Using strength design, compute the design tensile capacity of a 1/2-in. diameter, A307 bent-bar anchor with a 1-in. hook, embedded vertically in a grouted cell of a nominal 8-in. wall with a specified compressive strength, f²m , of 1500 lb/in.2. Assume that the bottom of the anchor hook is embedded at a distance of 4.5 in. This example might represent a tensile anchor used to attach a roof diaphragm to a wall.
First, compute the effective embedment, lb. In accordance with Sec. 1.16.5 of the 2008 MSJC Code, this is equal to the total embedment of 4.5 in., minus the diameter of the anchor (to get to the inside of the hook), and minus an additional anchor diameter, or 3.5 in. As shown in Fig. 5.29, the projected tensile breakout area has a radius of 3.5 in. (diameter of 7 in.). Because the masonry wall has a specified thickness of 7.63 in., the projected tensile breakout area is not affected by adjacent ungrouted cells or regions outside of the wall.
Now compute the nominal tensile capacity as governed by steel yield. In this computation, Ab is the effective tensile stress area of the anchor bolt, including the effect of threads. According to ANSI/ ASME B1.1,
Now obtain the design capacity by multiplying the nominal capacity by the corresponding strength-reduction factor from Sec. 3.1.4.4 of the 2008 MSJC Code:
φB C anp = 0.65 × 3481 lb 2008 MSJC ode, Sec. 3.1.4.4
φB = 2263 lb
The governing design tensile capacity is the lowest of that governed by masonry breakout (2981 lb), yield of the anchor shank (8100 lb), and pullout (2263 lb). Pullout governs, and the design tensile capacity is 2263 lb.
If this problem had involved an anchor with deeper embedment (so that the projected tensile breakout area would have been affected by adjacent ungrouted cells or regions outside of the wall), only the anchor capacity as governed by tensile breakout would have been affected, due to a reduced projected tensile breakout area.
Similarly, if this problem had involved adjacent anchors with overlapping tensile breakout areas, only the anchor capacity as governed by tensile breakout would have been affected, again due to a reduced projected tensile breakout area.
