Resumo em Inglês:

Abstract In this study, the wavy honeycomb's initial peak crushing force (IPCF) and energy absorption (EA) were estimated using the decision tree algorithm. First, using experimental results, Ls-Dyna models of honeycombs were verified. In this way, the stress-strain curves and shapes were compatible. Secondly, the effect of parameters was examined. Waves contribute significantly to values. In particular, for honeycombs with the same geometric properties, when the wavenumber is 3, the IPCF and specific energy absorption (SEA) values increase by 121.59% and 75.08%, respectively. In addition, when the wave amplitude is 0.15mm, IPCF and SEA increase by 60.89% and 71.3%, respectively. Afterward, using the full factorial, a data set with various parameter values was prepared. The parameters (inputs) and values (outputs) in the data set were used to train and verify the decision tree algorithm using Python. Finally, new data was introduced into the algorithm, and values were estimated. Errors ranged from 0.17% to 14.65% between Ls-Dyna and the algorithm results. These findings show that machine learning is suitable for wavy honeycombs.

Resumo em Inglês:

Abstract The Mega-Sub Controlled Structure System (MSCSS) is a new type of seismic structural system. This research aims to find weak members in the structure and better describe the failure state. To achieve this, we enhanced the story drift ratio indicator by combining it with the structural failure path and proposed a new comprehensive indicator that can more accurately describe the seismic behavior of the structure. The new concept of seismic behavior is proposed. The seismic waves used in the analysis in this article are generated by the Hilbert-Huang transformation method. The failure path of the structure under random seismic waves is calculated by the weighted rank-sum ratio method. The comprehensive indicator is checked on the MSCSS with or without lead-rubber bearings and traditional Mega-Sub structure. The calculation results show that the story drift ratio alone cannot fully reflect the damage of structures in earthquakes. The new indicator combined with the failure path can describe the seismic behavior of the MSCSS more comprehensively and can better assist the seismic design and optimization of structures.

Resumo em Inglês:

Abstract Fiber-reinforced polymers are materials used to recover/strengthen reinforced concrete structures load capacity. This material exhibits good mechanical properties with low self-weight. This work performed a series of nonlinear finite element analyses in one-way (OW) wall panels with a central cut-out opening, strengthened using carbon fiber-reinforced polymer (CFRP). The experimental tests conducted by Mohammed et al. (2013) were used as a benchmark. The numerical simulations were carried out in the commercial code ATENA, in which the material and geometrical nonlinearities were accounted. As a result, the numerical models reasonably predicted the ultimate load of the walls, and all models presented a crack pattern similar to the experimental tests, verifying that the CFRP addition caused a more distributed crack pattern. The results obtained in this work revealed that CFRP strengthening caused 24-50% enhancement of the ultimate load. Additional models were carried out to extend the numerical results and proposed a new equation that can be used to predict the ultimate load of OW walls with and without CFRP strengthening.

Resumo em Inglês:

Abstract This study presents a free vibration analysis of three different curved laminated composite plates having end-to-end decomposition under fixed opposing straight edges. The curved structures have been mathematically modeled by employing the Classical Laminated Plate Theory and the Finite Element Method to perform the location-based effect of decomposition. Besides, the relation among the decomposition, curvature characteristics, and stacking sequences is examined in terms of natural frequencies. For this purpose, the end-to-end decompositions are defined in two different levels and re-positioned along the curved edge for each vibration analysis. The frequency ratio is obtained by proportioning the natural frequency of the damaged structure to that of the healthy structure and considered to interpret the effects of the decomposition location. Cross-ply and angle-ply structures having elliptic, circular, and parabolic curvatures are considered. It is concluded that the effect of the end-to-end decomposition on the natural frequencies varies to its level, the stacking order, and the bending regions of the relevant mode shape.

Resumo em Inglês:

Abstract Using the Separate Hopkinson Pressure Bar test device, a series of dynamic impact tests were carried out on the single coal and white sandstone near the incident bar. When the stress wave propagates in a complex with different wave impedance matching effects, its dynamic mechanical properties change, energy dissipation law and damage characteristics are studied. The research results show that: (1) With the increase of impact velocity, the peak stress and DIF of layered composite coal-rock increase linearly. At the same speed, when the stress wave changes from hard to soft, the peak stress and DIF are larger than the stress wave from soft to hard. (2) The dissipated energy density of layered composite coal-rock increases in a quadratic function with the increase of the incident energy density, and the composite body with better wave impedance matching effect has a higher dissipated energy density. (3) The fractal dimension and the degree of fracture of layered composite coal-rock increase with the increase of the speed. The white sandstone component is mostly shear failure, and the coal component is mostly crushed.

Resumo em Inglês:

Abstract According to the need of cable force monitoring of space cable structure, a new fiber Bragg grating monitoring method is proposed by analyzing the mechanism, advantages and disadvantages and application scope of existing cable force monitoring methods. The results of practical engineering show that: the mechanism of this method is clear and easy to implement; the advantages of clamp cable, tension meter, and Jack monitoring method are fully used to avoid their disadvantages; in the mutual check stage of Jack and clamp cable tension meter, the monitoring data error of the two testing methods is less than 5%, which indicates that the clamp strain gauge is accurate and effective; this method has little influence on construction, and can make full use of the engineering project The clamp cable tension meter is arranged in the process of cable tension in stages, which can realize the implementation without affecting the original construction process. It provides an experience reference for similar cable tension process and cable force control in service stage in the future.

Resumo em Inglês:

Abstract The properties of fibre reinforced concrete were studied under monotonic loads according to Japanese, North American and European codes. Two different types of SIKA polypropylene fibre were with different dosages. One hundred and eighty tests were performed, obtaining resistance to compression, tension, bending, toughness, and energy absorption in the hardened state. The results show that the addition of fibres affects the workability of the concrete mix. The increase in fibre dosage does not affect compressive, tensile, or flexural strength. However, the failure changes from brittle to more ductile, allowing it to reach residual strengths of 50% of the maximum reached and 200% deformation. The dissipated energy increased with increasing fibre dosage. The performance achieved by both fibres was similar, although the optimal dosage was 6 kg/m3 for type A fibres and 8 kg /m3 for type B. Therefore, the replacement of flexural reinforcing steel in the foundation slabs of one-story buildings can be performed if adequate dosages are used in compliance with established analytical procedures for industrial floor design.

Resumo em Inglês:

Abstract The silicon carbide (SiC)/metal composite armors with the composite cover on the front of the SiC plate were impacted by 12.7mm armor piercing incendiary (API) projectiles at velocities from 412.6m/s to 802.2m/s. The resulting projectile core and ceramic fragments were collected and then screened through a range of standard sieving screens. The mass distributions of fragments produced by projectile and ceramic impacting each other were obtained. The failure mechanism of the rigid-brittle core of 12.7mm API projectile after impacting SiC/metal composite armor was studied by examination of the failed core. The results show that the cumulative mass of core and ceramic fragments follow the Schuhmann distribution law. With the increase of impact velocity, the mass proportion of small core fragments increases, while for ceramic fragments, the mass proportion of fragments in different fractions does not change. The failure mechanism of the large equivalent diameter fragment ( >8mm) is tensile brittle fracture mainly. In contrast, the local plastic shear fracture exists on the fragments with an equivalent diameter of less than 2mm.

Resumo em Inglês:

Abstract The construction methods currently adopted for multi-story concrete buildings resorts the strategy to cast columns and slabs with high and normal compressive concrete strength, respectively. The intersection region affects the load transfer performance of the columns, causing expressive confinement stress in interior columns. However, when the confinement is only provided by two sides, as corner columns, it is not enough to increase the lateral stress. The structural behavior of corner columns, represented by isolated columns, also called sandwich column, is investigated in this paper through numerical nonlinear models. The lateral stresses induced by the uniaxial load applied to the sandwich columns are computed when the influence of concrete strength column-slab ratio, slab thickness and the column width ratio and the biggest dimension of the column’s cross section were tested. A set of expressions were proposed to calculate the effective compressive strength of the column based on numerical results. The predicted effective strength has shown a good agreement with experimental results collected from the literature.

Resumo em Inglês:

Abstract The lithology and thickness of the rock beam affect its mechanical properties and acoustic emission characteristics when it is fractured. In this study, three-point bending tests of rock beams were carried out. Then, we proposed to utilize the percentage of peak energy to characterize the intensity of energy release during fracture. Finally, the energy release mechanism of coal roof fracture was discussed. The evolution process of acoustic emission includes five stages. The acoustic emission amplitude distribution of rock beams has three typical patterns. Most of the cracks after fracture are tensile cracks, the proportion of tensile cracks is positively correlated with the elastic modulus. The percentage of peak energy is positively correlated with thickness and elastic modulus. More energy is released when thick and hard roof fractures. When necessary, measures such as reducing the thickness or the strength of the roof could be taken to improve the safety of mining.