RC Columns – (ACI318-11)

[Refaat]

 Dear Colleagues

   Here is an attachment file of multistory building. I want to design the Columns according to (ACI318-11). 

   But, I have faced some unclear points; I would like to clarify them from you:

1.Capture (000) for RC column (bar 20), How does Robot in required reinforcement calculate the value of (MZ) = 104.65 KN.m while in the analysis results only (4.37 KN.m). Knowing that I allowed buckling effect only in (Z-direction) (Length coefficient = 1)?  May I know the equation to calculate this value?

2.Capture (001) for RC Column (bar 20), How does Robot also in provided reinforcement calculate the value of (MZ = 2980.90 KN.m) at the middle section of the column?  It is very huge value.

3.Dose Robot in required reinforcement calculation for columns consider (the values of axial force and moments) of upper node when the buckling effect take in an account while treat with (the values of axial force and moments) of lower node when the bucking effect doesn’t take in an account?

4.Capture (002), what is the meaning of element type is “beam” while this bar is  a column?

https://www.mediafire.com/?ji55n4im0t89k3h

Best Regards

Refaat

@Refaat Artur Kosakowski marked post as the solution. If it did not work as an answer, please post your reply in this thread so that I can unmark the solution. 

[Artur.Kosakowski]

1 and 2. See the RC Column calculation note. The values depend on amount of reinforcement in the column and the huge value for 2) is due to the fact that with the reinforcement that you have in the column you are below the critical force. If you add more rebars it will decrease:

3. I'm not sure if I understand what you mean.

4. It stands for bar type element. Could also be truss or cable when such attributes are assigned. 

[Refaat]

Dear Artur

Greetings

Thank you for your response.

 1.Yes, I decreased the value of (Mz) in provided reinforcement as you suggested by increasing the reinforcement ratio. But still I am not able to know     how does Robot calculate the value of (Mz) in required reinforcement calculation (Mz=104.65 KN.m)?

Could you take a look to the attached capture (003) and tell me what is your explanation?

2. My inquiry regarding to required reinforcement calculation for RC Columns.

• Case I : When buckling takes into the calculation

  Dose Robot design the column based on the force and moments of upper column node?

• Case II : When buckling doesn’t take into the calculation

Does Robot design the column always based on the force and moments of lower column node?

 Please, take a look to capture (004).

Best Regards

Refaat

[Artur.Kosakowski · Accepted solution]

 1.Yes, I decreased the value of (Mz) in provided reinforcement as you suggested by increasing the reinforcement ratio. But still I am not able to know     how does Robot calculate the value of (Mz) in required reinforcement calculation (Mz=104.65 KN.m)?

Could you take a look to the attached capture (003) and tell me what is your explanation?

2. My inquiry regarding to required reinforcement calculation for RC Columns.

• Case I : When buckling takes into the calculation

  Dose Robot design the column based on the force and moments of upper column node?

• Case II : When buckling doesn’t take into the calculation

Does Robot design the column always based on the force and moments of lower column node?

In the RC Colum module program assumes larger axial force from top and bottom nodes whereas in the member required reinforcement the force is taken from the verification point. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Refaat]

Dear Artur

Greetings

Thank you for your confirmation. now it became clear the reason behind the difference of value (Mz) between required and provided reinforcement calculation .

However, I would like to draw your attention that the value of (M2) in the note should adopt the largest calculated moment occurring anywhere along the member (ACI318 -10.10.6.4) otherwise the correction factor calculation (Cm) will be not correct… (Please take a look to the attached capture 005).

Concerning my second inquiry, what do you mean by saying that (in the member required reinforcement the force is taken from the verification point.)?
And what is the base to select the verification point?

With Best Regards
Refaat

[Artur.Kosakowski]

Dear Refaat,

However, I would like to draw your attention that the value of (M2) in the note should adopt the largest calculated moment occurring anywhere along the member (ACI318 -10.10.6.4) otherwise the correction factor calculation (Cm) will be not correct… (Please take a look to the attached capture 005).

Thank you for pointing our attention to this part of the calculation note. It seems that it needs some changes however M2 is calculated as per code requirements:

Concerning my second inquiry, what do you mean by saying that (in the member required reinforcement the force is taken from the verification point.)?

It is taken from one of the 3 points indicated on the picture above (A, B or C).

And what is the base to select the verification point?

The verification is done for all of them and the forces from the "worst" one are displayed. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Refaat]

Dear Artur

Greetings

Thank you for the support given.

I am very sorry to annoying you. Still I need more clarifications for this issue. As appear in the attached capture Robot doesn’t assume the larger axial force(worst) in case (I) while as assumes the larger one in case (II).

What is your comment for this situation?

Yours Sincerely

Refaat

[Artur.Kosakowski]

"In the RC Column module program assumes larger axial force from top and bottom nodes whereas in the member required reinforcement the force is taken from the verification point. "

For this module the axial force will correspond to the verification point (one of three) where the ratio is the largest. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Refaat]

Dear Artur

 Greetings

“For this module the axial force will correspond to the verification point (one of three) where the ratio is the largest. “

May I get more explanation which ratio do you mean and how does Robot calculate it?

With Best Regards

Refaat

[Artur.Kosakowski]

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Refaat]

Dear Artur

Greetings

Thank you for your clarifications and your willing to help. Really I appreciate your effort to explain how Robot selects the design forces either RC Column module or member required reinforcement.

I would like to suggest if there is a possibility of using the same design forces for both (RC Column module and member required reinforcement) to avoid any confusion or lack of clarity

Yours Sincerely               

Refaat

[Artur.Kosakowski]

Dear Refaat,

In fact the forces (apart from the axial one which follows the rule I described previously) are the same and as I explained the check is done in 3 the same verification points in both discussed modules of RSA . The difference in which verification point is indicated as the governing one may in the situation when the safety ratio is similar in all of them be caused by the fact that in the RC Member Required reinforcement there is no exact reinforcement distribution whereas in the RC Column module the capacity verification takes into account the real position of each of rebar. 

I hope this helps. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Refaat]

Dear Artur

Many thanks for your guidance

Refaat

[Artur.Kosakowski · Accepted solution]

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@Artur.Kosakowski wrote:

Dear Refaat,

However, I would like to draw your attention that the value of (M2) in the note should adopt the largest calculated moment occurring anywhere along the member (ACI318 -10.10.6.4) otherwise the correction factor calculation (Cm) will be not correct… (Please take a look to the attached capture 005).

Thank you for pointing our attention to this part of the calculation note. It seems that it needs some changes however M2 is calculated as per code requirements:

Corrected in RSA 2017 SP2.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.