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  1. mitchelon

    vibrating rod or tampering rod

    What is accurate? Will a 4" cube sample yield results similar to those of a 6" x 12" cylinder? The ASTM standard and the ACI variability allowances are based on a tampering rod. So why even bother. Cost savings? Agree w/ soilsguy. Beware of the hype of new technologies; they are not always what...
  2. mitchelon

    ACI minimum area of steel

    271828, Sure: ACI 10.5 - Minimum reinforcement of flexural members ACI 10.5.4 - For structural slabs and footings of uniform thickness, As,min in the direction of the span shall be the same as that required by 7.12. If you would not split the As,min required by 10.5.1, 10.5.2 and 10.5.3, why...
  3. mitchelon

    ACI minimum area of steel

    Clansman, I guess this thread will not die. 271828, All the steel needs to be on the tension face if your are designing for flex. steel. If desinging for T&S, then it can be distributed. It is not like asking 100 people about Bin Laden. Most people have no factual data or experience in what...
  4. mitchelon

    ACI minimum area of steel

    Because I am now one more person who agrees with the definition described by Taro; thus the probabilities that he is correct have increased. :)
  5. mitchelon

    ACI minimum area of steel

    Taro, I was wrong about the 0.0018bh. Completely agree w/ you that it should be used as min flex reinforcement for slabs and footings. So folks, please listen to Taro. UcfSE, what do you propose the 3 in 3?(f'c)/fy should be? In my derivation of 3?(f'c)/fy, I assumed a fr of 12*fc^0.5.
  6. mitchelon

    Shear tie splices

    I am no foundation mat expert, but 12 ft??? No one considered to use a different type of foundation after seeing this number. Are you talking about ties to transfer the shear between horizontal cold joints?
  7. mitchelon

    Pile Uplift

    Is your geotech engineer "old school?" No ofense to the old-schoolers out there. I am not an expert on piles and am also a relatively young engineer, but think that the 20% may have been commonly used in the past as a "guesstimate." Chin et al. (1973) noted that shaft resistance from uplift load...
  8. mitchelon

    ACI minimum area of steel

    271828, That is correct. I think it is important to reiterate that these are two completely different requirements. 0.0018*b*h is a T&S requirement for stresses perpendicular to the main flexural reinforcement. For example, this applies to one-way slabs in the long direction. The main flexural...
  9. mitchelon

    ACI minimum area of steel

    StructuralEIT, I do not disagree. I was just explaining the reasoning behind the minimum requirement and how the equations were developed as it appears to be confusing some folks. 10.5.3 is very straightforward and I did not feel the need to explain it, but thanks for mentioning it as I can see...
  10. mitchelon

    ACI minimum area of steel

    ...is based on the requirement that the ultimate strength of the member be greater than the cracking moment.” Here is how it was developed: Mcr = S*fr = (bh^2/6)*approx 600psi for fr My = As*fy*jd = rho*bd*fy*approx 7/8d for jd My > Mcr 7/8*rho*bd^2*fy > (100/0.81)*bd^2 rho > 140 / fy...
  11. mitchelon

    Vibrations:Reinforced Concrete

    The strength of the concrete is a function of the material properties.
  12. mitchelon

    Dynamic Cone Penetrometer for Foundation Design

    BigH, thanks. I will check those other threads. The DCP in question is a 1-3/8"diam rod with a 45deg cone point and a 15 lb steel ring weight falling 20" on an E-rod slided drive.
  13. mitchelon

    Dynamic Cone Penetrometer for Foundation Design

    Have any of you, with experience working in a geotechnical testing agency, developed correlations for the soils in your area between the DCP and soil properties or between DCP and any other penetration test (i.e. SPT)? I always thought of the DCP as a method for pavement analysis/design and for...
  14. mitchelon

    Foundation design for Biaxial Momoent

    Your equivalent footing (in contact with soil) will be: B'xL', where B'=B-2eb, L'=L-2el, eb=Mb/P (Mb=moment in the B direction) and el=Ml/P (Ml=moment in the L direction). The equivalent bearing pressure will then be: (P+Wf)/B'L'. You will also need to use the B' and L' values in your bearing...
  15. mitchelon

    Removal of bays of 2 way floor slabs

    Also, is this a flat plate/slab or are there beams at the column lines? If there are beams, then you need to calculate the torsion in the beams created by the unbalanced moment at the discontinued slab sections. If it is a flat plate/slab, the unbalanced moment will be resisted through shear and...
  16. mitchelon

    HVFAC

    Class F is definitely used in mass concrete. Class C can generate more heat; therefore it is not used for this purpose. Concerning your questions, typical replacement values for 28 days performance are 15 to 25%. With strength requirement delayed to 56 days, 90 days, or later, dosage rates can...
  17. mitchelon

    unreinforced concrete slab

    Just FYI, the real value of fr is much greater than the allowable value in ACI. Around 9-11*sqrt(f'c). Most codes are conservative and use 6-7.5. 12 is allowed in some cases in prestressed concrete design.
  18. mitchelon

    Design of stirrups for column

    It is always really important as MYerges stated. You do need to provide us with more information. Are you in a seismic area (in addition to shear strength, stirrups are extremely important for concrete confinement and longitudinal steel stability)? Is the building symmetrical (this is important...
  19. mitchelon

    Foundation design for uplift during construvtion period

    Think about reality and not about what the code says. There are few codes for temporary structures. In the US we have ASCE 37-02, which is still not extremely popular. ASCE 7-05 recommends a basic wind speed of 140 mph for the coast of NC. ASCE 37-02 reduces this BWS to 90 mph. In addition, it...
  20. mitchelon

    Cast-in Place Bars versus Epoxied

    What nutte said is correct. It has nothing to do with the surface area of the cone. The transfer of forces occurs by chemical adhesion between bar and concrete, frictional forces, and mechanical anchorage of the ribs. Pullout tests were the method of choice many years ago, but it is no longer...

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