Rola L. Idriss

Multiplexed Bragg grating optical fiber sensors for damage evaluation in highway bridges

A multiplexed Bragg grating optical fiber monitoring system is designed and integrated at the construction stage in an experimental full scale laboratory bridge. The test bridge is a 40 ft span non-composite steel girder concrete deck bridge. The network of sensors is used to measure the strain throughout the bridge, with sensors bonded to the tension steel in the slab and attached to the bottom flange of the girders. Resistive strain gages and Bragg grating sensors are placed side by side to compare results. The strain data are obtained for the pristine structure, then damage is introduced at midspan for an exterior girder. Several levels of damage in the form of cuts in one of the girders are imposed with the final cut resulting in a half depth fracture of the girder. The load path in the structure is obtained using the built in sensor system.

High-sensor-count Bragg grating instrumentation system for large-scale structural monitoring applications

We describe an instrumentation system which provides the capability to monitor a large number of Bragg gratings using a common source and a scanning narrowband filter. The system described has the capability to monitor 12 FBG sensors along each of 5 fibers for a total of 60 sensor elements. We demonstrate the use of this system to address multiple sensors embedded in and attached to a quarter scale bridge span.

Dynamic strain monitoring of an in-use interstate bridge using fiber Bragg grating sensors

We describe the monitoring of the dynamic strain response of an in-service I-10 interstate bridge due to traffic loading. FBG sensors were attached to the center support girder of one span of the structure. Using a fiber Bragg grating interrogation system based on a wavelength division multiplexer, the sensors were monitored for various vehicle loading conditions.

Effects of Steam Curing Temperature on Early Prestress Losses in High-Performance Concrete Beams

Accurate prediction of prestress losses is a very important step in the design of a highly stressed high-performance concrete (HPC) girder and can affect the service behavior of the girder, such as deflections, camber, and cracking. Current methods for calculating prestress losses according to AASHTO and the Prestressed Concrete Institute were developed for conventional concrete. Further research is needed to determine if the current empirical equations provide an accurate estimate of prestress losses for an HPC girder. Actual prestress losses in HPC girders need to be measured and compared with the predicted losses by use of these equations. The higher the prestressing force in the girder, the larger the concrete compressive strength that is needed at the time of release of the prestressing strands. To help achieve the higher release strength, the precast plants have been using longer curing times. Many precast plants are using steam curing to increase the curing rate. A better understanding of the effects of this heating on HPC is needed. An optical fiber monitoring system was designed and built into a three-span HPC highway bridge. The Rio Puerco Bridge, located 15 miles west of Albuquerque, New Mexico, is the first bridge to be built with HPC in New Mexico. The bridge has three spans each with a length of 29 to 30 m. It is designed to be simply supported for dead load and continuous for live load. HPC was used for the cast-in-place concrete deck and the prestressed concrete beams. A total of 40 long-gauge (2-m-long) deformation sensors, along with thermocouples, were installed in parallel pairs at the top and bottom flanges of the girders. The embedded sensors measured temperature and deformations at the supports, at the quarter spans, and at midspan. Measurements were collected during beam fabrication (casting of the beams, steam curing, strand release, and storage), bridge construction, and servicing. The data collected were analyzed to calculate the prestress losses in the girders, to compare the losses with the predicted losses by available code methods, and to get a better understanding of the properties and behavior of HPC.

Integrated sensing system for highway bridge monitoring

An integrated optical fiber sensor system is being developed for highway bridge monitoring. Laboratory small and large scale testing were performed to explore the feasibility of the system. Large scale reinforced concrete beams were fabricated in the laboratory, and artificial flaws in terms of delaminations were simulated in the beams during construction. The sensing system was used to evaluate the effect of these damages on the behavior of the beams.

Damage assessment of a full-scale bridge using an optical fiber monitoring system

A network of distributed optical Bragg grating sensors is used for monitoring of a full scale laboratory bridge in its pristine and damaged state. Damages consist of a series of cuts that are introduced in an external girder to simulate fracture or fatigue crack of a main load carrying bridge component. The after fracture behavior is described in terms of load path redistribution and strain level changes in the structure.

Fiber Optic Sensor System for Bridge Monitoring with Both Static Load and Dynamic Modal Sensing Capabilities

We describe a fiber optic Bragg grating distributed strain sensor system for large scale structural monitoring applications, such as bridge monitoring. The system is capable of assessing both long term static structural loading changes and dynamic/modal behavior of the structure using two different optical interrogation schemes to address the same sensor array. The system has been used to monitor over 45 sensors attached to or embedded in a single-lane bridge span, for damage assessment.

In-Service Shear and Moment Girder Distribution Factors in Simple-Span Prestressed Concrete Girder Bridge: Measured with Built-in Optical Fiber Sensor System

An optical fiber monitoring system was designed and built into the I-25 bridge at the Dona Ana exit in Las Cruces, New Mexico. The bridge is a simple-span, high-performance prestressed concrete girder bridge. The girders are six BT-63 high-performance-concrete girders with a span length of 112.5 ft (34.2 m). Fiber Bragg grating optical fiber deformation sensors along with thermocouples were embedded in the girders during fabrication. Sensors were installed along the top and bottom flanges and at midspan and quarter spans. Pairs of crossed sensors in a rosette configuration were embedded in the webs at the supports. The bridge was monitored for 2 years, from transfer of the prestressing force through service. The sensor data were analyzed to evaluate shear and moment girder distribution factors, in situ material properties, pre-stress losses, camber, dynamic load allowance, and bridge performance under traffic loads. This study focuses on the lateral load distribution in the bridge. Shear and moment girder distribution factors are obtained from a finite element model, sensor measurements under a live load test, as well as regular traffic loading and compared with the values specified by the AASHTO standard specifications (2002) and the AASHTO load and resistance factor design specifications (2007).