Abstract in English:Abstract The present study explores a retaining wall with an intermediate slab. To reduce the lateral earth pressure on the wall, the substitution of part of the soil by blocks of expanded polystyrene (EPS) with high density is proposed, which could result in significant economic savings. Also, the possibility of building the wall elevation with smaller thickness (preexisting wall reinforcement) will be analyzed. To do this, the situation and optimum geometry of the EPS blocks will be studied in detail, besides a study of two scaled models, one without EPS and another with blocks with rectangular distribution. The obtained results allow us to affirm that the reduction in pressure is very significant if the blocks are arranged with the proper geometry and situation over the sliding plane but without eliminating the beneficial effect of the weight of the ground located over the slab.
Abstract in English:Abstract In the present paper, the free and forced vibration of multiple cracked multi span continuous beams made of functionally graded material (FGM) is investigated by the dynamic stiffness method. First, there are constructed dynamic stiffness matrix and nodal load vector of multiple cracked FGM beam element using Timoshenko beam theory and massless double spring model of crack. Then, effect of cracks parameters on free and forced vibration of the FGM continuous beams is examined. The theoretical developments are validated by numerical examples. The obtained results provide an efficient method to analyze free and forced vibration of multiple cracked FGM framed structures and assessment of the behavior of damaged structures.
Abstract in English:Abstract Strain-rate effects can distort model testing with geometrically-similar models. In impact modelling this problem is usually addressed by revising the impact conditions, but such kind of method is inadequate for modelling impact on a reticulated dome. A new technique was proposed and tested. Apart from adjusting the impact conditions, the technique adds additional mass to components of the model to balance the strain-rate effects. That allows studying in model scale more complex structures in which the strain rate varies over the structure’s components. Model scale tests of impact on a reticulated dome showed good agreement with full scale in terms of displacements and axial forces on the structure’s rods. Those results verify the effectiveness of the new technique.
Abstract in English:Abstract A large number of cracks occur in concrete structure after projectile penetration. The study of crack distribution and propagation process is the basis of damage assessment, structural repair and high dynamic fracture mechanism. In this paper, wire saw cutting, X-ray computed tomography (X-CT) and mechanical property testing of damaged concrete were carried out on deep penetration targets. According to X-CT images of radial core samples in target and the mechanical properties of damaged concrete, the crack distribution in the target was divided into a plastic damage zone and a brittle damage zone, and the microcracks only existed in the plastic damage zone. The initial growth process of three-dimensional cracks was obtained by X-CT images of axial core samples in target, that is, the cracks in the pure mortar target gradually developed from the radial direction to the tangential direction, and the target containing coarse aggregate directly formed tangential cracks. The propagation progress of cracks was obtained through the target section, that is, the tangential cracks bent in the pure mortar target, and were relatively straight in the target containing coarse aggregate. A crack propagation model was established, and the tangential crack formula and the crack propagation velocity were obtained.
Abstract in English:Abstract Offshore installations activities entail the hazard of explosion accidents with potentially severe consequences to safety of workers, integrity of system, pollution of the environment, and economic losses. Blast walls are generally used for the purpose of reducing the explosion consequences. This study introduce a new concept of blast wall (perforated blast wall) which can disrupt loaindg pressure during the explosion. A dynamic finite element analysis was performed to investigate the effects of the geometric characteristics on the performance of perforated blast walls. A series of computations were performed varying with opening size, plate thickness and opening layout associated with Blockage Ratio. A proposal formula was derived as a function of those design parameters for easily expecting the dynamic structural response characteristics.
Abstract in English:Abstract The aim of this paper is to develop new computational tools to study fatigue crack propagation in structural materials. In particular we compare the performance of different degradation strategies to study fatigue crack propagation phenomena adopting peridynamic based computational methods. Three fatigue degradation laws are proposed. Two of them are original. Initially a cylinder model is used to compare the computational performance of the three fatigue laws and to study their robustness with respect to variations of discretization parameters. Then the fatigue degradation strategies are implemented in a peridynamic framework for fatigue crack propagation analyses. Both cylinder model and peridynamic simulations show that the third proposed degradation law is unique in its combination of high accuracy, high stability and low computational cost.
Abstract in English:Abstract The passive vibration control of mechanical systems under unwanted vibrations can be accomplished in a very effective way by using devices incorporating viscoelastic materials. The design of such devices requires a broad knowledge of the dynamic properties of the employed viscoelastic material, usually supplied by adequate mathematical models. Among the available mathematical models, the fractional derivative (FD) model and the Golla-Hughes-McTavish (GHM) model, along with either the Williams-Landel-Ferry (WLF) equation or the Arrhenius equation, are now very prominent. The current work investigates the use of these models in a wide and integrated dynamic characterization of a typical and thermorheologically simple viscoelastic material. It focuses on experimental data collected from 0.1 to 100 Hz and -40 °C to 50 °C, which are simultaneously manipulated to raise both the frequency and the temperature dependencies of the material. In fitting the models, a hybrid approach - combining techniques of genetic algorithms and nonlinear optimization - is adopted. The ensuing results are evaluated by means of objective function values, comparative experimental-predicted data plots, and the Akaike’s Information Criterion (AIC). It is shown that the four-parameter fractional derivative model presents excellent curve fitting results. As for the GHM model, its modified version is the most adequate, although a higher number of terms is required for a satisfactory goodness-of-fit. None the less the fractional derivative model stands out.
Abstract in English:Abstract Structural Health Monitoring using raw dynamic measurements is the subject of several studies aimed at identifying structural modifications or, more specifically, focused on damage assessment. Traditional damage detection methods associate structural modal deviations to damage. Nevertheless, the process used to determine modal characteristics can influence the results of such methods, which could lead to additional uncertainties. Thus, techniques combining machine learning and statistical analysis applied directly to raw measurements are being discussed in recent researches. The purpose of this paper is to investigate statistical indicators, little explored in damage identification methods, to characterize acceleration measurements directly in the time domain. Hence, the present work compares two machine learning algorithms to identify structural changes using statistics obtained from raw dynamic data. The algorithms are based on Artificial Neural Networks and Support Vector Machines. They are initially evaluated through numerical simulations using a simply supported beam model. Then, they are assessed through experimental tests performed on a laboratory beam structure and an actual railway bridge, in France. For all cases, different damage scenarios were considered. The obtained results encourage the development of computational tools using statistical indicators of acceleration measurements for structural alteration assessment.
Abstract in English:Abstract Horizontally curved bridges have more complex seismic behavior than straight bridges and have been more vulnerable to earthquakes. The present study aimed to evaluate the seismic response of concrete bridges with straight and arched box girder decks in isolated and non-isolated states. The results indicated that increasing the curvature of the non-isolated bridge could increase the irregularity. In addition, increasing the curvature of the deck leads to an increase in shear force, bending moment, and displacement in the piers in the radial direction of the arc, and causes vulnerability of the piers in this direction. Further, in the deck of the bridge, the reduction of the arc radius, especially in the non-isolated bridges, considerably increases the radial shear force, torsion and minor bending moment of the deck. In both isolated and non-isolated cases, the demand in the piers and deck of the bridge under the influence of near-fault ground motions is greater than that of the far-field earthquakes. Seismic isolation results in reducing the force demand in the pier, and the deck of the bridge, leading to a reduction in the force demand rate caused by increasing the central arc angle on the bridge deck.
Abstract in English:Abstract Effect of the presence of perforations on thin structure has been extensively investigated for decades. Various perforation parameters were investigated in past studies. However, study on thin cylinder with multiple perforations has not been carried out. In searching for lighter structural members, the concept of perforated hollow section has been inspired by the shape and arrangement of multiple perforations observed in the Cholla skeleton. Effects of multiple perforation parameters on circular hollow section have been the main interest. This paper presents the verification of FEM simulation with test results. A non-perforated circular hollow section (control model) and a circular hollow section penetrated with 12 nos. of circular shape perforations in array arrangement were selected for the verification process. Both test specimen and FEA models were subjected to compression, flexural and torsional loads. For result comparison within the material linear range, FEA models show good agreement with test results for compression and flexural load cases, and for control models under torsional load case. For perforated models under torsional load, FEA results correspond well with the inclined strain gauge readings. FEM analysis method is considered capable to produce reliable result for loading within the material linear range for circular hollow sections with multiple perforations.