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  1. ludvik

    Failure criteria for FEA of glass

    You always want to use principle stresses for glass analysis, not von mises. Von mises = ductile materials, principle = brittle.
  2. ludvik

    glass wall

    1) Do you have a regular double IGU, or do you have a triple IGU? Regular IGU's are covered by ASTM E1300, though I suppose you could use the spirit of the code and split the load between lites according to their thickness cubed. 2) You can just treat the glass like a simply supported beam, and...
  3. ludvik

    Post tensioned concrete plastic hinge

    ishvaag: I can't find the mathcad document you are refering to. It sounds good though, so if you could email it to me at mludvik@hardesty-hanover.com, I would appreciate it. dik: You make a good point about the applicability of plastic hinges to my structure. One thing i would like to establish...
  4. ludvik

    UNIT OF JOINT MASSES in SAP 2000

    If you are using kN & m, the units of mass will be metric tonnes (1000 kg). So if you have a weight of 100kN, the mass will be 100/9.8 = 10.2t. The rule for the units of mass is you take your units of weight, and divide by the acceleration due to gravity in the units of length you are...
  5. ludvik

    I am currently trying to determine

    I am currently trying to determine the plastic hinge properties of a bridge pier with precast post tensioned segments. Plastic hinges will form at the base of the piers under high seismic loads, and I am trying to perform a pushover analysis. There is plenty of guidance out there for...
  6. ludvik

    Post tensioned concrete plastic hinge

    Ishvaag: As you guessed, all that i need is a method of calculating the moment-rotation relationship. Is there some way of using an assumed plastic hinge length? If not, is it related to the bond length of the strand? I can calculate the moments at which the section will yield and the ultimate...
  7. ludvik

    Post tensioned concrete plastic hinge

    I am currently trying to perform either a pushover analysis or non-linear time history of a bridge with precast post tensioned piers. Plastic hinges will form at the base of the piers under high seismic loads, and I am trying to determine the properties of this hinge. There is plenty of...
  8. ludvik

    Profit Margins?

    JTMcC, Sorry for being slow getting back but I was on vacation. Also sorry didn't recognize the amount of expertise you have in the field of the economics of construction. You obviously know what you are talking about. So I've been digging around for some hard data on exactly what construction...
  9. ludvik

    Profit Margins?

    JTMcC, 12% to 20% sounds like what contractors use for overhead + profit, which is frequently confused with straight up profit. Overhead includes head office, jobs which they lost money on etc. Are you sure is wasn't O+P that you read about? Insofar as I'm aware, no highway contractor of any...
  10. ludvik

    Profit Margins?

    The answer to your questions depends on which business you are in. I'm assuming you are a consulting engineer PorkChopBaby. You can expect about 5% over the long run. 10% in this business is considered great. Management consultants get about 30%, lawyers do about the same, and contractors do...
  11. ludvik

    Pinned or Fixed Connection?

    As StephenEd points out, it is a matter of the connection type - is it a full moment connection between the beam and the column? Secondly, if the columns are long and slender they will not provide much rotational fixity, but if they are short and fat they will. If you assume the supports to be...
  12. ludvik

    Site Classification fees in Australia

    You can think of HIH as Australia's answer to Enron. HIH was the largest insurance company in Australia, and it collapsed recently in a blaze of scandal. The American equivalent would be AIG (American International Group) going under. The thing was that even if you got your insurance through...
  13. ludvik

    Site Classification fees in Australia

    I'm not a geotechincal engineer, but possibly i can offer some comment anyway. I certainly agree with you that fees should go up to account for increased insurance premiums. It like a game of chicken - who will do it first? If you do it first and noone else does, you are in big trouble. You...
  14. ludvik

    California PE Exam

    Thanks jtstruct and ClydeMule. I think I will get some of the ppi2pass stuff. As you rightly point out, practice questions are the key, and I need to get my hands on some good ones. I also work with a structural firm doing seismic analysis as it happens. I haven't worked on any California...
  15. ludvik

    California PE Exam

    Does anyone out there have there have experience with the CA PE? Because of the peculiarity of my situation, I have the option of taking the PE pretty much anywhere in the country except where I live (NY). I am a seismic guy by profession, so taking the additional California seismic portion of...
  16. ludvik

    Battered piles under seismic conditions

    Novs: Sands settling on the battered piles is an aspect that i haven't heard of before, though it does make sense. We did a liquifaction analysis, and in most areas it was fine, but in limited areas i think we concluded that the soil was only marginally adequate for liquifaction, so i guess...
  17. ludvik

    Battered piles under seismic conditions

    Yes Focht3, there will a whole slew of people second guessing my decisions. In fact i am more a second guesser than an original decision maker in this instance (i'm just doing the seismic analysis right now). It is a pretty big project. Its a 2200 foot long concrete box girder viaduct structure...
  18. ludvik

    Seismic Load on Underground Structures?

    First of all i should say that i am a bridge man and not a building man, but for soil pressures on bridge abutments and retaining walls under seismic conditions we have a simple technique. We generally use Mononobe Okabe method, which is basically a modification of the simple coulomb method for...
  19. ludvik

    Battered piles under seismic conditions

    Thank you for your responses. My bridge is just outside of New York City on long island, so its not in a major seismic zone. It is however classified as a critical bridge and has to be designed for a 2500 year earthquake. We will most likely have site specific ground motions to work with, and...
  20. ludvik

    Battered piles under seismic conditions

    I have recently been told that battered piles do not perform as well as straight piles under seismic conditions. Why is this? The only justification that i have been able to find is that battered piles are stiffer laterally than straight piles and thus attract more load. They have greater...

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