Trimmer bars at re-entrant corner 2

[sdz]

Is there a rational method to design the trimmer bars required at a re-entrant corner? Or even an empirical method?

(Trimmer bars are additional bars usually placed at 45 degrees across a re-entrant corner to reduce shrinkage cracking.)

 

[dik]

Not that I'm aware of, but I usually use them... they typically cross the crack that forms at right angles... so they are containing the crack... I typically trim the opening with 2-15M (#5) bars in each direction extending 24" past the opening, and add an extra 15M x 4' long diagonally... so, there's a whole cluster of rebar...

Dik

 

[asixth]

Not really. Whenever I'm on-site and I ask the builder to install trimmers prior to placing concrete they always say "but they don't work". They don't prevent the onset of cracking but do help in reducing the size of the crack. I normally place a minimum 2 no.4 bars (12mm) 5' long tied to the inside of the wall or floor reinforcement.

 

[sdz]

So no one really knows except what is done as common practice. Maybe I can get a phd researching the topic. I thought some guidance might have come out in the last few years and I had missed it.