106_10431 Mai SAKAI

Supervisor : Prof. Junichiro NIWA

Fundamental Study on Mechanical Behavior and Repairing Method of Corroded RC Beams Including Anchorage Damage

2Backgrounds

Repairing

Steel corrosion is one of the significant problems of RC structures.Corroded RC

There are few studies on repaired RC beams.

Previous research• If the span of RC beam is corroded…• Shear capacity increases because tied-arch

action is formed.

Anchorage corrosion is not considered, even though anchorage is corroded in the real structures.

spananchorage

Issues of previous research

Anchorage corrosion

3Objectives and Flow of the Experiment

To investigate the mechanical behavior of corroded RC beams including anchorage damageTo examine the effect of repairing method of corroded

RC beams

Objectives

Series 1: Corroded RC beams Series 2: Repaired RC beams

Corrosion tests: 5 specimens

Repairing

Loading tests: 3 repaired beamsLoading tests: 2 corroded beams

Cast RCbeams 200

150

155

Unit: mmanchorage

425D6D16

1000(span)anchorage

150

4Corrosion Test and Repairing Method

② Remove the rust

① Remove the concrete in the corroded area

④ Back-fill mortar

Stainless steel plate

Specimen

NaCl aqua

Electric corrosion test

Corroded steel No corrosion

Formwork

Back-filling

Area loss of tensile rebar:5 and 10%

③ Un-bond processto cut the bond of tensile rebar and mortar in the span

Patch repair

Corrosion product

Vinyl tape

Clay

Corroded area

5

0

40

80

120

0 1 2 3 4 5 6 7 8

Series 1: Corroded RC Beams

Anchorage failureCA5

Cracks occurred in the corrosion testCracks occurred in the loading test

Failure mode was changed from shear failure to anchorage and flexural failure.

Tied-arch action was formed even though anchorage was corroded.

Experimental cases

Flexural failureCA10

0105Area loss(%)NCA10CA5Name Shear failureN

Displacement (mm)

Load (kN)

CA5CA10

N

Diagonal crack occurred.

Increase

6

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8Displacement (mm)

Load (kN)Series 2: Repaired RC Beams

①CA5-NNnormal mortar

③CA5-UHhigh strength mortar

un-bond process

②CA5-UN

un-bond processnormal mortar

3types of repairing

Area loss: 5%

By using high strength mortar with un-bond process, load carrying capacity considerably increased.

N

Not corroded

High strength mortar & un-bond

Normal mortar& un-bond

Normal mortar

Experimental Cases

①CA5-NN

③CA5-UH

②CA5-UN

Increase

• In RC beams using normal mortar, load carrying capacity did not increase comparing to the non-corroded RC beam.

7Evaluation Method of Tied-Arch Action

To calculate jd from strain distribution

Shear carrying mechanism

jd2jd1T1 T2

jd2jd1 T1 T2

Beam Action Tied-arch Action

M ＝ T・(jd)

T: tensile force, jd: length of moment arm

To measure strains

+

V ＝ dM ＝ ⊿T ・jd + T・⊿jddMdx ⊿x

⊿T ⊿jd⊿xBeam Tied-arch

Δx

Concrete gaugeTensile rebar strain gauge

Shear force is divided into beam and tied-arch action.

ΔT=T2-T1

T = (T1 + T2 )/2jd = (jd1 + jd2 )/2Δjd=jd2 - jd1

To obtain these values To substitute to…

⊿jd= 0⊿x

⊿T = 0⊿x

jd1 jd2

T1 T2

146.9 644.7

8Evaluation of Tied-Arch Action

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, tied-arch action is dominant from early phase of the loading.

CA5-UN

Total shear force (kN)

without un-bond processCA5-NN with un-bond process

Total shear force (kN)

Shear resistance (kN)Shear resistance (kN)

0

10

20

30

40

0 10 20 30 40

tied-arch

beam

Diagonal crack

occurred.

0

10

20

30

40

0 10 20 30 40

tied-archbeam

obtained by the calculation

obtained from the experiment

9Conclusions

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 beamsconsiderably 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.