Resumo em Inglês:

Abstract This paper has evaluated the bending performance of a novel prefabricated MVFT steel-concrete composite girder. 9 meters pilot MVFT girder was analyzed by validated finite element model. In the pilot test, the height of web, the length of grouted concrete in the girder and net spacing between webs were parametrically modeled to discuss their effect to the bending strength. An ultimate bending strength formula has been obtained, which was based on the regression of parametric results. In the meantime, the two Machine Learning (ML) models, BP neural network and Least Squares Support Vector Machine, have been also implemented to train and then predict the ultimate strength of MVFT girder. Three factors were selected as input in ML models: the distance between steel girder’s Tensile Centroid(TC) and slab’s Compressive Centroid(CC), the distance between steel girder’s TC and its CC, the compressive area of steel girder. After the completion of the ML training, the ultimate strength predictions of 30 meters MVFT girder by BP model and the formula have been compared, which agrees well with each other and validates their accuracy.

Resumo em Inglês:

Abstract This study aims to investigate the effect of the infilled frames through various important parameters (i.e., the openings’ percentage in infill walls - several columns on the first floor are removed - partial infilled) in the RC structures, subject to progressive collapse scenarios. To this end, 3D finite element models were constructed by using the software ABAQUS. Numerical and experimental results were compared to substantiate the finite element models’ capability of simulating the experimental models’ behavior of Al-Chaar et al. (2002) in an accurate manner. The results showed that there was good agreement between experimental and numerical results. Moreover, the results indicated that there was a significant effect, which cannot be neglected, on the progressive collapse resistance; the reduction ratios in vertical displacement at the regions removed columns can reach up to 80%.

Resumo em Inglês:

Abstract The suitability of employing the second-order shear deformation theory to static bending problems of thin and moderately thick isotropic circular cylindrical shells was investigated. Two variant forms of the polynomial second-order displacement models were considered. Both models account for quadratic expansions of the surface displacements along the shell thickness, although the second model (SSODM) was augmented by the initial curvature term. The equilibrium equations were derived by use of the principle of virtual work. Navier analytical solutions were obtained under simply supported boundary conditions. The results of the displacements and stresses revealed that the theory formulated on the SSODM provides a good depiction of the bending response of thin and moderately thick shells and are in close agreement with those of the first and higher-order shear deformation theories (FSDT; HSDT). The ability of the theory formulated on the first model (FSODM) to predict adequate values of displacements and stresses in thin shells was found to be significantly affected by changes in length to radius of curvature (l/a) ratios.

Resumo em Inglês:

Abstract To better understand the penetration mechanism of the elliptical cross-section projectile (ECSP) into semi-infinite concrete target, penetration experiments using three types of ECSPs with different shape ratios (1, 1.25 and 1.61) and with striking velocities ranged from 550 m/s to 1050 m/s were conducted. Penetration depths, penetration trajectory and mass erosion rates of the projectile were obtained after the experiments. The experiment results show that the penetration performance and ballistic stability of the ECSP are equivalent to those of the circular cross-section projectile (CCSP). Based on the theory of complex variable function and conformal transformation, a semi-analytical model which can calculate the cavity boundary stress distribution of elliptical section cavity controlled by the displacement boundary condition was established and the model was validated by comparing the model degenerate solution with Kirsch problem results. Theoretical calculation results show that the radial stress of elliptical section cavity increases progressively from the minor axis to the major axis. In addition, a formula combining with the semi-analytical theoretical model and the local interaction theory was developed. The predicted penetration depths were compared with 30 groups of experiment data with different projectile parameters and striking velocities and coincide quite well with the corresponding experimental data. Finally, the influence of shape ratio and caliber-radius-head (CRH) on the penetration performance of projectile and the application prospect of ECSPs on hypersonic weapon platform were studied.

Resumo em Inglês:

Abstract Using bonded piezoelectric transducers (PZT), this study evaluates damage to reinforced concrete beams at lap splices of tensile rebars. Four reinforced concrete beams with a span of 2700mm and a cross-section of 200 x 250mm were cast and simply edge-supported on roller supports 2250mm apart. In the zone of constant moment, the tensile reinforcements of the beams were spliced with varying lap lengths (10ϕ, 20ϕ, 30ϕ and 40ϕ). Two PZT patches (one to operate as an actuator and the other as a receiver) were bonded on steel rebars and placed 50mm apart from their lapping edges. The wave propagation technique was used to record the signals experimentally, and the signals were processed further using wavelet packet analysis. By setting the time lag results of waves under pulse excitation, the damage of beams were identified. Damage indices were calculated based on the wavelet packet energy to ascertain the damage levels. The PZT was very sensitive to detect the pull-out bond failure and ductile flexural failure at the lap slices of steel rebars in the beam and it gives an advance indication before the structural collapse due to brittle failure.

Resumo em Inglês:

Abstract The present paper aims to test recent (Truly self-starting two sub-step method and three-parameter single-step implicit method) and classical (Generalized-α, HHT-α, and WBZ-α methods) time integration methods using the geometrically nonlinear Positional Finite Element Method (PFEM). The numerical formulation is based on the total Lagrangian approach and uses the Hessian matrix to obtain the response. The mixed hardening inelastic model applied to PFEM is also presented. Two examples validate the time integration algorithms and the inelastic model. In the first example, the mixed hardening inelastic model is compared with the the bilinear stress-strain model and the elastic-perfectly plastic hinge model, and aspects such as amplitude decay and period elongation are discussed. In the second example, the implemented algorithms are verified in a severe geometrically nonlinear example, considering the influence of numerical dissipation, time interval, and the number of elements in the response. Results show the relevance of numerical damping for numerical stabilization and the good performance of the Generalized-α algorithm.

Resumo em Inglês:

Abstract This study investigates the biomechanics of the spine after insertion of vertebral body tethering (VBT) with different cord pretensions. For that purpose, a Finite Element model of the average thoracolumbar spine was stepwise calibrated and validated. The VBT instrumentation was inserted in the left side of the L1-L2 segment with different cord pretensions. As a second test, the L1-L2 segment was submitted to an external pure moment of 6 Nm in left and right lateral bending. The range of motion (ROM) for the spine with VBT was determined with respect to its initial post VBT position. Pretension forces of 100 N and 300 N resulted in a change of scoliotic angle of 2.7° and 5.3° to the left side of the spine, respectively. The ROM of the native spine was 4.5° in right lateral bending and reduced to 1.8° and 1.4° for the cases of the spine with a cord pretension of 100 N and 300 N, respectively. In left lateral bending, the absolute ROM of the native spine was 4.6°. For the cases of a cord pretension of 100 N and 300 N, the spine bent 1.9° and 0.8° to the left side from its initial post VBT position, respectively.

Resumo em Inglês:

Abstract To study the complex mechanism of the high-dimensional nonlinear cable systems, a 3 degree-of-freedom model reduced from the tower-cable-beam structure is proposed and investigated in this paper. Based on the D’Alembert Principle, the dynamic equations of in-plane and out-of-plane vibration are established and simulated by the 4th-order Runge-Kutta method. The results exhibit the phenomenon of coupling internal resonance under the systematical conditions revealed by the analytical analysis on the dynamic equations. The smaller mass ratio of the cable-beam would lead to a greater vibration intensity while the tensile stiffness and initial force of the cable have no significant effect. The in-plane and out-plane cable vibrations are independent, and the internal resonance would not be excited by the harmonic excitation in the cable axis. Additionally, applying damping on any component of the system is verified to be an effective approach to vibration reduction. Compared with ordinary cables, cables with less-weight and high-strength materials would be exited to less vibration intensity under the same external excitation.

Resumo em Inglês:

Abstract The Structural Optimization process has an increasing importance in industry and academic fields, assisting in the development of designs at the initial stages of a project. Nowadays, the structural optimization methodology can be conducted by Topology Optimization Method (TOM), which is an efficiently combination of the Finite Element Method (FEM) with an optimization algorithm, in order to find the optimized material distribution inside a given design domain subjected to a set of constraints. Application of the FEM in TOM suffers from a series of instability problems, being one of them the checkerboard pattern. This paper investigates the impact of the Generalized Finite Element Method (GFEM) and Stable Generalized Finite Element Method (SGFEM) in the implementation of the TOM algorithm. This work shows that these unconventional FEM formulations are able to solve most of the checkerboard pattern problem when combined with an enriched mesh designed specifically to each example evaluated. Significant improvement in results of the topology optimization is achieved when compared to the conventional formulation of TOM.

Resumo em Inglês:

Abstract Peak ground acceleration (PGA) is frequently used to describe ground motions accurately to defined the zone is critical for structural engineering design. This study developed a novel models for predicting the PGA using Artificial Neural Networks-Gravitational Search Algorithm (ANN-GSA) and Response Surface Methodology (RSM). This paper grants the prediction of PGA for the seismotectonic of Iraq, which is considered the earlier attempt in Iraqi region. The magnitude of the earthquake, the average shear-wave velocity, the focal depth, the distance between the station, and the earthquake source were used in this study. The proposed models are constructed using a database of 187 previous ground motion records, this dataset is also utilized to evaluate the effect of PGA’s parameters. In general, the results demonstrate that the newly proposed models exhibit a high degree of correlation, perfect mean values, a low coefficient of variance, fewer errors, and an acceptable performance index value compared to actual PGA values. However, the composite ANN-GSA model performs better than the RSM model.