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Workshop on Cracking and Durability of Reinforced Concrete

Workshop on Cracking and Durability of Reinforced Concrete. Concerning the Serviceability Limit State. Starting points of structural analysis. Analysis in ULS and SLS: - main concern  safety; - durability of minor concern. According to code VBB 1995: - dead weight  = 1,5;

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Workshop on Cracking and Durability of Reinforced Concrete

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  1. Workshop on Cracking and Durability of Reinforced Concrete Concerning the Serviceability Limit State J.M. Zwarthoed

  2. J.M. Zwarthoed Starting points of structural analysis • Analysis in ULS and SLS: - main concern  safety; - durability of minor concern. • According to code VBB 1995: - dead weight  = 1,5; - traffic loading  = 1,5. • According to code NAD ENV 1991-3: - dead weight  = 1,35; - traffic loading  = 1,42; - with the actual traffic lane subdivision; - with reduction of structure service life.

  3. J.M. Zwarthoed Requirements SLS - NEN 6720 • For all structures important  crack width! • Maximum permissible crack width depends on environmental exposure conditions: - humid (outside): wmax = 0,3 mm; - aggressive (outside&salt): wmax = 0,2 mm; - in case of pre-stressing: wmax = 0,1 mm.

  4. J.M. Zwarthoed Possible locations with regard to exceeding maximum crack width (1) 3 1 2 4

  5. J.M. Zwarthoed Possible locations with regard to exceeding maximum crack width (2) 7 8 5 9 10 6 11 12 13

  6. J.M. Zwarthoed Analyses crack width calculations reinforced concrete slab • five different calculation methods • concrete slab: K300 (C20/B25), CEM I • rebars: 16-200 QR40 fs = 329 N/mm2 (FeB 400) hot rolled steel • cracked section • crack width during and after completion of crack development phase

  7. J.M. Zwarthoed Comparison result calculations appr. region of steelstresses SLS

  8. J.M. Zwarthoed Crack width calculation pre-stressed concrete slab • concrete bridge deck: B37,5 (C30/37) CEM I • rebars: 12-250 FeB 400 hot rolled steek • pre-stressing: 35·1182 mm2 FeP 1860 • Md/Mu = 21988/23145= 0,95 [kNm/kNm] • Mrep = 14659 kNm

  9. J.M. Zwarthoed Result calculations • bridge deck meets all requirements ULS except fatigue, meets none with regard to SLS • assumption: no imposed deformations • during stage of development crack pattern wmax = 0,4 mm • in case of fully developed crack pattern wmax = 0,32 mm

  10. J.M. Zwarthoed Conclusions (1) The first main problem is: • insufficient transversal rebar reinforcement in decks causing cracks according to model 1, 2, 5 and 13 with wmax  0,2-0,4 mm.

  11. J.M. Zwarthoed Conclusions (2) The second main problem is: • insufficient longitudinal rebar reinforcement in combination with main pre-stressing reinforcement causing cracks according to model 6, and 7 with wmax  0,5 mm; • insufficient longitudinal rebar reinforcement causing cracks according to model 11 and 12 with wmax  0,2-0,4 mm.

  12. J.M. Zwarthoed Note! One has to keep in mind the following aspects: • We assume the calculated crack width according to NEN 3880 as an upper limit. • Calculations bases on the 28th-day concrete strength. • Did the actual SLS loading occur?

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