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  1. gravityandinertia

    Interpreting FFT results for vibration testing of concrete floor

    I'm not that familiar with the dynamics of concrete slabs, however 32 Hz feels high to me for the lowest natural frequency of a concrete slab. That's some quick vibration! My gut would lean towards the 16Hz as well, but with no basis to back that up other than your data and my feel of concrete...
  2. gravityandinertia

    Boundary conditions on tank

    In addition to what goeasyon said, if you are running this as a static, linear elastic analysis and the loads are high enough and the walls are thin enough, this problem may need a non-linear solver. If the walls behave as membranes due to their thin nature, then solving in one step...
  3. gravityandinertia

    Fined by the city for claiming to be an engineer - Suing on grounds of free speech

    @drawoh, My opinion on the FEA code is that a license shouldn't be required to write it. Licensure happens to protect the general public because without specialized training (the same training required to make them an engineer), they have no way of evaluating an Engineer's claim of competence...
  4. gravityandinertia

    Is the paranoia over making simulation data secure justified?

    Gaining accurate material data for simulations is also an expensive endeavor, particularly S-N curves for fatigue with enough samples for a proper statistical variability to be calculated. If a company has spent hundreds of thousands or millions of dollars of the years accurately characterizing...
  5. gravityandinertia

    Confirmation about failure theories and Von Mises

    First of all, failure theories are used in beam design for code based systems, however their application were done by the code writers in their investigation of what is safe. From there, along with testing they derived the limiting states and values that the codes use. Additionally, I think...
  6. gravityandinertia

    Stress induced in a cantilever beam with End point load and half sine wave shock

    Are you trying to compare to the results in SOLIDWORKS Simulation?
  7. gravityandinertia

    Base Shear Resistance for Ground Supported Tank

    You would have to specify the finish/treatment to get the desired coefficient of friction you want, and it would have to be maintained over the life of your structure to ensure it still exists should the design event happen. That's the case against it.
  8. gravityandinertia

    Modern Steel Construction Steel Quiz

    I showed this video to someone who made a claim they did it in a class at school with 40 people! I know the math works out that everyone is essentially carrying about 1 body weight on their legs, but I still can't picture a 40 person circle of this. It would look insane!
  9. gravityandinertia

    VIBRATION ANALYSIS- EFFECTIVE MASS OF (WAREHOUSE) FLOOR SYSTEM ON DETERMINING ITS NATURAL FREQ.

    As has been said already, mass is a difficult choice to make. However, also consider this, mass generally lowers frequency. So if you're natural frequency fully loaded is high enough above the expected excitation frequency you're likely fine. If not, then it becomes a very difficult guessing game.
  10. gravityandinertia

    Modern Steel Construction Steel Quiz

    I wonder if this was inspired by an engineer reading this post. Human Reciprocal Frame
  11. gravityandinertia

    Calculating Stiffness Value Over Unit Area

    KD = F is the typical equation for a spring. If you make F = 1 you can get your spring displacement to be 1/D. If you do the equivalent of this but rather than applying a uniform load, apply a uniform pressure, you should then get what you are looking for.
  12. gravityandinertia

    FEM Analysis of Pipe Support

    What are you trying to figure out. Plate thickness?
  13. gravityandinertia

    Analysis report clarification

    Your going to have problems. You have 16kg of steel, supporting the weight of an F350 hanging from it. Just from gut, doesn't that seem off to you? Add in that you've significantly passed the yield strength and I don't see any mention of stress-strain curves, or bilinear material models being...
  14. gravityandinertia

    Soil arching action

    Not a geotech here, but the load spreads as it goes deeper. This is due to a combination of the soil properties, friction, and fluid pressure if present. So the deeper you go, the more that load is spread over a larger area. That makes it feel like increased loads have very little impact and...
  15. gravityandinertia

    Wind Loads on Wood Gambrel Truss

    That document is a great piece of engineering history!
  16. gravityandinertia

    Axial Buckling about Non-Principal Axes

    I'm not sure if I'm missing something. What would be the mechanism for creating buckling that wouldn't occur on a principal axis? The only thing I can think of is you are mixing up your coordinate system with the principal axes of the member. If that's the case then it's simple buckling. Ignore...
  17. gravityandinertia

    FEA, thermal stress analysis, brittle material

    Max. Principal stress is usually reserved for brittle materials. von Mises criteria is for ductile materials, where they can yield and have interactions between their different stress directions.
  18. gravityandinertia

    correct and best welding on a gusset plate

    I know there exist information about balancing the weld, however, when I worked for a joist manufacturer, we always did a full weld along any overlapping edges. The only check was that we had enough overlap to cover our minimum for our design loads. Right or wrong due to eccentricities that...
  19. gravityandinertia

    steel trusses (angle sections) - gusset plate connection optimized with skew angle cut?

    @lolobau There are a couple more things about why B, not C as Jayrod indicated cost of the weld for one. On top of that, you can get more weld length in B on the gusset and along multiple faces which is good for redundancy, though that's sort of a tertiary benefit. The last thing would be that...
  20. gravityandinertia

    steel trusses (angle sections) - gusset plate connection optimized with skew angle cut?

    Typically the point of a gusset is to be able to increase your weld length because your loads are to in your web members for the sizing of your top or bottom chords to get enough weld to safely transfer the load. With that said, your image B would be preferable, because for the proportions shown...

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