Rana

Moderators
  • Content count

    762
  • Joined

  • Last visited

  • Days Won

    201

Everything posted by Rana

  1. I think its time now to categorize questions based on the difficulty level. For example; A toddler asking very basic question like what is mass source or time period, should be classified under lets say Easy or 0 or Beginner or Simple etc category. And as such specific moderators should be assigned to take care of that forum. Then we can make other sections like moderate or difficult. Where one really need to relearn/review the question and think about the answer carefully. I think all the internet is full of the same basic questions like time period, base shear etc. Isnt it the time to take SEFP a step ahead and not just another forum full of the same basic questions? How can we re-categorize the SEFP sections to give it a new feel, not just like concrete, steel, software issues etc. What do you think?
  2. So what is the question?
  3. By consistent, it means that in order to draw the ‘design’ response spectrum you got to know the PGA, PGV and PGD. Usually when these are unknown, PGA is taken as 1g. PGD and PGV are estimated by the relationships given by Newmark and Hall (see Chopra book). However, in your case, you already got PGV and PGD for PGA=1.0g, right? Now you have to make the pseudo-accelration/velocity/deformation spectrums based on this. After that, you have to scale the calculated response spectrums for 0.25g simply by multiplying them by 0.25. For more on this refer to Chopra book (4th edition) section 6.9.
  4. 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.
  5. 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.
  6. You question to me is unclear. Could you clarify what you wanna ask (may be in bullet points)?
  7. 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?
  8. @Hira Malik Your signatures stand out quite big. Mind making it in line with font size of rest of the posts?
  9. 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.
  10. Refer to any structural design book. To me, this thickness would be safe; req thk = 10 (700*4.448)^0.5 in mm
  11. 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.
  12. 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.
  13. 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.
  14. 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
  15. You can take directly the model quantities from ETABS itself.
  16. 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.
  17. 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.
  18. 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
  19. 1. Your observation is correct that Sin(6.8) on calculator = sin(radians(6.8) provided your calculator is set in degree units. What you have used in Excel formulas [ sin(radians(6.8) ] is correct if; the angle 6.8 originally was in degrees. Was it in degrees? See the formulas you have attached in Excel. I do not think so. Why? Because circular frequency (w) is usually is rad/s. So your units are already in rad and you do not need convert them further and Excel is already set in rad units so just use directly the sin(6.8). This is what @Saad Pervez pointed out.
  20. Avoid it. Totally avoid it. Just put the expansion joints.
  21. That is a common FEA problem. You get infinite stress at supports due to infinite stiffness.This is a problem of stress concentration. For commercial design purposes what you did is okay.
  22. 1. You need to divide the buildings to avoid irregularities especially in zone 4. 2. start with a crude model, no shear wall (only columns) and try to get the general feel of the structure. For that you could also roughly estimate the gravity loads (for mass source). For example 15-20 kpa let say (including sw+sdl+ll) as gravity load. 3. Iterate by putting in shear walls where you need it. Once the crude geometry is finalized you can go for detailed modelling/design and you will find out the importance of concept stage design at early stage.
  23. Suarez, we do not handle pirated/cracked stuff. Please be aware in future.
  24. 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.