Grout, with respect to post-installed anchorages, is specified by the design official. When post-installed anchors are tested for the development of design values, the grout is specified according to applicable ASTM standards. Design engineers are encouraged to become familiar with the characteristics of the grout used in performance testing to better understand the applicability of the design loads published in this guide.
3.0 Anchor design in masonry
The Strength Design method for anchor design in concrete has been incorporated into several model codes such as IBC and ACI 318. The method assigns specific strength reduction factors to each of several possible failure modes, provides predictions for the strength associated with each failure mode, and compares the controlling design strength with factored loads. The Strength Design method is a more accurate estimate of anchor resistance as compared to the Allowable Stress Design( ASD) method. The Strength Design method is state-of-the-art, and Hilti recommends its use where applicable.
Anchor design in masonry base materials is adopting the framework of the Strength Design method from ACI 318 Chapter 17 with only a few modifications specific to masonry base materials. For full discussion on the mechanical anchor design provisions for masonry, please reference ICC-ES AC01 Section 3.0. For full discussion on the adhesive anchor design provisions for masonry, please reference ICC-ES AC58 Section 3.0. The similarities and differences between anchor design in masonry and anchoring design in concrete will be discussed in the following sections.
Fully grouted CMU construction
Based on Section 3.3 of ICC-ES AC01 and AC58, the tension failure modes for post-installed anchors in fully grouted CMU construction are steel failure, masonry breakout failure, pullout failure( mechanical anchors only), and bond failure( adhesive anchors only). The shear failure modes for post-installed anchors in fully grouted CMU construction are steel failure, masonry breakout failure, pryout failure, and masonry crushing failure.
The corresponding equations and variables are provided below. For further discussion and commentary, please refer to ACI 318-19 section / equation references provided below parenthetically( e. g., 17.6.1.2). Additionally, some design values will be provided in the technical data of this guide or can be located in the applicable third-party evaluation report( i. e., ICC- ES ESR or IAPMO UES ER).
Tension— Nominal strengths
Steel strength N sa = A se, N ƒ uta
where:
Masonry breakout
where:
where:
where:
where:
A se, N = Effective cross-sectional area of an anchor in tension, in. 2
ƒ uta = Minimum ultimate tensile strength of anchor, psi
A Nm = Projected masonry failure area of a single anchor or group of anchors in tension, in. 2( 17.6.2.1.1)
A Nmo = Projected masonry failure area of a single anchor in tension if not limited by edge distance or spacing, in. 2( 17.6.2.1.4)
9h ef 2
h ef = Effective embedment depth of the anchor element, in. ψ ec, N, m = Breakout eccentricity factor( 17.6.2.3)
=
1 1 + e ' N
1.5h ef
≤ 1.0
ψ ed, N, m = Breakout edge effect factor( 17.6.2.4) = 1.0 if c a, min ≥ 1.5h ef
= 0.7 + 0.3 c a, min 1.5h ef if c a, min < 1.5h ef
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 f ' m h ef 1.5
k m = Effectiveness factor for breakout strength in masonry taken from third-party evaluation report
ƒ ́m = Masonry compressive strength, psi
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