Daniel Slegh's Activities

RAM Mass Participation with Ritz Vectors

Daniel Slegh — Mon, 08 Jun 2020 14:03:07 GMT

Hello,

I have been trying to use the Ritz vector solution to get 90% mass participation in my model. I have noticed something I find odd, but perhaps this there is a rational explanation for this. Running 30 eigenvalue modes the mass participation in X-direction does not reach 90%, however running 35 modes it reaches 90% by the 25th mode.

I was using the Ritz Vector method to determine how many modes to run and then switching to the more accurate Subspace method for the number of modes required to get 90% mass participation in both X and Y. However, now that I think about it, this might not make sense. Perhaps this is more of a theoretical question, but if the subspace method is only capturing 70-80% of the mass does that mean that extra 30-20% mass is not considered in the combination of the modes (or is more mass actually included as the Ritz vector method finds)?

Thanks,

Dan

RCDC Shear Forces for Sway not Calculated from RAM Import

Daniel Slegh — Sat, 23 May 2020 13:02:19 GMT

Hello,

I am using RCDC Advanced Concrete after using RAM for the analysis. I have imported the beam info from RAM after running RAM Frame and RAM Concrete analyses.

I am having issues with the V(D+L) and Vu-sway calculation from Skip Positive and Skip Negative LL imported from RAM (equilibrium shear per IS 13920:2016 Article 6.3.3).

I have assigned the Skip Positive and Skip Negative load cases as Live Load (this is the only LL imported from RAM file, and I defined it in RCDC as Live Load rather than Skip Load type in order that the Load Combinations generated will include the 1.2DL + 1.2LL + 1.2EL combinations which it does not consider with skip load):

After a beam design successfully completes, and I check the RCDC beam calcs, I see that the V(D+L) = 0, and so do all the sway shears:

RCDC does actually generate these shears if I specify one of the other load cases as Live Load (for example the EQ load), rather than the Skip Positive or Skip Negative. Is the issue that the Skip Positive and Skip Negative LL are envelope live loads exported from RAM?

If someone is knowledgeable about the implementation of equilibrium shear for these sway cases, I'm curious if other provisions of IS 13920:2016 Article 6.3.3 are implemented (namely: partial safety factor of 1.2 and beam considered simply-supported). I'm also concerned about the implementation of LLR in RCDC if it is not able to correctly identify the live load forces from the skipped loads.

I would love to hear about options on how to resolve this.

Thanks,

Dan

Live Load Reduction not Applied to RAM Reactions and in RCDC

Daniel Slegh — Wed, 27 May 2020 08:54:23 GMT

Hello again,

I'm having some issues with the integration of RAM and RCDC. I am using the NBC of India.

Is Live Load Reduction meant to be applied in RAM to the reactions? It does not appear to be incorporated in the reactions.
It appears that RCDC takes the reactions from RAM (not member loads) and thus it is not possible to apply live load reduction in RAM per RCDC documentation below (Option 2). This is the case whether I input the LLR manually for each column or if I use the 'calculated' option.
I have also found that toggling the Live Load Reduction option in RCDC has no effect on the live loads (which are skipped loads imported from RAM) in RCDC.

This is in the help file in RCDC and I am not able to see LLR applied in any of the methods:

Thank you,

Dan

RAM Frame - IS 1893:2016 Response Spectra Analysis Scale Factor

Daniel Slegh — Mon, 11 May 2020 12:55:58 GMT

Could someone please confirm that scaling the Response Sectra Analysis generated in RAM Frame using the Indian Standard IS 1893:2016 code does not include an adjustment for the Zone Factor, Z? If this is the case, I would assume the scale factor should be what some call the direction factor = (Z/2)*(I/R)?

This scale factor was recommended for STAAD.Pro with Response Spectrum (https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/12317/is-1893-part-i-2002-response-spectrum-philosophy)

The current FAQ on this subject only mentions scaling by I/R which would apply to ASCE 7 for example (https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/4029/ram-frame---dynamic-analysis-faq).

I would also note that if this is the correct starting scale factor, I'm assuming an iterative approach needs to be taken using this factor on the first run, then comparing with the base shear from the equivalent static method (some would interpret this to mean using a dynamic analysis but with Ta fundamental period as used in equivalent static method) and adjusting the scale factor so that at least that base shear is maintained as a minimum (IS 1893:2016 7.7.3).

Thank you,

Dan

Patterning (skip loading) of Live Loads in RAM

Daniel Slegh — Wed, 29 Apr 2020 11:44:23 GMT

I have been doing some extensive reading on these forums and in the help but still don't have clarity, so please help me with a few questions:

I am modeling a 4 story reinforced concrete moment frame in RAM and then will export the model to RCDC (Advanced Concrete) after running RAM Frame and RAM Concrete. I am using Indian Standards.

It appears load patterning (skip loading) is not done for roof live loading (nor in RAM Frame). I would like load patterning to still be implemented at the roof level. Is there any downside to using Live Load - Reducible instead of Live Load - Roof at the roof level? I will be using Indian Standards and LLR includes the roof as one of the floors that is counted.
RAM Concrete has an Analysis option that reads "Consider Load Polygons as Load Cases on Two-way deck (for pattern loading). However, the documentation also says that "Currently, the surface loading applied to two way decks does not generate any skip loading cases on beam lines". What does this Load Polygons option do? Ideally load patterning would have been done from the Surface LL (yes I know this is complicated), but since I read the second note about it not applying to two-way decks, I have resolved my surface LL to line loads. Is there a way to get patterned live load from a surface load using this load polygons option?
RAM Frame apparently does not use skip loading. What are the gravity loads in RAM Frame used for?

Thank you for your time.

Regards,

Dan

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Tue, 07 Apr 2020 00:24:40 GMT

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Check Soft Story using IS 1893 - 2016

Daniel Slegh — Tue, 07 Apr 2020 08:15:19 GMT

Hello Bentley Community,

Could someone please give some clarity in what exactly the CHECK SOFT STORY 1893 2016 command does?

Specifically, I'm curious what STAAD considers to be a soft story, since the IS 1893:2016 no longer makes mention of 60% to 80% figures to define the difference in relative lateral stiffness. All that is stated in (IS 1893:2016) Table 6.i is "A soft storey is a storey whose lateral stiffness is less than that of the storey above." This is reflected also in Figure 4A. However, there is a bit of a different explanation for 7.10.3 which allows for the definition of 80% of lateral stiffness IF RC structural walls are provided (for an open story situation, but I think we can infer, even if an open story is not present but RC walls are). I know this must be difficult to apply since the code itself is not abundantly cleary.

STAAD help currently only mentions 60-80% lateral stiffness methods from previous versions of IS 1893, though it says that the latest (2016) is implemented:

https://docs.bentley.com/LiveContent/web/STAAD.Pro%20Help-v9/en/STD_CHECK_SOFT_STORY.html

I'm sorry if that has already been answered, but the most-related topic I could find was the answer posted here by DSANJU:

https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/170698/open-ground-storey-design

Regards,

Dan