In this study, a corrosion threshold-controllable sensing system of long period fiber gratings (LPFG) is developed and validated for life-cycle monitoring of steel bars in corrosive environments. Three Fe-C coated LPFG sensors with two bare LPFG sensors in LP₀₆ and LP₀₇ modes for strain and temperature compensation were multiplexed and deployed inside three miniature, coaxial steel tubes to measure three (long-term in years) critical mass losses through the penetration of tube walls and their corresponding (short-term in hours) corrosion rates in the life span of steel bars. The strain/temperature and mass loss measurements are based on the changes in grating period and refractive index of surrounding medium, respectively. Thermal/mechanical loading and accelerated corrosion tests were conducted to validate the functionality, sensitivity, accuracy, and robustness of the proposed sensing system. Since both the steel tube and Fe-C layer represent the material composition of steel bars in the context of corrosion, the mass loss correlation among any two of the steel tube, Fe-C layer and steel bar is independent of the test conditions such as the current density and sample length, and thus applicable to engineering practices. The outer tube can notably delay and decelerate the corrosion process of its inner steel tube due to the reduced current effect.

Excessive vibration may cause premature fatigue failure on structural components if it is not properly controlled. One effective way to attenuate vibration is to attach a tuned vibration absorber to the main structural component. Passive tuned vibration absorbers are mainly effective to attenuate vibration at a specific range of frequencies and thus they become infective under varied environmental conditions which can significantly alter the tuning frequencies. The present study aims at development of a wide-bandwidth and light-weight adaptive tuned vibration absorber (ATVA) featuring a magnetorheological elastomer (MRE) which is tuned to absorb the vibrations of a flexible beam. The accelerance transfer function is derived for both beam with and without ATVA. The effectiveness of the ATVA to control vibration of the flexible beam caused by external excitation under wide range of frequencies is demonstrated. The proposed ATVA consists of C-Shape frame with winding coils, two isometric MRE specimens with 40% volume fraction, and active mass. An empirical model for the MRE has been developed through an experimental identification method in order to predict the MRE's elastic modulus under various levels of excitation frequencies and applied magnetic fields. Using MRE models and magneto-circuit analysis, the frequency bandwidth of the ATVA is analytically obtained. The analytical model is then used to develop a multidisciplinary design optimization formulation to minimize the mass and maximize the frequency bandwidth of an ATVA featuring MRE given several geometrical and physical constraints. Finally, a tuning algorithm has been presented to determine the required applied magnetic flux density to the MRE layers based on the identified phase difference between the absolute acceleration of the host and relative acceleration of the host and ATVA's resonator.

In recent decades, researchers have developed many technologies like energy dissipating dampers to improve the response of structures in seismic events but still limitations persist in earthquake-resistant design. Residual drift is still a significant problem encountered while using dampers which results in a reduction in their performance. Many types of dampers have been introduced to localize the damages in a defined section of a structure to prevent structural failure and decrease the repairing cost. However, in general, rehabilitation of a structure using a damper is not an economical option because residual deformation occurs due to limitations of constituent materials of the damper. Therefore, in this paper, a shape memory alloys (SMAs) damper is proposed to mitigate the performance degradation problem caused by residual deformation of a structure and to reduce maintenance and repairing costs. The shape memory alloys can reduce residual deformation at room temperature due to the superelastic effect. In addition, a pretension force was applied to prevent damage by reducing the fastening force of the shape memory alloy bar and to improve the load performance. Finite element analysis was performed to verify the performance of the damper to which the pretension was applied. Furthermore, recentering performance and energy dissipation capacity of the damper were analyzed. The analysis results show that the proposed damper can reduce the residual strain by recentering, as well as improve energy dissipation and ultimate capacity.

Seismic structural health monitoring (SHM) of structures is critical not only to detect earthquakes to send early warning, but also to enable rapid structural condition assessment to ensure safety. Traditional monitoring systems using wired sensors are expensive. Wireless sensors offer tremendous opportunity to reduce costs, which remains elusive for seismic structural monitoring due to two main obstacles. First, there are constraints on power resources. Most wireless sensors are duty-cycled to preserve limited battery power; and hence, can miss an earthquake in power-saving sleep mode. Second, there is a lack of support for rapid post-event data collection and processing. Conventional data transmission after sensing can introduce significant delays, and real-time data acquisition that eliminates these delays has limited throughput. In this paper, an intelligent wireless monitoring system, xShake, is developed for cost-effective real-time seismic SHM. It consists of: 1) energy-efficient wireless sensor prototypes utilizing on-demand sensing technique, 2) live-streaming framework that supports high-throughput real-time data acquisition, and 3) a rapid condition assessment application, enabling real-time data visualization and processing for end users. The performance of the xShake is validated through lab tests, demonstrating that it can capture high-fidelity synchronized data under earthquakes and enable real-time structural condition assessment.

In this project, the hygro-thermo-mechanical bending behavior of perfect and imperfect advanced functionally graded (AFG) ceramic-metal plates is analytically investigated using an integral plate model for the first time. The plate is assumed to be supported by a two-parameter elastic foundation. Because of the technical problems encountered in the manufacture of AFG, porosities and micro-voids can occur in AFG specimens, which can result in reduced density and strength of materials. Thus, due to the presence of porosity, a modified rule of mixture is adopted to predict the material properties of the AFG plates. The governing equations are deduced by adopting the "principle of virtual work" and an integral plate model. The analytical Navier's method is considered to solve the obtained differential equations for simply supported AFG porous plate. The results obtained are checked by comparing them for non-porous and porous AFG plates with those available in the open literature. Finally, this work will help us to design advanced functionally graded materials to ensure better durability and efficiency for hygro-thermal environments.

The goal of this manuscript is to develop a nonclassical size dependent model to study and analyze the dynamic behaviour of the perforated Reddy nanobeam under moving load including the length scale and microstructure effects, that not considered before. The kinematic assumption of the third order shear deformation beam theory in conjunction with modified continuum constitutive equation of nonlocal strain gradient (NLSG) elasticity are proposed to derive the equation of motion of nanobeam included size scale (nonlocal) and microstructure (strain gradient) effects. Mathematical expressions for the equivalent geometrical parameters due to the perforation process of regular squared pattern are developed. Based on the virtual work principle, the governing equations of motion of perforated Reddy nanobeams are derived. Based on Navier's approach, an analytical solution procedure is developed to obtain free and forced vibration response under moving load. The developed methodology is verified and checked with previous works. Impacts of perforation, moving load velocity, microstructure parameter and nonlocal size scale effects on the dynamic and vibration responses of perforated Reddy nanobeam structures have been investigated in a wide context. The obtained results are supportive for the design of MEMS/NEMS structures such as frequency filters, resonators, relay switches, accelerometers, and mass flow sensors, with perforation.

In recent years, bacteria-based self-healing concrete has been widely exploited to improve the compressive strength of concrete using different bacterial species. However, both the identification of the optimal involved reaction parameters and theoretical framework information are still limited. In the present study, both experimentally and numerical modelling using machine learning (ANN and ANFIS) and response surface methodology (RSM) were implemented to evaluate and optimse the evolution of bacterial concrete strength. Therefore, a total of 58 compressive strength tests of the concrete incorporating new bacterial species were designed using different concentrations of urea, cells concentration, calcium, nutrient and time. Based on the results, the compressive strength of the bacterial concrete improved by 16% due to the decrement of the pore percentage in the concrete skin; specifically, 5 mm from the concrete surface, compared to that of the control concrete. In the same context, both machine the learning and RSM models indicated that the optimal range of urea, calcium, nutrient and bacterial cells were (18-23 g/L), (150-350 mM), (1-3 g/L) and 2×10⁷ cells/mL, respectively. Based on the statistical analysis, RMSE, R², MPE, RAE and RRSE were (0.793, 0.785), (0.985, 0.986), (1.508, 1.1), (0.11, 0.09) and (0.121, 0.12) from both the ANN and ANFIS models, respectively, while; the following values (0.839, 0.972, 1.678, 0.131 and 0.165) was obtained from RSM model, respectively. As such, it can be concluded that a high correlation and minimum error were obtained, however, machine learning models provided more accurate results compared to that of the RSM model.

This study proposes a new hybrid method that uses both of post-earthquake reconnaissance data and numerical analysis results based on a finite element (FE) model. As the uncertainty of a capacity threshold for a structural damage state needs to be estimated carefully, in the proposed method, the probabilistic distribution parameters of capacity thresholds are evaluated based on post-earthquake reconnaissance data. Subsequently, the hybrid fragility curves were derived for several damage states using the updated distribution parameters of capacity thresholds. To illustrate the detailed process of the proposed hybrid method, it was applied to piloti-type reinforce concrete (RC) buildings which were affected by the 2017 Pohang earthquake, Korea. In the example, analytical fragility curves were derived first, and then hybrid fragility curves were obtained using the distribution parameters of capacity thresholds which were updated based on actual post-earthquake reconnaissance data about the Pohang city. The results showed that the seismic fragility estimates approached to the empirical failure probability at 0.27 g PGA, corresponding to the ground motion intensity of the Pohang earthquake. To verify the proposed method, hybrid fragility curves were derived with the hypothetical reconnaissance data sets created based on assumed distribution parameters with errors of 10% and 1%. As a result, it was identified that the distribution parameters accurately converged to the assumed parameters and the case of 1% error had better convergence than that of 10% error.

This study proposes a combination of nondestructive testing methods for detecting soil cavities behind retaining walls, which adversely affect the stability of the sloping ground or retaining structures. An experimental study is conducted using a soil chamber filled with dry sands retained by a concrete wall plate. A hemispherical soil cavity is simulated just behind the wall plate, and elastic wave reflections of impacts on the wall are measured using accelerometers. The measured elastic waves are analyzed using the signal energy in time domain and predominant frequency and mobility spectrum in frequency domain. In addition, spatiotemporal changes in the surface of the wall during heating and cooling sequences are monitored using infrared thermography. The captured thermal image is then used for identifying the cavity. Experimental results show that the cavity leads to increases in the signal energy, predominant frequency, and flexibility in the mobility spectrum. The contrasts in the thermal images effectively reveal the shapes and locations of the soil cavity. This study demonstrates that the hybrid testing method that conducts a careful inspection by elastic waves on areas suspected in the preliminary scanning by the infrared thermography can be competitive and effective for detecting soil cavities.

Extensive studies have been performed by researchers to increase the ductility and energy-absorption of concentrically braced frames. One of the most widely used strategies for increasing ductility and energy-absorbing is the utilization of energy-dissipation systems. In this regard, the energy-dissipation system consisting of a steel dual-ring damper (SDRD) with different construction details is presented, to improve hysteresis behavior and performance of steel ring dampers (SRD). The most important cause of energy-dissipation in SRDs are the development of bending plastic hinges in the rings. Therefore, by adding an inner ring to the SDR system, it increases the number of moment plastic hinges and in turn increases energy dissipation. Parametric studies havse been performed applying the nonlinear micro-finite element (MFE) procedure to investigate the improved models. The parametric studies comprise examining the efficacy of thickness parameters and the inner ring diameters of the improved models. The SRD models was selected as the base model for comparing and evaluating the effects of improved dampers. MFE models were then analyzed under cyclic loading and nonlinear static methods. Confirmation of the results of the MFE models were performed against the test results. The results indicated that the diameter to the thickness ratio of inner ring of SDRDs has a considerable influence on determining the hysteresis behavior, ductility, ultimate capacity and performance, as well as energy dissipation. Also, the results show that the details of the construction of the internal and external ring connections were a considerable effect on the performance and hysteresis behavior of SDRDs.