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Progresses in sensor and energy technologies have been an important driving force for the rapid development of these industries and have drawn the attention of researchers on environmental concerns. In particular, carbon nanomaterial (carbon nanotubes, graphene, graphite, etc.)-based composites are widely used for sensor and energy harvesting applications owing to their excellent electrical, thermal, and mechanical properties. In this review, we have discussed various aspects of the use of carbon nanocomposites for the development of sensor and energy harvesting devices. These devices have shown outstanding sensing and energy harvesting performances. Various carbon nanomaterial-based composites with sophisticated structural and material designs have been developed to improve their sensing performance for various applications. We have also reviewed recent technological developments in carbon nanocomposite-based energy generators that adopt thermoelectric and triboelectric working mechanisms. Further research on the development of carbon nanocomposites with enhanced sensing and energy harvesting properties will expand the range of their applications to automotive, aerospace, artificial skin, healthcare, and environmental/infrastructure industries.

In this study, a vibration-based procedure for residual capacity estimation of bridges after damaging earthquake events is proposed. The procedure starts with estimation of collapse capacity of the intact bridge using incremental dynamic analysis (IDA) curves. The collapse capacity is defined as the median intensity level of the earthquakes that cause global or local collapse within the structure. A database of post-earthquake modal properties is created by calculating the analytical modal properties of the bridge after each nonlinear response history analysis performed for generation IDA curves. After the damaging event, experimental modal properties of the bridge are identified from vibration measurements of the bridge. These properties along with the modal properties database are used to find ground motionintensity pairs that can drive nonlinear FE model of the structure to the current damage state of the bridge. The IDA curves corresponding to the damaged FE model of the bridge are subsequently used to estimate amount of loss in collapse capacity of the damaged structure. Estimated loss in capacity of the bridge besides the bridge-site-specific seismic hazard curves are used to update the functionality status of the bridge. Proposed procedure is applied to experimental data from a large-scale shake table test on a quarter-scale model of a short-span reinforced concrete bridge. The bridge was subjected to a series of earthquake ground motions introducing progressive seismic damage to the bridge which finally led to the failure of one of the bents. Residual collapse capacity and functionality status of the bridge are updated at different stages of the experiment using the proposed procedure.

This study investigates the performance of a vibration-based technique for damage assessment of reinforced concrete bridges from non-stationary and incomplete acceleration response measurements during high amplitude earthquakes. The proposed damage assessment technique is targeted to be used in the aftermath of a major earthquake event to rapidly and remotely assess the functionality status of the bridge and identify potential hazards to the public safety. As the first step of the procedure, time-frequency representation of the response of the bridge is achieved by applying stochastic subspace system identification technique to successive and overlapping windows of the response measurements. The timefrequency representation is then used to identify the longest ending segment of the response with relatively stable modal properties. Post-earthquake experimental modal properties of the bridge are subsequently extracted from the identified stable portion of the response. These properties are used to estimate the amount of degradation in stiffness of the structural elements through an optimization-based finite element model updating technique. The Genetic Algorithm optimization technique is used to update the stiffness properties of the structural elements by minimizing the error between analytical and experimental modal properties of the bridge. The proposed damage assessment procedure is applied to experimental data from a large-scale shake table test during which a quarter-scale model of a reinforced concrete bridge was subjected to a series of earthquake and low-amplitude white noise base excitations. The meaningful agreement between the stiffness correction factors identified from both types of motions at the same damage state of the bridge demonstrates that the proposed procedure can effectively be applied for post-earthquake damage assessment of the bridges from nonlinear responses during high amplitude earthquakes.

This paper deals with the realization of finite dimensional, linear, time-invariant models of structural systems in the state space description from the response (output) of the system. The theory and and underlying principles of two stochastic system identification algorithms are first described. The applications of the algorithms to two civil engineering structures follow the theory. Ambient vibration data collected from a building and a bridge, both are permanently instrumented by accelerometer networks, are used to derive the models. The vibration characteristics, i.e., the frequencies, damping ratios, and associated mode shapes, of the structures are then retrieved from the models. The stochastic system identification algorithms prove to be very effective in identifying the vibration characteristics of the structures.

Steel corrosion in concrete is a main cause of deterioration and early failure of concrete structures. A novel integration of electromagnetic heat induction and infrared (IR) thermography is proposed for nondestructive detection of steel corrosion in concrete, by taking advantage of the difference in thermal characteristics of corroded and non-corroded steel. This paper focuses on experimental investigation of the concept. An inductive heater is developed to remotely heat the steel rebar from concrete surface, which is integrated with an IR camera. Bare rebar and concrete samples with different cover depths are prepared. Each concrete sample is embedded with a single steel rebar in the middle, resulting an identical cover depth from the front and the back surfaces, which enables heat induction from one surface and IR thermogrphay from the other simultaneously. The impressed current method is adopted to induce accelerated corrosion on the rebar. IR video images are recorded during both heating and cooling periods. The test results demonstrate a clear difference in thermal characteristics between corroded and non-corroded samples. The corroded samples show higher rates of heating and cooling as well as a higher peak IR intensity than those of the non-corroded samples. This study demonstrates a potential for nondestructive detection of rebar corrosion in concrete.

This paper reports the development of and an experimental study on an optical fiber sensor for monitoring civil infrastructure systems. This optical sensor employs a vibrating wire whose tension can be modulated by external force, strain, or vibration and transformed into the change of frequency of wire vibration. The frequency of wire is detected by light sent to and reflected from the wire through an optical fiber cable. Compared to other optical fiber sensors developed so far, the proposed sensor has two significant advantages: one is that the sensing head is a vibrating wire (rather than an optical fiber), which can sense a specific physical quantity without being inter fered by miscellaneous effects; the other is that the wire vibration is a well understood and reliable physical phenomenon and its frequency is optically measured and transmitted without attenuation or distortion through the optical fiber to recording and other devices. These advantages make the sensor extremely simple, reliable and robust, and hence more readily deployable in civil infrastructure ap plications. Three prototypes have been developed and their static and dynamic characteristics have been experimentally tested. One of the prototypes was embedded into a concrete specimen to measure its strain and the result agrees with that from a conventional strain gauge. The experimental study with prototypes demonstrates the high performance of the developed optical sensor in terms of accuracy, high frequency range, and other characteristics.

This paper presents the results of an experimental study on an innovative electro-optical fiber sensor developed for measuring the dynamic response of civil structures such as buildings and bridges, which can be used for non-destructive evaluation of structural systems. This electro-optical sensor employs an electric circuit, LC oscillator, in which inductance and capacitance are connected in parallel. The resonant frequency of the LC oscillator is modulated by the external displacement transmitted through the core of the induction solenoid. This frequency is detected from the optically-transmitted oscillatory signal and the LC oscillator is optically powered. Compared to the conventional optical fiber sensors developed so far, the proposed sensor has two significant advantages: 1) the sensing head is an electric circuit (rather than an optical fiber cable), which can sense a specific physical quantity without interference from miscellaneous effects and is expected to be much more durable than the sensing head made of optical fiber cable as seen in usual extrinsic optical fiber sensors; 2) the LC oscillator is a well understood and reliable circuit with its resonant frequency measurable and transmittable without attenuation or distortion through an optical fiber cable over a long distance to recording and other devices. These advantages make the sensor extremely simple to design and manufacture, durable, reliable, robust to use, and hence, more readily deployable in civil structural applications. A prototype electro-optical strain sensor has been developed and its static and dynamic characteristics were experimentally tested. This sensor was also installed on a steel frame to measure the dynamic strain response when subjected to seismic ground motions during a shaking table test. The experimental study using the prototype demonstrated excellent performance of the electro-optical sensor in terms of accuracy, wide frequency range, and other advantageous characteristics for civil structural applications.