## Robot Structural Analysis

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# Using multiply factor on Ig

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Hope you get my point.....and hopfully my point make sense.

# Re: Using multiply factor on Ig

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# Re: Using multiply factor on Ig

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# Re: Using multiply factor on Ig

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For exaple slab t=200 bars 12mm center to center 100mm gives Ig=6,7e+8 and Ic=1,35e+8 approx. Is it realistic to set the multiply factor 1,35/6,7=0,2 ?? Or maby take the middle value between 1 and 0,2 saying assuming that the slab doesnt crack everywhere......or am I misunderstanding the use of this factor completly? How are you Robot users using this factor?

# Re: Using multiply factor on Ig

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Check ACI code (as an example) for guidance. Off the top of my head ACI recommends to model slabs as 0.25 x Ig (similar to the number you came up with).

# Re: Using multiply factor on Ig

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You may try to use the stiffness map that shows reduction of the stiffness with with the required reinforcement for a guidance.

*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.*

**Artur Kosakowski**

# Re: Using multiply factor on Ig

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Artur,

Can you please explain the calculation or method of calculation behind the process that creates this map?

Cheers,

Tony

# Re: Using multiply factor on Ig

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This is the ratio between stiffness calculated based on the properties of the panel (thickness) and 'cracked' stiffness calculated based on selected code provisions with the influence of amount of reinforcement needed for calculations and SLS cases you used for reinforcement calculations.

**Artur Kosakowski**

# Re: Using multiply factor on Ig

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Thanks so much for taking time discussing this matter.

According to your answer Artur then it is possible to assume this factor during the code-check calculation for slabs, as I understand it. Could you please show this method in a attached picture. I woud very much appreciate it if you could do that.

But would it be necessary to repeat the calculations. What I mean is that first the slab is calculated with this factor set as zero, run the code calculations and estimate this factor, set the factor as assumed and then run code check again??

Could be that I am misunderstanding this completly being a new user of Robot.

kind regards

Ingolfur

# Re: Using multiply factor on Ig

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According to your answer Artur then it is possible to assume this factor during the code-check calculation for slabs, as I understand it.

The stiffness distribution I indicated is used during the cracked deflection calculations (elastic approach).

If you want to influence the static analysis of the model you should use the method described by Tony. To do so (and use the value from the map) you may need to follow two steps you mentioned below:

What I mean is that first the slab is calculated with this factor set as zero, run the code calculations and estimate this factor, set the factor as assumed and then run code check again??

*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.*

**Artur Kosakowski**