Abstract in English:Abstract This study investigates the free vibration characteristics of an adhesively bonded double-strap joint with viscoelastic adhesive layer. To simplify the spatial finite element mesh generation and efficiently model the adhesively bonded joint, a layerwise plate finite element was extended to accommodate to the modeling of the joint, where the joint structure is treated as a special sandwich laminate. The proposed method was validated by three-dimensional finite element analysis and then applied to generate sampling points for training artificial neural networks (ANNs). The effects of the adhesive material properties and joint geometrical parameters on the joint dynamic characteristics were investigated in detail using the trained ANNs. The optimum design problem is defined as a multi-objective optimization problem considering maximizing the first natural frequency and corresponding loss factor while minimizing the total structural weight. The nondominated sorting genetic algorithm combined with the ANNs were employed to tackle the problem. The proposed method provides a computationally efficient alternative for analyzing and optimizing the adhesive double-strap joints.
Abstract in English:Abstract The perforation tests of 45 # steel target plate and 2A12 aluminium alloy target plate by PELE (the Penetrator with Lateral Efficiency) were carried out in this paper to study the perforation failure characteristics of metal target plate. The macroscopic morphology of perforation on the target plate and the plug was observed, and the perforation wall was cut and polished to observe the distribution and trend of the cracks in the perforation wall by scanning electron microscopy (SEM) and metallographic microscopy. The magnitude and direction of the force produced by PELE on the target during penetration were calculated by numerical simulation. The experimental and numerical results show that, the perforation failure of metal target plate by PELE is different from the ductile perforation by conical-nosed projectile and the punching failure by flat-nosed projectile. The longitudinal cross section of the perforation is funnel-shaped and the shape of the plug is like a circular truncated cone. In the process of penetrating the target plate, the expansion of the filling causes the jacket to exert a force with a certain angle to the direction of projectile movement, which is the main reason for the funnel-shaped perforation and the circular truncated cone shaped plug.
Abstract in English:Abstract The current paper aimed to model failures and fractures in single-lap bolted joints of woven fabric kenaf fiber reinforced polymer (KFRP) composite plate to fail in net-tension. The approach was based on the assumptions that micro-damage events were densely concentrated ahead of the notch tip and crack growth were readily seen along net-tension plane in a self-similar fashion. A 3-D finite element modelling framework were developed to explicitly incorporate bolt clamp-up in a range of KFRP series following tested experimental datasets. Lay-up types, normalized W/d, temperature exposure with constant bolt torque of 5 Nm were considered. It was found that KFRP plates under elevated temperature were stronger than under room temperature due to matrix toughening. Traction-separation relationship was incorported within Extended Finite Element Method (XFEM) framework to model damage within KFRP composite plate by using independent experimental datasets, here incorporates un-notched plate strength, σ o and fracture toughness, G c of all testing lay-ups. Constitutive model used is associated with stress concentration, therefore good agreement between predicted and experimental bearing stress at failure with net-tension failure mode is perhaps not suprising.
Abstract in English:Abstract This paper proposes a method to optimize the reinforcement layout of RC structures under multiple load cases (MLCs) using the planar truss-like material model. It is assumed that concrete is filled with truss-like materials. Two families of orthotropic members in the truss-like materials are used to simulate steel bars. The densities and orientations of steel bars at nodes are considered as design variables. The optimization problem is to minimize the total volume of steel bars with stress constraints. First, under each load case, the distribution of steel bars is optimized as per the fully stressed criterion. Second, based on the results obtained above, the directional stiffness of steel bars under MLCs, described by a closed quadratic curve, is determined using the least squares method. Finally, by solving the eigenvalues problem of the coefficient matrix of the quadratic curve, the optimal distribution of steel bars under MLCs is obtained.
Abstract in English:Abstract The main contribution of this research is to develop a FE model for evaluating impact loading against fabrics. Although the fabric model has been studied by some authors, this article contributes with a FE model with a new material formulation which takes into account the stress-strain limit to simulate the fabric rupture. As a case study, the author uses a bulletproof vest impact analysis and determine the number of sheets necessary to resist the ballistic impact. A sophisticated numerical algorithm is used. New constitutive equations are developed capable to take into account the material damage, yield stresses and rupture limits. This is based on elastoplasticity theory, with an adaptation of the function related to the hardening of the material. With this, it is possible to control the limits of the permissible stresses on the yarn and coating of the structural fabric and accurately represent the physical behavior of the materials used. The elastoplasticity and damage theories are developed and, finally, a numerical algorithm is presented for the determination of stresses, displacements and material deformations.
Abstract in English:Abstract In practical rock engineering, it is of considerable significance for the study of mechanical behavior of rock containing flaws. The uniaxial compression failure mechanism of granite containing intersecting two-flaws is investigated through the flat-joint modeling approach. The flat-joint model is introduced briefly, and numerical models of intact granite specimens are established. After that, a series of micro-parameters are confirmed by comparison with the laboratory tests of intact granite specimen. Then uniaxial compression simulations are conducted on granites with intersecting two-flaws. The numerically simulated results show good consistency with laboratory tests, including the strength properties, deformation properties, and failure modes. The strength and deformation characteristics of the granites are dependent on the relative position length. Furthermore, the relationship between the crack evolution process and the stress-strain curves for the specimens is studied concerning the relative position length. Finally, the crack propagation mechanism and cracking type of granite specimens are revealed by analyzing the micro-force field.
Abstract in English:Abstract Maintenance work is very important for the continuation of the long service periods planned in engineering structures. Some damage to the steel elements, such as the growth of the holes in the structure, leads to reduced buckling strength and shortened service life. Moreover, the criterion of the hole is uncertain for steel structures. For this reason, it is very important to predict and evaluate the buckling strength of a damaged structure and to take necessary measures. Therefore, in this article, a series of systematic experimental studies are carried out to calculate the buckling strength of elliptical perforated steel columns. Deformation shapes and load-displacement graphs of the test columns are plotted. In addition, the behavior of the column under axial load is analyzed by constructing a finite element model. Numerical simulations are performed with Dynaform finite element package. The effect of the elliptical hole on the column buckling strength by changing the width, height and center is investigated numerically and experimentally. Prepared samples are subjected to axial loading test and compared with numerical results. In light of the data obtained from the numerical results, the effect of the width, height and center of a single elliptical hole on the buckling strength of the column is clearly demonstrated.
Abstract in English:Abstract Hybrid multistory buildings are every day more common in the construction industry. However, there is little understanding of the performance of the hybrid connections. In this research, the static and dynamic response of cross-laminated timber (CLT) composites combined with reinforced concrete (RC), hollow steel profiles and laminated strand lumber (LSL) has been investigated. In addition, the effects of posttensioning stresses as well as distinct types of connectors such as nails, self-tapping screws and self-tapping dowels has been accounted for. After experimental work, numerical modelling for simulating the static and dynamic behavior for these hybrid connections was also investigated. Results indicate that such massive timber composite connections behave reasonably similar to conventional timber connections, except in that inelastic deformations may increase up to 200%. In addition, it has been found that existing hysteretic models like the modified Stewart hysteretic model (MSTEW) fit for modelling purposes except that very asymmetric hysteretic behavior can be found for timber-concrete hybrid connections.
Abstract in English:Abstract This article investigates the shear behavior of reinforced concrete beams without transverse reinforcement. Two types of concrete were produced: a Reference Conventional Concrete (RCC) and a Lightweight Self-Consolidating Concrete (LSCC), all with an average 28-day compressive strength (fc) of approximately 30 MPa and characterized by rheological and mechanical tests. Twelve 15 x 30 x 200 cm beams were manufactured for shear failure during a four-point bending test. Concrete properties, longitudinal reinforcement ratios (0.89%, 1.27% and 1.68%) and shear-span to depth ratio (1.87 to 2.71) were determined. The studied beams were compared in terms of cracking pattern, diagonal cracking load, shear strength, specific concrete and longitudinal reinforcement deformation at failure. The strength values obtained experimentally were compared with ABNT NBR 6118 (2014), ACI 318 (2019) and CEN EC-2 (2004). The tested beams of LSCC showed less shear strength when compared to beams of RCC.
Abstract in English:Abstract This discussion raises a few comments and questions on the paper by Mehmet ADA and Yusuf AYVAZ [ADA, M. and Y. AYVAZ, The Structure-Soil-Structure Interaction Effects on the Response of the Neighbouring Frame Structures. Latin American Journal of Solids and Structures, 2019. 16(8)].