Experimental analysis of friction between sand and reinforcing elements using ring simple shear tests

This article assesses numerically the potential of two different spectral estimation approaches supporting non-uniform-in-time data sampling at sub-Nyquist average rates (i.e. below the Nyquist frequency) to reduce data transmission payloads in wireless sensor networks for operational modal analysis of civil engineering structures. This consideration relaxes transmission bandwidth constraints in wireless sensor networks and prolongs sensor battery life since wireless transmission is the most energy-hungry on-sensor operation. Both the approaches assume acquisition of sub-Nyquist structural response acceleration measurements and transmission to a base station without on-sensor processing. The response acceleration power spectral density matrix is estimated directly from the sub-Nyquist measurements, and structural mode shapes are extracted using the frequency-domain decomposition algorithm. The first approach relies on the compressive sensing theory to treat sub-Nyquist randomly sampled data assuming that the acceleration signals are sparse/compressible in the frequency domain (i.e. have a small number of Fourier coefficients with significant magnitude). The second approach is based on a power spectrum blind sampling technique considering periodic deterministic sub-Nyquist “multi-coset” sampling and treating the acceleration signals as wide-sense stationary stochastic processes without posing any sparsity conditions. The modal assurance criterion is adopted to quantify the quality of mode shapes derived by the two approaches at different sub-Nyquist compression rates using computer-generated signals of different sparsity and field-recorded stationary data pertaining to an overpass in Zurich, Switzerland. It is shown that for a given compression rate, the performance of the compressive sensing–based approach is detrimentally affected by signal sparsity, while the power spectrum blind sampling–based approach achieves modal assurance criterion >0.96 independently of signal sparsity for compression ratios as low as 22% the Nyquist rate. It is concluded that the power spectrum blind sampling–based approach reduces effectively data transmission requirements in wireless sensor networks for operational modal analysis, without being limited by signal sparsity and without requiring a priori assumptions or knowledge of signal sparsity.

This paper proposes an application of already established higher-order models and, namely, investigates the free vibration analysis of civil engineering structures subjected to nonstructural masses. The refined one-dimensional theories adopted are based on the Carrera unified formulation (CUF). The stiffness and mass matrices are obtained by means of the principle of virtual displacements in conjunction with the finite element method (FEM). According to CUF, in fact, their formulation is performed in terms of fundamental nuclei, which depend neither on the adopted class of beam theory nor on the FEM approximation along the axis. In order to account for nonstructural localised masses, the fundamental nucleus of the mass matrix has been opportunely modified. In this work, Lagrange polynomials have been employed in the framework of CUF to develop pure translational displacement-based refined beam models. The models obtained using this approach are referred, in the literature, to as component wise (CW), which allows to model each structural component as a 1D element. The free vibration analysis has been carried out for different cases of nonstructural mass distribution in typical civil buildings. The results obtained are compared with classical Solid/Shell FEM solutions from the commercial code MSC Nastran. The capabilities of the CW models are demonstrated, since this formulation is able to replicate the 3D solid results with enhanced performances in terms of computational efforts. Moreover, the importance of taking into account the correct distribution of the nonstructural masses is shown to be of fundamental importance in vibration analysis of civil buildings.

Facing the escalating demands in both technical competence and financial accountability, practicing structural engineers are being forced into an ever-intensified fast-pace working environment. With more and more structural design codes becoming lengthy and cumbersome and, meanwhile, the time allocated for structural engineering design being drastically reduced, the quality assurance of the structural engineering design has been becoming more critical than ever for practicing structural engineers to succeed. Structural engineering design errors and failures have been observed in a variety of design phases and categories. Among them, there are several typical problems needed to be discussed and a systematical procedure of quality assurance of the structural engineering design shall be studied and developed. As a part of our collective professional effort to assure the quality of the structural engineering design, this paper will discuss following eight typical aspects related to quality control and assurance of structural engineering design and a number of real world practical examples will be presented to assist in illustrating the importance of the quality control and assurance for real world structural engineering design projects.

Fabrication and characterization of lithium metasilicate/disilicate glass ceramics and yttria tetragonal zirconia polycrystals for dental restorations

A study of the thermal buckling behavior of a circular aluminum plate using the digital image correlation technique and finite element analysis

The strength theory is concerned with yield or failure of material under complex stress states. It is used to provide strength design criteria for analysis and design of engineering structures.

As robotic technologies advance and robots move out of factories and labs into the real world, grip on a variety of surfaces (e.g. smooth or rough) in a variety of conditions (e.g. dry or wet) becomes increasingly important. Bioinspired "microspines" have been previously explored, but primarily for vertical climbing applications or for small-scale robots applying low forces (less than 1 N). Further, these works primarily focused on rough surfaces. To advance this area of research, we present a composite material comprising high- friction rubber and compliant nitinol microspines which can passively retract below the surface of the rubber. We show that the composite can support large loads (greater than 75 N) with a high coefficient of friction on both smooth and rough surfaces (p > 1.1), outperforming microspines alone on smooth surfaces and rubber alone on rough surfaces, especially when wet and oily. Further, due to the retraction of the microspines, the composite does not damage relatively soft, smooth surfaces, like wood flooring. We also test durability, and show that it is improved by microspine compliance, and test the effects of varying microspine diameter, angle, and tip shape. Finally, we demonstrate that a small RC car can climb steeper slopes and stop more quickly in wet conditions with microspines.

Different types of plant leaves exhibit a broad spectrum of wetting behaviour because of their different pubescence, wax layer, scales, veins, etc. The wetting tension is used to express the wetting of a leaf with βsf = σf. cos θ (σf = the surface tension of a liquid and θ= the contact angle of a liquid to the surface of a leaf). Three different methods are used for measuring contact angles: the contact angle goniometer method, the meniscus rise method and the Wilhelmy plate method. All three methods are based on completely independent theories and produce absolutely uniform contact angles on smooth paraffin surfaces. Closed cup systems which could be thermostatted were used for making the measurements. Substantial differences in the contact angles become apparent when contact angle measurements on roughened and smooth firm surfaces are compared, as for example contact angles on smooth and roughened paraffin surfaces. If the figures for the contact angles on a smooth surface are 90° or > 90°, they will be bigger on a roughened surface; if they are <90° on a smooth surface, they will be smaller on a roughened surface. These results obtained with paraffin were confirmed by contact angle measurements made on plant leaves. The contact angles, measured on plant leaves with the help of the three different measuring methods, show a high degree of uniformity.

The apparent temperatures of smooth and rough terrain surfaces are calculated for frequencies between 1 and 75 kMc, for angles of incidence between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5\deg</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80\deg</tex> , and for observation altitudes between 2 km and 32 km. The attenuation and thermal radiation caused by the atmosphere are accounted for by an experimental model atmosphere, and the surface emissivities are based on measured complex dielectric constants (for the smooth surfaces) and measured radar return (for the rough surfaces). It is found that perpendicular polarization provides the greatest temperature contrast between rough and smooth surfaces, and that the contrast decreases as the altitude of observation increases; at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f=75</tex> kMc (approximately the resonant frequency of the oxygen molecule), there is likely to be little, if any, contrast between rough and smooth surfaces.

Even with the state-of-the-art technology of computer-aided design and topology optimization, the present structural design still faces the challenges of high dimensionality, multi-objectivity, and multi-constraints, making it knowledge/experience-demanding, labor-intensive, and difficult to achieve or simply lack of global optimality. Structural designers are still searching for new ways to cost-effectively to achieve a possible global optimality in a given structure design, in particular, we are looking for decreasing design knowledge/experience-requirements and reducing design labor and time. In recent years, Artificial Intelligence (AI) technology, characterized by the large language model (LLM) of Machine Learning (ML), for instance Deep Learning (DL), has developed rapidly, fostering the integration of AI technology in structural engineering design and giving rise to the concept and notion of Artificial Intelligence-Aided Design (AIAD). The emergence of AIAD has greatly alleviated the challenges faced by structural design, showing great promise in extrapolative and innovative design concept generation, enhancing efficiency while simplifying the workflow, reducing the design cycle time and cost, and achieving a truly global optimal design. In this article, we present a state-of-the-art overview of applying AIAD to enhance structural design, summarizing the current applications of AIAD in related fields: marine and naval architecture structures, aerospace structures, automotive structures, civil infrastructure structures, topological optimization structure designs, and composite micro-structure design. In addition to discussing of the AIAD application to structural design, the article discusses its current challenges, current development focus, and future perspectives.

The development of erosion-resistant coatings requires the knowledge of their complex failure mechanisms. Here, the damage due to erosion on smooth and rough surfaces is investigated and compared experimentally and numerically. In a low-speed collision, the smooth surface damage is always symmetrical. Still, the rough surface damage is different depending on the shape of the impact location, and there is no symmetry. In a high-speed collision, there is no difference between the rough and smooth surfaces because the particle energy is high enough to destroy the surface roughness. The effect of particle parameters on gas turbine blade erosion is investigated. For this purpose, the damage to the turbine blade is evaluated using scanning electron microscope (SEM) images. The results show that particle size is an effective parameter in gas turbine blade erosion, more than particle velocity (2.37 times) and particle density (3.21 times). Furthermore, the vertical impact on the rough surface is like an oblique impact on the smooth surface regarding the erosion rate. The relationship between particle parameters, including particle size, density, and velocity, with the particle's kinetic energy is analytically expressed.

In general, the analysis and design of civil engineering structures are based on deterministic approaches where uncertainties in various parameters (soil characteristics, loading, etc.) are not taken into account. In recent decades, the description and analysis of uncertainty in geotechnical engineering, with a focus on the safety of structures, have become increasingly important issues. To fix the level of risk for which geotechnical parameter values must be determined, the Eurocodes have introduced an approach based on the statistical processing of soil data. This paper presents the statistical modeling of geotechnical parameters (cohesion, friction angle, specific weight) of a shallow foundation soil from Daral Peulh area located in Thies in Senegal. Laboratory tests for soil identification were conducted on 26 samples. After outliers, values determined and treated with boxplot method, graphical methods and Kolmogorov and Shapiro-Wilk tests were used to determine the probability distributions associated with geotechnical parameters and the bearing capacity of a shallow foundation. The results conclude after outliers treatment with 5% risk, the probability distributions of the cohesion, the friction angle and the specific weight are normal distributions and can be used for probability design. However, the variability around their means is high for the cohesion, the friction angle and the bearing capacity. For the bearing, the most suitable probability distribution in this case is the lognormal distribution.

Probability density evolution method for seismic displacement-based assessment of earth retaining structures

Rock is a typical non-homogeneous material. The behavior of a rock block under compression and the process of micro-fracture in that block are phenomena of considerable interest in understanding the strength characterization of brittle rock. In this study, the effect of the non-homogeneity on limit bearing capacity of rock block based on Rock Elasto-Plastic Failure Process Analysis code (REPFPA) are simulated and investigated. Numerical simulations find out that there exists a functional relation between the heterogeneity coefficient and the limit bearing capacity of rock block. For specimens with the same heterogeneity, however, the numerical simulations show that the failure modes depend greatly on the crack initiation location, which is found to be sensitive to the local disorder features within the specimen. In addition, the characteristics of acoustic emissions with the changing of heterogeneity coefficient were also found. These identifications are crucial for better understanding and interpreting the experimental results and consequently, improve our concepts in design or analysis of rock engineering structures.

Civil Engineers are the builders of a nation. They always have played a significant role in providing the infrastructure required for the society. Ever increasing population, rapid urbanization and industrialization, global warming and climate change, increasing incidents of natural and manmade hazards and environmental degradation have become major concerns of the society today and these concerns pose several challenges to the Civil Engineers. There has been a noticeable change in the environment within which civil engineers carry out their work. There is a growing concern on the adverse consequences of the development activities. There is a need for Civil Engineers to rise up to face these challenges and contribute to the development and betterment of the nation in all core areas. A multitude of threats confront us in our effort to achieve the same. Civil engineers have always been looking for innovative tools and techniques for solving the challenging problems that they face during planning, analysis, design and construction of civil engineering structures. It was in this context that the Department of Civil Engineering, National Institute of Technology Calicut, Kerala, India, has come out with the proposal of organizing an International Conference on Materials, Mechanics and Structures 2020 (ICMMS 2020) with major funding from Technical Education Quality Improvement Program-Phase III. This conference was aimed to provide a forum to all Civil Engineers to deliberate on the innovative tools and techniques that are needed to face the challenges in the fields of Materials, Mechanics and Structures.List of Comittees and editors are available in this pdf.