5028,5027,5035

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5028,5027,5035

  1. 1. DESIGN OF DOUBLY REINFORCED BEAM BY <ul><li>BY LIMIT STATE METHOD </li></ul>
  2. 2. <ul><li>TYPES OF BEAMS </li></ul><ul><li>Doubly Reinforced beam </li></ul><ul><li>Singly Reinforced beam </li></ul>
  3. 3. Need of doubly reinforced beam
  4. 4. <ul><li>MINIMUM AND MAXIMUM STEEL AS COMPRESSION STEEL IN BEAMS </li></ul><ul><li>The minimum area of steel in compression </li></ul><ul><li>= 0.4% of area in compression steel </li></ul><ul><li>The maximum area of steel in compression </li></ul><ul><li>= 4% of the total sectional area of the beam </li></ul>
  5. 5. YIELD STRESS IN COMPRESSION STEEL <ul><li>IS 456 ASSUMES THAT THE YIELD STRESS-STRAIN RELATIONSHIP FOR STEEL IN COMPRESSION AND TENSION REMAIN SAME </li></ul><ul><li>Design yield stress = 0.87 ƒy </li></ul>
  6. 6. Z S Z C C C d’ C S 0.0035 d’ 0.002 b X u Є s d Є’ s Action of doubly reinforced beam T STRAIN DIAGRAM STRESS DISTRIBUTION
  7. 7. <ul><li>T = C C = C S </li></ul><ul><li>M U = C C Z C + C S Z S </li></ul><ul><li>C S = Compressive force due to concrete </li></ul><ul><li>C C = Compressive force due to steel </li></ul>
  8. 8. <ul><li>ANALYSIS AND DESIGN OF DOUBLY REINFORCED BEAM </li></ul><ul><li>Choose value of x, the depth of neutral axis. Assuming compressive strain of 0.0035 </li></ul><ul><li>Total tension in steel, T = ƒ ast A st </li></ul><ul><li>Total compression in steel, C = 0.36 ƒckbx </li></ul>
  9. 9. <ul><li>The total compression, C = C S + C C </li></ul><ul><li>Check- if T = C, the assumed neutral axis is satisfactory . </li></ul><ul><li>Moment of resistance of section </li></ul><ul><li>M U = C C (d-k 2 x) + C S (d-d΄) </li></ul>
  10. 10. <ul><li>Thank you </li></ul>

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