Reinforced Masonry - Partial Grout 2

[RFreund]

Does anyone have any good examples for Partially Grouted Reinforced Masonry Walls subject to axial and bending forces?

I'm looking for one example of a wall subject to in-plane forces (shear walls) and one for out-of-plane forces with Axial Load.

I have read through most of the Reinforced Masonry Engineering Handbook, 6th Edition (great reference btw) however all of the discussion and examples involve solid walls (Except for a partially grouted wall subject to bending and shear only).

I'm trying to develop a spreadsheet or Tedds for word calc that can handle a partially grouted wall subject to in-plane or out plane forces. I believe the calc will be very similar to a solid wall except I need to adjust the compression area so that only the grouted cells, flanges and webs are used. From there I can use basic statics of equilibrium approach for ASD or Strength design.

Thanks in advance!

EIT

 

[concretemasonry]

Take a look at the ACI 530 and accompanying commentaries.

Keep in mind that the wall is considered and structural element and not a collection of pieces. Most of the allowables depend on the f'm of a hollow prism that is really dependent on the strength of the strength of the masonry units. The grout strength is not critical and grout is just used to transfer the load between the rebar and the masonry units, which are usually the most highly stressed because they are the outer fibers.

Some engineers set a maximum compressive strength allowed on the grout in an effort to create a balanced design.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JedClampett]

The TEK manuals are a great help. And they're free. I looked at manual 14-7B.
Here is a link (

http://www.ncma.org/etek/pages/TEKList.aspx).

If it doesn't work, go to the NCMA website (

http://www.ncma.org/resources/design/Pages/Map_Sponsor.aspx)

and pick a local supplier. They all have links to the TEK manuals.

 

[RFreund]

Thanks for the referance.

I believe I have read this before and it is helpful.
The only issue is that it deals with flexure and axial separately. Then suggests to superimpose the stresses (this is similar to the unity approach). Which is fine and I may write a spreadsheet for this as well. However they also suggest a computer or iterative approach which is what I would like to see an example of.

I will work on it some and maybe draw a sketch to highlight any specific questions.

My main point/question, I guess is that if you are going to do an iterative approach you must use the T-flange approach when finding your compressive area.

EIT

 

[concretemasonry]

RFreund -

Just go back to the test results and information that has been developed over the past 50 years according to prescribed standards.

Much of it was conducted at the NCMA laboratory that has the capability of full height walls (20' high or so) that also does contract testing for numerous organizations.

Granted, the individual results may be confidential, but the staff has learned a great deal about the behavior of masonry, that unfortunately many people try to cut up into small pieces to micro-manage a structure. For years, the engineers have been active in the writing of many papers and in the formulation of the masonry codes (MSJC/TMS/ACI 530 and previous papers) to put the information into code and design language.

The companion to the ACI 530 document (Masonry Designers Guide?) reflects the practical aspects of masonry behavior.

Unfortunately, many of the older masonry design books (west coast seismic related) are based on the old concept of full grouting since it was done because it was cheaper at the time. Since then there have been some more efficient methods of design and construction based on different units and higher strengths, better controls, inspection methods that allow better use of masonry (based on the errors and misconceptions of seismic use from the 1960's) without changing the codes. - "We use the old codes, but use them better".




Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

concretemasonry - Good points but I think RFreund is looking for design approaches - going back to "test results" probably isn't going to do him any good.

 

[concretemasonry]

JAE -

The comments were meant to provide background and credibility to the resources available. The design approaches need to understand the basis of the real results that the codes are based on. Unfortunately, the design approaches just add to the credibility of the codes established.

When you go through the several days of seismic effects and the resulting damage followed by the revealing after shocks in the Northridge,CA events as a disaster study, and end up seeing a 20' high wall tested a few days later for out of plane loading at a lab and then sitting through a few days of MSJC/ACI/MSJC meetings to develop the first ACI 530 code you develop a relationship between the real structural action/reaction and adapting it to codes gives confidence in the resources available for the world of design.

Dick


Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

concretemasonry. I understand that you have lots of experience in masonry and you are trying to be helpful.

But your post above that I responded to simply didn't appear to answer the original question that RFreund asked.

You first told him to go look at some past test results that NCMA had done. Then stated that the results were confidential but not to worry - the staff learned a lot. Then we find that the test results (or is it the staff knowledge - not sure) are cut up into small pieces and micro-managed.

You then refer to ACI 530 and the Masonry Designer's Guide but do not state whether they include procedures for developing an interaction equation between axial and bending in a partially reinforced wall…which is the whole point of the original question.

Your last paragraph simply sounds like a little history lesson and NCMA commercial.

I’m just suggesting that if you can answer his question, then answer it.

 

[concretemasonry]

JAE -

I was involved in the writing of the original ACI 530 and the documents it was based on before we formed the TMS and MJSC in the 1980's.

Sometimes you have to look beyond the sanitized "code language" documents to understand the principals, since often the codes cloud the real understanding.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

... good to know. I guess.

 

[hokie66]

This thread, near the bottom, seems to have a reference to what you are looking for. I probably shouldn't post it, as I normally fill all cores...

thread507-194036

 

[RFreund]

Dick - I appreciate your knowledge and wisdom, but I can't get a feel for your tone. Are you suggesting that the codes are too conservative or too liberal or they just don't accurately reflect the real behavior?

JAE - Thanks for trying to keep everyone on track. As I do appreciate Dicks comments, they were not what I was looking for.

Hokkie - I think that is what I'm looking for. I just wish I would have found it sooner (I did try to search on the site). However I will look it over and it may answer my questions. As for filling all cores - do you always fill all cores or just for masonry piers? It doesn't seem like filling all cores is very typical here atleast for small (4-stories or less, midwest, USA).

All- I've attached a calc that I plan to use to write the calculation in TEDDS for Word and maybe an Excel sheet. I would be very interested in your comments and I do have a couple questions regarding the use of the modular ratio, what checks are appropriate and what is the shear area to use? I seem to be getting a little confused as I'm used to a concrete approach.

I'm sure some errors will become apparent after I write the calc. I will post it once complete and start on a similar calc for shear walls. Then hopefully a strength design for each and for slender walls.... Need. More. Free. Time.

EIT

 

[msquared48]

Unless it is needed for strength, I do not fill all the cores except in columns as you mentioned, or CMU below the ground level. Adding extra grout in the high seismic area I am in just adds to the strength requirements of any diaphragm in the building and is counter-productive.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

RFreund,
I am in Queensland, Australia, so my comment relates to typical practice here. Most of our builders prefer to fill all cores as a matter of course rather than fiddling around with partial filling, especially where there is horizontal reinforcement. So that is the way we design it...usually. Our masons are accustomed to using blocks, either H-blocks or knockout blocks, that allow for easy complete filling.

As to the seismic issue noted by Mike, we don't have much problem with seismicity here. But if we did, I don't know if I agree with that philosophy. I see the technical argument, but it is akin to arguing about appropriate live loads.

 

[RFreund]

Quick question - Does anyone have an example of how the net properties are determinded in NCMA TEK 14-1B. I beleive I have it correct however I wanted to verify. My question is this:

The Tek considers the face shell grouted, 3/8" grouted joint, the cell where the rebar is located, and the web each side of where the rebar is located as being grouted. Correct?

EIT

 

[JAE]

Correct.

 

[concretemasonry]

I agree with JAE.

The face shells are normally laid in a 3/8" full mortar bed (depending on local codes) and configuration of the masonry units used. The mortar strength is usually not critical (Type S or M mortar). The mortar bedding is to provide a continuous, contained cell for proper grouting procedures.

In some jurisdictions, the webs do not have to be mortared if it can be shown that the grout (large cores and coarse grout) in the cells/cores can be contained, and is not usually necessary in full wall grouting. It is up to the units used, jurisdiction, codes and inspection practices.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[RFreund]

Attached is the calc I wrote based on my previous attachment. It is a Tedds for Word calc, not a spreadsheet as The Tedds for word calcs are usually more 'clear' and easier to follow.

Basically instead of the calc using different kd (neutral axis) values and deriving a interaction diagram I just manual iterate kd.

Basic philosophy/procedure of calc:

1.) Determine a required eccentricity, ed=M/P based on loading.
2.) Assume actual masonry stress is equal to allowable, fm=Fm=1/3f'm
3.) Find stress in steel based on compatiblity which must be less than allowable. fs<Fs
4.) Based on equilibrium sum forces P+Cf+Cw-T=0 solve for Pns.
5.) Based on equilibrium sum moments and solve for Mns.
6.) find actual eccentricty ea=Mns/Pns.
7.)ea=ed
8.) Check Pns>P, Mns>M
9.) check fa<Fa

Sound ok?

I'd like to check this vs another calc.
JAE - Do you think I would still be able to contact the professors you referred to in the other thread? Or if you comfortable posting it that would be great too. (Assuming it includes partially grouted walls)

EIT

 

[JAE]

RFreund,
Attached is an excel spreadsheet that I received from a masonry seminar some time ago (Dr. Max Porter I believe). See if this helps.
There were two of them and I'll try to follow this post with the second one. I haven't looked at these for quite a while so no guarantees - check them well.

 

[JAE]

Here's the second one: