Masonry Anchor Strength Design Guide 2024 where : c a , min
= minimum distance from center of an anchor shaft to the edge of masonry , in . ψ c , N , m
= Breakout cracking factor ( 17.6.2.5 ) = 1.0 if k m is taken from third-party evaluation report
N b , m
= Basic single anchor breakout strength in tension , lb
= k m ƒ ́m h ef
1.5 where : k m
= Effectiveness factor for breakout strength in masonry taken from third-party evaluation report
ƒ ́m = Masonry compressive strength , psi
Pullout Strength ( Mechanical Anchors Only )
N pn
= ψ m , P x N p where :
ψ m , P
N p
= Pullout cracking factor taken from third-party evaluation report
= Basic single anchor pullout strength taken from third-party evaluation report
Bond Strength ( Adhesive Anchors Only )
N mag
=
where :
A Na
A Nao
A Na
A Nao ψec , Na ψ ed , Na
N ba , m
= Projected influence area of single adhesive anchor or group of adhesive anchors , in . 2 ( 17.6.5.1.1 )
= Projected influence area of a single adhesive anchor if not limited by edge distance or spacing , in . 2 ( 17.6.5.1.2 )
= ( 2c Na
) 2 where : c Na
= projected distance from center of an anchor shaft on one side of the anchor required to develop the full bond strength of a single adhesive anchor , in .
= 10d a т uncr
1,100 where :
d a
= Nominal outside diameter of postinstalled anchor , in . т uncr
= Characteristic bond stress capacity in uncracked masonry taken from thirdparty evaluation report , psi ψ ec , Na
= Bond eccentricity factor ( 17.6.5.3 ) =
1
1 + e ́N c Na
≤1.0 ψ ed , Na
= Bond edge effect factor ( 17.6.5.4 ) = 1.0 if c a , min
≥ c Na
= 0.7 + 0.3 c a , min
c Na if ca , min < c Na
N ba , m
= Basic single anchor bond strength , lb = т ( cr , uncr ), m πd a h ef where :
т ( cr , uncr ), m
= Characteristic bond stress capacity in cracked or uncracked masonry , respectively , psi .
Where analysis indicates cracking at service load levels , use т cr , m
. Where analysis indicates no cracking at service load levels , use т uncr , m
.
SUSTAINED LOADS AND OVERHEAD USE
For adhesive anchors that resist sustained tensile loading , Section 3.3.2.5 of AC58 requires an additional calculation be satisfied for the sustained portion of the factored load per ACI 318-19 Section 17.5.2.2 and 17.5.2.2.1 . Design of adhesive anchors to resist sustained tension loading shall satisfy the below equation :
0.55ФN ba , m
≥ N ua , s ( 17.5.2.2 ) where :
N ua , s
= factored sustained tensile load ( dead load + any sustained live load )
When using the tables presented within this Masonry Anchor Strength Design Guide for the design of adhesive anchors to resist sustained tension loading , sustained loading is calculated by multiplying the value of ФN n or N r by 0.55 and comparing the value to the tension dead load contribution ( and any sustained live loads or other loads ) of the factored load . Edge , spacing , and masonry thickness influences do not need to be accounted for when evaluating sustained loads .
Masonry Fastening Technical Guide Edition 24 Hilti , Inc . 1-800-879-8000 | en español 1-800-879-5000 | www . hilti . com | Hilti ( Canada ) Corporation | www . hilti . ca | 1-800-363-4458
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