Article Applying Appendix D

Article Applying Appendix D

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Unformatted text preview: up of anchors far from an edge. They include ec for non-uniform loads that would result in eccentric load on a group of anchors, ed for close edges, c for cracking and cp anchor that are not cast-in-place. The second subscript covers the type of anchor R T S resistance mechanism, N for tension, P for pullout or V for shear. Here is the good news, for a concentrically loaded group of cast-in-place bolts located away from the edge of a slab that is assumed to be cracked, all eight factors are equal to 1.0. The least understood of the ψ factors is ψec,N, the modification factor for anchor groups loaded eccentrically in tension (Appendix D Section D.5.2.4). t An engineer who his designing the ig anchor boltsofor r a column base plate py C that carries an overturning moment and axial tension typically thinks of eccentricity as the distance from the centroid of the anchor group to the resultant axial force. Unfortunately this is not the eccentricity that is being addressed in Section D.5.2.4. Figure 1 shows an example of an eccentrically loaded base plate. To calculate the concrete capacity for this example, apply equation D-5 of ACI 318 Appendix D. C U Equation D-5 Note that the 10 kips uplift load is applied at a twelve inch eccentricity from the centroid of the anchor bolt group. Twelve inches is not the e´N to be used in equation D-9 of ACI 318. Also note that by assuming concrete is cracked, all of the ψ factors except for ψec,N are equal to 1.0. If we assume that for a thick base plate the applied load will cause the plate to rotate as a rigid body about the left edge, then a simple hand calculation can be E R 3” EMBED 2” 4” e n i z a g a m ® U T Ncbg = (ANc/ANco) ψec,N ψed,N ψc,N ψcp,N Nb Figure 1: Eccentrically Loaded Plate. performed to determine the loads on the anchor bolts (Figure 2). The 120 in-kip moment applied to the centroid of the plate will result in 5.77 kips per bolt on the right side of the attachment, and 1.15 kips per bolt on the left side of the attachment. The 10 kip tension load is assumed t...
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This document was uploaded on 01/28/2014.

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