huangyhg

horizontal construction joints in conc. box culverts
we have designed a deep cover (44') box culvert using the box car program. the box is 8'x 8' with 12" haunches at the interior corners. wall thickness was selected to accomodate shear and then vertical reinf. selected for resulting bending. we are calling for a construction joint just above the bottom haunch (bending steel will be continuous thru joint), a peer review is asking for confirmation of shear transfer across the joint. was wondering if anyone has had to supplement similiar program output before, and how. otherwise manual check of joint shear friction and/or shear across bending steel presumed most applicable?
if you have a reasonable amount of reinforcing, shear friction should work ok. besides that, i don't know what your peer reviewer is after. maybe you need to ask for a clarification.
i'm just not sure aci meant shear friction to apply to this kind of joint. aci 318 article 11.7.1 is vague, if you ask me.
looking at pca notes on aci 318-02, figure 14.2 shows "applictions of the shear friction concept...". seven applications are shown. all are significantly different from this application. pca goes on to say, under "additional requirements", that shear friction steel should be anchored in confined concrete. confinement may be provided by beam or column ties, "external" concrete, or special added reinforcement.
i would add that the aashto specifications has the simlilar provision in 5.8.4 "interface shear transfer." (i bring up the aashto since boxes are often highway structures.) that being said, i can't say that i re
the aashto lrfd specs agree with pca, in that, aashto 5.8.1.3 provides that the "interface" between two elements be designed per shear friction provisions of aashto 5.8.4.
aashto 5.8.1.4 rules out the use of shear friction for slabs and footings. all the pca examples involve the interface between two elements, one much larger than the other, intersecting at 90 degrees.
in this case, by "haunch", i believe we're talking about a 12 inch fillet between the bottom slab and the side wall. the intersecting angle would be 45 degrees.
i think the reinforcing crossing the joint could be considered as confined if the longitudinal reinforcing is detailed on the outside, opposite to convention.
why not ask your local concrete pipe plant for some help? are you going to open cut this project? maybe precast will work better for you.
richard a. cornelius, p.e.
thanks guys, after reviewing all suggestions, and discussing with reviewer (corps of engineers), we demonstrated meeting the requirements of aci 318 17.5 & 11.7, and had to specify minimum surface roughening amplitude for the joint construction.

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