Masonry Joint Reinforcement

[abusementpark]

I'm curious what everyone's thoughts are on masonry joint reinforcement. Do you use ladder style or truss style?

The truss style is stronger, but crosses the filled cells and may adversely affect the concrete fill consolidation. The ladder style will be weaker, but it doesn't cross the cells.

Which is better?

I know that Alexander Newman (ASCE's webinar fido) recommended ladder style during a masonry webinar, but I don't remember if he outlined the reasoning.

 

[JAE]

Ladder style. The truss diagonals on the truss style may add some "strength" but it is certainly not strength that I rely on in terms of wall stability and load capacity.

 

[JedClampett]

One point one of my colleagues made to me was that he preferred truss type becuase you could verify from looking down the cells if it was installed or not.

 

[ACE58]

I used to specify truss-type, but the masonry contractors were always asking to substitute ladder-type because the truss wires interfered with the placement of vertical reinforcing bars.

 

[concretemasonry]

If you bother to look closely at the core dimension and spacing for most low grade commonly specified block and joint reinforcement, you will find that very little really aligns, so you always have the semi-justified reason.

Obviously truss type joint reinforcement will also impinge in the assumed masonry core size, spacing and alignment.

At one time laddur-type reinforcement had 15" o.c. ties, but 16" o.c. was available with an advance order. - Unfortunately, few engineers look at modularity from a construction standpoint since normal block are two core and really do not provide a true structural system that permits quality masonry construction. The last portion applies only to those people doing highly engineered loadbearing structures and not just infill or over designed lightly stressed masonry walls where the type of joint reinforcement in immaterial.

Just an opinion from an engineer interested in quality construction and proper specifications.

Dick

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

 

[hokie66]

Another opinion. "Joint reinforcement" is useless. Use horizontal bars.

 

[rowingengineer]

I second Hokie's opinion.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[JAE]

hokie66, I agree with you on strength that wire reinforcing really doesn't do much - in the US, the building codes require two 9 gage (sorry - don't know the mm) wires, horizontally, every 16 inches on center....i.e. every other vertical 8" joint.

 

[dik]

The horizontal wall reinforcing provides flexural strength both in the plane of the wall as well as normal to the wall. The strength is limited, but it's like chicken soup... doesn't hurt. It also increases the toughness of the wall... Most mortar joints aren't wide enough to ensure proper bond with regular reinforcing... a #3 bar is 3/8" and a 10M is slightly thicker...

Dik

 

[hokie66]

dik,
I wasn't suggesting putting bars in the mortar joints. They go in the body of the block. In Australia, our blocks have recessed webs or knockout webs to accommodate the bars. We usually fill all cores. Wire in the mortar joints is not used. Not really my concern, but a code requiring wire in joints because it "doesn't hurt" seems a bit eccentric to me.

 

[JAE]

Well, hokie66...you know us USA types...eccentric from the start

 

[hokie66]

Yeah, I know, including me.

 

[JAE]

That's right...VT.

 

[jike]

We use truss type for single wythe CMU. We use ladder type for cavity walls, CMU / brick. The ladder type then allows for differential longitundinal movement between CMU and brick.

 

[doka1]

Want horizontal bars? Use ivany block. Very nice for structural block walls as the cells are larger.

 

[abusementpark]

So it sounds like to me like the main issue with specifying truss style joint reinforcement is that it interferes with the placement of the vertical wall reinforcement.

Are there any concerns about poor concrete fill consolidation due to the truss style joint reinforcement?

 

[JLNJ]

I like to specifiy heavy weight sidewire reinforcement in the hopes that it will minimize cracking.

It like taking a bowl of chicken soup when the doctor ordered just a cup.

Of course you do need to fend off the complaints from the masons who bid the job with the 9 gauge and then find out they overlooked the heavyweight requirement...

 

[dik]

Hokie... I generally detail that the web be cut and 'knocked out for providing top rfg for bond beams, etc. but, I still use heavy wall reinforcing each second or third course depending on the interior strength... you can actually calculate the added flexural strength from the wall reinforcing, and also can increase the flexural depth because the rfg is located closer to the face (where it serves the best purpose) than cutting the webs and installing rebar. Unless the rebar is properly placed with grout consolidated about it, then bond may be an issue, whereas, it is easy to get bond on small dia wires... even with lower strength mortar.

Dik

 

[boffintech]

If you prefer your vertical rebar to be consistently misaligned always specify truss type.