Embedded Anchor Bolts In Concrete Masonry

[EIT2]

I need to design an anchor bolt connection, in an 8" concrete masonry wall, to resist 15.3K uplift.

When using NCMACN EQuations 7-1 through 7-4, EQ 7-4, being the prerequisite to EQ 7-1, results in such a low tensile value as a result of edge distance alone, taking no consideration for embedment length.

Does edge distance in concrete masonry, in this type of tensile application, control so much that embedment length, of the anchor bolt, has no significance?

Is there an alternative solution?

Thank you!

 

[dik]

You'll need a fair amount of wall to resist the 12K... You may want to consider grouting dywidag threadbars into the wall (like a rebar, but the deformations accept a proprietary nut) to develop a sufficient chuck of wall to resist the load. You can then bolt the dywidag bar to whatever it is that's pulling... the lower strength bars are only slightly more costly than rebar... they make up for it on the nuts and coupling devices... also grades of steel range from 60ksi to 200ksi+/-...

 

[EIT2]

To "dik":

Thank you for the alternative solution. I will consider this.

However, since the project has been bid, and I want to avoid an add for additional rebar, I would like to consider the anchor bolt with a significant embedment depth into a grouted core. Whether this is the final decision or not, for future reference, I am still curious, and the question remains:

Does edge distance in concrete masonry, in a tensile application, control so much that embedment length, of the anchor bolt, has no significance in increasing the allowable tension?

Thank you!

 

[dik]

Whether you're using a long AB or a length of threadbar, the distance/thickness of the wall shouldn't have much bearing unless it's 'high' so that in-plane bending (stability) becomes an issue (wall buckling like a deep beam). The effective area of the wall could extend from the length of development up, flared out at about a 30deg angle from horiz (tight) or a 45deg from horiz (conv). A single #6 threadbar will give you a load factor of about 1.5 on the 15K (sorry for the 12K typo before). The threadbar nuts are about $8 each and you can use the full .44 sq.in. of bar area at the rebar yield... Check with a local Dywidag supplier and get the current costs and availability... You can also substantiate material costs so you don'nt get roped by the contractor for the extra to contract... My standard drawing notes spec Dywidags for all AB's greater than 1" U/N... Embedment, splice length, etc. is just like 'real' rebar...

 

[Ron]

In the theory of this type of anchorage, the embedment and subsequent pullout resistance are considered on a radial basis with a conical failure plane. For a depth of embedment greater than 4 inches, your failure plane would be intersected by the block edge in two directions. This is not a big deal other than it places more stress on the remaining failure plane, thus requiring greater depth of embedment to achieve equivalent pullout resistance. If there is any shear on the anchor, the proximity to the edge is significantly more critical.