Retaining Wall Bond type

[ReverenceEng]

Quick one - after fruitless google search, thought i'd try here for an easy one.

Have a client needed engineering on a short (about 3') retaining wall. Not sure why, but it is what it is.

Anyway, he wants to do a stack bond, vice the normal running bond. I am not worried about the wall itself here, rather more about construction practices, anything in masonry code, or building code, that anyone knows of that could render this design "not allowed" or something of the like.

Thoughts?

 

[oldestguy]

Most areas that I know of call this landscaping ruled. As a rough rule of thumb if it's width is at least one third the height, it likely will not require any"design".

 

[ReverenceEng]

There are multiple walls terraced and surcharge at the top, so the city is requiring this guy to get it engineered. Normally we refer clients with walls like this to use the city standards.

Either way, my question is really about the stack bond vice a running bond...

 

[XR250]

I don't know of any. I would put ladder wire in every course and a bond beam on top.
And, of course, vertical rebar as req'd by design.

 

[hokie66]

I would use bars horizontally rather than ladder wire. Even though only a short wall, you want to tie the stacked joints together. And use knockout blocks so the grout is continuous horizontally as well as vertically.

 

[oldestguy]

For overall stability of multiple walls in a slope, yes a global stability analysis is needed. Normally this is done by a geotechnical engineer. The exact details of the wall can be as the above posts recommend.

 

[cvg]

quite a bit on google

http://www.ce.udel.edu/courses/CIEG407/TEK 14-06.pdf

http://www.masonryconstruction.com/how-to/avoiding-cracks-in-stack-bond_o

 

[ReverenceEng]

CVG - your googling skills impress with what you have found good sir or madam.

 

[dhengr]

ReverenceEng:
Stacked bond is kinda like an infinitely long line of 16" long blocks stacked 6 or 8 high. And the question is does it take one finger or two and a thumb pushing on the third block down to tip that block stack over. Then, do the next stack, etc. and ask ‘what retaining wall?’ All you’ve got is mortar/conc. blk. bond at the bed and head joints, no interlocking action; unless you do some serious grouting and reinforcing. Then, you are going to terrace these walls, and the top one has a surcharge loading, and it surcharges the next wall down. You can get a special block which has the face scored vert. at the center cross shell, so it looks like and 8x8 stacked bond, but it is laid in running bond. I think you need some engineering help on this if your only question is running vs. stacked bond, and you should involve a GeoTech guy too.

 

[concretemasonry]

There is no good reason to use stack bonded concrete masonry except for "architectural" purposes. Running bond (or really "other than stack bond") gives all of the benefits for structural wall panels. All of the full wall tests that were built for and were used for code requirements used the traditional running bond. Stack bond just does not provide strength and is more costly to lay than running bond.

Grouting and reinforcing walls can be done with with running bond and can be more efficient with the units commonly available. The ideal concrete masonry units have 2 webs at 8" on center with a single center core to provide clear open vertical cores for grouting, steel or insulation. I have seen them used for 6", 8", 10", 12", 14" and 16" thick single wythe walls.

The faces of the units can be scored at odd non-modular spacing (1/3, 1/5 lengths) to be used for a wall with no discernible pattern. Split units with the same scoring patterns are also available depending on the local suppliers.

Dick



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

 

[XR250]

OK, so I got a FLW house that the Arch. wants to use polished CMU in stack bond (see attached). As far as running horizontal reinforcement, can #3 rebar be used in the mortar joints or should they slot the webs of each block? I am hesitant to specify Ivany block until I know they can get it in a polished face. Also, I need to connect the 8" CMU to the 12" to act as a prop for the sill cantilever. I am showing a hairpin. Does anyone have a better idea? I am going to show vertical control joints at 24 ft. O.C. I assume it is OK to use running bond for the backup 12" CMU?

Thanks!

 

[dik]

Stack bond is a bad idea, you will not have uniform loading on the back of the wall and with a short time, the wall will likely fail.

Dik