1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
7. Anchor Channel
Design Code
8. Reinforcing
Bar Anchorage
9. Special Anchor
Channel Design
10. Design
Software
11. Best
Practices
7.6.3 SEISMIC CONSIDERATIONS SHEAR
Requirements for shear loading is stated in ACI 318-14
Section 17.2.3.5
Blow-out
Pull-out
Concrete breakout
Figure 7.6.2.3 — T
ensile anchor channel failure modes with an additional
0.75 reduction strength when resisting earthquake forces
According to ACI 318-14 section 17.2.3.4.4 The anchor design
tensile strength for resisting earthquake forces shall be
determined from consideration of (a) through (e) for the non steel
tensile failure modes assuming the concrete is cracked unless it
can be demonstrated that the concrete remains uncracked:
• According to ACI-318-14 section 17.2.3.5.1. Where the shear
component of the strength level earthquake force applied
to the anchor or group of anchors is equal to or less than 20
percent of the total factored anchor shear force associated
with the same load combination, it shall be permitted to
design the anchor or group of anchors to satisfy 17.5 and the
shear strength requirements of 17.3.1.1.
12. Instructions
for Use
14. Design
Example
13. Field Fixes
• 17.2.3.5.2 Where the shear component of the strength level
earthquake force applied to anchors exceeds 20 percent
of the total factored anchor shear force associated with the
same load combination, anchors and their attachments shall
be designed in accordance with 17.2.3.5.3 as described in
Figure 7.6.3.1 and 7.6.3.2 .
N sa for a single anchor, or for the most highly stressed
(a) ϕ
individual anchor in a group of anchors
(b) 0.75ϕN cb or 0.75ϕN cbg , except that N cb or N cbg need not be
calculated where anchor reinforcement is provided
(c) 0.75ϕN pn for a single anchor, or for the most highly
stressed individual anchor in a group of anchors
Design of Attachment
Option a)
Yielding
Anchor Ductility
(e) 0
.75ϕN a or 0.75ϕN ag
Seismic Load
Option b)
Non-yielding
Option c)
Overstrength Factor
(d) 0.75ϕN s b or 0.75ϕN sbg
Anchor
where ϕ is in accordance with ACI 318-14 section 17.3.3.
(b) A
nchorage designed for capacity of
structural system 17.2.3.5.3(b)
c) A
nchorage designed for a multiple of the
calculated seismic force 17.2.3.5.3(c)
Figure 7.6.3.1 — Seismic provisions for tension; ACI 318-14 Section 17.2.3.5.3.
Option a
(Ductile yield
mechanism in
attachment)
Seismic Detailing: Shear
5. (1.2+ 0.2SDS) D+ Ω o Q E + L + 0.2S
6. (0.9- 0.2SDS) D + Ω o Q E + 1.6H
Ω o overstrength factor for architectural component can be
obtained from Table 13.5.1 of ASCE 7-10 and for structural
components from Table 12.2.1.
ASCE 7-10 chapter 12 Table 12.2.1
Ω o Non structural
component ASCE 7-10 chapter 13 Table 13.5.1
Option b
(Non-yielding
attachment)
Seismic Design
for E
Option c)
(Design for E
o
Finish
)
Figure 7.6.3.2 — Flow chart - Seismic provisions for tension; ACI 318-14 Section 17.2.3.5.3
194
Cast-In Anchor Channel Product Guide, Edition 1 • 02/2019
195
Ω o Structural
component
a) A nchorage designed for a plastic
hinge 17.2.3.5.3(a)
Where anchor reinforcement is provided in accordance with
17.4.2.9, no reduction in design tensile strength beyond that
specified in 17.4.2.9 shall be required. The reduced anchor
nominal tensile strengths associated with concrete failure
modes is to account for increased cracking and spalling in the
concrete resulting from seismic actions. Because seismic design
generally assumes that all or portions of the structure are loaded
beyond yield, it is likely that the concrete is cracked throughout
for the purpose of determining the anchor strength. In locations
where it can be demonstrated that the concrete does not crack,
uncracked concrete may be assumed for determining the anchor
strength as governed by concrete failure modes.
Option d) The anchor or group of anchors shall be designed for
the maximum tension obtained from design load combinations
that include E, with E increased by Ω o . The anchor design
tensile strength shall satisfy the tensile strength requirements
of 17.2.3.4.4, which states that an additional seismic reduction
factor of 0.75 is applied to the concrete or non steel tensile
design strengths. This seismic provisions intend to ensure
anchors resisting significant seismic forces do not undergo
sudden brittle failure. One way to achieve this is to add sufficient
extra strength to the anchor by design, so that the failure must
occur elsewhere in the system. Increasing the earthquake
inertial load with an overstrength factor Ωo has been included
in the ACI 318-14 standard as one of four possible options for
preventing premature anchor failure. Here ACI refers us back to
ASCE 7-10 load combination 5 and 7 of chapter 12.
6. Loading
Option (c) The anchor or group of anchors shall be designed
for the maximum tension that can be transmitted to the anchors
by a non-yielding attachment. The anchor design tensile
strength shall be calculated from 17.2.3.4.4, which states that
an additional seismic reduction factor of 0.75 is applied to the
concrete or non steel tensile design strengths. This option may
apply to a variety of special cases, such as the design of sill
bolts where the crushing of the wood limits the force that can be
transferred to the bolt, or where the provisions of the American
National Standards Institute/American Institute of Steel
Construction (AISC) Code Seismic Provisions for Structural
Steel Buildings (AISC 341) specify loads based on member
strengths.
5. Base material
Option b) The anchor or group of anchors shall be designed
for the maximum tension that can be transmitted to the anchor
or group of anchors based on the development of a ductile
yield mechanism in the attachment in tension, flexure, shear, or
bearing, or a combination of those conditions, and considering
both material overstrength and strain hardening effects for
the attachment. The anchor design tensile strength shall be
calculated from 17.2.3.4.4, which states that an additional
seismic reduction factor of 0.75 is applied to the concrete or
non steel tensile design strengths. For the design of anchors,
the force associated with yield of a steel attachment, such as an
angle, baseplate, or web tab, should be the expected strength,
rather than the specified yield strength of the steel.
4. Design
Introduction