CT4860 STRUCTURAL DESIGN OF PAVEMENTS

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In the Dutch design method it is assumed that the joint efficiency W of a free edge of a plain or reinforced concrete pavement (at the outer side of the carriageway) is not 0% but 20% (in the case that below the concrete pavement a unbound base is applied) or 35% (in the case that a bound base is applied) or 70% (in the case that a widened bound base is applied). These values resulted from calculations for concrete pavements on a Pasternakfoundation. A Pasternak-foundation is a more realistic foundation model consisting of coupled vertical springs that allow the transfer of shear stresses (see figure 27). The Winkler-foundation, used in the Dutch design method, consists of uncoupled vertical springs without transfer of shear stresses (see figure 6). In the current Dutch design method the following values of the joint efficiency W are used for longitudinal joints in plain or reinforced concrete pavements: - non-profiled construction joints without ty bars in plain concrete pavements on unbound base: W = 20% - non-profiled construction joints without ty bars in plain concrete pavements on bound base: W = 35% - contraction joints with ty bars in plain concrete pavements: W = 70% - profiled construction joints in plain concrete pavements: W is calculated by means of equation 60a - joint in reinforced concrete pavement (where always an asphalt layer is applied below the concrete pavement): W = 35% For transverse joints/cracks the following values of the joint efficiency W are used in the Dutch design method: - cracks in reinforced concrete pavement: W = 90% - profiled construction joints or contraction joints, both without dowel bars, in plain concrete pavements: the joint efficiency W at long term is calculated by means of the equation: W = {5.log(k.l 2 )–0.0025.L–25}.logNeq–20 log(k.l 2 )+0.01.L+180 (41a) - profiled construction joints or contraction joints, both with dowel bars, in plain concrete pavements: the joint efficiency W at long term is calculated by means of the equation: W = {2.5.log(k.l 2 )-17.5}.logNeq-10log(k.l 2 )+160 (41b) In the equations 41a and 41b is: W = joint efficiency (%) at the end of the pavement life L = slab length (mm) k = modulus of substructure reaction (N/mm 3 ) l = radius (mm) of relative stiffness of concrete layer (see paragraph 3.4.2) Neq = total number of equivalent 100 kN standard axle loads in the centre of the wheel track during the pavement life, calculated with a 4 th power, i.e. the load equivalency factor leq = (L/100) 4 with axle load L in kN 44
Example L = 4.5 m = 4500 mm k = 0.105 N/mm 3 ν = 0.15 (concrete quality C28/35 (B35)) E = 31000 N/mm 2 (concrete quality C28/35 (B35)) h = 210 mm l = 695 mm transverse joint without dowel bars (equation 41a): Neq = 10 5 : W = 67.3% Neq = 10 6 : W = 54.5% Neq = 10 7 : W = 41.8% transverse joint with dowel bars (equation 41b): Neq = 10 5 : W = 84.3% Neq = 10 6 : W = 78.5% Neq = 10 7 : W = 72.8% This example clearly shows on one hand the beneficial effect of the application of dowel bars and on the other hand the detrimental effect of the number of heavy axle loadings on the joint efficiency W in transverse joints. 3.5 Stresses due to unequal settlements Generally concrete pavement structures will not be applied in areas where substantial unequal settlements of the subgrade can be expected. These unequal settlements will result in a low riding quality that only can be improved by means of very expensive maintenance measures. When nevertheless a concrete pavement structure is designed for a subgrade showing unequal settlements, one has to realize that these settlements introduce extra ‘settlement flexural stresses’ in the concrete slab because, due to the deadweight, the slab tries to follow as much as possible the settlement profile (figure 21). Figure 21. Settlement profile. Assuming a sinusoidal settlement profile (in figure 26: δ1 = δ2 = δm, T1 = T2 = T), the maximum settlement stress σs in the most heavily (by unequal settlements) loaded concrete slab (cross section 2 in figure 21, flexural tensile 45
Page 1: CT4860 STRUCTURAL DESIGN OF PAVEMEN
Page 5 and 6: Table of Contents 1. INTRODUCTION 3
Page 7 and 8: 1. INTRODUCTION In many countries c
Page 9 and 10: main part of the traffic loading. T
Page 11 and 12: Well graded crusher run, (high qual
Page 13 and 14: Property Sandcement Lean concrete A
Page 15 and 16: In the Dutch design method for conc
Page 17 and 18: 2.6 Layout of concrete pavement str
Page 19 and 20: widened (e.g. to 8 mm) to a certain
Page 21 and 22: The pavement was constructed in two
Page 23 and 24: p = ground pressure (N/mm 2 ) on to
Page 25 and 26: Lightweight fill material Density (
Page 27 and 28: Example Sand subgrade: ko = 0.045 N
Page 29 and 30: Figure 10. Mean distribution (%) of
Page 31 and 32: 2. Directly besides the central par
Page 33 and 34: where: h = thickness (mm) of the co
Page 35 and 36: Positive temperature gradient ∆t
Page 37 and 38: There exist a lot of (modified) Wes
Page 39 and 40: P = 50 kN = 50000 N p = 0.7 N/mm²
Page 41 and 42: Figure 15. Influence chart of Picke
Page 43 and 44: Figure 17. Influence chart of Picke
Page 45 and 46: 2 Ed I d S d = (36) 2 3 1 + ( 1 +
Page 47: slab wu = deflection (mm) at the jo
Page 51 and 52: Figure 22. Factor F as a function o
Page 53 and 54: Example In this section an example
Page 55 and 56: Table 10 clearly shows that in the
Page 57 and 58: For instance, on the basis of numer
Page 59 and 60: Although the increase of the flexur
Page 61 and 62: 4. DESIGN METHODS FOR CONCRETE PAVE
Page 63 and 64: Figure 28. AASHTO design chart for
Page 65 and 66: 4.2.3 The BDS-method The British de
Page 67 and 68: Figure 32. Additional plain concret
Page 69 and 70: of the concrete layer. Figure 34 sh
Page 71 and 72: where: nij = predicted number of re
Page 73 and 74: 5. DUTCH DESIGN METHOD FOR CONCRETE
Page 75 and 76: Only the technical aspects of the o
Page 77 and 78: 2 ' ⎛ ⎞ L σ = 0.85 σ”t = 0.
Page 79 and 80: 5.3 Revised design method In the ea
Page 81 and 82: Therefore in the revised method the
Page 83 and 84: The tensile flexural stress at the
Page 85 and 86: w l = 4.8 e -0.35.log Neq (74) The
Page 87 and 88: Axle load group (kN) Number of carr
Page 89 and 90: 5.4.3 Climate In the years 2000 and
Page 91 and 92: - W according to equation 81a at pr
Page 93 and 94: 5.4.8 Thickness plain/reinforced co
Page 95 and 96: W = load transfer at longitudinal e
Page 97 and 98: ‘reference temperature’ at the
Page 99 and 100:
The central tensile force N in the
Page 101 and 102:
σs,cr = tensile stress in reinforc
Page 103 and 104:
In the Dutch design method for conc
Page 105 and 106:
10% 5% reference 5% 10% smaller sma
Page 107 and 108:
13. Houben, L.J.M. Finite element a
Page 109 and 110:
31. Guide for the Standardisation o
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CT4860 STRUCTURAL DESIGN OF PAVEMENTS

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