Here the Rayleigh - Ritz method has been applied to derive the shell vibration frequency equation. This equation has been formed as an eigenvalue problem form. MATLAB software package has been utilized for extracting shell frequency spectra. Nature of materials used for construction of cylindrical shells also has visible impact on shell vibration characteristics. For isotropic materials, the physical properties are same everywhere, the laminated and functionally graded materials vary from point to point. Here the shell material has been taken as functionally graded material. Moreover, the impact of ring supports around the shell circumferential has been examined for the various positions along the shell axial length. These shells are stiffened by rings in the tangential direction. These ring supports are located at various positions along the axial direction round the shell circumferential direction. These variations have been plotted against the locations of ring supports for three values of exponents of volume fraction law. For three conditions, frequency variations show different behavior with these values of exponent law. The influence of the positions of ring supports for simply supported end conditions is very visible. The frequency first increases and gain maximum value in the midway of the shell length and then lowers down. The comparisons of frequencies have been made for efficiency and robustness for the present numerical procedure.

Due to the benefits of the early prediction of concrete slump, introducing an efficient model for this purpose is of great importance. Considering this motivation, four strong metaheuristic algorithms, namely electromagnetic field optimization (EFO), water cycle algorithm (WCA), teaching-learning-based optimization (TLBO), and multi-tracker optimization algorithm (MTOA) are used to supervise a neural predictive system in analyzing the slump pattern. This supervision protects the network against computational issues like pre-mature convergence. The overall results (e.g., Pearson correlation indicator larger than 0.839 and 0.807 for the training and testing data, respectively) revealed the competency of the proposed models. However, investigating the rankings of the models pointed out the superiority of the WCA (MAE_train = 3.3080 vs. 3.7821, 3.5782, and 3.6851; and MAE_test = 3.8443 vs. 4.0326, 4.1417, and 4.0871 obtained for the EFO, TLBO, and MTOA, respectively). Moreover, the high efficiency of the EFO in terms of model complexity and convergence rate, as well as the adequate accuracy of prediction, demonstrated the suitability of the corresponding ensemble. Therefore, the neural systems trained by these two algorithms (i.e., the WCA and EFO) are efficient slump evaluative models and can give an optimal design of the concrete mixture for any desirable slump.

This paper presents crack opening phenomenon evaluation using digital image correlation (DIC) with a statistically optimized subset size. In conventional DIC analysis, the subset sizes varying from several pixels to more than hundred pixels have been often selected by experts' subjective judgement based on conventional subset size determination algorithms. Since these conventional subset size determination algorithms, however, calculate speckle pattern features at a certain location of a single target image, it is difficult to consider not only all speckle pattern features within region of interest (ROI) but also the random measurement noises during the digital image acquisition process. To overcome the technical limitation, a statistical optimization algorithm of the subset size, which calculates the optimal subset size by the 3-loop iteration of normalized cross correlation within the entire ROI, is newly proposed. In addition, the optimal subset-based DIC analysis is applied to crack opening phenomenon evaluation in a mock-up concrete specimen under step loading conditions. The validation test results show 3.6 ㎛ maximum error compared with the ground truth which is obtained by direct measurement, while a conventional subset size determination algorithm-based DIC analysis produces the maximum error of 62.7 ㎛.

A plate-type eddy-current damper with high energy-dissipation capability is designed and analyzed. The damper is configured in a dimension of 270 mm × 500 mm × 80 mm by employing 16 pairs of rectangular magnets and a rectangular copper plate. The paired magnets are arranged as two rows of 4-by-4 arrays with polarities alternating along the moving direction, while the copper plate is embedded inside two rows of magnets. A finite-element model is developed to investigate eddy-current force. The damping coefficient of damper under a constant velocity of 0.2 m/s is 24.44 kN-s/m. The eddy-current force under harmonic motion can be fitted as a sum of a linear elastic force and a linear damping force. The stiffness coefficient is increased by 77 times and the damping coefficient is reduced relatively by 19%, for vibration frequency increased from 0.5 to 10.0 Hz. The sensitivity of stiffness and damping coefficients on the physical dimensions of magnet and copper plate are discussed. The phase lag is sensitive to copper-plate thickness but insensitive to clear gap between two rows of magnets. The damper is implemented on a based-isolated structure. It is shown that the damper could reduce the peak of base drift and absolute acceleration response spectra by 71.9% and 73.1%, respectively.

Bolt loosening is one of the most common types of damage for bolt-connected plates. Existing vision techniques detect bolt loosening based on the measurement of bolt rotation or the exposure of bolt threads. However, these techniques examine bolt tightness only in a qualitative manner, or require a reference measurement at the initially tightened state of the bolt for quantitative estimation. In this study, the exposed shank length of a bolt is quantitatively measured using an RGB-depth camera and a mask-region-based convolutional neural network but without requiring any measurement from the initial state of the bolt. The performance of the proposed technique is validated by conducting lab-scale experiments, in which the angle and distance of the camera are varied with respect to a target inspection area. The proposed technique successfully detects bolt loosening at exposed shank length over 3 mm with a resolution of 1 mm and 97% accuracy at different camera angles (40°-90°) and distances (up to 65 cm).

Structural fuses are manufactured from oriented steel plates for use in seismic protective systems to withstand significant lateral shear loads. These systems are designed and detailed for concentrating the damage and excessive inelastic deformations in the desired location along the length of the fuse to prevent the crack propagation and structural issues for the surrounding elements. Among a number of structural systems with engineered - cut-outs, a recently developed butterfly-shaped structural fuses are proposed to better align the bending strength along the length of the fuse with the demand moment, enhancing controlled yielding features over the brittle behavior. Previously, the design methodologies were developed purely based on the flexural stresses' or shear stresses' behavior leading to underestimate or overestimate the structural capacity of the fuses. The aim of this study is to optimize the design methodologies for commonly used butterfly-shaped dampers through experimental investigations considering the stresses are not uniformly distributed stresses along the length of the fuse system. The effect of shear and flexural stresses on the behavior of butterfly-shaped are initially formulated based on the Von-Mises criterion, and the optimized geometry is specified. Subsequently, experimental tests are developed for evaluating the optimized design concepts for butterfly-shaped dampers considering the uniform stress distribution and efficient use of steel. It is shown that butterfly-shaped dampers are capable of full cyclic hysteric behavior without any major signs of strength or stiffness degradations.

In the field of structural health monitoring (SHM), cameras record videos and tracking methods can be applied to calculate the structural displacement. Commercial and unmanned aerial vehicle (UAV) cameras are promising non-contact sensors owning to their high availability and easy installation. However, effective tracking methods need to be developed. In this study, we firstly propose an end-to-end vision measuring framework with a novel deep neural network (DNN) tracker, named Siamese Single Decoder Network (SiamSDN). The system requires no target installation and uses cellphone cameras. For SiamSDN, the position and scale of bounding box are formulated through statistical parameter estimation. Unlike generative trackers, SiamSDN does not require manually extracted features or pre-defined motion areas. The tracking object is solely identified in the first frame. A shaking table test of a five-storey structure is carried out to demonstrate the efficiency. Besides, a UAV is used to simulate the field test. To minimize the error caused by the vibrations of UAV, digital video stabilization (DVS) is proposed to eliminate the drifts. Videos taken by both the commercial and UAV cameras are analyzed to calculate the displacements. Comparing our DNN tracker with feature point matching approach, SiamSDN improves the displacement measuring accuracy by 66.16% and 57.54%, respectively, and the frequency characteristics are obtained precisely.

The objective of this study was to determine friction ratios that maximize energy dissipation on a seismic damper. The aforementioned friction damper basically consists of mass blocks that are able to slide on a flat surface. To carry out this analysis, a numerical-experimental approach was used. Firstly, the theoretical background and equations of motion for a SDOF system consisting of a mass supported on a flat surface with friction are introduced. Special emphasis is made on the fundamentals of stick-slip motion as well as energy considerations. Secondly, experimental studies carried out on a shaking table with harmonic and seismic records are described. These tests consisted of lead blocks contained on a U-shaped channel type aluminum section with its open end facing upwards. This configuration allowed blocks to slide solely in the direction of the base motion. Five different types of contact interfaces were considered to determine potential friction coefficients for the damper's design. Additionally, computational models based on rigid-body dynamics are presented. Numerical results were satisfactory particularly when comparing model's dissipated energy with empirical results. An analysis was carried out by calculating dissipated energy for the experimentally-calibrated models with varying friction ratios. For this purpose, eight near-fault seismic records were selected. Intervals with friction coefficients that maximize energy dissipation are proposed for each record. Finally, relationships between the computed friction ratios and register's peak ground acceleration (PGA) and root mean square acceleration (RMS) are discussed.

Corrugated and flat circular diaphragm-based piezoresistive pressure sensors are designed and proposed for different applications. Regarding to different criteria including maximum stress, sensitivity and natural frequency, different diaphragms with semicircular, sinusoidal and trapezoidal corrugation are modeled, simulated and investigated in finite element software. The finite element model is validated by experimental results from the literature and also with theoretical formula to ensure the accuracy of the finite element modeling process. Wavelength and location of the corrugation are optimized to achieve best performing sensor. For the application with large acceptable induced stress, circular flat diaphragm is proposed. To enhance the sensitivity of the sensor as a crucial parameter, semicircular corrugation for circular diaphragm with 360 ㎛ wavelength and 240 ㎛ distance from the center is designed and proposed. This configuration shows obvious improvement of the sensitivity with more than 18% enhancement. To extend the working range of the sensor regarding to input frequency, trapezoidal corrugation with 360 ㎛ wavelength and 240 ㎛ distance from the center is proposed to reach more than 29% enlargement in first natural frequency. Eventually, this paper tries to provide an overview to design the optimal pressure sensor according to desired specifications.

In this work, a new theory quasi-3D shear deformation is presented to analyze the bending of thick FGM (functionally graded materials) plates resting on Pasternak elastic foundations, whose number of variables is limited to five. The mathematical model used presents a new range of displacement based on indeterminate integral variables where the stretching of thickness is taken into account according to the power laws P-FGM, E-FGM and S-FGM. The compositions and volume fractions of the constituents in the FGM are supposed to change through the thickness. The principle of virtual work, as well as the Naiver method, is used in this study to solve the governing equations of motion to study these types of plates. The equilibrium equations according to the FG plate resting on Pasternak foundations are presented. The results obtained are compared to those determined by the other authors. It was observed from the comparative studies that quasi-3D theories that take into account thickness stretching effects can predict bending behavior more accurately than other theories.

For the efficient management of geo-infrastructures in the field, engineering properties of the subgrade should be reliably and rapidly investigated. The objective of this study is to estimate and compare the strength and stiffness parameters of subgrades using portable in-situ devices. An automated dynamic cone penetrometer (ACP), dynamic cone penetrometer (DCP), and light falling weight deflectometer (LFWD) are adopted and applied at nine points of soft ground in South Korea. The N-value from the ACP (N_ACP), which efficiently assesses the relatively deep subgrade, is correlated with the dynamic cone penetration index (DCPI) and dynamic deflection modulus (E_vd). Test results show that the DCPI and E_vd can be estimated in terms of N_ACP. In particular, the relationship between E_vd and N_ACP is improved when the strain influence factor of the target ground is considered. For the assessment of strength and stiffness parameters, the California bearing ratio (CBR), relative density (D_r), internal friction angle (ɸ), and elastic moduli determined by the plate loading test (PLT), soil stiffness gauge (SSG), falling weight deflectometer (FWD) are estimated using N_ACP. The ACP test with the relationships between engineering parameters and N_ACP may be an effectively method to assess the overall characteristics of the subgrade.

This study examined the relations between permeability of the concrete due to addition of new cracks. The different concrete types analyzed were standard concrete, reinforced steel fiber concrete, and reinforced concrete polypropylene fiber. In consideration of the improved polypropylene content of polypropylene fiber reinforced concrete, the crack diameter was decreased by 72-93% for up to 0.25% fiber and cracks were eliminated with 0.3% fiber inclusion. In terms of steel fiber-reinforced concrete, the results showed that steel reinforcing macro fibers decrease the permeability of cracked concrete at wider crack widths. While the permeability of unreinforced concrete was the highest, 0.5% steel content resulted in lower permeability while a higher steel content concrete with 1% steel had the lowest permeability. Crack stitching phenomenon and the effect of multiple cracks may be attributed to the decrease in the permeability. With respect to normal concrete, the findings showed the crack opening displacement at the highest tension is less than 20 microns. At this loading stage, after unloading, around 80% of the displacement is restored and the residual crack opening is notably small, indicating the low impact of cracking on concrete permeability (CP) and showing that CP was increased with crack width. As a result, adding polypropylene aggregate to concrete could significantly reduce the width of crack, while adding steel fiber to concrete reduces the permeability of cracked concrete compared to normal concrete which may result in a minor crack on CP.