RC Frame moment and shear output values versus 2D frame analysis

[Mark_SHL]

Hi,

I have modelled a 5 level RC framed building which is presently being peer reviewer as part of the local authority checking process prior to consent to build is being issued.

The issue I am having is the RC frame moments and shears in the Robot model differ to those the peer reviewing engineer is obtaining using a Mulitframe 2D frame check by up to 50%.

Where do I go from here?  Is the model wrong; have I incorrectly loaded the building; are the load cases incorrect?  Can anyone please assist.

Regards,

Mark Sullivan

Engineer

Auckland

New Zealand.

[Artur.Kosakowski]

Hi Mark,

Having RSA model only it is hard to tell where the differences are. First of all you may start with creating 2 frame in Robot to see if you have the coherent results. Then I'd suggest that you check the total sum of reactions first for each of load cases to see if you have the same loads applied as well as their values to compare the distribution of loads between 2D and 3D models . Also check deformation to see if both models behave in the same way. This should allow you to identify where to look at. In addition check if there is any reduction of elements stiffness due to cracks in Multiframe.

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.

[Mark_SHL]

Hi Artur, Would you mind having a look over the model for us and let me know if you think it is correct. I was reasonably confident prior to the peer reviews moment and shear checks. So you are aware, the floors span between the beams. Upon trying to check the "load distribution direction" using the Display Robot does not want to let me see the symbol. There are some weird things happening with this particular file I feel. Kind regards, Mark Sullivan [Description: SHL email signature logo] BE CPEng MIPENZ. p : (09) 839 7044 f : (09) 835 4791 m : 021 117 4436 Side Entry, Level 1, 2 Waipareira Ave, Henderson, Auckland. 0610 www.sullivanhall.co.nzDisclaimer The information and attachments in this electronic communication are the views of the author and may not reflect the views of Sullivan Hall Chartered Engineers. Any attached files are provided on the basis that the recipient and the end user assumes full responsibility for any consequence or damage (directly or indirectly) as a result of this communication or any of its attachments. Confidentiality Information contained with this electronic communication is confidential. Any electronic communication and its attachments may not be forwarded on to any third party without the expressed permission of Sullivan Hall Chartered Engineers. If you have received this communication in error, please delete it and contact us by return email.

[Artur.Kosakowski · Accepted solution]

The load distribution symbol is not displayed as it is dione via stiffness of elements of mesh you generated. It will be displayed when you change the panel calculation model:

I'm sorry but I have too little background about the concept of your building to tell if the model is right or wrong (e.g. are walls intended to transfer vertical loads if you don't have them in the 2D frame model?) but I may look at the particular issue you indicate. Mind that this would require the reference to your frame model to see e.g. shear force diagram and what kind of load was applied to the frame.

[Mark_SHL]

Hi Artur, There is still something weird happening with the model as despite changing the floor plate calculation model type it would still not allow me to graphically show the load distribution direction on the floor panel. Regardless; I've remodelled the building by deleting the concrete side walls (ensuring I kept the forces similar to the original model) to mimic a 2D frame type analysis. The result was similar beam and column moments and shears were arrived at to the 2D analysis calculated by the Peer reviewer. Our conclusion was that the 2D frame analysis underestimates the contribution of the concrete side walls and the resulting moments and shears were over conservative. However, this did make us wonder whether the analysis should or should not include the stiffness of these walls. Our position is, because we have detailed for the walls to be adequately reinforced to carry the out-of-plane moment, and, have provided the necessary connection into the concrete floor slab, that we can utilise the concrete walls. Thank you for your assistance. Kind regards, Mark Sullivan [Description: SHL email signature logo] BE CPEng MIPENZ. p : (09) 839 7044 f : (09) 835 4791 m : 021 117 4436 Side Entry, Level 1, 2 Waipareira Ave, Henderson, Auckland. 0610 www.sullivanhall.co.nzDisclaimer The information and attachments in this electronic communication are the views of the author and may not reflect the views of Sullivan Hall Chartered Engineers. Any attached files are provided on the basis that the recipient and the end user assumes full responsibility for any consequence or damage (directly or indirectly) as a result of this communication or any of its attachments. Confidentiality Information contained with this electronic communication is confidential. Any electronic communication and its attachments may not be forwarded on to any third party without the expressed permission of Sullivan Hall Chartered Engineers. If you have received this communication in error, please delete it and contact us by return email.

[Artur.Kosakowski]

Reading your comments I'd assume that 2D frame approach is inaccurate as IMHO you at the same time disregard walls in load transfer and design reinforcement for them which means that you assumed that they actually carry this load 

If you attach your latest version of the model I will check this part:

"despite changing the floor plate calculation model type it would still not allow me to graphically show the load distribution direction on the floor panel"

[Mark_SHL]

Hi Artur, Sorry, I hadn't seen the graphic you posted as I responded using the email received in Outlook. After changing to a one way slab the load direction came up. Thank you. Regards, Mark

[Artur.Kosakowski]

Hi Mark.

I'm glad it worked for you. I hope you don't mind if I mark this topic as solved