Resumo em Inglês:

Abstract The present paper investigates the transverse vibration of a non-uniform axially functionally graded Timoshenko beam with cross-sectional and material properties varying in the beam length direction. The Chebyshev collocation method is used to spatially discretize the governing partial differential equations of motion of the beam into time-dependent ordinary differential equations in terms of Chebyshev differentiation matrices. An algebraic eigenvalue equation in matrix form is then formed to study the free vibration behavior of non-uniform axially functionally graded Timoshenko beams. Several results of natural frequencies of the beams are evaluated and compared with those in the published literature to assure the accuracy of the proposed model. The effects of taper ratio, material graded index, slenderness ratio, material compositions and restraint types on the natural frequencies of tapered axially functionally graded Timoshenko beams are examined.

Resumo em Inglês:

Abstract While structural strengthening is not the consequence of a structure's condition of failure, it does take place as a result of a need to increase the structural stiffness and load capacity when a change in the structure's usage occurs. As a result, various techniques must be presented to enhance the structural elements by considering economic and time requirement factors and load-bearing capacity. In this study, the issue is demonstrated using a steel I-beam that was strengthened using six different techniques to postpone the beam's lateral torsional buckling to achieve its full plastic flexural capacity. Finite element (FE) analyses were carried out with the use of Abaqus software to predict the response of both unstrengthened and strengthened steel I-beams in a four-point bending test for a total of 56 specimens with different parameters studied. In order to understand which strengthening techniques are most appropriate for a new or existing steel building, an analysis of the costs was conducted for each strengthening technique to reach a conclusion regarding which strengthening techniques would be ideal for use.

Resumo em Inglês:

Abstract The main goal of this research is to study the postbuckling behavior of nonlocal functionally graded beams. Eringen’s nonlocal differential model is used to evaluate the influence of the material length scale in the bending response. An improved shear deformation beam theory with five independent parameters is utilized, which is suitable for the use of 3D constitutive equations. A finite element model is derived with spectral high-order interpolation functions to avoid shear locking. The formulation is verified by comparing the present results with the ones found in the literature. Functionally graded beams with different boundary conditions, nonlocal parameters, and power law indices are analyzed. It is shown that the present model can accurately predict the behavior of nonlocal beams due to the use of high-order terms in the displacement field in comparison with classical beam formulations. Finally, new benchmark problems are analyzed to show the capabilities of the present model to evaluate the effect of the nonlocal parameter and the power law index on postbuckling beam behavior.

Resumo em Inglês:

Abstract A mechanical model was developed to evaluate the reliability of very slender columns subject to creep, employing the nonlinear moment-curvature relationship. Second-order effects were considered by the finite difference method. Numerical tests were carried out on 432 columns with a slenderness index between 100 and 200. The general nonlinear method was adopted to determine the design load, applying the displacement of the stress-strain diagram for consideration of creep. The reliability index was calculated using the Monte Carlo method and the First Order Reliability Method. Among the results obtained, it was observed that it is important to review the safety criterion of the Brazilian Standard NBR 6118 about the very slender columns (90 < λ ≤ 200) by performing the calibration of the additional coefficient γn1. In addition, it was observed that an increase in the reinforcement ratio commonly produces a reduction in the reliability index; an increase in the first-order relative eccentricity promotes a decrease in reliability, among other evaluated factors.

Resumo em Inglês:

Abstract Applying the Covariance-driven Stochastic Subspace Identification method (SSI-COV) involves uncertainties in the numerical process of identifying modal parameters in a system. The main issue is that the method does not compute the uncertainty in the results, which is required in some problems such as outlier detection. Currently, one method is available to assess the uncertainty in modal parameters obtained using the SSI-COV. This method based on the sensitivity analysis of the modal parameters to perturbations in the collected data and is efficient but highly complex for its computational implementation. Thus, this article presents a validation of the uncertainty results obtained with this procedure through the uncertainty limits obtained using the Bootstrap technique. The validation is performed on the modal parameters of a numerical beam-type structure with controlled noise levels and the modal parameters of a concrete block of the Itaipu Hydroelectric Dam. The uncertainty limits obtained using the two methodologies showed similarities in the two examples, which allowed validating the sensitivity analysis procedure.

Resumo em Inglês:

Abstract The response of a reinforced concrete structure is influenced by the variability of design parameters such as materials strengths, geometry, and load intensity. One of the most rational ways to assess the safety level of a reinforced concrete structure is to employ a probabilistic approach. This paper aims to compare the reliability indexes for a set of reinforced concrete beams according to two different methodologies, based on the association of First Order Reliability Method (FORM) with the ANSYS software. In the first methodology, the reliability indexes were assessed through the direct coupling of the FORM to the Finite Element model. In the second methodology, a response surface was employed to fit a flexural resistance function, based on the FE results, being the reliability indexes assessed by an external FORM algorithm. The results showed that both methodologies led to equivalent reliability indexes and that the safety level of the beams, which were designed according to the Brazilian code NBR 6118:2014, is mainly influenced by the load combination, presenting unsatisfactory values when the live load increases.

Resumo em Inglês:

Abstract The stability and comfort of vehicles depend on the operation of the suspension system. To increase the smoothness and comfort for passengers in the vehicle, the stiffness of the suspension system needs to be changed flexibly. The conventional pneumatic suspension system can partially meet these requirements. However, the change is not much. This paper introduces a model of the pneumatic suspension system integrated with a hydraulic actuator. This is a completely novel and unique method. In the case that the excitation is random, average values of displacement and acceleration of the sprung mass are only 12.56 (mm) and 3.78 (m/s2) if the vehicle uses the integrated pneumatic suspension system. In contrast, this value is very large, up to 30.70 (mm) and 6.53 (m/s2) if the passive suspension system is used. Similarly, this change is also very large in the remaining survey situations. Overall, the values ​​of acceleration and displacement of the sprung mass are significantly reduced when the vehicle is equipped with an integrated pneumatic suspension system. The results of the research showed the advantages of this method compared to other methods.

Resumo em Inglês:

Abstract This paper investigates the stress transferring mechanism of a pressure tunnel strengthened with CFRP. A simplified mechanical model of the internal water pressure transfer from the CFRP to the lining concrete is established, and the key parameters that influence the internal water pressure transfer between the CFRP and lining concrete are identified. A solid-spring-solid three-dimensional finite element model is established. Using the numerical model, the influences of the above key parameters on the ratios of the internal water pressure borne by the concrete and CFRP are investigated. Based on the above results, a reinforcement scheme of the Yellow River Crossing Tunnel is studied and optimized as a case study. This reveals that the elastic modulus and thickness of the CFRP are the two most important factors that affect the ratios of the internal water pressure borne by the concrete and CFRP, and increasing the elastic modulus and thickness of the CFRP can decrease the ratio of the internal water pressure borne by the concrete and improve the stress state of the lining concrete.

Resumo em Inglês:

Abstract The plastic anisotropy behavior of ferritic stainless steel (FSS) sheets was analyzed and modeled under associated and nonassociated flow rule approaches. Three orthotropic flow functions, known as quadratic Hill48 and nonquadratic (Yld2000-2d and BBC2005), were developed and employed under an associated and nonassociated flow rule hypothesis. For the NAFR based on the initial anisotropy, the mechanical behavior was described by the nonexponential model functions of Yld2000-2d and BBC2005 to predict the directional dependence of mechanical parameters. It provided a considerable advantage in terms of flexibility and good agreement with the experiment. According to the results, the polynomial fit functions of the transverse versus longitudinal true plastic strain curve were used to describe the designated properties corresponding to a selected level of strain. To describe the evolution of anisotropic hardening and potential plastic hardening, seven different loading conditions were considered. The proposed evolutionary non-AFR Yld2000-2d and BBC2005 criteria showed good accuracy in predicting the evolution of hardening yield and Lankford coefficients depending on the plastic deformation.

Resumo em Inglês:

Abstract The current study addresses the influence of the excitation frequency content on the efficiency of a tuned liquid column damper (TLCD) to control the displacement response in structures subjected to seismic excitations. A time-domain stochastic stationary analysis is performed, and an equivalent statistical linearization for the TLCD is obtained. The results show that the TLCD is more efficient in structures subjected to broadband processes. In narrowband processes, the maximum performance of the TLCD occurs when the linear equivalent period of the system TLCD-structure tunes the TLCD period, and the frequency of the structure matches the predominant frequency of the input motion. Results derived from this analysis are validated through two time-history seismic analyses.