Existing Concrete Buildings - how many cores? 2

[QC-engr]

Our group is looking to undertake a testing & analysis of some concrete warehouse to confirm the Owner's intent of storage purposes (PSF)
Unfortunately, we don't have any existing drawings, so we're needing to get some concrete cores initiated but I'm sure how many cores to request.

Some info:
* (3) identical warehouses
* 4-story, 32,000 SF per floor
* simple square concrete frames at perimeter, interior columns ~24" dia
* elevated floors are flat (no girders, waffles, etc), panels and capitals at interior columns.
* supposedly all built around the same time. all within a mile of each other.
* photo surveys put the construction around 1930-1950s
* existing signs say the floor has 300 psf capacity

I suspect I'll need sample collections (separate) of the columns vs. the floors.

Not looking for anybody to do the math (but I'll hear opinions) - just looking for some guidance towards the right text/guide to use?

TLDR:
how many samples fulfill a "representative sample" across an entire building (and bonus - if there are triplets of the same building, do I need to triple the corings, or can the other two have abridged versions of that testing/coring program)

THANKS SO MUCH IN ADVANCE!

 

[JAE]

ACI 318-14 (and later) - Chapter 27 makes reference to sampling cores in existing building.
They reference ACI 214.4R as a source guide for sampling and statistical determination of f'c based on your cores, the size of building, etc.

 

[Luceid]

I remember doing this for a warehouse type building a few years ago - and I believe I was referencing ASCE 41 which has similar checkboxes to what JAE is saying - based on square footage, number of floors, etc. Look for the concrete chapter in there

 

[lexpatrie]

Why not just specify out live load testing?

The reinforcement schemes in this time frame were all over the place, and the code didn't recognize the full static moment until 1971.

As to the number of cores - the number needed to be statistically meaningful is fairly large. I wonder if there was a tendency back that far to use different strength for the columns versus the slab or if that was a later trend.

 

[milkshakelake]

Besides cores, I think you'd also need a ton of rebar scanning. And the rebar would be 40 ksi or something, instead of 60 ksi.

 

[lexpatrie]

An excellent point on the rebar yield stress.

Caltrans, in the absence of anything else, has some values, (including values for old structural steel).

Bridge Design Memo 4, Material Properties for Existing Structures, Caltrans, October 2022.

This seminar may prove useful -

https://www.youtube.com/watch?v=CZ23grNlrog

 

[QC-engr]

Very much appreciating all the feedback!

Wanted to ensure - in addition to the concrete coring, yes, we're getting rebar coupons tested and GPR to find the rebar layout.

 

[TLHS]

lexpatrie, presumably before live load testing you'd need to do enough investigation to make sure it's safe enough to be worthwhile. Otherwise you're potentially just breaking things. To me, you load test stuff where you basically already know that it should be okay but calculation or full validation would be impractical. So, things like old construction that isn't going to meet current codes or that you can't figure out documentation on, but you're pretty comfortable that overall strength should work, or construction that wasn't done in full conformance but that you expect the major load carrying portions are intact.

The other stuff you load test are things that are basically screwed if they don't pass. This is stuff like new buildings where something got majorly screwed up, or certification of things that have been through major incidents like fires or earthquakes.

Primarily deflection controlled structures like low rise wood would be a different situation, obviously.

This is totally not my wheelhouse, though, so maybe live load testing is typical in more conventional conditions than I think?

 

[milkshakelake]

Personally, I've never load tested stuff. ~30% of my work is existing buildings. It's always been calculations along with material testing and investigation. It's not that I'm against load testing, but I'm not sure how you would account for things like pattern live loading. Also, if you have 300 psf live load in a 20'x20' bay, that's 120 kips of materials you need to forklift over, which is about the total dead load of a house. Though I guess presumably, it would be done with hydraulic jacks, like with pile load testing. Now that I think about it, you could put a bunch of hydraulic jacks between floor and ceiling slab, and have the concentrated loading done to approximate uniform loading. The upper slab will be fine because the dead load will counteract the live load. The bottom slab will be complicated because I don't know how a strain gauge can read how much is being applied to one slab only. Some gravity load from upper slab might be transferred to the lower one.

 

[lexpatrie]

I wouldn't say live load testing is typically done, no. The business never took off so there aren't many providers around, if you ask me. It's just a route, and if you're dealing with something goofy, i.e. 1940s building, then it's got to be some kind of option, particularly if it's a warehouse floor and they don't want to use it as a warehouse anymore you could just live load test it for the "degraded" live load and go.

It's most commonly done with water bags, though. There are other means that are described in the following paper. Loading rams, etc.

Load Testing of Concrete Structures, Gustavo Tumialan, Ph.D., P.E., Nestore Galati, Ph.D., P.E. and Antonio Nanni, Ph.D., P.E., Structure Magazine, June 2014.