Anchor Chair Reinforcing Pad
Anchor Chair Reinforcing Pad
(OP)
When designing the anchor chairs in the API 650 tank that I'm currently designing, the stress in the shell (around the anchor chair location) exceeds the allowable stress (25,000 psi, per Table 3-21b). Options to decrease the stress are to increase the shell thickness, add more bolts or increase the chair height. Could I use a repad around the anchor chair location instead? Has anyone done this before? What is a good reference for the design of these repads? I'm currently using Steel Plate engineering Data Vol. 2, but it does not address this issue.
Jorge L. Ramos, Jr., MSCE, PE
Alonso & Carus Iron Works, Inc. (www.alonsocarus.com)
Euro-American Steel Co., Inc. (www.euroamericansteel.com)





RE: Anchor Chair Reinforcing Pad
The allowable stresses on Table 3-21 are for the anchor bolts, not the stresses on the tank shell. Check API 650 para. 3.12.6 or 3.12.7 for evaluation of localized shell stresses.
RE: Anchor Chair Reinforcing Pad
Thanks for the reply. However, the last column on Table 3-21b clearly states that the allowable shell stress at the anchor attachment is 25,000 psi when seismic loads are considered. This is the stress occurring just above the top of the chair. I'll check with ASME Section VIII Div. 2, Appendix 4, as noted in paragraph 3.12.7. May be my interpretaion is wrong.
Jorge L. Ramos, Jr., MSCE, PE
Alonso & Carus Iron Works, Inc. (www.alonsocarus.com)
Euro-American Steel Co., Inc. (www.euroamericansteel.com)
RE: Anchor Chair Reinforcing Pad
RE: Anchor Chair Reinforcing Pad
Consider making the chairs wider as well as higher. If the tank isn't built yet, maybe make the bottom ring thicker just for this purpose.
RE: Anchor Chair Reinforcing Pad
You are right about the last column (allowable shell stress) on Table 3-21. That column was added on Addendum 4, December 2005.
I was looking at an older API 650 std, Addendum 3. Silly me. Sorry about that.
RE: Anchor Chair Reinforcing Pad
Jorge L. Ramos, Jr., MSCE, PE
Alonso & Carus Iron Works, Inc. (www.alonsocarus.com)
Euro-American Steel Co., Inc. (www.euroamericansteel.com)