Resumo em Inglês:

Abstract To evaluate the fatigue life of Q420C steel welded joints, fatigue tests were performed on butt-welded joints, cross-butt-welded joints and cross-fillet-welded joints. The fatigue strength S-N curves of the joints were fitted. Then the formation and development of fatigue cracks were analyzed by fracture morphology. The fatigue properties of joints were compared with literature data and standard curves. The results showed that the fatigue test data of the three types of welded joints were roughly above the standard curves. Moreover, the fatigue strength of butt-welded joint was significantly higher than the calculated values of standards, indicating a large safety margin. The test value of cross-butt-welded joint was close to the calculated values of standards, so it is suggested to moderately reduce the standard values. In addition, all the three standards could well predict the fatigue life of cross-fillet-welded joint. The fracture morphology of the specimens showed the development process of fatigue damage, and the fatigue displacement curve and damage curve proved the formation of the fatigue fracture in specimens.

Resumo em Inglês:

Abstract Blast loads have been increasingly studied in the past decades, especially regarding civil structures. Until recently, the negative phase of these loads has been disregarded, but studies concluded that the effect of suction must be included. In the case of plates, nonlinearity plays an important role, and the membrane effect should also be considered. This work focuses on the influence of nonlinearity in plates subjected to blast loads. Equations were developed for the calculation of blast load parameters, considering that positive and negative phases are approximated by the Friedlander equation and cubic polynomial, respectively. The plate is modeled as a SDOF system using von Karman's theory of large displacements. The development of the nonlinear dynamic differential equation is reviewed, considering a simply supported plate, and its solution is based on fourth order Runge-Kutta numerical method. A reference example is used as a benchmark and then parametric studies are conducted, in which the influence of scaled distance, mass of explosive, and the consideration or not of the negative phase is analyzed.

Resumo em Inglês:

Abstract Numerical form-finding is an effective method for determining the equilibrium configurations of tensegrity structures. However, the connectivity matrix is required to be input as initial data in most form-finding methods, and it is time-consuming and inconvenient for the designer in processing a complex structure with a large number of components. To address this issue, a novel automatic method of generating a connectivity matrix is proposed for three dimensional N-4 type tensegrity structures in this paper. The novelty of our algorithm is that the number of nodes is the only required parameter for the proposed method. Numerical examples are employed to validate our method. The results show that the proposed method is competent inform-finding for three-dimensional N-4 type tensegrity structures in terms of accuracy, efficiency and convergence.

Resumo em Inglês:

Abstract The suspension system has the role of regulating and extinguishing oscillations in the vehicle. To improve stability and comfort, the active suspension system is proposed to replace the passive suspension system. There are many algorithms used for active suspension system control, such as PID, LQR, Fuzzy, etc. Among them, the nonlinear control method which uses the SMC algorithm gives a stable performance. This research proposes the use of the SMC algorithm to control the operation of the active suspension system equipped with a quarter dynamics model. The process of linearization of the hydraulic actuator is presented in the paper. As a result of the simulation, the values of displacement and acceleration of the sprung mass were significantly reduced when the vehicle used the active suspension system controlled by the SMC algorithm. The SMC controller established in this paper provides stability in many situations. Therefore, the vehicle's smoothness and comfort have been significantly improved. In the future, intelligent algorithms can be combined with SMC algorithms to improve the efficiency of the controller.

Resumo em Inglês:

Abstract ‎ The present study analyzes the bending of a simple electro-elastic cylindrical shell by the compound matrix method‎. The cross-section of the circular cylindrical shell is a non-circular curved shape‎, ‎with μ1 a function of AB and the mode number‎, ‎where A and B are the pre-deformation inner and outer radii of the cylindrical shell‎, ‎and μ1 is the ratio of the deformed inner radius to A ‎. ‎In the first step‎, ‎a numerical model of the problem is developed to obtain specific differential equations‎. ‎The modeling yields a system of two Ordinary Differential Equations with three boundary conditions of the same type‎. ‎Next‎, ‎it is shown that the dependence of μ1 to AB has a boundary layer structure‎. ‎Simple numerical observations were made for bifurcation conditions‎. ‎The analysis is‎, ‎in fact‎, ‎based on the variations of the inner and outer radii A and B ‎, ‎assuming a=μ1 A and b=μ2 B, ‎and based on the bifurcation of μ1 and μ2 ratios with respect to radius‎. ‎For this purpose‎, ‎the compound matrix method is used to show the validity of the arguments‎.

Resumo em Inglês:

Abstract The development of a numerical formulation is presented to describe viscoelastic behavior considering shear effects. The nonlinear positional formulation of the Finite Element Method is used considering plane frame elements with Reissner kinematics. The description of the viscoelastic behavior is considered through the adoption of a stress-strain relation based on Boltzmann rheological model. The used kinematics allows to describe the decoupling between the rotations and the displacements in element cross-sections. This approach allows to evaluate the contribution of shear effects in viscoelastic behavior in an original way. Based on the developments and the results obtained, it is possible to observe that strains and displacements due to viscoelastic behavior are significantly superior to the results obtained considering Bernoulli-Euler kinematics hypothesis. It is possible to notice a better agreement between the obtained numerical results and the results in the literature. Results obtained from the developed formulation allow the assessment of the shear effects on the viscoelastic behavior of plane frames.

Resumo em Inglês:

Abstract The industrialized building system has specific characteristics that set it apart from the conventional concrete wall system, namely, a reduced wall thickness, the use of electro-welded wire mesh, and a lack of boundary element confinement. These conditions have attracted the interest of researchers, who have developed various experimental programs to evaluate the behavior of these walls. However, evidence on the seismic performance of buildings remains scarce. In this study, the performance of 5-, 8- and 12-story buildings was evaluated by nonlinear chronological analysis. Numerical models were constructed using the Shell Layered element of the ETABS software and adjusted based on the results from tests of isolated walls and the periods of one of the buildings identified in an ambient vibration test. The findings suggest that these buildings may fail to meet the life safety performance level in high seismic hazard areas.

Resumo em Inglês:

Abstract In the field of warhead design, non-cylindrical warhead, especially elliptical cross-section warhead, has received considerable attention. In this study, the initial velocity and distribution characteristics of the preformed fragments of a columnar projectile with an elliptical cross-section were examined. To obtain the velocity distribution of the fragments in this kind of projectile, three elliptical cross-section projectiles with different geometric sizes were test based on the static detonation tests. Then, the numerical models of the elliptical cross-section projectile have been established and validated according to the experiment results. Besides, two kinds of initiation types were studied by the simulation model, and the results indicate that not only the geometric size but the initiation type do great influences on the fragment velocity distribution in the direction of the axis. An empirical model was proposed based on the fragment two-step acceleration progress, and it was in good accordance with numerical results.

Resumo em Inglês:

Abstract This paper aims to perform the experimental test and numerical FE analysis of the cold-formed steel frame structure to provide new proposals to improve the strength, rotation capacity, and seismic energy dissipation in these structures. A 3D full-scale three-story CFS frame structure is experimentally investigated under four sets of input data for 100% and 50% scales of Northridge and Kocaeli earthquake acceleration records using the shaking table test. In each test, the frame acceleration and displacement are observed. A FE model is employed to assert the validity of the experimental test. The results indicated that the maximum story drift ratio of the frame ranges from 1.14% to 3.70%. It is observed that the average similarity ratio of the maximum displacement results between FE analysis and shaking table test is 92%. It is shown that the translational stiffness for the system decrease as the earthquake acceleration records decrease. It is also shown that using the image processing technique in the shaking table test can offer much more acceptable and economical solutions in determining the displacement parameters.

Resumo em Inglês:

Abstract Two full-scale corner beam-column joints with and without fuse bars were designed, constructed, tested, analyzed and modeled under in-plane lateral cyclic loading presented herein. The first specimen was designed using Eurocode 8 and equipped with four fuse bars. Second specimen was designed using BS8110 (non-seismic code of practice) with corbel. All the specimens have similar size of foundation beams, columns and beams. Visual observation during testing showed that specimen with fuse bars suffered less damage as compare with specimen without fuse bars. Furthermore, specimen with fuse bars has higher lateral strength capacity, stiffness, ductility and equivalent viscous damping than specimen without fuse bars. Finally, there is good agreement of lateral strength capacity, ductility, stiffness and equivalent viscous damping which lies between 2% and 20% between experiment and modeling hysteresis loops. Thus, it is recommended that fuse bar as a green structural material can be installed inside the corner beam-column joint for RC buildings to cater strong earthquakes in high seismic regions.