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Note for Design of Reinforced Concrete & Brick Masonry Structures - DRCBMS By Engineering Kings

  • Design of Reinforced Concrete & Brick Masonry Structures - DRCBMS
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CE2401 – Design of Reinforced Concrete & Brick Masonry Structures Mr.R.PERUMAL.ME, AP/CIVIL, 9529/SCADEC UNIT I RETAINING WALL Retaining wall – Retains Earth – when level difference exists between two surfaces A) Gravity wall (h<3m) – Masonry or Stone ww w.E asy B) Cantilever wall (h>3m and h<6m) C) D) Counterfort wall (h>8m) En gin eer ing .ne _________________________________________________________________________________________________________________________ 1 t

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CE2401 – Design of Reinforced Concrete & Brick Masonry Structures Mr.R.PERUMAL.ME, AP/CIVIL, 9529/SCADEC E) Buttress wall [Transverse stem support provided on front side] F) Bridge abutment [Additional horizontal restraint from bridge deck] ww Stability – Overturning and Sliding – Avoided by providing sufficient base width. w.E Earth pressure and stability requirements: asy En gin eer ing .ne Pressure, P CJ e Z Where, Z = depth, J e = Unit weight Ca = 1  SinI ; 1  SinI Always, Cp > Ca. Cp 1  SinI 1  SinI Eg: If ф = 300, Ca = 1/3 and Cp = 3. In sloped backfill, ª CosT  Cos 2T  Cos 2I º Ca = « »CosT ; 2 2 ¬« CosT  Cos T  Cos I ¼» Cp 1  SinI 1  SinI _________________________________________________________________________________________________________________________ 2 t

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CE2401 – Design of Reinforced Concrete & Brick Masonry Structures Mr.R.PERUMAL.ME, AP/CIVIL, 9529/SCADEC 1. Effect of surcharge on level backfill: ww w.E Pa = Pa1 + Pa2, where, Pa1 = Ca.W s.h = Ca.γe.hs.h & Pa2 = Ca. γe.h2/2 [h/2 above heel] [h/3 above heel] asy Note : Purpose of retaining wall is to retain earth and not water. Therefore, submerged condition should be avoided by providing and maintaining proper drainage facilities [including provision of weep holes]. 2. Effect of water in the backfill: Stability requirements i) Overturning: FOSoverturning = En FOS against gin eer ing .ne Overtuning ≥ 1.4 Sliding 0.9 Mr ≥ 1.4 Mo h'3 h' = Ca. J e . .Cos T 6 3 Mr = W (L – Xw) + (Pa.Sin T ).L a) For sloping backfill, Mo = (Pa.Cos T ). _________________________________________________________________________________________________________________________ 3 t

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CE2401 – Design of Reinforced Concrete & Brick Masonry Structures Mr.R.PERUMAL.ME, AP/CIVIL, 9529/SCADEC b) For level backfill [with surcharge, Mo = (Pa1(h/2) + (Pa2(h/3). Mr = W (L – Xw) [as T = 0o] ii) Sliding: [Friction between base slab and supporting soil] F = μ.R [where, R = W ] R -> Resultant soil pressure at footing base μ -> Coefficient of static friction [0.35 – Silt & 0.60 – Rough rock] FOSsliding = 0.9 F ≥ 1.4 Pa CosT When Pa is very high, shear key projection can be provided below footing base [Produces passive resistance Pps, which is generally neglected, otherwise]. Sliding is reduced by providing shear key [like a plug, anchors inside] ww w.E asy En Pps toe. 2 2 CJ e (h2  h1 ) / 2 gin eer ing Xsk -> Flexural reinforcement from stem is extended straight into shear key near the .ne Note: For economical design, soil pressure resultant(R) must be in line with front face of wall. Preliminary proportioning of cantilever retaining wall: 1. 2. 3. 4. 5. The thickness of base slab is h/12 or 8% of the height of wall + surcharge. The base thickness of stem should be greater than the thickness of base slab The top thickness of stem should not be less than 150mm. Clear cover for stem is 50mm and base slab is 75mm Minimum length of base slab is given by § C a · h' ¸ Lmin ¨ ¨ 3 ¸D © ¹ R where, αR = Coefficient depending on the pressure distribution αR = 0.5 for rectangular pressure distribution & 0.67 for trapezoidal pr.dist. 6. Minimum length of heel slab is given by _________________________________________________________________________________________________________________________ 4 t

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