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Structural Engineering Forum Of Pakistan

Rana

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Everything posted by Rana

  1. Rana

    Rotational spring constants in ETABS

    First, the stiffness of this beam is 2EI/L. See here; http://classes.mst.edu/civeng217/concept/12/03/index.html Second, see the fixed end beam in this link, hope it clarifies. Do share the findings afterwards please. https://waseemrana.com/2013/04/16/how-to-partial-fixity-in-etabs/
  2. Rana

    MS Distant learning

    I did mine from Heriot Watt, UK. Distance Learning. But I would not recommend it. Its a pain in the back. Plus the fee is almost the same.
  3. The analysis is Linear. Automatic redistribution would have been possible if analysis were Non-Linear. In order to approximate redistribution (during cracking), the USER has to put some kind of stiffness modification. This applies to shear, torsion, moments, axial...everything.
  4. Forget check Ax on dynamic. If you need to check, then check as on ETABS online wikki. If so, you have to combine all modes manually. That's time taking and complex. Check Ax on all static load combinations and whatever is the value, apply this in response spectrum.
  5. The paper says that upon cracking the internal redistribution occurs. However like for moments, ETABS does not redistribute Torsion automatically. If you want it, then release (or apply modifiers) to redistribute forces. That is why I said, after this, you need to check for increased forces in slab. Its that simple.
  6. Rana

    Islamabad Gathering

    It was short 2 day trip. Came back already. Next time.
  7. I will be in Islamabad for a weekend from 12th april 9PM to 13th full day. Let's meet?
  8. Checking torsional irregularity from dynamic analysis is complex. Do as follows; 1. Make all static load combinations with static E. 2. Check Ax 3. Apply the required amplification in response spectrum cases. Don't check Ax on dynamic (unreasonable results, wrong results). Also, don't include all static seismic directions in single load case (e.g. in newer versions of ETABS like 13 onwards). Make each static load case separately like in older ETABS 9. Combined case will give you wrong Ax. Also, if amplification is too high, check manually that joint, which might be unrestrained or at the corner. You might need to change it's framing etc.
  9. Rana

    Foundation Design

    Foundation should be designed for response spectrum cases too if they are used for super structure design also.
  10. First of all my apologies, if my question seems stupid because of my unfamiliarity with the topic. When defining response spectrum load case in ETABS, we have three directions; u1, u2 and u3. Lets assume the excitation angle = 0 and building principle direction is u1 So I will apply response spectrum function (per IBC 2006) in u1 direction by a scale factor. My question is why we don't apply u2 and u3 in the SAME LOAD CASE. My understanding is, according to WILSON in his book on STATIC & DYNAMIC ANALYSIS, CHAPTER 15. The response is calculated for each direction separately. Then this response is combined by different methods (CQC, SRSS etc) which is called MODEL COMBINATION. In CQC method response in 2 directions is assumed to be a portion of 1 direction means S2=a.S1 Where a = 0 to 1.0, recommended value is 0.50 to 0.85 I know in EQ building has only one principle direction. Although EQ can hit from any direction but there is always one major direction. or you can say major acceleration in 1 direction. Lets say u1. As in CQC method the response in other direction will be some portion of response in major direction. I also know that If we have equal spectra CQC is reduced to SRSS method which is independent from the excitation angle theta. My confusion is we will do MODAL COMBINATION (cqc or srss) only when we want to combine u1, u2 and u3 at the same time. But if we are applying only u1 in one response spectrum load case, then we DONT have to do modal combination. It is the same thing as in CQC S2=a. S1. Now in this case a=0. so S2=0. All we have is only response in u1 direction. Then in my building models what i do? include u1 and u2 both in one load case or in separate load cases?
  11. Rana

    raft punching

    Moments should not differ by that much amount (10x in your case). Yes you can calculate punching directly based on 450kn.m like in RCM Builder. We use it daily, its my company software. Or you can calculate manually or by any sheet. I dont know why you are getting huge moment in SAFE. Probably because of the loading from raft? check your model again or try checking only on self weight...
  12. Rana

    FEM- internal meshing

    Yes the program still divides it. Thats why I say ETABS is not a true FEA tool. They have made it damn easy for majority of the engineers. It is not for FEA analysts.
  13. Rana

    Structural Systems according to UBC-97

    There is no seismic design category in UBC. Its simply zone 2B in UBC. What you probably meant is the equivalent seismic design category of ASCE 7 related to zone 2B of UBC. If so, then you have to convert your zone 2b spectra to ASCE 7 spectra and to find out S1 and Ss. After that you can find out the sdc from ASCE tables based on this S1, Ss and Fa and Fv.
  14. Rana

    Calculate T in ETABS

    Who said so? For majority of the buildings (low rise) dynamic time period is way lesser than 1.4Ta. Read code to understand about these limits. It should have been; if Tmode>1.4Ta then T=1.4Ta. Just a typo mistake i think, but inside ETABS it takes it correctly for both UBC and IBC/ASCE codes. Don't worry.
  15. Rana

    moment of inertia in shear walls

    pretty simple check stresses in walls, if they are more than modulus of rupture they are cracked, use 0.35 otherwise they are un-cracked so use 0.7. Then iterate. Cracked walls will be in high rise with more seismic loads. See above.
  16. Rana

    Temperature Loading on walls.

    What are the restraints to circular walls? Is it open from top? The circular shape is it self restraining (hoop stresses). Outward and inward? Yes, if bowing action but you need to apply gradient temperature then in softwares. Sign will determine if it bows outwards or inwards. Which software you are talking about? Yes application of any load in any software and even in papers depends on the direction in which you want to apply. Yes 1.2 factor for T, but not all combinations. You need to find out logically where you will need to use 1.2T. I mean effects should not be counteracting.
  17. Rana

    Cost per square feet

    I can connect you with some on this if you like...
  18. Rana

    Raft Modeling In Etabs

    Make one and post for us please!
  19. Rana

    Shear wall design

    How do I know what is your confusion without you writing it down for me?
  20. Rana

    Bearing Capacity

    I dont think code dictates that but yes common sense sure does. I wouldnt design foundation unless from some source I have the bearing capacity information. Even if it is preliminary design and you put a note that "the foundations have been designed assuming.....capacity", you should do some research of nearyby buildings. You cant just guess, i think.
  21. Rana

    Required force method

    First off, is your Limcon cracked or purchases? If cracked, there are certain variables in the software that are "FIXED". They do not change if you change values. So beware!
  22. Rana

    raft punching

    Depends if the sheet is correct? Does the sheet take into account moments?
  23. Rana

    Structural Systems according to UBC-97

    Really? Moment frame type has nothing to do with location except some limitations in codes. Can't you have special moment frame in Zone 2? Yes, you can! Type depends on the ductility and framing of building system. Do you think it has enough ductility? If yes then it could be special even in Zone 0. But obviously it will cost more to provide that ductility and detailing for zone 0. But generally speaking, you could design special frames in zone 2B or ordinary in higher zones, depends on the framing.
  24. Rana

    Assigning Of Temperature Load In Etabs And Safe

    not true in all cases. uncontrolled internal temperature has the same effects like outside sun heat on the structure. There are usually documents stating weather station data. You should use mean yearly average highs and lows not daily. It also depends on approval authority. For example in Dubai, limit is 45m. Expansion joints are nice from structural point of view only. As a structural engineer, Id try my best to avoid them. Construction isnt that easy for expansion joints. What about water leakage? Except ground floor columns and walls that will have huge forces due to restrain (supports). This is my opinion. I don't think T+E should be added.
  25. Rana

    Bearing Capacity

    Known or unknow?
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