or the foundation?

 

[JLNJ]

Maybe, rather than try to justify a different set of combinations, you need to see if you can spec a dowel system which can develop some tension force. Seems reasonable given the nature of the beast. It sounds like it wouldn't take much to make it work.

 

[shacked]

Thanks guys. Actually the load combination that, in my case would reduce the DL to 0.45 is due to vertical seismic effects such as a jump in the ground motion. At least that is what I remember reading the rational is for the 0.2SdsD.

I am providing anchorage and foundation plans for this wall.

Actually, long story about the wall. It was originally intended to be used but for some odd reason it was scrapped. Then some guy found it and he wants to have it erected in the city. Now I am starting to wonder if it was abandoned because of a defect in manufacturing or something along those lines.

Either way it looks like the base of the granite wall should be restrained by some method other then the 2 anchor bolts extending into the foundation.

 

[oldrunner]

Have you considered doing a test of the assembly after completion? On this type of kinda unusual arrangement, I have had a testing company provide a physical test. My client wasn't happy.

 

[jjl317]

Out firm does a lot of work in stone engineering, and what I would typically expect to see on something like this is a concrete (or CMU) structural base wall behind the stone, to which the stone could be laterally anchored (for wind and seismic) - then the base wall carries the lateral load. In some cases, we will see the entire base wall wrapped in stone, to hide structure behind.

If the stone is already fabricated, this option might not be appealing to the design team. Another possibility might be to add a structural steel frame (tube steel?) around the stone, to provide lateral support the stone - though this might pose some challenges for thermal movements

In terms of the analysis of the stone itself, typically standard ASTM tests (C99 Modulus of Rupture and C880 Flexural Strength) are considered in the design, with the results used to check the stone itself. Many projects will have specific tests done for the project, or in some cases, at a minimum, the quarry can provide historical data that can be used. Granite is typically one of the strongest stones, so at least you have that going for you.

 

[LittleInch]

It may not be to the artistic designers desire, but would a 10" wide channel not be required buried in the ground for some sort of height up the sides? Maybe note the full height, but I can't see the lateral loads being able to be contained by those two dowel pins, for wind or seismic.

Or can you not just drill those holes a lot longer, say 4 feet or so inside?

And then lower it onto two poles to be embedded in the foundation?

As currently drawn . built, it just looks all wrong. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[shacked]

Thanks guys. This confirms what I had initially thought about the anchorage.
I will have to let the client know that there has to be some type of additional structure at the base of the wall to prevent overturning and go from there.