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Assalam o alaikum. I have two questions. 1) Since I have provided my tie beams at plinth level so in my case , do tie beams, plinth beams, grade beams, all mean same? 2) ACI 21.12.3 deals with grade beams and Slab on grades. ACI 12.12.3.2 says "Closed ties shall be provided over the length of beam spaced at a maximum of one half the smallest orthogonal cross sectional dimensions of the beam or 12 inch, which ever is lesser." Moreover ACI 21.12.3.3 says "grade beams and beams that are part of a mat foundation that is subjected to the flexure from the columns that are part of seismic force resisting system shall have reinforcing details confirming to ACI 21.5 for flexure members of special moment frames. But ACI 21.5 says hoops shall be provided at a spacing not more than d/4. Does it mean that restriction of 21.5 only applies to tie beams if tie beams are suffering from flexural effects? And kindly explain what "flexure from the columns" means?