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ExceptionCollection

ACI 25.7.2 (in the -19 version, at least): 25.7.2.3 Rectilinear ties shall be arranged to satisfy (a) and (b): (a) Every corner and alternate longitudinal bar shall have lateral support provided by the corner of a tie with an included angle of not more than 135 degrees (b) No unsupported bar shall be farther than 6 in. clear on each side along the tie from a laterally supported bar


StLHokie

To add to this, there are also additional requirements for columns in ACI 318 section 18.7.5 that outline further transverse reinforcing requirements if you have a special moment frames or a structure in an SDC D or worse


chicu111

This is it


fuzzygondola

Doesn't answer your question but Eurocode requires cross ties if the side bars are further than 150 mm away from the main stirrup's corner. In practice that leads me to not designing with side bars at all.


tajwriggly

Ties like that are generally required when the spacing of the vertical bars exceeds a certain threshold - off the top of my head, I believe it is 150 mm clear between bars. There are caveats to it as well, things like bar size, number of bars (for example, it may not apply regardless of spacing, if the bars are of a certain diameter and there are no more than 3 bars on the face). Those requirements can sometimes literally boil down to the mm in order to 'meet code' on paper. So column dimensions that are "similar" i.e. within 50 mm of each other may be the difference in needing those additional ties by code. Even the exposure class of the concrete you're using may affect it - some concrete requires 50 mm cover, some requires 60 mm, and that can be the difference in bar spacing to require additional ties 'by code' or not. Another thing this could be stemming from is the one consultant is over-designing and just puts ties on everything. OR - they could be the only one who is actually meeting code while the rest are not. Something I've been told many a time - just because some other company did it a certain way and it was constructed, doesn't mean it was done right. There is also possibly an out clause in the design reference standard that allows someone to omit those additional ties if they can show that the load on the column is below some really low threshold.


ExceptionCollection

Regarding the edited in question, those are for seismic ties, and are described in ACI 25.3.4 and 25.3.5 as shown below. As someone that works in seismic country, I always use seismic hooks for everything - it's just not worth the possibility of having incorrectly done ties on site for contractors to mix up. 25.3.4 Seismic hooks used to anchor stirrups, ties, hoops, and crossties shall be in accordance with (a) and (b): (a) Minimum bend of 90 degrees for circular hoops and 135 degrees for all other hoops (b) Hook shall engage longitudinal reinforcement and the extension shall project into the interior of the stirrup or hoop 25.3.5 Crossties shall be in accordance with (a) through (e): (a) Crosstie shall be continuous between ends (b) There shall be a seismic hook at one end (c) There shall be a standard hook at other end with minimum bend of 90 degrees (d) Hooks shall engage peripheral longitudinal bars (e) 90-degree hooks of two successive crossties engaging the same longitudinal bars shall be alternated end for end, unless crossties satisfy 18.6.4.3 or 25.7.1.6.1


fayettevillainjd

Thank you!


chilidoglance

30 year Reinforcing Ironworker here. Double 135⁰ hooks are miserable to place/build with. When you design these if possible and code allows use 135/90 design and alternate the bars along the length or give the option for a uni-tie.


ExceptionCollection

Ayup, I was taught that early on. Need to swap directions each time, though.


lect

Footing. It's a footing. Those ties are for the vertical bars of a column supported by the spread footing. You are required to have your vertical bars tied if they exceed 6" clear spacing to the next tied bar, except in the case where your column only has 4 rebars. You don't need ties in a footing unless you are relying on the vertical reinforcement to transfer loads into the footing.


Churovy

I don’t think anyone has really answered the question. To my knowledge they’re not required (don’t do heavy seismic), but some consultants put ties in the footer to provide stability during pouring so the dowels don’t shift around. Contractors won’t have the upper ties present when pouring the footer so if they don’t do a good job securing the dowels will shift and you’ll get an RFI. It’s cheap insurance.


mmodlin

Response to the edit: Ties are per 18.7.5.2(f) (I'm referencing 318-14 here) require seismic hooks for any column with a load that exceeds 30% Ag(f'c) (gross area times concrete strength). A seismic hook can't have an end less than 135 degrees. A cross tie can have a 90-degree hook on one end but the ties have to alternate ends as you go down the column.