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INTRODUCTION Railway sleepers made of concrete have only been the standard during the last decades in Sweden. According to Andersson & Berg (1999) pine was substituted for concrete as material in the 1950s when prestressed concrete became available for sleepers. The advantages of the concrete sleepers were e.g. the longer service life, higher bearing capacity and no use of environmental hazardous chemicals such as creosote (used to increase the service life of the timber). A railway sleeper has several functions such as: being elastic foundations to the rails, keeping the right distance between the rails, cooperating with the rail so the railway track is resistant to flexuous movement in the horizontal direction, etc. If all abovementioned reasons are considered it is easily understood that a sleeper must withstand various types of loads, weather conditions etc., without losing its properties during its service life. Normally concrete sleepers sustain their properties for more than 50 years. However in Sweden some sleepers made between 1992 and 1996 have started to deteriorate. They have obtained cracking of a more or less severe kind and some of them have even lost most of their bearing capacity. The cracking is believed to be caused by delayed ettringite formation, which leads to an internal expansion and with time cracks, see e.g. Tepponen & Eriksson (1987). This process might reduce the service life to as few years as five. The Swedish National Rail Administration has started investigations. Bad production methods are believed to be the cause of the deterioration. In order to increase the production speed, the cement amount was increased from ordinarily 420kg/m 3 to 500kg/m 3 and steam curing was used during the hardening process in some of the production plants. In this paper results from strength capacity tests are presented. The purpose of the tests has been to get an idea of how the cracking influences the load carrying capacity. In Figure 1 a principal drawing of a Swedish railway sleeper is presented. The sleepers are made of prestressed concrete with the concrete class K60 (compression strength 60 MPa tested on 150mm cubes). The sleepers are prestressed with 10 strands (each strand consists of 3 wires with the diameter 3mm each). - 2 -
Figure 1 Principal drawing of tested concrete sleepers. The load carrying capacity of sleepers and especially the fatigue capacity have earlier been studied at LTU, see Gylltoft & Elfgren (1977) and Gylltoft (1978). Damages on sleepers have earlier been observed in Finland, Tepponen & Eriksson (1987), in the U.S., Hime (1996) and Collepardi (1999), and in Germany, Stark et al. (1998). Often delayed ettringite formation has been the reason for the damage. VISUAL INSPECTION AND CLASSIFICATION Visual inspection When the Swedish National Rail Administration became aware of the problem with the cracked sleepers, several investigations were initiated. These showed among other things that the damaged sleepers could be found all over Sweden. About 3.5 million sleepers have been inspected and there are about 300 000 sleepers that are cracked. The only way of finding them is by walking along the railway tracks making a visual inspection. Knowing this, it is easy to understand that the investigation is very difficult and time consuming to perform. The investigations are performed in the way that two inspectors walk along the railway track on opposite sides. Since the sleepers are covered with macadam as in Figure 2, it is only possible to notice damages that are on the upper side of the sleeper and the top 1 to 2 cm along the sides. This makes it very difficult to discover sleepers that are in the beginning of the failure process. - 3 -
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LICENTIATE THESIS Evaluation of Con
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Preface This licentiate thesis pres
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Evaluation of Concrete Structures I
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Evaluation of Concrete Structures I
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Evaluation of Concrete Structures 4
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A. Simplified check A1. In-situ ins
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Evaluation of Concrete Structures 2
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Evaluation of Concrete Structures G
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Lok-Strength & Capo-Strength F [kN]
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Page 31 and 32: Evaluation of Concrete Structures t
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Page 41: 6 Outlook Evaluation of Concrete St
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Page 47: Paper A CONCRETE STRENGTH DEVELOPME
Page 50 and 51: determine the in-place strength of
Page 52 and 53: strength could be the fact for all
Page 54 and 55: German Petersen & Poulsen (1993), s
Page 56 and 57: Rebound test (Schmidt-hammer) The r
Page 58 and 59: expected (about 8 MPa). But for the
Page 60 and 61: Figure 8 shows the location where t
Page 62 and 63: Tensile strength [MPa] 6.0 5.0 4.0
Page 64 and 65: Table 4 Mean value and standard dev
Page 66 and 67: Lok-Strength & Capo-Strength F [kN]
Page 68 and 69: fcc fct concrete compression streng
Page 70 and 71: The values that have been used are:
Page 73: LOAD CARRYING CAPACITY OF CRACKED C
Page 77 and 78: Class 3. OK / Green: No visible cra
Page 79 and 80: 0.5 1.0 +15 kNm 0.5 0.5 1.0 0.5 -11
Page 81 and 82: Horizontal force [kN] 100 80 60 40
Page 83 and 84: TEST SET-UP AND RESULTS Bending cap
Page 85 and 86: The displacement was measured by fo
Page 87 and 88: Figure 18 Failure of sleeper no. 10
Page 89 and 90: Sleeper No. 17 looks more like the
Page 91 and 92: c2 75 á 100 where ψ ′ c = = = 0
Page 93 and 94: The obtained stress σ t = 4.45 MPa
Page 95 and 96: M f,rail moment bearing capacity at
Page 97: Paper C CONCRETE FATIGUE CAPACITY.
Page 100 and 101: FATIGUE OF CONCRETE A common way to
Page 102 and 103: notch is deep enough that is). When
Page 104 and 105: Figure 5 Test set-up uniaxial tensi
Page 106 and 107: Table 1 A summary of all uniaxial t
Page 108 and 109: Strain [‰] 0.8 0.6 0.4 0.2 0 Phas
Page 110 and 111: 11) the start of phase 3 takes plac
Page 112 and 113: ACKNOWLEDGEMENTS The study has been
Page 114 and 115: APPENDIX A Evaluated data from the
Page 116 and 117: C = dε / dN [× 10 −6 ] 100 10 1
Page 118 and 119: Test series A: S min = σ min / f c
Page 121: Paper D SHEAR FATIGUE CAPACITY - A
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1 Introduction The codes that have
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Dead Loads: Slab: 0.320 m á 24 kN/
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the equations to calculate the desi
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where ηγm is 1.5 for concrete (co
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different besides the strength clas
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Table 4.2 Fatigue strength. Number
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The shear force capacity, V Rd1, fo
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σ cd,min,equ lower stresses of the
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6.2 Strength values at fatigue load
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6.3 Strength values at fatigue load
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1 − 0.7166 14 ⋅ = 4.71 < 6 ⇒T
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The “new” equation for the desi
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Appendix A. Concrete Codes Excerpt
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DOCTORAL AND LICENTIATE THESES Divi
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