How to determine Anchor Rod tension and shear area per ACI 318 App. D? 1

[StructureMan44]

ACI 318-11 Appendix D section D.5.1.2 and D.6.1.2 require the use of the effective cross-sectional area of an anchor in tension (Ase,N) and shear (Ase,V) respectively. In my situation I'm mounting equipment with cast-in-place or post-installed adhesive anchors 0.5in Ø ASTM F1554 Gr. 36 anchor rods. How do I determine the effective cross-sectional area of an anchor in tension and shear? I am assuming the threads will excluded from the area in both cases. Additionally, if the anchor rod does not have a nut or bearing plate at its bottom, then is the effective cross-sectional area of an anchor in tension (Ase,N) used for the net bearing area of the anchor rod (Abrg)?

 

[mike20793]

Yes, exclude the threads if it is threaded the length of the rod since these are used to check the shear strength and tensile strength of the rod itself. If there is no head on the anchor or no washer and nut, then there is no Abrg. Abrg is the difference in area between the head/plate washer and the area of the anchor. There needs to be some kind of mechanism to resist pullout, so J or L bolts can be used and the bend in the rod provides the resistance.

 

[Leftwow]

There is a table in the aisc steel book with these values in the bolts section.

 

[StructureMan44]

Mike20793: Thanks. If I understand you correctly, a threaded rod without a washer/nut or bend (L or J) can't be used. If these a bend or fastener isn't used then Abrg would be 0 and the pullout strength in tension would then be 0.

Playswow: Thanks. Are you suggesting using the net tension area in Table 7-17 (AISC 325-10) for the Ase,N? Can this be used for Ase,V?

 

[wannabeSE]

The commentary to ACI 318-11 §RD5.1.2 has an equation for A_se,N and §RD6.1.2 has an equation for A_se,V. If I remember correctly, this is the same equation shown in AISC's table 7-17 notes. If the cast-in-place anchor does not have a head or nut (straight rod only),there is no bearing area and A_brg = 0.

If the threads are excluded in shear, you might be able to use the area of the unthreaded portion for shear. But, I would not rely on the contractor installing the cast-in-place anchors with the threads excluded and adhesive anchors typically require fully threaded rods.

 

[StructureMan44]

Thank you very much. Is there any reason to select coarse threaded F1554 when post-installing into concrete? The fine threaded gives you more effective cross-sectional area and I would think most engineers would choose fine threaded for this reason.