Masonry Reinforcement Placement

[RFreund]

How is reinforcement generally spaced or placed in the field when the wall length does not match the spacing? Say you have a 12' long wall with 32" oc spacing. So there are 18 cores so every 4th core would have a bar plus one at the beginning and one at the end.

Does the reinforcement get laid out starting at one end working toward the other so that at one end there is a bar in adjacent cells? Meaning there would be a bar in core 1, 5, 9, 13, 17 and 18. Or do they work toward the center or try to adjust the spacing some other way? Is there a standard?

I'm trying to match the calculation to what will happen in the field or atleast make it conservative so that the layout really doesn't matter.

Thanks in advance!


EIT

http://www.HowToEngineer.com

 

[hokie66]

There is no standard, at least none that is adhered to. Just do the calculation, specify the spacings, and check in the field to assure that enough bars are being placed, including one in each end core.

 

[asixth]

It gets placed every 4th core with one at each end. There are a number of ways to do it. I reckon the builder would take the reo out of the 17th core and put it into the 15/16th but otherwise there's no special way to do it.

They erect the wall over the starters. Once they get to 3m (10'), they corefill using the vertical bars to help consolidate the grout.

After the grout sets they go again.

 

[rowingengineer]

I think rodding of a wall was a mith created by a concretor to explain why his vibrator had no fuel.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[pittguy12]

Your biggest worry is making sure he gets enough bars in there, they are grouted properly, and he gets the horizontal reinforcement done they way you specify. The wall will span and carry the loads because masonry, like concrete, is fairly forgiving when it comes to design vs performance.

 

[ash060]

In my experience, reinforcing in masonry walls is typically placed one way - poorly.

 

[DST148]

I agree with the posts above; a bar in the cores each end and the spacing for the remaining bars adjusted to suit.
Our standard masonry details show rebars at the corners, intersections of the walls, ends of the walls etc. However, ......We typically use precast concrete lintels in multistory load bearing masonry structures with hollow core planks. For walls not part of Lateral Force Resisting System, we allow the bars to be placed in the last but one cores and fully grout the end cores. This is done since the bar in the end cores get interrupted at precast lintels. The bars are always calculated based on the total length of the wall. In your case the no. of bars required is 6, the bars may be placed in cores 2, 5, 8, 11, 14, and 17 @ 24" o.c. ACI 530 allows vertical reinforcement to be located within 16 in. of the ends of the masonry walls not part of LFRS. If the opening extends to the the underside of the planks / slab, then the bars are placed in the end cores. Any of the bar configurations mentioned above is acceptable to us.

For walls part of LFRS, we make sure there are bars in the cores at the ends. However, for flexural design purposes we ignore the bars in the end cores. For shear, d is taken to the center of the bar in the end cores.

 

[RFreund]

haha, I have enjoyed the comments thus far and they have been inline with what I figured but just wanted to check.

I know if your laying out wall studs/floor joist you start at one end and work your way to the next. But I guess even that can vary so I will adjust accordingly.

The question came about because I wanted to create a more accurate way to design a partially grouted masonry shearwall spreadsheet. In doing so I was going to assume a linear elastic stress distribution and find the stress/strain in each bar in tension (like a deep concrete beam). Iterate to find the NA then check P and M design strengths. However I could not decide on how to layout the reinforcement bars. I think I will just subtract the extra bar and space them evenly with one at each end. I believe this should be conservative.
Having said this I hope this isn't a case of measuring with a micrometer, marking with crayon and cutting with a chainsaw.

EIT

http://www.HowToEngineer.com

 

[RFreund]

DST - I posted before reading your comments or while you were posting. So you are saying that you do not include the end reinforcement in your shearwall design then?

So I could just use N bars = L/spacing then round up and either space evenly with S/2 at the ends...

EIT

http://www.HowToEngineer.com

 

[concretemasonry]

DST148 has the proper concept for good construction - vertical bars at the end cores of the wall and at all intersections. After that, make sure the amount of vertical steel is equivalent to that specified (same diameter) and spaced to provide the correct amount in the wall since a masonry wall is really designed as a unit and design parameters/codes are based on tests of wall/wall sections.

Unfortunately, few U.S. engineers understand the different sizes and shapes of masonry units used in their areas (3 core, 2 core, 1 core and 0 core) and the web configurations/spacing and the effects of the ends (flush, open ended). In other words, the wall is designed and not really detailed because the materials used are not fully understood. Part of this is due to the limited use, actual education in masonry design (not just seminars) and limited projects that lend themselves to sophisticated design and details.

The U.S. engineers are faced with 1000s of different CMU configurations just for one size due to different manufacturers, code structural requirements/loads and tradition construction techniques over a large geographic area.

I saw a set of drawings for 20 - 6" loadbearing CMU buildings (partially grouted) varying between 12 and 20 stories. There were 4 different heights. For each height there was a single page for floors above the first floor plan and every 2 or 3 floors had a different schedule of vertical bar placement and grouting schedules using a system of system of cross hatching the applicable cores based on the units selected by the design engineer. The building elevation showed the schedule of the different strengths (usually 3 or 4 different strengths that corresponded to the breaks in the level by level grouping of reinforcement. In this case the engineer actually designed and detailed the buildings in the complex and also supervised the pre-approval of the units (color coded) at the manufacturing plant and the random video inspection to eliminate the disruptive/detrimantal archaic "clean-out" inspection concept. - It was an eye-opener to see what an engineer can do to guarantee a quality construction in a country where reading is not common among construction workers.

Dick



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

 

[JLNJ]

If you wish to see the reinforcement in a specific location you will need a special detail showing it.

Without a detail, the bars won't be where you hoped to have them. Those bars adjacent to the openings (which will be critical) will be worthless because they will be interrupted by the steel/precast lintel. (I specify CMU lintels wherever possible to let these bars run through.)

 

[DST148]

@RFreund: I will not make a blank statement that we do not include the rebar in the end cores for flexural design of shear walls. We do show rebar in the end cores of the shear wall. However, in the design calculations we ignore the rebar in the end cores if interrupted by a precast lintel. This is because the contractors in my area prefer precast lintels over door and small openings; to avoid shoring of the lintel blocks. If you specify masonry lintel blocks over openings, then the rebars in the end cores of the wall can be continuous and may be included in the design.

 

[RFreund]

@DST148 - I see what you are saying, thanks.

EIT

http://www.HowToEngineer.com

 

[concretemasonry]

The items I observed on the numerous projects I referred to were the basics of seismic reinforced masonry developed in SoCal in the 1960's to 1980's where the engineers developed the basics of connectivity and making a building work as a unified structure instead of separate elements.

Because they usually worked for some of the large G.C/Developers, they took over the structural design based on performance, technical competency and economics. - that was about25 years ago and there have not been any problems. The buildings designed were not "column/wall" and floor systems but were unified to create a complete structure. The sections of the structures were tested on the seismic tables in Japan, even though the area did not have seismic activity. It was refreshing to see engineers having some control over the structure instead of designing individual elements.

Dick



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