Long-term monitoring of US202-NJ23 Bridge (Wayne, NJ)

Branko Glisic1, Daniele Inaudi2, Dorotea Sigurdardottir1

1Princeton University, Princeton, NJ, USA2SMARTEC SA (Roctest Group), Switzerland

IBS Workshop at CAIT

14-15 June 2011, Rutgers University, NJ, USA

Outline

• Introduction

• Aims

• Monitoring system

• Installation

• Preliminary results

• Acknowledgements

Introduction• SHM has potential to improve bridge safety and

management

• Although it is frequently applied to “signature” structures, SHM can truly be declared as “useful” if its utility is proven on “ordinary” (typical) structures

• Nevertheless, SHM is scarcely applied to typical structures due to several reasons among which are ease of use of data and the cost

• US202-NJ23 Bridge close to Wayne, NJ, is a good example of typical structure and excellent opportunity to test utility of SHM applied to typical structures

Aims of SHM• To deploy affordable SHM system

• To register structural behavior of bridge girders over long term and perform structural identification based on periodic dynamic measurements

• To identify unusual behaviors related to monitored parameters: average strain, average curvature, natural frequency, and evaluate concrete-steel interaction

• To evaluate suitability of employed monitoring system for achieving above aims in terms of measurement performance and longevity

• To estimate value of information and evaluate long-term costs and benefits of monitoring

Fiber Bragg Grating (FBG) Sensors

The reflected wavelength depends on the strain and temperature of the fiber: l1=Ce·De+CT·DT+l1,0

~ 10 mm

• FBG = periodic refractive index perturbation generated in the core• Strain and temperature in fiber change the back-reflected WL

l1(De1 ,DT1)

l1(De1 ,DT1)

l2(De2,DT2)

l2(De2 ,DT2)

Multiple FBG can be inscri-bed over the same fiber

Position of sensors

• Pairs of parallel sensors were installed in girders #2 and #5 of the southbound part of the bridge

• Positions of the sensors were adjusted to the site conditions

Summary of instrumentation • Reading unit:

– Dyn.: 250 Hz (1 kHz), 4 me, 1°C– Static: 0.4 me, 0.1°C– 12 (of 16) channels

• Girder #2: – Gauge length at quarter span = 1m– Gauge length at mid span = 2m– 6 strain + 6 temperature sensors

• Girder #5: – Gauge length at quarter span = 2m– Gauge length at mid span = 2m– 12 strain + 12 temperature sensors

Installation• Using L-brackets, by gluing

Installation, continued

Examples of results• Average strain generated by traffic has been

measured and several “events” were registered

• The following parameters will be calculated:

– average curvature

– position of center of gravity (concrete-steel interaction)

– natural frequency

– thermal expansion

– correlation in behavior of two girders

• These parameters will be observed in long term

Examples of results

Acknowledgements• Drexel University, in particular Prof. Emin Aktan, Prof.

Frank Moon, and graduate student Jeff Weidner for opportunity to participate in the project, organization, and help during the installation

• LTBP Program, NJDOT, and CAIT for opportunity to participate in the project

• IBS partners for comprehension in sharing the lifts during the installation

• Kevin for help in operating the lifts

• Yao Yao, graduate student of Princeton University for availability and help in installation of sensors