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S-Concrete not calculating the correct value of Fr as per CSA 23.3-14

Amrit Singh

1. S-Concrete is not calculating the correct value of Fr as per clause 11.3.9.2 of CSA 23.3-14. I believe it does not consider 0.5 Vs present in the equation. It shows me a warning "Steel area provided does not meet shear/torsional requirements Clauses 11.3.9.2 and 11.3.9.3 of A23.3"

2. Secondly S-Concrete also sometimes shows me a warning Shear reinf. spacing exceeds the allowable. Clauses 11.2.8.2 . 11.3.8.1, 11.3.8.3 ), but when I checked these clauses the shear reinf. provided meet all these clauses.

Could you please look into these issues?

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S-FRAME

v2022.1

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Andres Chavez

Hello Amrit,

Thanks for posting your question in the Altair Community. My name is Andrés and I’ll be happy to assist.

1. It might be worth clarifying the following to answer this question. S-CONCRETE uses what we call the ‘Required Vs’ based on the shear demand minus the resistance of the concrete, Vc, which in some cases, may result in a smaller Vs in the central equation that would be used if we chose the ‘Capacity Vs’, which could be larger and would therefore produce a smaller force. The logic behind using the Required Vs and not the Capacity Vs in this equation is that it is a capacity-based equation that combines the effects of the moment, axial and shear force. As this is a force equilibrium equation, in which Vs is the force contribution of the stirrups in resisting the applied shear force, Vf, S-CONCRETE conservatively considers the contribution of the stirrups equal to the force Vs = Vf – Vc, rather than the shear strength of the stirrups. This will ensure that an overestimated value of Vs is not used for this purpose, considering the interaction between shear in the two directions and torsion. This can be consulted on S-CONCRETE's Help System, under the topic titled 'Shear and Torsion Provisions - Canadian Standard (CSA-A23.3-04 & 14)'. I am attaching an excerpt of this topic below, more precisely, the 'Additional Longitudinal Steel Area for Torsion (Beams Only)' section. Please see Image 1 below in the attachment section for reference.

2. For your second question, it might be better to take a closer look at your SCO file and see why S-CONCRETE is addressing this warning message for the shear reinforcement spacing to provide a more accurate answer. Feel free to send us your model to the following email address to have a separate case created in our technical support platform, Service Now, as it might not be possible to send the SCO file through the Altair Community forum:

sframe-support@altair.com

Just for reference, these are the clauses referred to in this message found in S-CONCRETE’s Internal Help System, for beams, columns, and walls, but we’ll be glad to take a closer look at your particular case when we receive the model. Please see Image 2 in the attachments.

We hope this information helps clear things up. Feel free to ask any additional questions in the meantime. We can carry on with the conversation on Service Now, we look forward to hearing from you again.

Kind regards,

Andrés Chávez Burgos

AEC Solutions Engineer

Image 1 - Calculation of the Force for additional longitudinal steel area for torsion.png

Image 2 - Reference clauses for the shear reinforcement spacing.png

James Anderson

Hi @Andres Chavez

In my opinion, the approach that S-CONCRETE uses is overly conservative and is not the intent of the clause in CSA A23.3.

CSA A23.3-14 Clause 11.3.9.3 states that Vs should be used in the equation. A limit in the Clause stating that Vs is not to be taken greater than Vf is put in place as to not overestimate the added benefit of shear reinforcement.

It should be noted that the contribution of Vc to resisting shear force Vf is neglected in the equilibrium equation (see A23.3 Commentary). The equilibrium of forces can be maintained by utilizing the full capacity of Vs provided (up to Vf), as additional capacity in the stirrups can be utilized before additional capacity is required in the longitudinal reinforcement.

There are examples in the CAC Concrete Design Handbook that go through using this equation in the same way I have explained.

It would be beneficial if Altair were to implement this less conservative, code-compliant approach in S-CONCRETE. Most beam designs I complete that have any shear demand often show a "Warning" on the Code Check summary due to the Longitudinal Steel Requirement Check being over-conservative in its underlying assumptions.

Andres Chavez

Hi @Andres Chavez

In my opinion, the approach that S-CONCRETE uses is overly conservative and is not the intent of the clause in CSA A23.3.

CSA A23.3-14 Clause 11.3.9.3 states that Vs should be used in the equation. A limit in the Clause stating that Vs is not to be taken greater than Vf is put in place as to not overestimate the added benefit of shear reinforcement.

It should be noted that the contribution of Vc to resisting shear force Vf is neglected in the equilibrium equation (see A23.3 Commentary). The equilibrium of forces can be maintained by utilizing the full capacity of Vs provided (up to Vf), as additional capacity in the stirrups can be utilized before additional capacity is required in the longitudinal reinforcement.

There are examples in the CAC Concrete Design Handbook that go through using this equation in the same way I have explained.

It would be beneficial if Altair were to implement this less conservative, code-compliant approach in S-CONCRETE. Most beam designs I complete that have any shear demand often show a "Warning" on the Code Check summary due to the Longitudinal Steel Requirement Check being over-conservative in its underlying assumptions.

Hello James,

Thank you for getting back to us. We appreciate your input on this topic, as our users' opinion is always of great interest to help us make our solutions more user-friendly.

We have passed on your comments to the rest of the team and we are currently looking into it. We appreciate your patience while the discussion takes place, we will be getting back to you as soon as we have more information on this. Please remain attentive to our comments on this forum post, and once again, do not hesitate to ask any other questions or make any other remarks if necessary. We are here to help.

Kind regards,

Andrés Chávez Burgos

AEC Solutions Engineer

Andres Chavez

Hi @Andres Chavez

In my opinion, the approach that S-CONCRETE uses is overly conservative and is not the intent of the clause in CSA A23.3.

CSA A23.3-14 Clause 11.3.9.3 states that Vs should be used in the equation. A limit in the Clause stating that Vs is not to be taken greater than Vf is put in place as to not overestimate the added benefit of shear reinforcement.

It should be noted that the contribution of Vc to resisting shear force Vf is neglected in the equilibrium equation (see A23.3 Commentary). The equilibrium of forces can be maintained by utilizing the full capacity of Vs provided (up to Vf), as additional capacity in the stirrups can be utilized before additional capacity is required in the longitudinal reinforcement.

There are examples in the CAC Concrete Design Handbook that go through using this equation in the same way I have explained.

It would be beneficial if Altair were to implement this less conservative, code-compliant approach in S-CONCRETE. Most beam designs I complete that have any shear demand often show a "Warning" on the Code Check summary due to the Longitudinal Steel Requirement Check being over-conservative in its underlying assumptions.

Hello James,

We appreciate your patience. As promised, I wanted to give you an update on this topic. We have met with our development team and shared your feedback for consideration in future releases. We appreciate your willingness to help improve the software.

We wish you an excellent rest of the day, feel free to reach out again, we are always interested in our users' feedback.

Kind regards,

Andrés Chávez Burgos

AEC Solutions Engineer