Manual for Design and Detailings of Reinforced Concrete to Code of ...

Version 2.3 May 2008M30 to 40 for the same2 , but increases at grade 45 due to the change of thebdlimit of neutral axis depth ratio from 0.5 to 0.4 with moment redistribution notexceeding 10%. The same phenomenon applies to tensile steel also. Withmoment redistribution exceeding 10%, the same trend will also take place.Reinforcement Ratios for Doubly Reinforced Beams d'/d = 0.1Grade 30 Ast/bd Grade 30 Asc/bd Grade 35 Ast/bd Grade 35 Asc/bd Grade 40 Ast/bdGrade 40 Asc/bd Grade 45 Ast/bd Grade 45 Asc/bd Grade 50 Ast/bd Grade 50 Asc/bd141210M/bd 2864200 0.5 1 1.5 2 2.5 3 3.5 4Reinforcement ratios A/bd (%)Chart 3-1 – Reinforcement Ratios of Doubly Reinforced Beams for Grade 30to 50 with Moment Redistribution limited to 10% or belowzAs similar to BS8110, there is an upper limit of “lever arm ratio” which is dthe depth of the centroid of the compressive force of concrete to the effectivedepth of the beam section of not exceeding 0.95. Thus for calculated values ofzd≥ 0.95approach,xor ≤ 0. 111 in accordance with the simplified stress blockdAstM=bd 0.87 f ( 0.95d)bdyDesign Charts for grades 30 to 50 comprising tensile steel and compressionsteel ratiosA stA and sc are enclosed at the end of Appendix C.bd bd3.4.2 Design in accordance with the Simplified Stress BlockThe design will be simpler and sometimes more economical if the simplified19