Inspection and dynamic measurement of the Pilot-Study Bridge of the Long-Term Bridge Performance Program in New Jersey Tomonori Nagayama Assistant professor the department of Civil Engineering University of Tokyo

Univ of Tokyo Involvement (April 19-21, 2010) 1.Visual Inspection following Japanese Bridge Inspection Standard 2.Three days of a dynamic measurement campaign using dense wireless sensors and wired accelerometers.

Inspected spans A1A2 B1B2 Four spans were inspected by Mr. Haneoka for three days. Identified damages are evaluated one by one. No overall rating (health index) for the bridge nor substructures are provided in inspection. Some owners have their own ways of rating for asset management. (ex. 100 % – Σ damage i ) evaluation A Damage is not confirmed or little, Repair is not needed. B Repair may be needed depending on the situation. C Repair is needed immediately. E1 Emergency response is needed for the safety. E2 Emergency response is needed for other reasons. M Improvement is needed through maintenance work. S Detailed investigation is needed. Countermeasure assessmentClassification for each damage

Major findings from the inspection 1  Fatigue cracks at the gusset plates connecting the main beam and lower lateral bracing cut New connection Recommendation Stop-holes and bolts already stop the cracks, but potentially dangerous. Reduction of the stress concentration at all the gussets plates is recommended.

Major findings from the inspection 2,3  Two bolts connecting an intermediate bracing are lost. The other one is likely loose. New bolts need to be installed.  Bearing shoe stopper is cut or deformed B1 Lost bolts Loose bolt? 2 bolts are lost A1 B1 Cut Deformed Stopper ΔＬ ΔＬ Cut Deforme d

 Anchor bolts of bearing shoes are loose, or short.  A part of P2 concrete pier cap is degraded (cracks, missing concrete) Major findings from the inspection 4,5 Short bolts A2 B2 Lose bolt, deformed bottom flange Loose bolts Deformed flange

Possible fatigue crack locations All the assessed damages are written down on the drawing and listed in summary table formats. Visual Inspection report practice: summary figure (span A1)

The detailed description follows

Other points  The inspection cost is $50,000 for the eight spans. $18,000 is personnel cost for inspection. $23,000 is personnel cost for the other tasks (preparation, report, etc.).  For damages judged as “C” (and sometimes “B”), further investigation and repair work planning (may include health index evaluation) are ordered. Damages evaluated as “A” are referred to at the next inspection. “E1”, and “E2” need repair work immediately.  It is possible to provide “health index” for each substructure, but it is not a part of common bridge inspection practices in Japan. Based on inspection results, owners may rank each substructure for asset management.

4000 pix 100 millon pix 460 MB/TIF 1pix=1mm 0.5mm crack can be identified. Inspection by image processing techniques (demonstration) Width legend －－： <0.5mm ， －－： 0.5mm ～ 0.7mm ， －－： >0.7mm Mr. Sugimoto applied image processing techniques to assess the substructure condition.

0.2mm 1.4mm 1.6mm 800mm Crack on the abutment A1; Photos taken 22 meters away; The resolution can be as good as 0.1mm/pix if appropriately prepared.

Automatic crack detection About 70 % of the cracks are identified Mr. Sugimoto’s overall impression about the bridge: “Very good condition” as compared to bridges in Japan.

Dynamic Measurement Campaigns  Wireless sensors, Imote2s, were employed on the two outer spans (A1,B1 and A4, B4). (41 nodes = 123 channels at a time)  Wired accelerometers were employed on the two inner-spans (A2, B2, A4, and B4) ( A1A2 B1B2 A4 B4

Findings: motions below and above bearings MoveFix Longitudinal direction -> fix Longitudinal direction -> move Longitudinal direction -> fix A little different “Move” condition is not always satisfied. Fix is not necessarily satisfied either. Depends on the direction. Direct relationship with the inspection results has yet to be found.

Finding: acceleration amplitude distribution among girders A1 B1 A1 B1 Lateral vibration: large at outer girders Vertical vibrations: similar among girders -> Emphasis on the fatigue cracks corresponding to the lateral motions Malfunctioning sensor Lateral acceleration Vertical acceleration

Findings: global motion Acceleration power spectral density Freq(Hz) Freq =2.81 Hz Freq =14.5 Hz 9 modes were identified. Some nodes giving noisy data could have distorted the estimated mode shapes Mode shape of Span A1

Conclusion  Major findings from the visual inspection are the fatigue cracks, gusset plate bolts, bearing stoppers and bolts, and the concrete pier cap.  Image processing has been demonstrated for concrete crack detection.  Vibration measurement revealed that the motion of bearings are not necessarily the same as the design conditions. Vibration modes are also identified. The insufficient quality of the data limits the analysis of the data.