Is a bond beam required in a fully grouted masonry wall?

[Uprising]

When designing a reinforced masonry wall, I was taught by a previous Engineer that if all the cores are grouted filled then a bond beam was not required.

Today I was looking over another Engineer's design who had specified that all cores be grout filled, with N12 at 400 vertically and horizontally and a bond beam in the top course (supporting a roof structure only).

I couldn't really find an answer today; the AS 3700 specifies that "Bond beams shall be provided at the top of all walls, where the wall is supporting a floor and under all windows wider than 1500 mm".

Most typical details show a bond beam being using in the top course. Is a bond beam always required or can it be omitted if all the cores are grout filled and only supporting a roof?

 

[JAE]

A bond beam is typically a horizontal tie in the wall - i.e. tension is involved.

With fully grouted and reinforced vertical cores, I don't see how they provide the necessary horizontal tie at all. There is no horizontal reinforcement.

I think a bond beam is required despite the non-grouted, partially grouted or fully grouted wall condition.

 

[UcfSE]

Agree with JAE

 

[EngineeringEric]

I always place a bond beam at the top. I like to think that the steel will act like a shallow beam in the transver direction to resist some minor out of plane loads.

JAE, I think horizontal joint reinforcement (ladder or truss) at a close spacing (16" o.c.) covers horizontal reinforcement for the code. But I still will place a bond beam at the top, regardless if it is all grouted solid below.

 

[hokie66]

JAE,
I don't understand your comment. The OP said that all cores are grout filled, so both the horizontals and vertical reinforcement are enclosed in grout. A "bond beam" exists wherever you have continuous horizontal reinforcement, so in the OP's case, he has bond beams at alternate courses, which should include the top one.

Uprising,
As you quoted AS3700, I assume you are in Australia. Fully grouted block walls, reinforced in both directions, are common here. The terminology "bond beam" generally applies to partially grouted walls, but in the case cited, the bond beam requirement is automatically satisfied.

 

[madmantrapper]

I'm not a SE or PE but I think the bond beam has a different purpose then the fully grouted wall. Also there was no mention of DuraWall being used or anything similar. I've grouted for vertical support but usually with a rebar toward the inside in some of the cores with a given spacing, but still used a bond beam.

Paul

 

[RareBugTX]

Agree with MadMan, grouting provides vertical continuity. Have not heard of horizontal grouting, it might work but special CMU or brick units would be deemed necessary. Provide Lintels!

 

[hokie66]

For information of those in the US and elsewhere, precast concrete lintels are not common in Australia. Neither is wire reinforcement such as DuraWall. The "special CMU units" are actually the typical ones here, and they allow placement of horizontal reinforcement.

 

[JAE]

hokie66,
In the USA here we have concrete masonry units with vertical cells (holes) that allow vertical bars in the walls with grout. The vertical cells are not inter-connected with anything other than the face shells of the block. It is very typical to grout only intermittent cells with some in between left open.

So if you have a "fully" grouted wall you would have vertical reinforcement in vertical grout shafts within the cells of the blocks but nothing horizontal.

We do specify horizontal wires in the mortar joints (usually a pair of 9 gage wires) but I've never counted on those for much.

At tops of walls, etc. we specify a bond beam block which involves either a "U" shaped block or a normal block with lowered webs to allow horizontal bars to pass through.

The OP sounded to me like the wall had nothing horizontal.

 

[hokie66]

I understand, but he did say there are "N12 at 400 vertically and horizontally".

We have your type blocks as well, but in a wall that is completely grouted, we tend to use either "H" blocks or "knockout" blocks. The knockout blocks have webs which are partially cut so the top part can be easily removed with a hammer. These type blocks facilitate the placement of horizontal reinforcement, and more or less complete grouting.

 

[Uprising]

Thank you for your replys.

hokie66,
Yes I am from Australia. While the wall does have horizontal reinforcement, it did not specify which block to use.

I agree that a bond beam is required and the use of "H" or "knockout" blocks with horizontal reinforcement will meet this requirement.
Do you specify the use of "knockout" blocks where ever horizontal reinforcement is located?

 

[hokie66]

Yes, this is normally a specification item. We do insist on "H" blocks in earth retaining walls, because the surety of complete filling is much better. In normal walls with horizontal reinforcement, the choice of block can be left to the builder. They can use H blocks, knockout blocks, or sometimes they prefer the ones with a recess in the web, specifically to accommodate the horizontals.

I look at fully grouted and reinforced block walls as just concrete walls without the requirement of formwork. The strength is not equivalent to a concrete wall, so as a building gets taller or perhaps depends on smaller shear cores, then reinforced concrete walls are required. But where reinforced masonry will suffice, it is the more economical option.

 

[JAE]

hokie66 - thanks for the clarification. I guess I saw the first sentence as one engineer's idea (just "fully grouted") and the second sentence as another engineer's idea (vert horiz. reinf) and Uprising was wondering about the opposing views.

 

[jayrod12]

I was talking with a couple of masons in our area and they pretty much use knockout blocks anytime full grouting is required whether it's a beam, wall or lintel. They feel more comfortable with the continuity of the grout that way and I agree with them.

 

[dik]

In addition to the horizontal 9 ga ladder type of reinf each second or third course, it is sometimes necessary to provide horizontal reinforcing (at top or elsewhere). I generally detail it so that the webs of the CMU's are cut out half depth (with saw or hammer) and horizontal rebar placed. Seems to work OK...

Dik