Complaint - Masonry f'm in US codes

[JAE]

For many years, here in the US, the IBC has provided two methods for determining the masonry compressive strength f'm.

1. Prism tests - where the block is laid up and a prism of several units with mortar are taken to actually test in a compression machine. Not too unlike concrete cylinder tests.
2. Unit Strength method - where the type of unit (its individual net compressive strength) and the mortar type is combined in a table where f'm values are simply provided.

Usually we use method 2.

Under more recent IBC versions, the tables have been removed from the code with reference to TMS documents.
In TMS 402, which is the engineer's masonry design code, there's no tables provided.
Instead, the tables are now found sunk into the masonry specification TMS 602.

Took us quite a while to find them. Very maddening.

I don't see the logic in putting this information in the TMS 602 specification, which isn't usually part of the DESIGNER's tool chest but rather a spec guide for creating actual project specifications for construction. Seems very non-intuitive.

I recently attended a masonry seminar where a lot of the attendees (who were masonry suppliers and contractors) were moaning about how masonry was loosing ground to cast concrete and other products.

My thought: [blue]Make the design and specification of masonry easier and perhaps engineers would use it more.[/blue]

Rant over, thanks for your patience.




Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Hokie93]

I don't follow the logic either and can relate to your rant. However, the f'[sub]m[/sub] table has been in the Specification since at least the 1995 version of TMS 602 so it is not exactly a recent change.

 

[JAE]

Perhaps so but the struggle for me was expecting it to be in the IBC and, not finding it there, went looking in TMS 402, where it is nowhere to be found. Only in the definition of f’m in 402 was there a reference to it in 602.

f’m is a DESIGN THING and should be in the design section of the CODE. Not hidden away in a sample specification.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[dhengr]

JAE:
Ah! But…, today codes and specs, design guides and the like are not really meant to make your life (our life, as engineers) easier. They are all part of the giant codes/specs. publishing mega-complex, mostly not well coordinated with each other, written by a bunch of voters in a vast demographic groups, democratically elected to participate from a very broad range of people, each with a very narrow view and opinion, and with little need for a broad understanding of the greater subject and how it is used in real life working world, and all wanting to guard their little domain and turfdom. These codes and specs., etc. get very little real peer review, proof reading, serious editing, and coordination, gotta get em out the door to increase the publishing revenue and number of expensive incoherent books sold. Remember, the next one is only a few years hence, so we gotta get started on it, while we are not furnishing errata for the current ed.

Remember when the material manufactures and their associations used to give them away or at least sell them at a reasonable price, and provide free seminars to get us to design with and understand their materials and systems? They even had magazines and journals which you could afford, and which helped you keep up with the progress and changes in the industry. That was before the publishing, short code cycle, ICC ESR’s and the like became an industry unto itself, which had to keep it churning at all cost and protect their job and turf from the poor s.o.b. who had to use their inferior product.

 

[masonrygeek]

I'll answer your question in a slightly facetious way to make a point. Once you choose what strength (f'm) to design your masonry why do you care how the masonry meets the f'm? I mean, you may want to specify the proper mortar type and ensure a minimum block strength, but once you specify f'm its up to the mason to figure out how to make the assembly meet that requirement. I think that is one of the reasons you'll find the information in the spec (TMS 602) vs the code (TMS 402). And the code and spec are always published together so the information is there, it just may not be obvious where to find it.

I also have to take exception to dhengr's comments about codes getting very little peer review, proofreading, etc. Actually, the broad distribution of experience on the committee allows the code to get vetted in many different ways. Of course, we always need more practicing engineers on the committee to show how they use the code and how it can be made simpler. Over the last couple of cycles, the masonry code has included more tables instead of text to make it easier to find and interpret code requirements. Compare that to ASCE 7 which has become a research tome. And each code writing body has a Technical Activities Committee that oversees the changes, makes sure they are accurate, and makes sure they have followed all of the proper procedures. While some requirements are hard to understand it could be that it is a very complicated issue with compromise being achieved with the final wording.

So please - keep these types of recommendations coming to make the code easier to use. I can guarantee that the committee is listening whether a change is made or not. BTW - the TMS 402/602 is now on a 6-year cycle (next version will be 2022) and that was a direct result of designers saying things were moving too fast.

 

[JLNJ]

The masonry guys need to get with Hilti and other fastener people to develop some tables for solid-grouted materials for other than f'm=1500. There are pages and pages of concrete fastening for any given Hilti product, yet one little table for masonry.

If we could get higher capacity out of the masonry it would make using and specifying masonry more appealing. Let's set the baseline at f'm = 2500 psi rather than 1500 psi.

 

[masonrygeek]

JLNJ I couldn't agree more!!! In fact, the 2016 version of TMS 402/602 has f'm = 2000 psi as a baseline (the values were calibrated with newer testing and ASTM C90 now requires block units to be above 2000 psi too). But many block units are stronger than the minimum so a higher f'm is possible on many projects.

 

[IRstuff]

So, apparently, this identical table was in two related, but different documents; I can certainly see the logic in removing it from one of the two documents, since there's always this annoyance for spec writers to have to update multiple copies of information and rev the document just to accommodate a change that was driven from something else.

So the question, then, is whether this table more naturally belongs in other document or the current document.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[JAE]

Once you choose what strength (f'm) to design your masonry why do you care how the masonry meets the f'm?

We have typically used f'm = 1,500 psi over the years but recent trends allow a higher value in DESIGN.
So it is nice, as a designer, to use that f'm table to determine a code acceptable f'm value based on what block strengths are available in the local area of the project.
Sure, we could simply say on our plans - f'm = 3,150 psi. But if that requires a special order on blocks and extra cost we don't want to just spend client's money like that.

So the question, then, is whether this table more naturally belongs in other document or the current document.

Exactly. Should be in 402.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[MrHershey]

I'll answer your question in a slightly facetious way to make a point. Once you choose what strength (f'm) to design your masonry why do you care how the masonry meets the f'm? I mean, you may want to specify the proper mortar type and ensure a minimum block strength, but once you specify f'm its up to the mason to figure out how to make the assembly meet that requirement. I think that is one of the reasons you'll find the information in the spec (TMS 602) vs the code (TMS 402). And the code and spec are always published together so the information is there, it just may not be obvious where to find it.

Kind of where I am. Specify the f'm you need and then it's up to the supplier/builder to get you there. Not sure it makes sense to put the details of attaining that f'm in TMS 402 any more than it would make sense to put the details of attaining a specific f'c into ACI 318.

Masonry code and specs in general have needed a lot of updating and cleaning up (which to their credit they're working on). But I'll defend them a bit here. These tables have been present in TMS 602 for a long, long time with IBC chapter 21 just duplicating them. Though the tables were removed from the IBC to avoid showing redundant information, the section on masonry construction materials where the tables previously were found (2103) now points directly to TMS 602 for blocks, mortar, grout, reinforcement, and accessories instead. TMS 602 is referenced at least four times in this section, TMS 402 isn't referenced once. Criticism seems a little harsh here. They removed redundant information and told users exactly where to find it.

 

[JAE]

OK OK - I get that we can very simply dump the requirement of achieving f'm onto the contractor via a specification for construction (602).

But I as a design engineer do not want to ONLY do that.

I like to have some semblance of control over my built projects and to have that control I prefer to know and understand my local material sources and what they can find.
If I just worked on projects in one small local town I could see relying on what is "always done" with regard to block strength + mortar type = designated f'm.

But with projects over larger regions, or perhaps the entire US, I want to know what sort of "standard" block strength" is locally available. They do vary.
That would then pair with the mortar type I specify and get me a truly achievable f'm.

But that is just my preference of course.

My main gripe and venting was due to the fact that the f'm table was removed from the IBC (historically a source for DESIGN efforts) and not added to TMS 402, which was and is a source for DESIGN efforts.
To me that would have made sense. It is a table that provides a designer (not a contractor) with a means of setting an appropriate f'm value.
Instead it was left in 602, which is a specification for "minimum construction requirements" per its own definition.

Contractors generally don't give a damn about f'm, or most likely, don't know what f'm even is.
They provide individual units meeting the specs and they provide a mortar type based on a proportion that meets the spec. That is all they typically want or need to know.

So basically - f'm is a thing that engineers/designers use and care about. f'm is not a thing that contractors tend to deal with. So why is it defined in 602 and not 402?

MrHershey - your quote: [blue]"Not sure it makes sense to put the details of attaining that f'm in TMS 402 any more than it would make sense to put the details of attaining a specific f'c into ACI 318."[/blue] confuses me a bit.

ACI 318 certainly does talk about acceptance of concrete in Chapter 5 - or chapter 26 of 318-14 and outlines how mixes are to be prepared, how cylinder tests are to be interpreted, etc. Even with that - concrete doesn't achieve f'c in the same way masonry achieves a set f'm using the Unit Strength method. There is no Unit Strength method in concrete for f'c.





Check out Eng-Tips Forum's Policies here:
faq731-376

 

[wannabeSE]

JAE
I think proportioning mixes is gone in ACI 318-14 and it directs you to ACI 301. If I remember correctly, you can’t get f’m less than 2000 psi with C90 CMU with the revised ASTM standard and TMS 602. Structural requirements have been disappearing from the IBC since it’s inception. Do you remember how few references were required with the 97 UBC?