ACI 318-19 Section 15.3.3.2 column vert bar hooks

[cliff234]

ACI 318-19 Section 15.3.3.2 requires column vertical bar hooks to be turned into the center of the column at the top of the column. In my opinion, turning the hooks inward into the column poses some problems, versus orienting them outward. The hooked bars would be easier to install if the hooks were turned outward. They would not be crashing into one another (especially if the hooks were on bigger vertical bars turning inward into smaller columns). The sketch shows #9 hooked bars turning into a 24"x24" column. Turning the hooks outward would also allow installation of the uppermost column ties to be installed immediately under the corners of the hooked bars (to facilitate development of those hooked vertical bars). I am just now reading through ACI 318-19. I don't think this requirement was in ACI 318-08 (the last version of ACI 318 that I was completely familiar with). What does turning the hooks into the column do that makes this "constructability challenged" hook orientation so important? Does anyone know what precipitated this change? Also, a number of other "top of column" details in various ACI publications show the hooks oriented outwards!

 

[HTURKAK]

The latest detail at acı 318-19 is better than the previous ones . Unluckily ACI 318 is silent for the reason and does not give specific guide lines for the design of joints. You can draw a STM model and see that the latest detail is more effective. The following figure is copy and paste from REINFORCED CONCRETE ( By James Kwight )
I will suggest you to look ACI 352 R and the Detailing of concrete structures ( By Jörg Schlaich , in GERMAN ).

 

[cliff234]

Thank you HTURKAK for your response! I’ll get a copy of the latest ACI 352. I still don’t see how turning the hooks into the joint will mitigate cracks, unless the hooks are made longer. I always had the mindset that the sole purpose of hooked bars was to facilitate the development of bars in tension. (The only time I use hooks longer than "standard 90-degree hooks" is on bars in cantilevered retaining wall footings as shown in detail (d).) Detail (b) (hooks turned outward) is labeled “unsatisfactory”. Detail (c) is labeled “satisfactory”. Interestingly, the hooks in detail (c) are graphically shown longer, but no other dimensional information is provided. Wouldn’t an alternative (and possibly improved) solution be to extend the column ties into the slab/beam/footing. In my opinion, the diagonal tension cracks shown in the illustrations would be better restrained by ties. Also, there are already continuous longitudinal bars parallel to the hooked bars – so why the need to turn the hooks inward if there is already reinforcing steel to restrain the cracks?