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Known or unknow?

Yes, more bars less dia is better. Also check what is commercialy viable. There is commercial as well as health & safety aspect to it as well. For example using less bars of dia 40 reduce congestion and easy handling and placing but is it safe for workers to carry such huge bar? Accidents?

Good point again. In such cases, you have to deal with the notorious huge nerve sapping temperature forces.

For the calculation of kl/r ratio

1) Go to Modify/Show grid >>On Top Right Corner go to reference Points >> Select then Delete . 2) First method shown in this PDF is available in Etabs, Both metgos are available in SAP 2000 Non Uniform Load.pdf

1- Place shear walls opposite to each other, let's say you put a wall at the far right of a building, put another one with the same length and thickness at the far left one, .. etc that is to ensure the center of rigidity ( governed by walls mostly) coincides with the center of mass of the building to eliminate torsional movement of the building. 2- The far the wall is placed from the center of the building the better, as walls near the center doesn't resist much shear force as walls at the outer perimeter and the latter is good to prevent torsional movement. 3- The following is copied directly from the ACI design hand book: '' Shear walls should be located within a building plan to efficiently resist lateral loading. Locating shear walls in the center half of each building is generally a good location for resisting lateral forces. This arrangement, however, can restrict architectural use of space. Although shear walls are commonly located at the ends of a building, such wall locations will increase slab restraint and shrinkage stresses, especially in long buildings and buildings such as parking structures that are exposed to large temperature changes. Symmetrical wall arrangements provide good flexural and torsional stiffness. Walls at the perimeter resist torsional forces most effectively. Walls away from the perimeter, however, could have a higher tributary area and, consequently, larger gravity axial force to resist uplift or overturning. They are, however, less efficient in resisting horizontal torsion An unsymmetrical arrangement, however, does not usually provide predictable torsional stiffness due to their eccentricity. Such a shear wall layout should be designed explicitly for torsion. A symmetrical arrangement is preferable to avoid designing walls for torsion.''

I have not seen such a limit written anywhere. However, the lowest value of bearing capacity (BC) for the building sites I have come across during my professional practice, was mostly 0.5 tons per square foot (TSF). In only one case, the reported BC was 0.25 TSF. However, the client was advised to change the site, as such a low BC indicates a very weak soil, ordinarily requiring a very heavy & expensive footing design. As such, IMO 0.5 TSF may be considered a reasonable lower limit of BC for a building site. Regards.