Anchor bolts loaded in tension can fail by breakout of a roughly conical body of masonry, or by yield and fracture of the anchor bolt steel. Bentbar anchor bolts (such as J-bolts or L-bolts) can also fail by straightening of the bent portion of the anchor bolt, followed by pullout of the anchor bolt from the masonry. Nominal tensile capacity as governed by masonry breakout is evaluated using a design model based on a uniform tensile stress of 4 square(f m²) acting perpendicular to the inclined surface of an idealized breakout body consisting of a right circular cone (Fig. 5.27). The capacity associated with that stress state is identical with the capacity corresponding to a uniform tensile stress of 4 quare(f m²) acting perpendicular to the projected area of the right circular cone. This design approach, while less sophisticated than that of ACI 318-08 App. D, has been shown to be userfriendly and safe for typical masonry applications.
Nominal tensile capacities for anchors as governed by masonry breakout are identical for headed and bent-bar anchors, and are given by Eqs. (3-1) and (3-3) of the 2008 MSJC Code. B A f Code anb pt m = 4 ² 2008 MSJC , Eqs. (3-1) and (3-3) In Eqs. (3-1) and (3-3), the projected area Apt is evaluated in accordance with Eq. (1-2) of the 2008 MSJC Code: A l Code pt b = Ï€ 2 2008 MSJC , Eq. (1-2)
As required by Sec. 1.16.4 of the 2008 MSJC Code, the effective embedment length, lb , for headed anchors is the length of the embedment measured perpendicular from the masonry surface to the compression bearing surface of the anchor head. As required by Sec. 1.16.5 of the 2008 MSJC Code, the effective embedment for a bent-bar anchor bolt, lb , is the length of embedment measured perpendicular from the masonry surface to thecompression bearing surface of the bent end, minus one anchor bolt diameter. These are shown in Fig. 5.27. As shown in Fig. 5.28, the projected area must be reduced for the effect of overlapping projected circular areas, and for the effect of any portion of the project area falling in an open cell or core.
Nominal tensile capacities for anchors as governed by steel yield and fracture are also identical for headed and bent-bar anchors, and are given by Eqs. (3-2) and (3-5) of the 2008 MSJC Code. In those equations, Ab is the effective tensile stress area of the anchor bolt, including the effect of threads.
In that equation, the first term represents capacity due to the hook, and the second term represents capacity due to adhesion along the anchor shank. Article 3.2A of the 2008 MSJC Specification requires that anchor shanks be cleaned of material that could interfere with that adhesion. The failure mode with the lowest design capacity governs.
