Fundamental Study on Mechanical Behavior and Repairing Method of Corroded RC Beams Including Anchorage Damage 06_10431 Mai SAKAI 1 Supervisor : Prof. Junichiro NIWA
Backgrounds Steel corrosion is one of the significant problems of RC structures. Previous research If the span of RC beam is corroded Shear capacity increases because tied-arch action is formed. Corroded RC Anchorage corrosion 2 anchorage span Issues of previous research Anchorage corrosion is not considered, even though anchorage is corroded in the real structures. There are few studies on repaired RC beams. Repairing
Objectives and Flow of the Experiment 3 Objectives To investigate the mechanical behavior of corroded RC beams including anchorage damage To examine the effect of repairing method of corroded RC beams Series 1: Corroded RC beams Series 2: Repaired RC beams Cast RC beams 425 150 D6 D16 155 200 anchorage 1000(span) 150 anchorage Unit: mm Corrosion tests: 5 specimens Repairing Loading tests: 2 corroded beams Loading tests: 3 repaired beams
Corrosion Test and Repairing Method Electric corrosion test NaCl aqua Specimen 1 Remove the concrete in the corroded area 2 Remove the rust Patch repair Corroded steel No corrosion 4 Stainless steel plate Corrosion product Corroded area Area loss of tensile rebar: 5 and 10% 3 Un-bond process to cut the bond of tensile rebar and mortar in the span 4 Back-fill mortar Formwork Clay Vinyl tape Back-filling
Series 1: Corroded RC Beams Experimental cases Name CA5 Area loss(%) 5 Load (kn) 120 80 Increase CA10 N 10 0 CA5 CA10 N Shear failure Anchorage failure CA5 5 40 N CA10 Flexural failure Diagonal crack occurred. 0 0 1 2 3 4 5 6 7 8 Displacement (mm) Tied-arch action was formed even though anchorage was corroded. Cracks occurred in the corrosion test Cracks occurred in the loading test Failure mode was changed from shear failure to anchorage and flexural failure.
Series 2: Repaired RC Beams Experimental Cases 3types of repairing Area loss: 5% 1CA5-NN 2CA5-UN normal mortar normal mortar un-bond process 3CA5-UH high strength mortar un-bond process 120 100 80 60 40 20 0 Load (kn) Not corroded Normal mortar 2CA5-UN & un-bond 0 1 2 3 4 5 6 7 8 Displacement (mm) By using high strength mortar with un-bond process, load carrying capacity considerably increased. N 6 High strength mortar & un-bond 3CA5-UH Increase Normal mortar 1CA5-NN In RC beams using normal mortar, load carrying capacity did not increase comparing to the noncorroded RC beam.
Evaluation Method of Tied-Arch Action Shear carrying mechanism Beam Action T: tensile force, jd: length of moment arm Tied-arch Action 7 jd = 0 x T jd 1 jd 2 + = 0 x jd 2 T 1 T jd 1 2 T 1 T 2 M = T (jd) dm T jd V = dm = T jd + T jd dx x Beam x To measure strains Tied-arch Shear force is divided into beam and tied-arch action. To obtain these values ΔT=T 2 -T 1 To substitute to Δjd=jd 2 -jd 1 jd = (jd 1 + jd 2 )/2 T = (T 1 + T 2 )/2 To calculate jd from strain distribution 146.9 644.7 Concrete gauge Tensile rebar strain gauge Δx jd 1 jd 2 T 1 T 2
Evaluation of Tied-Arch Action CA5-NN without un-bond process Shear resistance (kn) 40 Diagonal 30 crack occurred. 20 obtained by the calculation CA5-UN with un-bond process Shear resistance (kn) 40 30 20 beam 8 10 beam tied-arch 0 0 10 20 30 40 Total shear force (kn) obtained from the experiment 10 tied-arch 0 0 10 20 30 40 Total shear force (kn) In the case of the specimen without un-bond process, beam action is dominant at the beginning, but changed to tied-arch action after the diagonal crack occurred. In the case of the specimens with un-bond process, tiedarch action is dominant from early phase of the loading.
Conclusions 9 1. Even though anchorage of RC beams were corroded, tied-arch action was formed. However, failure mode changed from shear failure to flexure and anchorage failure. 2. Load carrying capacity of repaired RC beams considerably increased by using high strength mortar with un-bond process. 3. The contribution of tied arch action of repaired RC beams could be quantitatively evaluated.