Shear — Nominal Strengths
Steel Strength
V sa
= 0 . 6A se , V ƒ uta ( 17 . 7 . 1 . 2b ) where :
A se , V
= Effective cross-sectional area of an anchor in shear , in . 2 ƒ uta
= Minimum ultimate tensile strength of anchor , psi
Masonry Breakout
V mbg
=
A Vm
A Vmo ψec , V , m ψ ed , V , m ψ m , V
V b , m where :
A Vm
= Projected masonry failure area of a single anchor or group of anchors in shear , in . 2 . ( 17.7.2.1.1 )
A Vmo
= Projected masonry failure area of a single anchor in shear if not limited by edge distance or spacing , in . 2 ( 17.7.2.1.3 )
= 4.5 ( c a1
) 2 where : c a1
= Distance from the center of an anchor shaft to the edge of masonry in one direction , in . ψ ec , V , m
= Breakout eccentricity factor ( 17.7.2.3 ) =
1 +
1 e ́V
1.5c a1
≤1.0 ψ ed , V , m
= Breakout edge effect factor ( 17.7.2.4 ) = 1.0 if c a2
≥ 1.5c a1 = 0.7 + 0.3 c a2
1.5c a1 if ca2 < 1 . 5c a1 where : c a2
= distance from center of an anchor shaft to the edge of masonry in the direction perpendicular to c a1
, in . ψ m , V
= Breakout cracking factor ( 17.7.2.5 ) = 1.0 where analysis indicates cracking at service load levels = 1.4 where analysis indicates no cracking at service load levels ψ h , V
= Breakout thickness factor ( 17.7.2.6 ) = 1.0 if h a
≥ 1.5c a1
=
1.5c a1 if ha < 1.5c a1
ha where : h a
= thickness of member in which an anchor is located , measured parallel to anchor axis , in .
V b , m
= Basic single anchor breakout strength in shear , lb ( 17.7.2.2 )
= MIN [ V b , m1 ; V b , m2
]
V b , m1
= ( 7 ) l e
0.2 d a
V b , m2
= 9 ƒ ́m ( c a1
) 1 . 5 d a ƒ ́m ( c a1
) 1 . 5 where : l e
= MIN [ 8d a ; h ef
] for anchors with a constant stiffness over the full length of embedded section
Masonry Pryout
V mpg
= k MIN [ N ; N ( Adhesive Anchors Only )] mp mbg mag where :
k mp
= 1.0 for h ef < 2.5 in . k mp
= 2.0 for h ef ≥ 2.5 in .
N mbg
= Nominal masonry breakout strength in tension , lb
N mag
= Nominal bond strength in tension , lb Masonry Crushing
V mc
= 1750 x 4 ƒ ́mA se , V
Masonry crushing failure is based on an equation that has been used by The Masonry Society ( TMS ) 402 anchor design provisions for cast-in anchors . Masonry is often a softer material compared to concrete . When exposed to high shear loading , the steel anchor may crush and sink into the block of the masonry . Thus , this failure mode is unique to anchor design in masonry .
Compared to anchor design in concrete , there are a couple notable differences unique to the design process for masonry . The effectiveness factor for breakout strength in masonry ( k m
) will be lower than what is typically used for concrete ( k c
) to account for the inhomogeneity of masonry materials in breakout . Breakout cones for CMU construction can be greatly influenced by the presence of hollow head joints , which is the vertical mortar joint between two closedended CMU blocks in the same course and wythe . In addition to the ends and edges of walls , the nearest hollow head joint on a horizontal projection from the anchor shall be treated as an edge for design purposes . The minimum distance from the nearest adjacent hollow head joint as measured from the centerline of the hollow head joint in CMU construction shall be 2 inches for adhesive anchors or the c min , HJ value for mechanical anchors , which is provided in the product installation information tables . Please see
6 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