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  • Users: sebivaq
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  1. sebivaq

    "Illegal floating point operation"

    Dear curlyq, try tiping all your variables (or formula fields) with one decimal number (for example 1.0, 2.0). Best regards, Sebastian
  2. sebivaq

    Flat Slab Openings

    Dear mralhasani, when you use the merge command you are "joining" 2 or more shell elements (with the loss of precision that this implies). You can draw a single shell element with the real slab dimensions, and then make a division (in the same tool box as the merge command) in...
  3. sebivaq

    Mass Concrete

    Dear mscme, you should look in ACI 207.2R "Effect of Restraint, Volume Change, and Reinforcement on Cracking Mass Concrete". You should design in accordance to ACI 318, and then check with the Lutz equation (taking into account the volume change tension in steel) the crack width...
  4. sebivaq

    need instructions for vibration (modal) analysis

    Dear skicat, first of all make your model, with the proper stiffness and masses. If you want to consider same load as a mass for the dynamic analysis, go to define/mass source. When you run the analysis, activate "MODAL CASE" (as default is activated). Then you should go to...
  5. sebivaq

    Distributed Load - SHELL

    Dear rodmanera, you should do the following: Go to: Define/Joint pattern/Add new... Select the shell you want to load, and the go to: Assing/Joint pattern/ Select the Joint pattern name and specify the function you want for the load (in global axes). Then go to: Assing/Area...
  6. sebivaq

    Blast Loading: Structure as a whole.

    Dear 3doorsdwn, in my opinion for a plane-frame the charts could be valid (a frame can easily be modeled as a SDOF, in the horizontal direction). For a more complex structure, I would model the hole structure and the explosion as a load (in function of time). You should...
  7. sebivaq

    precast coil insert LCB-1

    Search in here: http://www.concrete-accessory.com/coil-insert Best regards, Sebastian
  8. sebivaq

    How to define a constant 5% damping coefficient?

    I would search which mode includes vertical displacements, using the animation tool. Then you should use the equation with the first and "the vertical mode". The problem is that for vertical modes the damping could be lower, in my opinion.
  9. sebivaq

    How to define a constant 5% damping coefficient?

    Dear zhddz, Yes, I ment the natural frequency from the first two modes of modal analysis. But for this structure, maybe you need to use another natural frecuency (please read page 420 of the previous attach). In my opinion the natural periods of the structure are very high for a...
  10. sebivaq

    How to define a constant 5% damping coefficient?

    Dear zhddz, with SAP 2000 you can easily find out the first two natural frecuencies (without any damping). Using the solution of Chopra, you can calculate ao and a1, even if you don't known the mass or the stiffness matrix. Regards, Sebastian
  11. sebivaq

    How to define a constant 5% damping coefficient?

    Dear zhddz, SAP 2000 uses "Rayleigh Damping". It considers a mass-proportional and a stiffness-proportional damping in order to achive the real damping (lets say 5%). These two values are the coefficients ao and a1. C = ao.M + a1.K Where: C = damping matrix M = mass...
  12. sebivaq

    How to plot Vertical Displacement vs. Percent of Load Diagram?

    You can make several load combinations, with different types of load percentages. For example: LOAD COMBINATION 1: 0.10 x DEAD LOADS LOAD COMBINATION 2: 0.20 x DEAD LOADS Representing, 10 and 20% of the dead load. Best regards, Sebastian
  13. sebivaq

    Good Earthquake Engineering Text

    In my opinion: Dynamics of structures - Theory and Applications to Earthquake Engineering by Anil K. Chopra
  14. sebivaq

    How to model a concrete drop beam

    Dear vsator, I would model the slab as a thick shell element, and the beam as a frame element (you can use the concrete design tool). In order to obtain results close enough to the hand calculations, you should: 1) Set the torsional stiffness of the beams to zero, to model a pinned...
  15. sebivaq

    Seismic Loads Due to Soil (Basement)

    In my opinion for underground structures it's important to consider the seismic load. In this case the structure will move with the soil, the inercial forces aren't very important. There are various ways of considering this load case: 1) Analytical (models with springs or with forces and...
  16. sebivaq

    Modal analysis after nonlinear time history

    You are welcome!
  17. sebivaq

    Modal analysis after nonlinear time history

    Dear iotoma, the non-linear combination for the modal analysis (as seen in the last attachment), should have non-linear load cases. Take a look at the new attach.http://files.engineering.com/getfile.aspx?folder=8ee0b5f3-c9dd-428a-982e-347e0b860948&file=a.JPG
  18. sebivaq

    Modal analysis after nonlinear time history

    Dear iotoma, have you set the non-linear case in the modal analysis? Take a look at the attachment.http://files.engineering.com/getfile.aspx?folder=4a5fb4db-1b1d-4aa4-8e89-808fe8490f7e&file=1.JPG
  19. sebivaq

    Modal analysis after nonlinear time history

    I think that the problem is that SAP2000 doesn't introduce plastic hinges where the section fails. As a result, you have the same stiffness, the mass will obviously be the same... and that's why your period is exactly the same. You need to define the non-linear properties of the material in...
  20. sebivaq

    Modal analysis after nonlinear time history

    Dear itoma, in order to increase the period, the structure should: a) have more mass or b) be more flexible (lower stiffness). In your case, you want to subject the structure to an earthquake and simulate the damage that this one does to the structure.. and this damage should increase...

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