Resumo em Inglês:

Abstract The problems concerns to the propagation of surface wave propagation through various anisotropic mediums with initial stress and irregular boundaries are of great interest to seismologists, due to their applications towards the stability of the medium. The present paper deals with the propagation of Rayleigh-type wave in a corrugated fibre-reinforced layer lying over an initially stressed orthotropic half-space under gravity. The upper free surface is assumed to be corrugated; while the interface of the layer and half-space is corrugated as well as loosely bonded. The frequency equation is deduced in closed form. Numerical computation has been carried out which aids to plot the dimensionless phase velocity against dimensionless wave number for sake of graphical demonstration. Numerical results analyze the influence of corrugation, loose bonding, initial stress and gravity on the phase velocity of Rayleigh-type wave. Moreover, the presence and absence of corrugation, loose bonding and initial stress is also discussed in comparative manner.

Resumo em Inglês:

Abstract An adaptation of the conventional Lanczos algorithm is proposed to solve the general symmetric eigenvalue problem Kϕ = λK Gϕ in the case when the geometric stiffness matrix KG is not necessarily positive-definite. The only requirement for the new algorithm to work is that matrix K must be positive-definite. Firstly, the algorithm is presented for the standard situation where no shifting is assumed. Secondly, the algorithm is extended to include shifting since this procedure may be important for enhanced precision or acceleration of convergence rates. Neither version of the algorithm requires matrix inversion, but more resources in terms of memory allocation are needed by the version with shifting.

Resumo em Inglês:

Abstract Based on transfer matrix theory and precise integration method, precise integration transfer matrix method (PITMM) is advanced to research free vibration characteristics of the conical shells. The influences of the boundary conditions, the shell thickness and the semi-vertex conical angle on vibration characteristics are discussed. Based on Flügge thin shell theory and transfer matrix method, field transfer matrix of conical shells is obtained. According to the boundary conditions at ends of the conical shell, natural frequencies of the conical shell are solved by precise integration method. The approach of studying free vibration characteristics of the conical shells is obtained. Contrast of natural frequencies from the paper and previous literature, the method of the paper is confirmed. On this basis, the effects of the boundary conditions, the shell thickness and the semi-vertex conical angle on vibration characteristics are presented.

Resumo em Inglês:

Abstract Shear waves (SH) propagation in piezoelectric composite under the influence of initial stress is investigated analytically and numerically. The dispersion equation of shear waves propagation in direction normal to the layering is obtained in presence of initial stress. Numerical solutions were obtained for evaluating the effect of stress on dimensionless frequency and phase velocity. The effect of stress on stop band is discussed in this study. It can be concluded from the results that initial stress has significant effect on propagation characteristics of shear waves. The variation of initial stress has small effect on the phase velocity of shear waves. This study provides insight for development of piezoelectric composite structure under the influence of initial stress.

Resumo em Inglês:

Abstract The impact resistance of concrete is considered as poor due to a relatively energy dissipating characteristics and tensile strength. Therefore, this paper investigates the feasibility of using polypropylene fibers (PF) to enhance punching shear capacity of reinforced concrete (RC) two-way slabs subjected to drop-weight impacts. The evaluated parameters included two slab thickness (70 mm and 90 mm), five different PF percentages (0%, 0.3%, 0.6%, 0.9%, and 1.2%), and two impact load height (1.2 m and 2.4 m). The tested slabs divided into three groups: not subjected to impact load, subjected to impact load at a height of 1.2 m, and subjected to impact load at a height of 2.4 m, resulting in a total of 25 slabs. The behavior of each two-way RC slab was evaluated in terms of the crack patterns, ultimate punching shear capacity. The present experimental data can be used for further assessment of the performance of PF reinforced concretes two-way slabs as well as providing a well-documented dataset related to the impact-resistant applications which is presently limited within the literature. The results showed that adding the PF at a dosage of 0.3 to 1.2% by volume of concrete and increasing the slab thickness from 70 mm to 90 mm leads to considerable enhancement in the overall structural behavior of the slabs and their resistance to impact loading. Interestingly, the degradation in the ultimate punching capacity of the slabs subjected to impact load at a height of 1.2 and 2.4 m is 30.5% and 34.6%, respectively. Finally, an empirical model was proposed for predicting the punching shear capacity of RC two-way slabs based on reliable experimental results available in literature

Resumo em Inglês:

Abstract The study aims to determine the dynamic properties of high volume fly ash nanosilica (HVFANS) concrete exposed to strain rates between 30.12 to 101.42 s-1 and temperatures of 25, 400, and 700 oC by using split Hopkinson pressure bar (SHPB) machine. The static and dynamic compressive strengths of HVFANS concrete were slightly lower than plain concrete (PC) at room temperature, while its values were higher at 400 and 700 o C. The results proved that the CEB model of dynamic increase factor is more reliable to estimate the behaviour of HVFANS concrete at studied temperatures. The toughness, critical strain, and damage of HVFANS concrete recorded a superior performance than PC under studied strain rates and temperatures that would reflect the possibility of use HVFANS concrete in structures to improve its resistant of fire and impact loads, as well as to decrease the demand on Portland cement which could lead to restrict the risks of liberated gases during cement production. Furthermore, equations were proposed to estimate the dynamic increase factor, toughness, and critical strain of both concretes under investigated conditions.

Resumo em Inglês:

Abstract This paper describes a three-level performance-based optimization model and an estimate method of residual top displacement for steel frames at three earthquake levels. The steel frames are supposed to be elastic at frequent earthquake, inelastic and hardening at occasional and rare earthquakes, respectively. The estimate formula is derived and estimate procedure is given in detail. The estimate method only needs to use (only) one pushover analysis until steel frames yield. The yield point is obtained automatically in the proposed method. The estimate method is able to make optimization process uninterrupted. Optimal design of a 3-story 2-bay steel frame is demonstrated to validate the proposed method.

Resumo em Inglês:

Abstract In this manuscript, stiffened carbon / epoxy composite cylinders under external hydrostatic pressure will be examined to minimize mass and maximize buckling pressure. The new approach proposed in this paper is single objective optimization of stiffened composite cylindrical shell under external pressure by genetic algorithm (GA) in order to obtain the reduction of mass and cost, and increasing the buckling pressure. The objective function of buckling has been used by performing the analytical energy equations and Tsai-Wu and Hashin failure criteria have been considered. Single objective optimization was performed by improving the evolutionary GA. Optimization have been done to achieve the minimum weight with failure and buckling constraints. Finally, optimal angles pattern of layers and fiber orientations are provided for cylinder under external hydrostatic pressure.

Resumo em Inglês:

Abstract In the present study, a new fifth-order shear and normal deformation theory (FOSNDT) is developed for the analysis of laminated composite and sandwich plates under cylindrical bending. The theory considered the effects of transverse shear and normal deformations. To account for the effect of transverse shear deformation, in-plane displacement uses polynomial shape function expanded up to fifth-order in-terms of the thickness coordinate. Transverse displacement uses derivative of shape function to account for the effect of transverse normal deformations. Therefore, the present theory involves six independent unknown variables. The theory satisfies traction free boundary conditions at top and bottom surfaces of the plate and does not require the shear correction factor. The principle of virtual work is used to obtain the variationally consistent governing differential equations and associated boundary conditions. Analytical solutions for simply supported boundary conditions are obtained using Navier’s solution technique. Non-dimensional displacements and stresses obtained using the present theory are compared with existing exact elasticity solutions and lower and higher-order theories to prove the efficacy of the present theory. The comparison shows that the displacements and stresses predicted by the present theory are in good agreement with those obtained by using the exact solution.

Resumo em Inglês:

Abstract Composite shells, which are being widely used in engineering applications, are often under thermal loads. Thermal loads usually bring thermal stresses in the structure which can significantly affect its static and dynamic behaviors. One of the possible solutions for this matter is embedding Shape Memory Alloy (SMA) wires into the structure. In the present study, thermal buckling and free vibration of laminated composite cylindrical shells reinforced by SMA wires are analyzed. Brinson model is implemented to predict the thermo-mechanical behavior of SMA wires. The natural frequencies and buckling temperatures of the structure are obtained by employing Generalized Differential Quadrature (GDQ) method. GDQ is a powerful numerical approach which can solve partial differential equations. A comparative study is carried out to show the accuracy and efficiency of the applied numerical method for both free vibration and buckling analysis of composite shells in thermal environment. A parametric study is also provided to indicate the effects of like SMA volume fraction, dependency of material properties on temperature, lay-up orientation, and pre-strain of SMA wires on the natural frequency and buckling of Shape Memory Alloy Hybrid Composite (SMAHC) cylindrical shells. Results represent the fact that SMAs can play a significant role in thermal vibration of composite shells. The second goal of present work is optimization of SMAHC cylindrical shells in order to maximize the fundamental frequency parameter at a certain temperature. To this end, an eight-layer composite shell with four SMA-reinforced layers is considered for optimization. The primary optimization variables are the values of SMA angles in the four layers. Since the optimization process is complicated and time consuming, Genetic Algorithm (GA) is performed to obtain the orientations of SMA layers to maximize the first natural frequency of structure. The optimization results show that using an optimum stacking sequence for SMAHC shells can increase the fundamental frequency of the structure by a considerable amount.