Masonry Reinforcement Placement
Masonry Reinforcement Placement
(OP)
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!
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!






RE: Masonry Reinforcement Placement
RE: Masonry Reinforcement Placement
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.
RE: Masonry Reinforcement Placement
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RE: Masonry Reinforcement Placement
RE: Masonry Reinforcement Placement
RE: Masonry Reinforcement Placement
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.
RE: Masonry Reinforcement Placement
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
www.HowToEngineer.com
RE: Masonry Reinforcement Placement
So I could just use N bars = L/spacing then round up and either space evenly with S/2 at the ends...
EIT
www.HowToEngineer.com
RE: Masonry Reinforcement Placement
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.
RE: Masonry Reinforcement Placement
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.)
RE: Masonry Reinforcement Placement
RE: Masonry Reinforcement Placement
EIT
www.HowToEngineer.com
RE: Masonry Reinforcement Placement
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.