Amirhossein Iranmanesh

Vibration-Based Method and Sensor for Monitoring of Bridge Scour

Scour is the major cause for many bridge failures and damage to piers and abutments. Scour is not easily discernible because it is hidden under the channel flow. Over the years, a number of sensors have been developed for detection of scour depth. Development, testing, and field implementation of a new and simple type of scour sensor is described in this paper. The scour depth detection concept is based on measuring the fundamental frequency of vibration of a rod embedded in the riverbed. The sensor uses a single fiber-optic Bragg grating (FBG) sensor for transduction of the vibration frequency. The inverse relationship between the fundamental frequency and the length of the sensor rod is used for detection of the scour depth. A computational approach is developed based on the Winkler spring reaction soil model for automated calibration of the scour sensor during installation in the riverbed. The scope of the research included development of the theoretical basis for the sensor, establishment of the computational methodology for detection of the riverbed foundation properties, proof-of-concept laboratory tests, small-scale field verification tests, and installation and remote monitoring of scour in a multispan scour critical bridge in Illinois. The results include laboratory test data from the measurements in soil, simulated scour tests in a hydraulic flume, and real-time data from remote monitoring of scour at the bridge site.

Energy-Based Damage Assessment Methodology for Structural Health Monitoring of Modern Reinforced Concrete Bridge Columns

Performance assessment of bridge structures instrumented with structural health monitoring systems requires development of deterministic methodologies producing quantitative information on different damage states. This aim can be achieved through defining engineering limit states that may be expressed by limiting values of quantities such as damage indexes. Displacement-based damage indexes for performance assessment of bridges do not consider the accumulated damage that results from plastic cycling. In more advanced approaches, the parameter that takes into consideration the effect of cyclic loading history and accumulation of damage is the dissipated energy. However, computation of dissipated energy for the purpose of structural health monitoring requires real-time measurement of lateral forces, which is beyond the capability of conventional sensing methodologies. This paper reports on the development of a methodology to evaluate the energy dissipation in reinforced concrete columns with circular cross sections based on the curvatures measured in the plastic hinge area. Integrating the introduced method in a normalized dissipated energy index provides the possibility of detecting and quantifying minor and moderate damage that is barely visible during visual inspection. The scope of the study included the evaluation of the proposed damage assessment method through hybrid simulation tests on 1/10-, 1/8-, and 1/6-scale hybrid models of a two-span bridge subjected to various amplitudes of near source ground motions of the 1994 Northridge earthquake. Fiber-optic sensors were employed for monitoring the deformation response of the columns in the plastic hinge area.