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Reinforced Masonry - Partial Grout
2

Reinforced Masonry - Partial Grout

Reinforced Masonry - Partial Grout

(OP)
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

RE: Reinforced Masonry - Partial Grout

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.

RE: Reinforced Masonry - Partial Grout

(OP)
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

RE: Reinforced Masonry - Partial Grout

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.

RE: Reinforced Masonry - Partial Grout

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.

 

RE: Reinforced Masonry - Partial Grout

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.

RE: Reinforced Masonry - Partial Grout

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.  
 

RE: Reinforced Masonry - Partial Grout

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.

RE: Reinforced Masonry - Partial Grout

... good to know.  I guess.

 

RE: Reinforced Masonry - Partial Grout

(OP)
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

RE: Reinforced Masonry - Partial Grout

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
 

RE: Reinforced Masonry - Partial Grout

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.  

RE: Reinforced Masonry - Partial Grout

(OP)
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

RE: Reinforced Masonry - Partial Grout

Correct.
 

RE: Reinforced Masonry - Partial Grout

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.

RE: Reinforced Masonry - Partial Grout

(OP)
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

RE: Reinforced Masonry - Partial Grout

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.

 

RE: Reinforced Masonry - Partial Grout

(OP)
Thanks, I'll take a look.

EIT

RE: Reinforced Masonry - Partial Grout

(OP)
In regard to strength design I have a few questions:

For walls subject to out-of-plane forces:

1.) The axial load (Pu/Ag (this is really Anet)) must be less than 0.2f'm. If the wall's slenderness ratio exceeds 30 than the axial load must be less than 0.05f'm. Is this correct? Looking at the RMHB 6th edition it appears that the steel does not contribute to Ag, correct? This seams low, what am I missing? For f'm=1,500psi the max compressive stress is 75psi if h/r=30? For ASD H/r=30 the Reduction factor is 0.95 which means the allowable axial stress is 0.95*0.25*1500=356psi.

2.) All walls are designed by an iterative process by checking the moment caused by the deflection due to out-of-plane loads and eccentricity of the DL/LL no matter what the slenderness ratio, correct?

3.) Does the slenderness reduction factor need to be applied? It doesn't seem like it should be applied as we are accounting for P-d and P-D effects.

EIT

RE: Reinforced Masonry - Partial Grout

(OP)
Oh crap.

So the slenderness ratio is h'/t not h/r which I was referring to in my example above. This is probably more reasonable - for an 8" wall you would be at about 20' tall.

Ok so my other 2 questions (2.) and 3.)) still apply. Couple additional comments:

2.) Going through the iterative process for checking moment then get deflection then moment again for all walls subject to axial and moment (no matter what the H/t ratio) seems like a lot of work. Unless you make a spreadsheet or something similar, no? So maybe I am missing something.

3.) It looks as thought the slenderness reductions only apply to shearwalls where you are not reiterating the moment-deflection calc.

EIT

RE: Reinforced Masonry - Partial Grout

Here is a link to some design calculation. There are alot of examples on this youtube site (Struct2009). They deal with both Masonry/Concrete design and Canadian Codes.

http://www.youtube.com/watch?v=8RliuJNL8Ys

Regards,


RE: Reinforced Masonry - Partial Grout

Late on this thread.....
@hokie66 - Thanks for the link
@JAE - Thanks for posting those two spreadsheets
RFreund - I have ACI 530-05. This is my interpretation of the provisions for strength design of masonry walls for out-of-plane loads:
Your posts dated Jan 12, and Jan 13: For engineered masonry the code does not have any specific slenderness limitations per say. The slenderness is accounted indirectly by:
a) Limiting nominal axial compressive strength of the member per eqns. (3 - 16) and ( 3 - 17)
b) Limiting factored axial stress at the location of maximum moment to 0.2 f'm for h / t <= 30, and 0.05 f'm for h / t > 30
c) Placing limits on mid-height deflections under gravity and combinations of gravity + lateral loads.

Iterations for calculating mid-height deflections are required for loadings under service gravity loads, service (gravity + lateral loads), and factored (gravity + lateral loads). I agree, spreadsheet or something similar is required.
 

RE: Reinforced Masonry - Partial Grout

(OP)
Thanks guys I've just about completed the strength design for out of plane loads.

JAE - thanks for the spreadsheats however they appear to be for full grout.

MisterBill - thanks for the video it was helpful. The codes are slightly different but helpful non the less.

It seems odd that the compressive stress is limited to 0.2f'm for any slenderness ratio and that you always have to use the iterative deflection process. I should note that for out-of-plane axial and bending it does not appear that the reduction factor for slenderness applies so I guess that's why you must use the iterative deflection method.

I will post the Tedds calc on Monday and I may turn it into a spreadsheet however I find that the 'Tedds' calc is easier to follow. Like a mathcad calc.  

EIT

RE: Reinforced Masonry - Partial Grout

@RFreund: Your last post, "I should note that for out-of-plane axial and bending it does not appear that the reduction factor for slenderness applies..."
Though the code does not directly impose any limit on slenderness, the reduction factor for slenderness does apply. For strength design of reinforced masonry walls subjected to axial load + out-of-plane loads, instability due to slenderness is accounted for by ensuring that the factored axial load on the wall does not exceed (phi * Pn) given by equation (3-16) for h/r <= 99, and eqn(3-17) for h /r > 99.
 

RE: Reinforced Masonry - Partial Grout

(OP)
@DST148 I thought that the slenderness reduction (eq 3-16 and 3-17) would apply as well but for out-of-plane wall subject to axial and flexural loads I do not think they apply (for shear wall yes).

Here are my reasons (I only have an older code in front of me '02) Walls are addressed in section 3.2.5 where they address the limit to axial loads as 0.2f'm and 0.05f'm then stability is addressed with the P-D iterative method and they do not refer to eqn 3-16 and 3-17. However in section 3.2.6 they address walls for in-plane load where they do refer to eqns 3-16 and 3-17. Also in the reinforced masonry engineering handbook's design example of a wall subject to out of plane forces they do not use the slenderness ratio. They use the iterative P-D Method.

But now I'm left to wonder how do you handle columns or piers...Use the P-D method or enforce the slenderness reduction factor? The 2011 code and designers guide should be out soon...I may have to look into that..

EIT

RE: Reinforced Masonry - Partial Grout

@RFreund - I agree with you.  Section on strength design of walls for out-of-plane loads does not refer to eqns. (3-16) and (3-17) directly. However,.....
I have Masonry Designers' Guide - 5th ed. which is based on ACI 530-05. There is a solved example for Strength Design of Masonry for out-of-plane loads., EX 10.4-5. It's a single story structure. Wall thickness, f'm, steel placement is assumed, and (phi.Pn)- (phi.Mn) interaction diagram is drawn. Check for adequacy of the section for strength is made after applying reduction per eqn. 3-16 or 3.17 to the interaction diagram. Then the adequacy of the section is checked for secondary effects per section 3.2.5, again using the interaction diagram.
For walls subjected to low axial loads, the author suggests that a moment-magnifier method would be more rational than the approach presented above in the Guide.     

RE: Reinforced Masonry - Partial Grout

(OP)
Attached is the calculation I came up with following the reinforced masonry engineering handbook 6th edition. In this method you iterate the position of the neutral axis similiar to developing a P-M interaction diagram however you are also considering the secondary effects when iterating so you must also iterate the deflection of the wall. The required eccentricity should match the design (or section) eccentricity. Then check if phi.Pn and phi.Mn are > Pu and Mu.
Feel free to comment.

DST- so your saying that in the MDG they create an interaction diagram with phi.Pn and phi.Mn which does not account for secondary effects then they reduce these values by the "slenderness reduction factor" (eqn 3.16 and 3.17). Then they follow the PD method (per 3.2.5) to get a magnified moment and check this vs the interaction diagram but this time they do not the "slenderness reduction factor".
Then after this the author says that a moment-maginfier method would be more rational for small axial loads. Do they suggest a what the maginifer should be (equation)? My Nawny concrete book (end has masonry design) suggests b=1/(1-(Pu/(Anf'm*(70*r/h)^2))) for 45< h/r <60 but I'm not sure how it applies as it is not presented very well (IMO).

 

EIT

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