Rana

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Everything posted by Rana

  1. Suarez, we do not handle pirated/cracked stuff. Please be aware in future.
  2. Solutions; 1. Why dont you import the cad drawing (as shown in image) into SAFE and draw footings with proper orientation? 2. Like you got reactions under so many combinations from ETABS for each column, in the same way, you could select all columns and export to EXCEL the local forces at and then filter for zero location and proceed with manual design. 3. Get global reactions (like you did already) but one group at a time. By one group i mean all the columns on one radial grid line. All columns on that grid will have same orientation and angle right. Export to EXCEL, transform forces in XY to that angle. New rotated forces will be; Fx' = Fx Cos theta + Fy Sin theta Fy' = -Fx Sin theta + Fy Cos theta there you go, you now have the new rotated forces. Repeat it for each radial line and then design footings manually.
  3. Depends on design moment combination. Thats why i always recommend putting in the right reinforcement in columns in ETABS and put it on 'check' instead of design.
  4. It might be this; "For concrete frame design using the ACI 318-08 and ACI 318-11 codes, the design report for "Shear Details" has been enhanced for "Sway Special" frames by adding the field Design Shear (Vu) for clarity. Previously, only the factored Vu was reported, which may not be the governing force for capacity design." Incident Id: 64173 in ETABS 2013 13.1.4 enhancement user notes.
  5. It could be. For example if you are checking shear at ground floor pier, it could be more than the shear force of floor diaphragm. This is due to the additive effects of upper stories. Meaning, shear in that pier will be the shear from floor diaphragm plus any residual shear force coming from upper stories, depending on shear force diagram. Yes, values will be either positive or negative. Is there any third possible sign? Secondly, you did not mention the results coming from static analysis or dynamic analysis? Remember that equilibrium from linear dynamic analysis such as MRSA are not possible.
  6. It looks like newer version of ETABS. Vu for frame or wall? I am sure there must be something written about Vu* in ETABS manual/help.
  7. Yes or by any other mean like manually applying the joint loads.
  8. You can do like this; What you have to do is to note down the z coordinate of each shell element along the height (in Excel e.g.) and calculate the force at top and bottom node of each element, then apply the average pressure in local axis 3 (plus or minus). Tip: Always model retaining walls/swimming pool etc so that all the walls have local 3 axis either inside the pool/container or outside. So you can select all the walls once and apply the pressure in one go. And for that turn on 3d view in XZ or YZ in ETABS and select top most mesh, apply pressure and so on. Its not that difficult. To calculate average pressure you can either make your own excel sheet or use the following I once made. Water Pressure on Walls in ETABS.xlsx
  9. Not sure about Pakistan building code, but this might be of your interest; http://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=750 Or in ACI 365.1R http://civilwares.free.fr/ACI/MCP04/3651r_00.pdf Or in terms of sustainability as per BRE (Building Research Establishment) or BREEAM program http://www.gov.scot/resource/doc/217736/0091011.pdf Also see this http://www.structuremag.org/?p=9459 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.193.1783&rep=rep1&type=pdf
  10. You can use ETABS 2015 or higher and use 'Tower' option to separate both buildings in the same model.
  11. Adding a basement for home construction is obviously the owner's choice. But as a structural engineer for home construction in Pakistan, I would highly recommend not to add basement. This is due to lot of additional expenses, like RCC retaining walls, waterproofing, flood control, toilet/bath expenses, ventilation etc. If designed and constructed properly you do not need to worry about earthquake. Again, I would have added one and half additional floors from the same money being spent on basement and also forget about the worries mentioned above. Or could have spent it elsewhere like finishes, elevations etc. And what do you mean by Pillar foundation?
  12. Design strips are required to get total reinforcement area by integrating stresses of area objects.
  13. As Waqas mentioned, screenshots would be helpful. I do not think there'd be much difference between two cases as long as two shells on either side of beams are drawn separately even though their meshing lines do not coincide exactly over beam provided the meshing is almost nearly 1m.
  14. What meshing you are talking about? Slab meshing supported on these beams or beam meshing itself? What I could discern is you are using a shell element supported on beam. In this case, you should mesh the slab so that slab has nodes along the length of beam. Shell transfers loads to nodes and if not meshed, all the loads would go to beam ends at point loads.
  15. Analyze a 3-bay planer multi-story frame with beam lengths twice the column lengths. Make the gravity load zero and apply a UDL horizontal load on left most columns all the way from base to up. See what is the bending moment of beams and then read chapter 3 of Reinforced concrete design of tall buildings by Tranath. It will help.
  16. You dont need to counteract it. Flow with the tide
  17. Lol, I was trying to write couple of articles 2 or 3 years ago and uploaded my draft (including the discussion of sefp) on scribd to download something as a trade-off. It was a draft, but if it has helped anyone, this is good to know.
  18. I am sorry, my statement is wrong. You are right in previous post. Ig of rectangular beam in FEA should have 0.70 factor.
  19. The statement of the quoted document (who is the author btw?); "Therefore, finally all columns and rectangular beam section's stiffnesses shall be reduced by a factor of 0.7..." is erroneous. It should have been as explained previous posts;
  20. And in LIFE as well Waqar, I did not get how you modelled. Hira, null lines will not transfer anyload, you have to apply a very small section to null line for proper load transfer. What I meant to say and what I understood was, there is only one single line column in the model, so you have two options. 1. Select top joint of column line and apply joint loads (P and Mx,My) or draw a horizontal line with length equal to e at top joint of column and apply the P at the other end of this line.
  21. Lol. We all are on different pages. Everybody is talking about different technique and everybody is not getting what other is saying. I think we should all improve our writing skills.
  22. What about if columns at base are fixed and lateral resisting system becomes a cantilever column system? First of all in flat slab system, connection is not hinged with shear walls or columns. Else it becomes a cantilever system for lateral loads. See above comments. Yes but would you design the system as cantilever columns? and make sure base is always fixed? Consider flat slab as wide shallow beam spanning between columns. Lateral load is resisted by axial and bending stiffness of beams and columns. Beams and columns will bend in double curvature developing the frame action. However in case of cantilever system (beams pinned), there will be no shear force and hence no moment in beams only the axial force and hence axial deformations. In columns there will be only bending deformations not axial. Several definitions; Aspect ratios Walls resist in-plane bending and shear, columns usually resist biaxial moments Rigid body rotation at base in case of walls poisson effects in shell elements as far modelling and fea is concerned Columns are usually compression elements, walls develop tension compression over large area.
  23. What do you mean by load will not be transferred to node in second option?
  24. Apply the moment manually or draw dummy cantilever line.
  25. Dear Umar, First-off, many thanks for the explanation and your interest in the topic. Highly appreciated. Perhaps, the RSA image added to the confusion than doing anything good, i guess. We are in the same boat as far as T within the range of maximum spectral acceleration is concerned, however, kernel of the discussion revolves around the "scaling of dynamic base shear with respect to ELF base shear". As such, analysis time period (used in RSA graph), even if lies within the maximum acceleration range might give dynamic base shear less than ELF V. For this, and as required by certain codes (American e.g.), for scaling up the dynamic base shear, we need to establish a "Time Period" for static procedures and calculate static base shear. So I wanna twist our discussion in another way. Let me ask, if T(dynamic) and T(static) are same, do we get same base shear from both methods? Static procedures V depend on R; a compound factor for ductility, damping, inelastic/elastic response etc. On the other hand, spectral acceleration from RSA is a function of Ca, Cv and damping but not specifically R. Dynamic base shear is the product of mass matrix, acceleration and participation factor of each mode then we add up all the modes by some type of combination, right. Now, even if time periods were same, and even if the structure behaved in fundamental mode (SDOF concept of RSA) with very rigid torsion response, base shears from both methods would still be little different due to partial active mass in dynamic analysis (maybe 90%?). Hence (and correct me), saying that T corresponding to Vmax of static procedures if used in RSA would result in same base shear would not be appropriate, i guess. Moreover, in my opinion, RSA analysis (although based on actual earthquake records), is a tool where you need to put up some boundaries; upper and lower. Whereas the empirical time period limitations make more sense as they were calculated based on actual buildings and earthquakes through statistical analysis. That might be the reason FEMA recommends using Ta.