Seismic - Are footings considered cracked elements?
Seismic - Are footings considered cracked elements?
(OP)
Here's the situation:
Wood framed building
Wood shear walls using proprietary hold downs.
Hold downs using cast-in or post-installed hold down anchor bolts
Design of the bolts per Appendix D of ACI 318
Bolts extending into a continuous trenched concrete footing.
Question:
Would the embedded bolts be considered to be in a "Cracked" concrete section or an "uncracked" concrete section? This makes a huge difference in load capacity.
Previous assumptions:
I always thought that the cracked condition was typically for the bottom of flexural beams with the concrete in tension. For a footing, the top of the footing isn't in tension - except in a seismic event, the footing may be uplifted by the shear wall and the deformed shape of the footing implies a tensile condition near the hold down anchor bolt.
Also - if the answer is to simply check to see if there is net uplift on the footing at the hold down - do you use an R = 1? Or do you use the R for the shear wall system?
Do you use 0.6D + .7E? Or the ACTUAL condition of D + .7E. Or do you use D + 1.0E?
Wood framed building
Wood shear walls using proprietary hold downs.
Hold downs using cast-in or post-installed hold down anchor bolts
Design of the bolts per Appendix D of ACI 318
Bolts extending into a continuous trenched concrete footing.
Question:
Would the embedded bolts be considered to be in a "Cracked" concrete section or an "uncracked" concrete section? This makes a huge difference in load capacity.
Previous assumptions:
I always thought that the cracked condition was typically for the bottom of flexural beams with the concrete in tension. For a footing, the top of the footing isn't in tension - except in a seismic event, the footing may be uplifted by the shear wall and the deformed shape of the footing implies a tensile condition near the hold down anchor bolt.
Also - if the answer is to simply check to see if there is net uplift on the footing at the hold down - do you use an R = 1? Or do you use the R for the shear wall system?
Do you use 0.6D + .7E? Or the ACTUAL condition of D + .7E. Or do you use D + 1.0E?






RE: Seismic - Are footings considered cracked elements?
Kept me out of trouble for 40 years!!
RE: Seismic - Are footings considered cracked elements?
RE: Seismic - Are footings considered cracked elements?
RE: Seismic - Are footings considered cracked elements?
I follow you. However, do you have an IBC section you can point me to that defines "cracked" conditions? I couldn't find one.
I understand they say "where concrete is cracked under service load conditions" in the Appendix D, but WHICH service load condition (see above about which R, which combination).
RE: Seismic - Are footings considered cracked elements?
ACI D3.3.4.4: The anchor design tensile strength for resisting eqrthquake forces shall be determined from consideration of a through e for failrue modes given in table D4.1.1 assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked
But, for non-seismic loading, I think we can go back to JAE's original assumption (about it only applying to the bottom of beams or such).