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Recent content by letrab

  1. letrab

    Concrete Weir Design Pressures

    Depending on the depth of flow over the weir you may have to look at negative pressure on the downstream slope of the ogee. Depending on your cut off and drainage you also need to look at uplift over a length of the foundations
  2. letrab

    Dam Wall

    Hi Jaco, Raising the dam wall will affect the stability of the wall. It is a basic gravity structure and the analysis is straightforward. The only tricky bit is the asumption on cohesion between the rock foundation and the concrete. From the piccie it seems as if the back slope is quite steep...
  3. letrab

    Unbonded Post-Tensioning

    Yes it is only the curvature from deflection
  4. letrab

    retention pond leak

    My first problem is with the question "A clay liner was built to seal the pond and unfortunately it has a slow leak.The leak is a problem because when the pond reaches normal water level, water flows out into a wetland area.We need water in the wetland." It sounds as if the slow leak is the...
  5. letrab

    Cracked Tiles

    Lack of expansion joints can also lead to several tiles failing. But for all the tiles to fail I would look at the quality of the tiles first
  6. letrab

    Shear Lag Factor Z-Purlin

    If I remember correctly the shear centre for a Z section lies on the centroid. Channels have the shear centre outside the section
  7. letrab

    Catchment area

    Hi Mike I agree that if you could estimate actual conditions to within 10% of the actual values you are doing well. However, if you start a basic process like measuring area and has a variance of 10 % you are in trouble. If you let your errors add up the chances are that your estimated final...
  8. letrab

    Torsion Confusion

    For a circular hollow section the Torsion constant J for pure torsion is 0.5 Pi*(R out^4 -R inner^4) Calculate the angle of twist theta with the formula given by graybeach. This is correct for pure St. Venant torsion
  9. letrab

    Catchment area

    Your error should be less than 10%. Use a square on the map 1km x1km and check it with the planimeter and CAD, maybe the scale used is incorrect but comparison with a square should indicate which method has the problem
  10. letrab

    questionable proctor results

    How much of this stuff is available. It sounds like it has potential for use as a hydrophilic waterstop if available in significant quantities.
  11. letrab

    soil structure interaction

    I think it is meant that the structure should be able to deform significantly without fracture ie ductile and stiff enough to transmit the loads to the foundation and resist the loads it is subjected to without breaking the finishes and partitions. I agree with Qshake that the foundation...
  12. letrab

    soil structure interaction

    I think it is meant that the structure should be able to deform significantly without fracture ie ductile and stiff enough to transmit the loads to the foundation and resist the loads it is subjected to without breaking the finishes and partitions. I agree with Qshake that the foundation...
  13. letrab

    Vinyl Sheeting in Dam

    Hi Erich The Bentonite soil cement in the trench seems like as good idea, why don't you continue it to the top and replace the timber with the plastic concrete barrier. It will be easier to place. If you want a plastic membrane, joining the adjacent sheets will be difficult. backfilling either...
  14. letrab

    Rotational Fixity of a Pad Footing

    Very small rotations are normally all that is required to drop the moment in the column to zero while fairly large deformations are required to mobilise passive resistance. I cannot see how both can be mobilised in a single application. Your footing seem stiff enough to transfer a moment to the...
  15. letrab

    PCA Circular Concrete Tanks

    Hi Dave, The way I understand it you have three options at the wall base connection Sliding, all in hoop tension in the wall Pinned base, water resisted by wall tension and vertical moment in the wall. The moment is obviously zero at the bas and consequently no moment in the base. The last...
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