A short analysis report of the STAAD results for EQ forces.

Re: A short analysis report of the STAAD results for EQ forces.

sureshprsharma — Wed, 12 Jan 2011 21:22:52 GMT

According to me deleting the existing surface and redoing is the only option where it is proposed to change the meshing size. If it occurs to somebody immediately after meshing that the size needs to be changed, then the undo option can be utilized.

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Sun, 12 Dec 2010 21:18:00 GMT

I modeled the shear walls using surface elements and while modeling the element was meshed by the program itself. Now as suggested by Er.Sureshprsharma I tried to edit after selecting the surface element but I could not edit it to reduce the mesh numbers.

Anybody can help how to edit the surface element to reduce the mesh?

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

sureshprsharma — Sun, 12 Dec 2010 03:33:38 GMT

Mr. Rangarajan,

In my view 12 hrs is a very very long period. Either your PC may not be fast enough with the current configuration. Some virous problem may also be there.One more thing I am suspecting is that you must have considered default meshing of 10x10 in the shear wall or that may be still closer. Closely spaced nodes take unexpectedly higher time. Change meshing to 3x3 or 4x4 and see what happens. Please do not apply plates with meshing to simulate the floor slab.

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Sat, 11 Dec 2010 22:08:33 GMT

Dear all,

As suggested by Er. Sureshprsharma I tried to model the shear wall-8No in my model for each floor thereby there comes to 160 shear walls. Having modeled I try to run but to my surprise and as I informed it took more than 12 hours and it went on and so I aborted. Can anybody suggest how to reduce the run time and start getting the analysis result and go to the next step for designing shear wall.

T.Rangarajan

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Fri, 10 Dec 2010 20:02:50 GMT

Mr.Sureshprsharma,

Thank very much.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

sureshprsharma — Fri, 10 Dec 2010 19:48:25 GMT

Mr. Rangarajan,

My first request to you and everybody in this forum would be to take everything sportingly. Never get offended. We are learning from each other. In fact many things which were not clear to me have been clarified by your posting coupled with the clarifications given by dear Arun.

In the morning your specific query was about the location of floating columns in the model. I can not say how many such colmns are there in the entire model because I have not examined the whole structure but I request you to have look into the following positions/locations:

i) Columns above node no.72 above the fixed support.

ii) Columns above node no.114 above the fixed support.

sureshprsharma

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Fri, 10 Dec 2010 09:24:50 GMT

HI A.Gowri,

Please refer to IS code IS 1893-2002 ( Part-I) where you will find what are the seismic weight to be considered. The Floor live loads are to be considered as % of total LL on floor i.e. 25% for load intensity < or equal to 3Kn/sq.m and for loads > 3Kn/sq.m -50% is to be taken into account for Seismic load. The roof LL is not to be accounted for. This is as per code.

Also while EQ takes place nobody likes to stay and that is the reason the LL is reduce.

The load combination 14 to 17 are entered as such.

Hope it is clear to you.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

a.gowri — Fri, 10 Dec 2010 09:01:49 GMT

hi to all

I have one quire In the STAAD Input file,

In LOAD COMB 14 to 17 Dead load and seismic load is considered. In that seismic load are calculated with live load is it ok.

Re: A short analysis report of the STAAD results for EQ forces.

a.gowri — Fri, 10 Dec 2010 08:57:01 GMT

hi to all

I have one quire In the STAAD Input file,

In LOAD COMB 14 to 17 Dead load and seismic load is considered. In that seismic load are calculated with live load is it ok.

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Fri, 10 Dec 2010 08:02:55 GMT

Dear Mr. Sureshprsharma,

Thanks for your comment. I tried to find the Floating columns but I could not trace them. Cay u if time permits run the file and inform me so that it can of use to me?

Hope meshing for an element can be 1/10 th thickness or 1 M. In this case to reduce the run time I allowed the program to mesh it.

I will check the shear wall height and hope that I followed some example where it was modeled as one unit. As soon as I come to know I will inform

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

sureshprsharma — Thu, 09 Dec 2010 20:58:38 GMT

Mr. Rangarajan,

Even the last file posted in the forum contains four or five floating columns. I have not run the file but in such circumstances Staad must be giving warning . The beam on which the floating columns are resting must be disastrously failing in design.

The shear wall as modelled has 10 divisions (default) vertically for a height of about say 70 meter from ground floor to the roof level. The meshing is grossly inadequate. Apart from above my common sense says that one node must be formed at the floor level because the storey shear which is proposed to be resisted by the shear wall acts at the the floor level. It is firm belief that the shear wall as modelled will not be able to serve the desired purpose . Anybody who believes otherwise is most welcome to correct me.

sureshprsharma

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Wed, 08 Dec 2010 21:38:12 GMT

Dear Mr.Arun,

The questions raised by Er.Sureshprsharma is worth to be noted but I would like to offer my views as follows:

1. The shear wall is provided with column heads of size 600x600mm against the wall thickness which is for offering more resistance to BM and stability. Hope reference to be made the design of shear wall.

2. Since modeling the wall in piece meal will create more mesh and the inter-connectivity of floor slab and the beams at the top and bottom will create more problem while using the tools to check the beam plate connectivity and normally the walls will be cast with the slab and the bell mouth portions. In the model I proposed only beams on the top and bottom of shear wall at each floor and made them as inactive so that it will not be accounted for in the analysis but will aid to generate the wind load by the program. Hope this will help to understand the model. Also if you view the results of the shear wall by double clicking after analysis you can find the output results-Fy, Fx, Mx etc are given at each height and it is what we need in designing the wall.

3. Since the shear wall is meshed automatically by the program support is only proposed for model over the column(Bell mouth ends) and if needed the supports can be added at the mesh points. Minimum supports modeled to get support reactions so that the footing for the shear wall as usually designed as either combined footing or a raft. It s a separate aspect to be taken care.

Hope that I expressed my views from my knowledge and if it is not correct may be informed to improve myself.

Thanks.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

sureshprsharma — Wed, 08 Dec 2010 20:27:11 GMT

Dear Arun,

I trust you have looked into the model prepared by sri Rangarajan to address his query alone. Let me first clarify that I have never designed Shear wall. I had only the opportunity to execute the shear wall designed by some one else. This the reason that I have been silently but carefully watching your posting and the model too. I request you to clarify my reservations about the model:

i) Sri Rangarajan has applied the shear wall in one stroke from the ground floor to the roof. Is it the right procedure? I feel it should be floorwise. Why because there is beam and column at every floor level surrounding the shear wall. The shear wall produced in the model posted by Sri Rangrajan is not going to be attached to the beam at the intermediate level. My view is that the surface incorporated in the model will not behave as shear wall.

ii) No support has been provided at the ground level for the shear wall

Please post your comments.

sureshprsharma

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Wed, 08 Dec 2010 19:30:48 GMT

Dear Er.Arun,

Yes, I also observed the same and now I removed the floating columns and added the member release for all the members meeting on the 10m span in the z direction. Also added the check soft storey command.

I am attaching the new file in which all the corrections were made so that other experts can put thier comments if any.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

Arunkumar Srinivasan — Wed, 08 Dec 2010 14:31:32 GMT

Dear Sir,

I just did a quick look at your model - the columns to the right of member 229 (and similarly 228, 230 and 231 in this plane and also 232, 233, 234 and 235 in the next plane) are missing below - that means the beam spans 10m with a huge column load (floating column) in the middle - I hope this is the reason for the high BM...

Arun

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Wed, 08 Dec 2010 10:33:14 GMT

Dear Er.Arun,

The use of INACTIVE and IGNORE STIFFNESS are very useful and powerful tools in STAAD PRO. You can find them in the technical manual. The INACTIVE is used for MEMBERS and IGNORE STIFFNESS is used for PLATES only and could not be applied. That is why I requested experts to help to find it in STAAD in my previous posting.

The INACTIVE is used to change tension or compression property while analysis and IGNORE STIFFNESS s used for the analysis of roof truss for the application of wind load or roof load using the program. You can find more explnation of this in the manual.

If you send your mail ID I can send you some examples from the prepared STAAD MAUAL which I would like to publish.

In the shear wall problem I modeled the beams at each level of 3 m length on the top of shear wall in order to generate the wind load as wind load can not be generated by STAAD unless there is closed polygon.

Please find attached latestes STAAD file of the shear wall in which I corrected all the inputs.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

Arunkumar Srinivasan — Wed, 08 Dec 2010 09:58:56 GMT

Dear Sir,

Could you post the updated input file? And also, could you explain the usage of INACTIVE command - I have not used it before...

Arun

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Tue, 07 Dec 2010 18:21:28 GMT

Dear Er.Arun,

I went through the input after correcting all the mistakes. Now I found that the member (BEAM) of 5 m span has an enormous amount of BM as per the attached PDF file under the load combination 1.5(DL+LL+ROOFLL) an other combination 8 and 9.

Kindly run the file and find out again what is the mistakes or where I went wrong since 5 m beam can not have so much BM.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Tue, 07 Dec 2010 17:06:37 GMT

Dear Er.Arun,

Thanks and I will try to model .

Re: A short analysis report of the STAAD results for EQ forces.

Arunkumar Srinivasan — Tue, 07 Dec 2010 15:09:59 GMT

Dear Sir,

You are welcome...

Regarding shear contribution from shear wall and frames there is no straight forward way to do this but here are my thoughts... I am not 100% sure of all of it, and I would like others to correct me if I am wrong...

1. Please note that IS1893 allows two different types of design for buildings with shear walls - (A) Buildings with Shear walls designed for earthquake load but frame not designed as MRF and (B) Buildings with Dual Systems where shear walls and frames jointly take the earthquake load - here shear walls can be ordinary or ductile and the frame can be OMRF or SMRF...

2. Based on the adopted system, the R value is to be considered.... Purely from behaviour point of view, IMHO it is better if either (a) Dual system of Ordinary shear wall and OMRF, or (b) Dual system of Ductile shear wall and SMRF is adopted as it is likely to reflect better real-life behaviour... But code is not limiting the designer to use only one of these two methods...

3. If we consider option (A) Building with Shear wall designed for eq load and frame not designed as MRF, then,

3.1. In the final STAAD model for the frame, we dont need to include the eq load cases. But the shear wall must be modeled. From this model, the design details for the frame only will be obtained....

3.2 For the shear wall, we can calculate base shear manually or by running this first in STAAD. Then, we calculate contribution to each shear wall (based on relative stiffness) and design the shear wall by separate staad model for each shear wall separately. The base shear can be distributed at each floor level as per IS code and the results obtained.

3.3 Alternatively, the STAAD model can be modelled as you have done this model, but with the R factor of 3 for Ordinary Shear wall and 4 for Ductile shear wall (table 7, items vi, vii). Then, we do not need to ensure that the MRF takes minimum 25% of base shear

4. If we consider option (B) Building with Dual System, we can use larger R factor (table 7, items viii to xi)

4.1 First we model the whole system just like you have done this model.

4.2 Open the results of the output, and check the total horizontal reaction in each direction...In each direction separately, we should check the total horizontal reaction of supports that are NOT PART OF SHEAR WALL... This partial sum must be greater than 25%... If not we have to create new load combinations for frame design where the EQ load is boosted....

For example, if total horizontal in X direction is 100 kN. The horizontal reaction on Shear wall supports is 90 kN and others is 10 kN.... The frames need to take 25% (25kN)... So, EQ factor has to be boosted by 25kN/10kN= 2.5 factor... So, in the combination 1.5 DL + 1.5 ELX, we will create new combination 1.5 DL + 3.75 ELX; for the combination 1.2 DL + 1.2 LL-reduced + 1.2 ELX, we will create new combination 1.2 DL + 1.2 LL-reduced + 3 ELX, and so on... These load combinations will be used for design of the frame while the original load combinations will be used for design of shear wall...

Sorry for the long post and hope it helps...

Arun

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Tue, 07 Dec 2010 14:16:39 GMT

Dear Er.Arun,

Thanks for your reply in the middle of your tight and busy schedule.

I also checked the input and I also recognized that the Member weight -brick load is not accounted for. Now I included and found that the out put comes alright. Yes for LL I presumed it including 3Kn/sq.m the proportion is 50% and now I corrected it also.

Because of your instigation I could be able to learn more. As result of this I am to state that:

Those who use any software has to check some data manually to verify whether the inputs are correct and any missing.

Now for seismic load application as pointed out by you must take care of every step like DAMPING ratio, the depth of foundation not to be included for RC frames etc.

Thanks once again for your help in understanding the STAAD.

I would like to know how to display the shear carried by the shear wall and the frames? As per code and ASCE the shear wall has to be taking 75% and a 25% respectively are to be allotted to frames. In that case how to make in the program as an input.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

Arunkumar Srinivasan — Tue, 07 Dec 2010 13:06:50 GMT

Dear Sir,

In the Dead Load case, you appear to have given brick work load as member load 12 kN/m and 5 kN/m probably for parapet... But this does not seem to be included in the seismic load definition... Please check after adding it...

Also, if LL is 3 kN/sqm, I think you should use 0.25*3=0.75 kN/sqm in seismic definition under floor weights - but you have used 1.5 kN/sqm... You have used correct factor of 0.25 in your pdf calculation...

Please note, these are comments that I have given without running the staad file (only basic reading the input file)... Have not had the time yet to run it and cross check it... Please inform if there are still problems (and post the corrected input file)... I will check again in greater detail...

Hope that helps...

Arun

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Tue, 07 Dec 2010 08:27:58 GMT

Dear Er.Arun

I checked again by inputting the Dampness value to 0.05 against the one by program and now the answer for Ah is in agreement with manual calculation. But need to know the difference between W calculated by the program and manual.

Thanks for your patient and kind guidance.

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

rangarajan — Tue, 07 Dec 2010 07:48:13 GMT

Dear Er.Arun,

I have not put the Damping ratio as 5 but in the dialogue box to generate the Seismic load as per IS 1893-2002 the table enters as 5% in the Damping ratio. So it is the program that enters. If it is wrong do we need to change it against the program generated one?

T.Rangarajan.

Re: A short analysis report of the STAAD results for EQ forces.

Arunkumar Srinivasan — Tue, 07 Dec 2010 07:02:22 GMT

Dear Sir,

Regarding the input file, I will need to go through it later today - hopefully post comments on it by tomorrow...

Regarding Structure Type, If you give ST 1, it considers RCC structure WITHOUT infill... Hence it will use different formula (common T for X and Z direction) from IS code... So, in my projects I usually give the periods after calculation with PX and PZ factors... But since the OP had not given that, I assumed that ST 3 was given...

Also, as mentioned by above post, DM should be 0.05... or it can be neglected (default value will be taken as 0.05)

Arun