LICENTIATE THESIS - Luleå tekniska universitet

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Evaluation of Concrete Structures Information on how the visual inspection and the classification of damages are performed is presented together with possible failure mechanisms of the fastener when loaded horizontally. The purpose with the tests have been to get information on how the cracking influences the load carrying capacity compared to an un-cracked sleeper. The test results have been compared with calculations according to the Swedish Rail Code for sleepers. The tests show that small cracks do not seem to influence the load carrying capacity and first when cracking is very severe the load-carrying capacity is reduced significantly. In paper C results and analyses are presented from cyclic tensile fatigue tests. The tests can be considered as initial ones. The fatigue tests in this paper are compared to a deformation criterion proposed by Daerga & Pöntinen (1993) based on an idea of Balázs (1991). The growth in deformation during fatigue can according to the model be described as three phases. In the beginning of the first phase the deformation rate is high but stagnates after a while. The second phase is characterised by a constant deformation rate. These two phases can be described as stable. During the third phase, the failure phase, the deformation rate increases rapidly leading to failure within a short time. The strain criterion for fatigue failure means that the strain at peak load during a static failure load corresponds to the strain at the changeover between phases two and three during a fatigue failure. These tests indicate that the strain criterion proposed by Balázs (1991) might also be applied on plain concrete subjected to cyclic tensile fatigue load. Though, further studies are needed. In paper D a comparison is made between the Swedish Codes and Eurocode regarding fatigue load for concrete. If the results are compared there are differences. The calculation with EC2-2 (1995) gives the least conservative values. The Swedish code is slightly more conservative than the EC2-2, but they are still fairly similar. The new version of Eurocode, EC2-draft (1999), is by far the most conservative one. Some of the differences are: The expression to calculate the shear force capacity. The expression to calculate the design fatigue strength. The Swedish Code gives an approximate value of the number of cycles before failure (the value is taken from a graph). The reason why EC2-draft (1999) is much more conservative than the EC2-2 (1995)/EC2-1 (1991) is the suggested reduction of the design shear strength. This leads to the fact that the trend regarding concrete fatigue goes in a conservative direction. The result presented in this paper indicates instead, that it rather would be possible to allow higher stresses. Keywords: concrete, bridges, strength development, Capo-test, cyclic tensile fatigue test, fatigue, strain criterion, sleepers. - vi -
Sammanfattning Evaluation of Concrete Structures Denna licentiatuppsats består av fyra artiklar, A-D. I artikel A presenteras drag- och tryckhållfasthetsutveckling hos ett antal gamla trågbroar av betong. Undersökningarna visar att tryckhållfastheten till skillnad från draghållfastheten har ökat med 50 till 100% över tiden för dessa trågbroar. När resultat från de utborrade cylindrarna jämfördes för en trågbro, visade det sig att tryckhållfastheten var ca 15% högre i balkarna än i plattan. I undersökningarna har även en relativt känd provningsmetod använts för att undersöka tryckhållfastheten in-situ, det s.k. Capo-testet. Resultat från Capo-testet har jämförts med resultat från de utborrade cylindrarna, vilken är den rekommenderade metoden för att undersöka tryckhållfastheten. Denna studie ger indikationer på att Capo-testet kan användas för gamla konstruktioner men med vissa förbehåll bl.a. vad gäller storleken på ballasten. Resultaten som erhållits på ett av provobjekten, bron över Lautajokki, visar att Capotestet i vissa fall kan ge för höga värden relativt utborrade cylindrar, dvs. på osäker sida. I artikeln presenteras ett nytt samband för att korrelera utdragskraften från Capo-testet mot tryckhållfastheten för gamla konstruktioner. Detta nya samband ger en bättre korrelation gentemot tryckhållfastheten än den generella som tillhandahålls av tillverkaren och den som Rockström & Molin (1989) föreslagit. Vidare studier är dock nödvändiga inom detta område. I artikel B redovisas provning och utvärdering av bärförmågan för uppspruckna respektive ej uppspruckna järnvägssliprar av betong. Uppsprickningen tros bero på s.k. försenad ettringitbildning. De test som utförts är: (1) Böjprov i mittsnitt. (2) Böjprov i rälläge. (3) Dragprov av befästning (horisontalkraftskapacitet). (4) Kontroll av sliprarnas betonghållfasthet. - vii -
Page 1: LICENTIATE THESIS Evaluation of Con
Page 5: Preface This licentiate thesis pres
Page 10 and 11: Evaluation of Concrete Structures I
Page 12 and 13: Evaluation of Concrete Structures 4
Page 14 and 15: A. Simplified check A1. In-situ ins
Page 19 and 20: Evaluation of Concrete Structures G
Page 21 and 22: Lok-Strength & Capo-Strength F [kN]
Page 25 and 26: Evaluation of Concrete Structures a
Page 31 and 32: Evaluation of Concrete Structures t
Page 33: Evaluation of Concrete Structures d
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Page 41: 6 Outlook Evaluation of Concrete St
Page 44 and 45: Evaluation of Concrete Structures E
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
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expected (about 8 MPa). But for the
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Figure 8 shows the location where t
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Tensile strength [MPa] 6.0 5.0 4.0
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Table 4 Mean value and standard dev
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Lok-Strength & Capo-Strength F [kN]
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fcc fct concrete compression streng
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The values that have been used are:
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LOAD CARRYING CAPACITY OF CRACKED C
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Figure 1 Principal drawing of teste
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Class 3. OK / Green: No visible cra
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0.5 1.0 +15 kNm 0.5 0.5 1.0 0.5 -11
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Horizontal force [kN] 100 80 60 40
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TEST SET-UP AND RESULTS Bending cap
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The displacement was measured by fo
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Figure 18 Failure of sleeper no. 10
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Sleeper No. 17 looks more like the
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c2 75 á 100 where ψ ′ c = = = 0
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The obtained stress σ t = 4.45 MPa
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M f,rail moment bearing capacity at
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Paper C CONCRETE FATIGUE CAPACITY.
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FATIGUE OF CONCRETE A common way to
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notch is deep enough that is). When
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Figure 5 Test set-up uniaxial tensi
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Table 1 A summary of all uniaxial t
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Strain [‰] 0.8 0.6 0.4 0.2 0 Phas
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11) the start of phase 3 takes plac
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ACKNOWLEDGEMENTS The study has been
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APPENDIX A Evaluated data from the
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C = dε / dN [× 10 −6 ] 100 10 1
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Test series A: S min = σ min / f c
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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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LICENTIATE THESIS - Luleå tekniska universitet

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