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BAZ last won the day on October 18

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  1. Thickness of footing

    Draw the shear force diagram for one way shear. Calculate the design bearing pressure for determining the demand for resistance against punching.
  2. Shear wall from 3rd storey

    The demand on the horizontal and vertical members that will transfer the forces of a wall to the foundation is a major concern. The demand will be calculated by considering the expected ductility and overstrength of the wall.
  3. Flange brace design

    Consult the document titled BRACING FOR STABILITY. Bracing is a function of the compressive strength of compression flange. As a rule of thumb, bracing force can be considered as 2-3% of the coompressive strength of the compression flange of beam. Read the document for better estimate.
  4. Seismic Analysis

    The time history is the most accurate way to estimate the demand as well as detect the shortcoming in a structure. It is time-consuming and most design offices do not use it unless they have specifically charged from the client for such analysis. If your building is regular, response spectrum will suffice; you can check modal mass participation to verify that. If you are getting more than 60% mass in principle modes, then time history will not offer a significant advantage.
  5. Seismic Analysis

    You will use Time history analysis when you want the analysis done in highest possible detail. Yes, it will depend on the building height, as well as on the structural irregularities. For regular structures less than 20 stories, pushover analysis will do. But if you want to consider the effect of higher in modes even in buildings less than 20 stories, you should go for Time history analysis.
  6. Shear capacity of Column

    Study section of ACI 318-11. The relation you have mentioned above does not include the effect of axial forces.
  7. ETABS reports the depth of neutral axis, as well as the required length of boundary element.
  8. 6-ft Mass Concrete

    Yes, Errect formwork, place and hold reinforcement and pour concrete in shifts.
  9. You can also get help from: Reinforced concrete design, 6th Ed., by Mac Gregor and James K Wright and Seismic Design of Reinforced Concrete and Masonry buildings by Paulay & Priestely.
  10. The analysis is not limited to high seismic zones and it is also not limited to weaker soils. That is why I posted it. We assume that hinge will form if longitudinal reinforcement of vertical members can develop 1.25fy, but that is not the only criteria. The author says that capacity design approach should be used for proportioning foundation. The proportioning of foundation for the design seismic forces is not enough.
  11. I posted the query because I recently read two articles: one is FOUNDATIONS FOR SHEAR WALL STRUCTURES by J.R. Binney and T Paulay, and the other one FOUNDATIONS FOR CAPACITY DESIGNED S T R U C T U R E S by P.W. Taylor and R.L. Williams. @Rana : This is not enough. These details ensure the development of column hinge at the bottom if it is possible. And that "if" depends on the soil-structure interaction and the strength of the soil. If the soil is strong enough to resist bearing pressure corresponding to forces (axial load + moment) that it may experience when the column will be in inelastic range (capacity design approach), and if you have designed the footing for the moment that it may experience when hinge (capacity design approach) will form in the column, which is, of course, greater than the moment that you will get from ETABS for the design Earthquake, then the hinge will form in the column. If the above scenario is not feasible then you may proportion the footing to allow the rocking behavior so that energy may be dissipated provided footing rotation is in permissible limits, which will depend on the soil-rotation relationship. @umer: In MAT, or other connected foundation types, the third option is to allow nonlinear behavior in the foundation. In that case, the foundation should be detailed for attaining necessary ductility levels. These things are not discussed in the ACI code. I have not read these things in RCC books as well.
  12. Does anyone practice the design philosophy that ensures the formation of plastic hinges at the bottom of the column, near the foundation, for isolated footing?
  13. 2D-Plate Analysis -Safe

    Yes, 2D plate analysis should be used. 3D analysis will give wrong results as the raft has confinement on all sides. If you are using the 3D analysis, then you must add lateral springs as well to get better results.

    Transfer slab/beam, and their supporting members, requires to be detailed for the forces resulting from the inelastic response of pick -up the column.
  15. Below is an excerpt from the document titled: Seismic Design of ReinforcedConcrete Mat Foundations. The document is prepared by NEHRP. Earthquake load effects, E, are defned in ASCE 7-10 §12.4.Inherent in the defnition of these seismic demand levels is thestructural response modifcation factor, R, which is dependenton the type of lateral force-resisting system considered for thesuperstructure. The same overturning that is determined at thebase of the superstructure is to be applied directly to the matfoundation. Consideration of higher foundation demand levelsis triggered only by unusual structural geometries, such as acantilever column system or a discontinuous lateral system,which require the consideration of a system overstrength factor,per ASCE 7-10 §12.4.3. By defining earthquake load effects with an inherent R-value, some inelastic behavior is assumed in the superstructure and therefore implies that a mat foundation also may experience inelastic demands. You can also study the document in this link: bulletin.nzsee.org.nz/13/2/0171

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