engineering training materials with respect to concrete masonry

[Kevin Fishburne]

I'm putting together a design draft of a home for later submission to an architect, and I'd like it to be as spot-on as possible without having to become an architect myself in the process. The home is primarily concrete block and heavy timber frame and I'm having some issues with laying the CMU courses such that they're structurally sound. I'm using 3dsmax to model it. The CMU pictured are standard

8x8x16 split-face blocks using stretcher bond. Here's a link to the latest draft:

My problem is how to deal with T intersections and in general places that will require a half block to be used repetitively through the courses. I understand there are steel ties that can bind a wall butted to another wall in a T intersection if the blocks between them can't overlap. I don't know where the half blocks should be placed as to not affect the structural integrity of the wall though. I've heard corners are bad places.

Does anyone have any suggestions as to how I can better design the courses, or know or any reference material (online or in print) that has good information about the structural engineering principles of concrete masonry? Thanks all.

Kevin

[Bobk207]

However........as we used to say in aerospace...... I think you're getting bogged down in the "omega double dots"

I'll venture a guess that the placement of the half blocks are at least a second order effect if the walls don't interlock / overlap you're gonna have a gap. You're gonna have to make a connection with rebar & at least local grout.

I'll also show my bias......CMU's aren't all that strong, if you want real structural integrity, lay in some decent vertical & horizontal rebar. And grout that puppy soild! :)

Of course, living in earthquake country can warp one's perspective :)

But tornadoes & hurricanes can be pretty nasty as well

cheers Bob

[Bob Morrison]

CMU walls when properly designed and constructed can be very strong.

I have worked on two buildings in the South Pacific that were designed to resist 130 mph winds coming off an open ocean (Exposure D). Reinforcing was fiberglass rebar (GFRP) to resist corrosion.

In some remote locations like this the only reasonable method of construction is CMU since everything must be carried by hand across the reef and the beach. All mortar and grout is site mixed, but it comes in 60 pound bags that must carried one at a time.

[Peter]

Briefly, what were the particulars of these buildings- height, wall CMU size, horizontal and vertical reinforcing pattern? I'm curious about the size and spacing of GFRP vs. steel as well as the reinforcing requirements to counter the high wind design loads.

[Bob Morrison]

Two-stories with floor to floor height of 12 feet. CMU is standard 8" normal weight. As I recall (the project file is in storage) the vertical reinforcing was something like #5 GFRP @ 16" o/c. Only the cells with reinforcing (GFRP) received grout.

The GFRP was equivalent in strength to a Grade 60 bar. However, the Young's modulus value is only about 6.5 x 10E6 psi, which makes the "N" ratio about 2 instead of more usual 9. Deflection checks at services loads become more critical.

At the time the design was done using Working Stress Design methods (had to pull out an old test book and quickly relearn) because ACI had not yet published ACI 440.

One of the more interesting details was figuring out how to hold down the

4x T&G cedar roof onto the Alaska Yellow Cedar glu-lam beams and then how to hold down the beams to the CMU.

[Matt Whiting]

No Dur-O-Wall?

Matt

[Bob Morrison]

Never use the stuff.

Well, almost never.

[Matt Whiting]

Too hard? Too costly?

Matt

[Bob Morrison]

Most masons hate the stuff. It slows down their production. Laying in bond beams every 48 inches seems to be a nice days work and is the most height you would want to drop the grout anyway.

The only time I MIGHT use Dur-O-Wall is to tie two disparate materials (like CMU and brick) together.

[Kevin Fishburne]

Thanks Bob, you are the man. It will have vertical rebar and some kind of steel reinforcement horizontally. I think I'm going to design it as a series of rooms with the courses designed to interlock independent of any intersecting walls, then allow the architect/engineer to figure out how to tie together the intersections. So basically each room will be oblivious to the fact that there are other rooms or walls that may abut to or intersect with it. I'm worried more about the aesthetics than anything else at this point since it's just a design draft. The placement of individual CMU is more for looks since it will be exposed on both the interior and exterior of the building.

[tmurf.1]

Your mason can lay out the bond or pattern of the CMUs for any interior partitions. You just need to show where toe walls go. As for the duro-wall it has been an industry standard for at least 40 years. If your mason does not like the stuff he might not be a professional.