huangyhg

bolting thru concrete
i am reinforcing an existing concrete beam in a foundation wall by attaching a c15x33.9 to each side, basically clamping it. i want to develop the end reactions by thru bolting. my question is, does anyone have a procedure for checking the concrete for the bolt loads?
i have checked with hilti, and they say they don't recommend that there adhesive anchors be used in a thru bolting application. would a shear friction appraoch be acceptable? if you rely on bearing on the concrete, what would the dstribution of bearing stress look like?
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hilti provides good tested values for bolts in concrete. just ensure you meet the criteria for the tested allowable loads. ie, ensure the concrete has steel developed for the shear induced in it properly, so the concrete doesn't just break off if it's loaded in tension.
sketch your connection. label the loads and reactions properly. perhaps the rep can't see clearly how your connection conforms to their criteria, or perhaps they may suggest how to design the connections so they do conform.
we need more information on your connection to evaluate it.
if you are trying to transfer the end reaction of the two c15's to the foundation wall, you should be a ble to rely on the shaer values for the epoxy anchors, provided you extend byonmd the opening(?) enough not to affect the opening.
you could also install short c below the c15 as a "column". the column could be fastened to the wall with epoxy anchors to transfer the load to the existing wall.
thanks for the replies. this is an example of the way that i have been doing it. if i have say a 12" thick wall with channels on each side, i say that each channel takes half the load. then i look at an adhesive anchor that can take this load based on an embedment of half the wall thickness, 6" in this case. i do take into acount possible reductions for anchor spacing and edge distance, considering the distance of the bolts to the opening. i also check the bolt to make sure the shear stress on each shear plane is ok. i just think there is probably a more refined way of doing it.
bjb,
can you field weld a 3/8" plate to the flanges of the channels so as to create a boxed section around the concrete at the same locations that you would place the bolts? i'm not saying box in the entire column, but just boxing the areas for about 8" sections at each location of the would be bolts.
unfortunately i can't because there is a window in the opening that can't be touched.
make sure you account for the increased bearing pressure on the concrete at the bolts. this can get quite high, especially for small bolts.
bjb,
i have done it in a simialr manner several times. i have thought of and tried to "refine" the methodolgy several times. unfortunately, each time i think i have an alternate way something comes along to bring me back to the way you described.
weron4u,
i haver added the plate in a few instances.....sort of belts and suspenders.....
bjb,
are you reinforcing a beam on a foundation wall or a 12" thick concrete wall at an opening?
if it is wall like a deep beam, the channels attached may not be rigid enough to help transfer load from wall. they may just work like a horizontal tie to form the truss mechanism.
even if it is only a concrete beam, you need to check the stiffness to see how much help the channel can provide. i mean if the channel stiffness is much less than the concrete beam, you need quite a deflection to get the load transfer, the deflection may not be accepted.
i did consider the relative rigidities. i basically designed the channels to replace the concrete beam, and made sure the deflection was compatible with the window below.

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