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  1. MHobbs

    Concrete cover on ends of bars

    As Hookie mentioned it is normal for prestressed elements to have exposed ends. I believe this is accounted for by the bearing lengths required and often by insitu pours or mortar beds at the ends of precast units. I guess the cover to the reinforcement that is presumed to be effective is...
  2. MHobbs

    Pretensioned Beam Deformation

    https://www.pci.org/PCI_Docs/Design_Resources/Guides_and_manuals/references/bridge_design_manual/JL-11-Winter_Precast_Prestressed_Girder_Camber_Variability.pdf This is a useful document. The shortening of the beam due to the prestressing force will have occurred before the erection stage and...
  3. MHobbs

    CFRP for over reinforced column

    KootK I read the first three words and saw the parenthesis, I was excited thinking you had written a book on concrete reinforcement.
  4. MHobbs

    Concrete Slump out of Spec but Break Strength Good

    As structural engineers I think we often only consider the compressive strength requirement of concrete. That is not the whole story. Tomfh and Smoulder are on the money. The Durability may have been affected and in this case it is likely durability that is the critical property not the...
  5. MHobbs

    Designing for Prestress

    Thanks for the advice Tiger Guy, when it comes to production I can heat the beds but its still quite a variable environment.
  6. MHobbs

    Designing for Prestress

    Hi all, I'm trying to find methods or advice for mix design focused on the next day strength. Our concrete needs to be a C28 strength in about 18 hours so the beds can be detensioned and stripped. I'm working on what proportion of GGBS I could possibly aim to include but want to do some mix...
  7. MHobbs

    Concrete Protective Posts

    If the light posts are getting hit all the time then maybe they need to be moved? Putting concrete posts in front will just make it even harder to park and the concrete posts would get hit even more no? Damage to the posts would be just as difficult to repair and I think look just as unseemly...
  8. MHobbs

    Krey method

    Is that not the value for L'
  9. MHobbs

    Krey method

    https://www.eng-tips.com/viewthread.cfm?qid=427296 I was very interested in this thread. I made this simple calculator have I correctly interpreted the Krey method? I have set it up for using with PCC concrete so a friction angle of 15...
  10. MHobbs

    Weight range for main gate

    I'm UK based so judging from your units of choice it won't help you. But feel free to have a look. https://www.naylorconcrete.co.uk/fencing-systems/
  11. MHobbs

    Weight range for main gate

    I'd say littleInch is about right there, my company make and manufacture some gates and the 2.4mx3m gates weigh 185kg or 343kg each depending on security level. One other thing to consider along with the weight of the gate is will there ever be a live load on the end. British standards apply a...
  12. MHobbs

    Gentlemen…

    hokie66 would you use the term cellular for circular holes in the web? In my experience while cellular is the more specific term it would still be considered a subset of castellated.
  13. MHobbs

    Mass concrete

    Sorry for slightly hijacking but I'm interested in what dik suggested. dik do you have a liturature or examples where using larger rocks to reduce concrete volume? I have googled intrusion prepact but I can't find a discussion of it. Kind regards
  14. MHobbs

    Durability and Compressive Strength, Low Tests

    Generally using 56-day strength rather than 28 can be a great way to take cement out of the concrete mix reducing cost and environmental burden. It won't be suitable for all construction practices but if the scheduling of construction can accommodate the concrete reaching the final design...
  15. MHobbs

    Hollow Core Slabs - Application in Marine Environment

    I agree that the hollowness is not the durability concern as the least cover to the reinforcement will probably still remain the distance from the bottom of the slab. Regarding the possibility of solid cores or ends or areas it is frequently done to provide an area for fixing into. The process...
  16. MHobbs

    Reinforcement in Precast retaining walls

    Thanks for the responses guys, seems like it might be worth looking into especially for taller units where the steel saving could be more substantial. I'm at a precaster but mostly we do prestsessed beams and slab so our traditional precast elements are quite low volume.
  17. MHobbs

    Reinforcement in Precast retaining walls

    Hi all, In my experience the reinforcement detailed in the stem of a retaining wall does not decrease with the distance up the wall. The moment to be resisted is obviously decreased, i.e the moment about A is greater than the moment about B in the image attached. Is my experience just very...
  18. MHobbs

    Brick Lintel load

    XR250 do you mean as the blue triangle I've marked up? I'm inclined to agree with the original markup in red, not forgetting to include the load(dead and live) from the concrete planks and floor span they represent.
  19. MHobbs

    Use of load triangles above lintels (BS 5977)

    Morning all, Thanks for the replies. HTU I know you said I'd get the point, but I am a bear of very little brain. The concrete slab would often be hollowcore but this would be a fairly typical construction. Is the same load dispersion mechanism not justifiable if it is concrete slab or...
  20. MHobbs

    Lowes Sells Fiberglass Rebar

    This is obviously data for a specific brand, Schöck Combar®, but this is their advertised values for their GFRP (Glass fiber reinforced polymer)

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