PSI - Issue 5

Takahide Sakagami et al. / Procedia Structural Integrity 5 (2017) 1370–1376 Takahide Sakagami / Structural Integrity Procedia 00 (2017) 000 – 000

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Objective member for evaluating stress severity reduction after the repair work was the vertical stiffener as shown in Fig. 5. A fatigue crack was detected at the upper weld part of the vertical stiffener. The employed repair method was the stiffening-plate method; illustration of the method was shown in Fig. 5. In this repair method, four angle stiffener plates were fastened to the vertical stiffeners and the lower cross beam flange using fastening bolts. The stress distribution on the vertical stiffener was measured before and after the repair. After the repair, the fatigue crack itself was left as it was. The objective structure was loaded with a vehicle (total vehicle load: 214 kN) driving on the traffic lane of the bridge at a constant speed of 80 kilometers an hour. A sprinkler truck with three axles was employed as a loading vehicle. The thermoelastic stress measurement was conducted using an infrared camera with a QVGA InSb array detector. From the temperature change observed by the infrared camera, the change in the sum of the principal stresses was calculated using Eq. (1) and material properties of the structural steel (JIS SS400). In this study the obtained sequential infrared data were processed using the self-reference lock-in technique developed by Sakagami et al. (2005) to obtain S/N improved stress distribution images.

-186MPa

(a) Stress distribution before repair

-137MPa

(b) Stress distribution after repair Fig. 6 Results of the thermoelastic stress distribution measurement before and after stiffening-plate repair.

Fig. 7 Stress reduction after stiffening-plate repair.