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Rana last won the day on March 13

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About Rana

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    FEA, Tall/long structures, Dynamic analysis, Seismic, Travelling, Writing

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  1. That might have caused some inconsistencies in the calculations (very small/large values) and could have caused this error. There is not much diff in behaviour if you change from 0.01 to 0.0001 so keep the previous value. That would not solve the problem i reckon.
  2. The biggest problem would be to control the excessive sway. The question you need to ask is if there would be any human occupancy in there/visiting deck etc? 99% chances are NO. There will be no human occupancy so limiting the sway & acceleration is out of the equation now. That leaves you with a sway limit of as high as 1/100 instead of usual 1/400 for buildings under service winds. You might need to pay attention to non structural components design for the drifts they gonna accommodate.
  3. You question to me is unclear. Could you clarify what you wanna ask (may be in bullet points)?
  4. Ask your self, why you dont check punching for the wall? Think about the load it has, think about the area over which this load would be distributed (area bounded by the parameter equal to A+d). What value of shear stress you get? very low right?
  5. @Hira Malik Your signatures stand out quite big. Mind making it in line with font size of rest of the posts?
  6. This is a quick check handy formula. Look for "buildings of moderate size and height" book. But that does not prevent you from going on checking in more detail.
  7. Refer to any structural design book. To me, this thickness would be safe; req thk = 10 (700*4.448)^0.5 in mm
  8. 1. Import the original text file again. 2. If it doesnt work, assuming you have lateral loads, goto Tables > and show reactions for Ex, Ey ..etc...once the reactions are tabulated. Close and then try again printing the summary report from File menu.
  9. First; minimum reinforcement (temp/shrinkage) reinforcement could be divided in half, for top and bottom. But in case of footing of such a huge size, i believe you are already providing more than minimum reinforcement at bottom, so at top you should provide full Asmin. Second; you do not need to consider the full 6' depth of base slab minimum reinforcement. Its a mass concrete. The exact reference slipped out of my mind. I will update if i come across the clause. But meanwhile may be you can dig a little more on google etc.
  10. Yes, when you export to SAFE, columns will be fixed. You can do following; 1. In SAFE, change the fixation to springs, iterating several times for spring stiffness, until you get the same deflection under each column matching with those in ETABS. Quite cumbersome (almost impossible). Also the SAFE deflections you would be comparing with those in ETABS are not compatible. In ETABS you modified the stiffness by assuming modifiers while in SAFE, the cracked inertia analysis is done based on section and reinforcement and moments. 2. So, the other option is to design it inside the ETABS. I guess in ETABS 2016 you can design slabs as well.
  11. Yes if you keep k=constant. That means for a given stiffness of a structure, higher mass would give higher T because the lower stiffness is unable to hold back the higher mass. Example: Tall buildings I guess you are working with long period seismic waves on tall buildings? If so I have done masters thesis on the same topic. Not sure what you gonna achieve but here is an excerpt from my thesis; Response of a building to ground displacement, velocity or acceleration depends on the time period of the building. For example, the response of a tall building (time period of more than 3 seconds) will be more sensitive to ground displacement as compared to ground acceleration and velocity and is recognized in some building codes; for example in Japan (Fédération internationale du béton, 2003, p. 94). Excerpt from the thesis; A rigid structure will vibrate as it is a part of the ground itself. A rigid building will move with the base; however the upper portions of a tall building do not move with the base due to the resistance of inertia of masses, and bend in many complex modes (Taranath, 2010, p. 348). The mass at top floors remain stationary while the base of structure moves with the ground (Taranath, 2010, p. 379). So the response of the structure and the input acceleration loads are lagged. It takes time for the shear forces to accelerate upper masses in a tall building depending on the stiffness and mass of storeys (Carr, 1994) as is shown in following figures. I have attached the relevant pages in this post. If you are working on the same topic I can share with you the whole thesis. Good luck. Chapter-3.pdf
  12. You can take directly the model quantities from ETABS itself.
  13. Why would you like to stick to static analysis? Perform the simple dynamic analysis using MRSA. Why use UBC when you can use ASCE (Dynamic base shear=85% of static as opposed to 100% in UBC for irregular structures). You save a lot here! Why not use some exciting concepts like scaling base shear to static base shear based on Ta if T-dynamic < Ta. Why not use a rigid diaphragm instead of a semi-rigid one. Try using 0% live load in seismic mass if it is not a ware-house/permanent storage. Try using weight/mass modifiers for beam (beam-slab over-lap) to reduce the overwall W. Think how can u reduce W even further.
  14. Your system most probably gonna fall under 'building frame system' = lateral from walls + gravity from frame Remember that, mere presence of frame with walls does not make the system as dual system or whatever...inertia of columns is usually so small to that of walls. A building could have very few walls and many columns but still the columns resist 0% of lateral loads. It depends on relative stiffness. Run the analysis as is wit any R factor, check the horizontal reactions for walls and columns. See how much percent they resist. You would notice in such type of structures that lateral resistance by walls is around 70% and rest is from columns. Check these numbers. If it is walls=100% and cols=0% for lateral and opposite for gravity, its an ideal building frame system. If however columns also resist 'few percentage' (see SEAOC) of lateral and walls resist 'few percentage' of gravity then there is an additional task to perform to make sure it is still a building frame system. Conceptually you have to make sure that, during an earthquake if walls are resisting portion of gravity load, they should possess this capacity (do not lose load carrying capacity during an earthquake). If so the framing is still a building frame system.
  15. Yes you are right. If loading direction is X, check x displacements on point 1 and 2 on the edge that is perpendicular to loading direction. Following will clarify; 1. Load in Y Direction Source: FEMA; https://c.ymcdn.com/sites/www.nibs.org/resource/resmgr/BSSC/Topic09-SeismicLoadAnalysis.pdf and 2. Load in X direction: Source: Reinforced Concrete Design by Tranath