Behavior of Concrete Beams Strengthened with Near surface mounted reinforcement, NSMR

Transcription

1 Behavior of Concrete Beams Strengthened with Near surface mounted reinforcement, NSMR - and -Live loading during the strengthening process Prof. Dr. Björn Täljsten Luleå University of Technology SWEDEN 1

2 Agenda, NSMR Curing with live loading Further work s 2

3 Near Surface Mounted Reinforcement Reinforcement is placed in cut grooves in the concrete cover Anchorage Execution Quality Plate bonding NSMR Durability 3

4 Impacts 4

5 Anchorage 5

6 Anchorage NSMR offers a better anchorage compared to Plate bonding 6

7 Anchorage 7

8 Laboratory tests 8

9

10 LVDT SG on concrete LVDT LVDT SG on steel x SG on laminate / rod : Reference beam One or two rods 3.2 and 4 m long rods Epoxy or cement as bonding agent High Strength or High Modulus fibres 10

11 Strengthening system BPE Systems AB Bonding Agent Rods BPE 465 BPE NSMRS BPE Crete BPE NSMRQS 11

12 Load [kn] BM4-cem BM3-cem Reference BS4-cem BS4 BS3-cem BS4-single Deflection [mm] 12

13 57 % increase of ultimate load, one HS rod % increase of ultimate load, two HS rods % increase of ultimate load, two HM rods 30 % increase of load for yielding of steel, one HS rod 60 % increase of load for yielding of steel, two HS rods 91 % increase of load for yielding of steel, two HM rods Cementitious bonding agent works for this type of strengthening 13

14 Real structures are often in environments a lot different from laboratory conditions 14

15 Specimens strengthened in normal laboratory conditions Placed in climate chamber at 28 ºC Tests performed at 28 ºC ( 19 ºF) Cubes tested at both 25 ºC and 28 ºC 4 m beams loaded in four-point bending 3.2 m NSMR rods Epoxy or cementitious adhesive 15

16 Load [kn] Reference Deformation [mm] BS-cold BS-cem-cold BS-stat Ref-cold Tests performed at 28 ºC 16

17 Curing with live load Laminate/Rod Laminate/Rod mm mm 17

18 Curing with live load Load [kn] % 49 % Yielding of control beam 40 kn (8 6 mm deflection) every 108 s during curing of the adhesive 0 7 % 0 5 Time [s] 18

19 Curing with live load Strain [10-6] Steel strain Fiber strain Mid-point deformation Mid point deflection [mm] Time [h] 19

20 Curing with live load Load [kn] Reference BM-dyn BM-stat BS-dyn BS-stat The strengthening effect remains Deformation [mm] 20

21 Curing with live load 200 Load [kn] Reference BS-dyn BScem-stat BScem-dyn Cementitious bonding agent do not work Deformation [mm] 21

22 Theory Stresses and strains h h d d A' A' s s b b d' d' s s x x εs εs s s ε ε ε ε εs0 ε c0 c0 s0 εcε c ε c ε c F' F' s s F F c c M A A s s F F s s A A f f b b f f εf ε f Live Live Load Load ε ε u0 u0 F F f f Depending on failure mode: M = A ' s f ' y ( ) 0.4x d + A f ( d 0.4x) + ε E A ( h 0.4x) ' s s y s f f f 22

23 Further work Prestressing Ancorage 23

24 s Testlab at Luleå University of Technology Håkan Nordin, Arvid Hejll, Otto Norling, Mattias Clarin Prof. Thomas Olofsson and Prof. Lennart Elfgren 24