rummaan17
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Everything posted by rummaan17
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Can someone explain as when to use non-linear allow uplift option for slab design ? Is it only when soil has uplift bearing pressure ?
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Dear Mohammad Shaker, This is to treat an evil with another. Though in most cases it favored me. Yes it would affect your result in drift but I haven't noticed any problem with P-Delta. Please check and share your experience.
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Dear All, I have a concern that I would like to address. Wugh, it consider joint stiffness with col_stiff. I have went through few discussion that favor modeling column on top also as half or full length with fixed or pin support. I would like to have input from respected engineers regarding their preferable method of practice and its effect. Thanks in advance.hile exporting slab to SAFE for design. SAFE only account for column below with restrains but not column on the top. Thanks in Advance.
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How To See The Reactions Under Shear Wall ?
rummaan17 replied to mhdhamood's topic in Concrete Design
Dear Shaker, ETABS joints reaction are just for the points that are manually meshed. That is the reason if you export your ETABS model to SAFE you will see far more points than that you see in ETABS Model. These are internal meshed points due to automatic meshing. You can always use the pier axial force to design footing. The answer is based on my understanding of the software and limited knowledge. Hope it helps. -
Hello Mr.Mohammad Shaker, If you have shell assigned as semi-rigid diaphragm you can always use F11,F22 & F12 =0.25 , to calculate temperature forces else it may result in very high forces which seems to me unrealistic. I have utilized this in a project and no comments showed up.
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Dear Mr.Rana, Can you please comment on my modal mass participation factor acquired from ETABS, what you can analyze seeing this results I am still confused about modes to be well separated. I have 15 storey building. I find my modes to be separated.
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Thanks Mr.Rana. I will go through it and will let you know if I need some help.
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Dear All, I received a peer review about the modal analysis I conducted in a high rise building. It states the following : "The preliminary mass participation factors indicate that mode 1 is predominantly translational in the transversal Y direction, mode 2 torsional and mode 3 translational in the X direction. It is not ideal to have torsional as mode 2". 1. What is the effect of Mode-2 on design as we usually concerned with fundamental frequency.? 2. How torsional modifier in ETABS is going to affect in this case? Any addition would be highly appreciated. Thanks in Advance.
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Mr. Umar Makhzumi, Thanks for your response. I have grade supported Raft under it.
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Dear SE Pakistan Members, I am trying to model pits in Raft in CSi SAFE. PIT Bottom slab is depressed 2m below the Top of RAFT. I have following concerns which I would be glad if anyone can address. 1- What is the criteria/condition to analyze raft slab at one level (continuous) and pit/ raft on different level. 2- What is the appropriate method to utilize in SAFE to model RAFT with Pits. I came across option of Vertical offset in SAFE and the other is to model wall at periphery and model slab at bottom. Generally, we model same raft thickness below PIT depressed at 45 degree angle . For this reason, I always modeled PIT on same level as that of RAFT. (See Attached Pic for RAFT Plan & Section of PITS).
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Slender Column Design - Second Order Moment
rummaan17 replied to rummaan17's topic in Concrete Design
Dear Mr.Rana Waseem, Thanks for your response. I am working on a tall building for which column magnification procedure is found to give inconsistent result. For elastic linear second-order analysis from what I understood, I am approaching as follows: 1. Assigning stiffness modifier to all structural members as indicated in ACI 318-11 10.10.4.1 2. Assigning eccentric column by using Frame insertion point option to option for addition moment from M=P.e. 3. For columns which have problem, I am dividing it into 5-6 segments depending on judgement to capture local P-delta effect of second order moment resulting from deflection in the chord of the frame element between nodes. i.e. M=P x d ( Small delta ) 4. Enabling p-Delta option in Etabs so that it can calculate moment that will result from deflection indicated in Step.3. 5. In design preference, I modified consider eccentricity option to "No" so that it doesn't consider additional moment as I have already defined it in Step2 and also put magnifier to 1. 6. After running the analysis, column with problem in loads that are close to Buckling load will give error. (Though I am still not in favor of conservative buckling load calculation made by ETABS). Any Addition would be appreciated. -
Dear All, I happened to encounter an issue while designing Slender column for which I would like you all to put your feedback on. In, ETABS slender columns are designed with one of the method, moment magnification. (ACI 318-11 10.10.5). This method often result in high magnified moments because of the lower flexure stiffness EI computed from =0.4EI/(1+Bdns) (ACI 318-11 Eq 10-15). This problem is also address in one of the paper from Sturcutre Magazine. http://www.structuremag.org/?p=1005 Has anybody have experience to utilize other method Elastic Second Order Analysis (ACI 318-11 10.10.4) or Non-Linear Second-Order Analysis (ACI 318-11 10.10.3) for design of Slender Column?. Especially with reference to ETABS. I appreciate sharing your kind knowledge and experience. Thanks
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Dear Mr.Rana and Umar, Thanks alot for your feedback. I followed the procedure as dictated in SAFE online Video but I was making one mistake that I was putting the uplift case in LOAD CASE in SAFE. For that reason, it keeps on doing iteration but since there is no load from the top it doesn't converge. Alhumdulillah, the things worked out. Thanks alot once again. I would like to continue one more discussion on SOIL STRUCTURE INTERACTION.
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- SAFE
- Foundation Uplift
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Dear Members, I am trying to model a Raft in Csi SAFE with water uplift pressure applied as a negative surface load on Raft. After analyzing the model, I get negative pressure values which doesn't depict the original condition. I have been through CSI Knowledge base about utilizing option of "Non Linear Allow Uplift" but my model keeps on doing iteration and doesn't show up any result. Has any body have similar experience in modeling Raft like this. Will appreciated your help. Thanks alot.
