Transverse Shear Reinforcement adjacent to concrete beam-column joint

[wayne_dwops]

I am in the process of designing a concrete beam-column joint that is not intended to be a part of the seismic or lateral force resisting system of a building. This joint will be transferring shear forces due to moment into the column and of course the vertical shear in the beam into the column.

While not related to the reason I am posting, my search led me to this post as I needed some clarification on what ACI 318-14 15.2.2 meant by "shear resulting from moment transfer". The report ACI 352R-02 mentioned in the link confirmed my suspicions that the "shear" should be taken as the difference of the tensile component of the integrated beam assuming a balanced cross section, and the shear in the column at the inflection point.

I feel I have successfully designed the transverse reinforcing within the joint, however I am unsure how far I should extend my transverse reinforcing past the joint. ACI 352R-02 references ACI 318-02 21.4.4.4 which explicitly provides this length (max of depth of beam at joint face, 1/6 clear span of the member, or 18 in). I am not seeing an equivalent section in ACI 318-14 Chapt. 25 or 10. As my column is only experiencing this moment and no deliberate lateral in plane loads, my critical section shear is simply due to the moment in the column and remains unchanged over the length of the column. Furthermore, the section in ACI 318-02 stipulates that the length they provide is based on potential inelastic lateral displacements, which I would assume is reserved for special concrete moment frames. I am hoping that someone knows of a code section or design theory I am missing...

 

[HTURKAK]

My points;

- Pls look ACI Detailing Manual MNL-66(20)

- The spacing of shear reinforcement shall be acc. to ACI 318 10.7.6.5.2

- The excerpt from ACI Detailing Manual ;

I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[wayne_dwops]

HTURKAK I do not have a copy of that detailing manual however I do have the guide it references (ACI 315R-18). The most direction the guide gives me is to follow ACI 318-14 10.7.6 and the detailing requirements of Chapter 25. Following this guide I would begin my column ties at the termination of the joint, which does not sit well with me. The previous guide in the ACI library, ACI 314R-16 (Guide to Simplified Design for Reinforced Concrete Buildings), does include some of the jargon I mentioned above on confinement tie spacing past the joints, so I will be moving forward as it appears ACI has not completely abandoned what was originally presented in 352R-02.

 

[KootK]

I think that this can be simplified a fair bit for a non-moment frame beam in a non-seismic application:

1) The column above the beam will have a constant shear demand over its entire length and should be reinforced for that demand, over its entirely length, with ties accordingly.

2) The column below the beam will have a different, constant shear demand over its entire length and should be reinforce for that demand, over its entire length, with ties accordingly.

3) I don't believe that there is a code requirement for column ties to extend through the depth of the beam. That said, some firms will do that anyhow as a perceived matter of good practice.

The column shear over the depth of the beam can be enormous when the goal is to design for plastic hinging in the beam at the joint.

 

[wayne_dwops]

Thank you for your response @KootK, I agree with your statements and if the beam were not designed as fixed (and even if it was and the moment was smaller) I would be inclined to send the design in that direction or even use a corbel. However, this joint experiences a fairly large amount of negative moment due to gravity loads from the beam and as you mentioned in 3) the EOR liked extending the joint reinforcing outwards. To put this in perspective, my beam is about 80% stressed and my balanced cross section force couple is about 380k.


Client was not a fan of my design, however, and pointed us in a different direction so this connection may never be built...

 

[KootK]

I agree with your statements and if the beam were not designed as fixed (and even if it was and the moment was smaller)

I'd intended all of my statement to apply to a condition where the joint between the beam and columns is rigid. Even in that situation, the shear demand outside of the joint zone will tend to be modest.