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Allowable Axial Tension for Masonry Headed Anchor Bolts

Allowable Axial Tension for Masonry Headed Anchor Bolts

Allowable Axial Tension for Masonry Headed Anchor Bolts

(OP)
I need an inexplicable change in the code explained to me.

For the allowable axial tension of a headed anchor bolt in masonry according to the ACI 530-05 chapter 2, the value is taken as the lesser of:
Bab=0.5Ap(fm')0.5
Bas=0.2Abfy

Now, for ACI 530-08 and 11 chapter 2, the allowable axial tension is taken as the lesser of:
Bab=1.25Apt(fm')0.5
Bas=0.6Abfy

That is a significant increase, and according to the IBC, you don't calculate Ap any differently than you calculate Apt. Why is the value much higher? What am I missing?

RE: Allowable Axial Tension for Masonry Headed Anchor Bolts

My best guess is that more recent testing has shown the older value to be too conservative.

I also know the masonry code people had a devil of a time dealing with the elimination of the 1/3 allowable stress increase, which was allowed for wind load design many years ago, but is no longer allowed. I read an article about unreinforced masonry design, specifically dealing with allowable flexural tension, and how the 1/3 increase should still be allowed. Then, at some point, the code people just increased the values in the code to match what everyone had been using.

DaveAtkins

RE: Allowable Axial Tension for Masonry Headed Anchor Bolts

(OP)
Yeah I saw that.
Thank you. I personally never designed anything using the equations with lower values. I simply used the equations from the ACI 350-11. I noticed the difference from the 05 to newer editions when a senior engineer questioned why my allowable tension was so high. But neither one of us could figure out why the increase was so significant in the newer editions.

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