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  2. ACI Code has not specified any stain-range for under reinforced beams. They just say that the beam should fail in tension before failure of compression region. By that definition, the tensile strain in steel must have a value of more than 0.002 before the compression strain in concrete reaches 0.003 for under-reinforced section.
  3. Last week
  4. May i put it like, if the strain ranges from .002 to 0.004 then it is more like under reinforced and above it is tension controlled?
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  6. I want to comment on some modelling issues in ETABS. Though some of these things are discussed elsewhere in the forum, I hope to extract some more useful conclusions. First thing is related to modelling the bending stiffness of flexural members, for strength level loads, that is representative of their condition near failure. The ACI code specifies the modifier of 0.35 on gross moment of inertia to represent its condition at yielding. Some people say that the factor should be multiplied by 2 to represent the stiffness of T-beam. This approach would be justified if you are not taking into the account the out of plan bending stiffness of slab. But, ETABS does include the out of plane bending stiffness if you have modelled the slab by using shell elements. So, a factor of 0.7 would overestimate the stiffness of your structure in this case, and will lead to under-design. If one has used the modifier of 0.35 in ETABS for beams in beam-slab floor system, then what value should be adopted for slab? It should not be 0.25, as this value has been specified for flat plates and flat sab floor system. If one is using some value of modifier for out of plane bending stiffness on shells, then the share of the bending moment in beams will be reduced accordingly. This approach is correct if one will be providing the reinforcement in column strips of slab. But, if you are providing reinforcement in slab in the direction perpendicular to supports only, i.e. beams, as is the general practice in Pakistan, then you are under-estimating the flexural demand in beams. Now, there is also a question of factors to be used while deciding the amount of reinforcement required in beams, columns and shear walls. If you are using factors 0.35 for beams and shear walls, and 0.7 for columns, then you are finding out the demand in members at the point of yielding, and this conforms to the code. But, this also means that the structure might experience unacceptable cracks widths. So, if you are using 0.35 for calculating the demand at strength-level forces, then you should also perform crack-control-check at service-level loads by using the factor of 1. If you are calculating the strength-level demand with a modifier of 1 for all structural members, after you have decided the location and the number of shear walls with modifier of 0.35, then you are overestimating seismic forces, as you are underestimating the time-period. But, the structural performance will improve.
  7. After running the analysis, one way is to look for the symbol that is used for displaying the deformed shape of your structure. The deformed shape will be displayed against a load case, or load combination. Once you have deformed shape, right click on the node where you want displacements. Limits are already discussed in the forum. Use the search facility, either on google, or in the forum.
  8. AOA hope you will be fine how to calculate building joint displacement from etabs specially for EQ loading and what are the code allowable limits for that .?
  9. Hello everyone I'm currently doing nonlinear static seismic analysis of a 4-story building considering post-earthquake damages using ETABS 2015. After applying the aftershock load and performing the second nonlinear static analysis, how can i apply specific additional live loads to the floors? and then perform the third nonlinear static analysis... I need to find out how many evacuees can enter the building considering the damages obtained by the earthquake main shock and aftershock. Thank you
  10. Great question. Current ACI design (2002 onwards) is based on strain limit and based on that you end up with tension controlled or compression controlled sections. Tension controlled being the sections where strain is steel is equal or greater than the limit provided by code (0.005 I believe). Previously (1963 to 2002), the reinforcement design was based on reinforcement ratios. This is where the terminology "under-reinforced", "over reinforced" and "balanced reinforcement" comes from. The simplest word to put this is that any steel that has strain greater than 0.005 (or whatever the code says) at time of concrete failure is termed as tension controlled. Both under-reinforced and balanced reinforcement sections will meet this criteria.
  11. to calculate participation factor, you first do modal analysis.. from first mode.. take the eigen values that would be the mode shapes at each storey... Take storey mass of each storey and solve it manually or using excel file.. By the way, if you want performance point, you can directly get from the SAP result where it shows caapcity and demand spectra. See the attached research paper for ur reference IRJET-V3I5479.pdf
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  13. BTW GOT THE BOOK AT [URL Deleted as it violates Forum Posting Rules]
  14. YES THANX ALOT. ITS REALLY HELPFUL.
  15. YES THANX ALOT. ITS REALLY HELPFUL.
  16. Check the following link. May be it could help. http://www.sepakistan.com/topic/115-pile-design/?do=findComment&comment=860 Regards.
  17. Does anyone have the soft version of Muni Budhu? If not then any other book which describes the pile foundation topic in such detail as in Muni Budhu.
  18. Legit request. Find attachment. 2011-12-lateral-stability-of-purlins-and-girts.pdf
  19. Earlier
  20. In addition to pushover curver (Base shear Vs displacement) SAP gives you the option of ATC -40 curve. So you can select that. Then go to the properties table of the curve and you can get the Sa and Sd values.
  21. Salam, What is the difference between the under reinforced and tension controlled section? Are they same with the exception of strain values of steel.? Many Thanks
  22. Can you add the reference, from where above excerpt has been taken? It is always a good idea to indicate the reference, whenever an excerpt is quoted to explain some technical matter or concept (especially when it is taken from some book or code). This helps the reader to consult the original reference and study in more details, if required. Regards.
  23. You can model sag rod as bracing (Sag rod properties can be defined in a frame section and modelled as a brace) provided your design condition allows the sag rod to behave like a brace as I mentioned in the previous post. Once you model them, see the forces and design accordingly.
  24. The horizontal members are the ones which will be braced using sag rods. yes its elevation view. We have similar horizontal member at the other side too and the 2 are to be braced using sag rods. Design of sag rods will be similar to that of cables, not sure if SAP2000 can design it accurately or at all, never did it. Or do u have anything on design of rods or cables in SAP2000?
  25. Can you please explain the image. What view is this.. looks like a elevation but what are we looking at? You can model sag rods but arrangement is key to understand if they are acting as discrete bracing or not. Read my reply below. I don't agree with your statement. How can they offer "vertical restraint"? Sag rods can act as "discrete bracing". Read the excerpt below:
  26. I think Uzair has replied to your question well. I was about to say the same thing for number 1 after checking my self. Try using a 4x4x1/2" or 3x3x3/4" as bracing. For top and bottom cord, go with a lightweight 8" section (like W200x36). Using 8" will allow you to do field bolts easily as 6" or less are tight for even 2 bolts. For L/r > 60, I am not sure what that is.
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