ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
(OP)
I have a base plate on a concrete pier with #8 bars & 1" bolts in the base plate. Does anyone have literature as far as the best way to calculate required development length of the anchor bolts? Would you develop the vertical bars? Would you use the 160 psi bond strength to figure development length? I know some people who develop the vertical bars & end up with anchor bolts 24"-36". Thank you for you comments.






RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
ACI 318-02 Appendix D contains the ACI requirements for designing anchor bolt embedments. It reflects current thinking on the subject, and is somewhat different than previous practice.
It is based on shear "pyramid" failure planes, previously capacity was based on a cone. The capacity is dependant upon an embedment of something like a bolt head, nut or sometimes a plate attached to the bottom of the anchor bolt. It is quite different from the development of a bar, and usually will be a good deal shorter embedment than would be calculated for a bar development.
chichuck
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
I have heard of using the 160 psi bond between concrete and an udeformed bar, but the anchor bolts may be oily from being fabricated, which would destroy the bond.
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
We detail our pier bars to have 90 deg hooks at the top, and angle the hooks toward the center of the bolt group. Then we make sure to have sufficient length to develop the hook bars. This prevents a chunk of concrete from being ripped off the top of the pier.
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
Here in upstate NY our bottom of footing elevation is 4 feet min. below grade for frost protection, and the wind loads are based on 90 mph, both of which I think greatly contrast with your conditions in Florida. I don't always have to hook the top of the pier vertical steel, but there have also been times that I have when due to thick footings and high loads I needed the hooks.
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
BJB - I am also from upstate NY and found some higher wind problems near the great lakes leading to some pretty big anchor rod patterns.
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
I currently practice near Albany, and most of the buildings I work on are fairly small. I designed a special moment frame for a fire house with seismic design category "D" that had large anchor bolts and embedments. I also had to use hooked bars at the top of the column piers, but when possible I avoid doing that. I agree with your comment about congestion at the top of the pier from hooks at the top of the pier vert reinf.
RE: ANCHOR BOLT UPLIFT DEVELOPMENT LENTGH IN PIERS
Consequently, I have always used a method similar to "bjb", where I develop the tension by lapping the anchor bolt with the vertical bars in the pier. It has always seemed logical and practical to me, but I never saw any literature to confirm same. In fact, I have had discussions with a few engineers who do not find believe this method is suitable.
Recently, an article in Structure Magazine, July 2004, entitled "Alternatives to ACI 318-02, Appendix D- 'Anchoring to Concrete'", by Colleen Bush and Ed Schweiter, confirmed my analysis method. It's an article worth reading. It is especially helpful where you have a drilled pier, with a large overturning moment, such as a large, single-pole sign, or large light pole for highway or playing field lighting.