Resumo em Inglês:

Abstract Severe permanent deformations of buildings during earthquakes have been found as one of the major causes of the instability and failure of structures. The application of superelastic Shape Memory Alloy rebars at the plastic hinge region of reinforced concrete beam-column joints (SESMA-BCJs) can eliminate the seismic residual deformations. Such self-centering structures can maintain their reusability even after severe earthquakes. This research proposes a simple - yet practical - technique for more accurate modeling of SESMA-BCJs using VecTor2 software. Both material and geometric nonlinearity were considered. Efficiency and versatility of the modeling approach were verified against a number of test results at both material and structural levels. According to the results, the adopted modeling approach can be reliably used for the prediction of the cyclic response of hybrid SESMA-BCJs under changing various design parameters which are beyond the scope of the experimental tests. Furthermore, using the calibrated model, a comprehensive seismic parametric study was conducted to investigate the influence of various design parameters on the seismic performance of SESMA-BCJs. Finally, a new Fe-based SESMA-BCJ with a lower amount of SESMA and higher seismic performance than NiTi-based BCJs was introduced and numerically investigated.

Resumo em Inglês:

Abstract A new finite element with an additional degree of freedom at the crack location is derived for static bending analysis of a transversely cracked uniform slender beam. In the simplified computational model, which is based on Euler-Bernoulli's theory of small displacements, the crack is represented by a linear rotational spring connecting two elastic parts. The derivation of the transverse displacements, the coefficients of the stiffness matrix as well as the load vector for uniformly distributed load along the whole beam element was based on the utilization of polynomial interpolation functions of the fourth degree and all derived expressions were obtained in the closed form. The novelty of the new model, by comparison to the previously presented simplified finite element models, is that the transverse displacements functions obtained by utilization of the newly presented interpolation functions for the case of uniform continuous transverse load along whole beam element, as well as the functions of the bending moments and transverse forces, are accurate. The values obtained by the simplified model also exhibited good agreement in additional comparison with the results from more demanding and more detailed 2D models.

Resumo em Inglês:

Abstract yyTo date, a large number of finite element methods have been developed to study the dynamics of shell structures. Most of them are generally based on the degenerated solid approach and other less in shell theories, but introducing, in this last case, some assumptions to analyze this problem: some of them refer to shallow shells (slightly curved shells), or consider thin shells neglecting shear deformation, or dispense some terms in their stress-strain developments like the off-diagonal components of the curvature or metric tensors (orthogonal coordinates). In the present work, we present an improved finite element method for the linear dynamic analysis of shells, from thin to moderately thick and thick shells, developed in general curvilinear coordinates, based on a refined shear deformation shell theory and free of the well-known shear locking effect. Exact constitutive equations, including higher order moments-strains relations, are also deduced for the adequate analysis of thick shells. To circumvent the shear locking problems, the mixed interpolation of the tensorial components (MITC) of the linear strain tensor is used. An exhaustive study of different surfaces is performed, especially in doubly curved shells, and interesting conclusions of the higher order modes of vibration and the strain energy of the element are derived. Other desirable features like a low computational effort, a straightforward extension to nonlinear formulation and applications for composite shells are found in this novel and general formulation. Very good results in the proposed practical cases have been found.

Resumo em Inglês:

Abstract The aim of this study was to select an appropriate material model for a polyurethane rail pad. The considered material was assumed to be hyper-elastic, and model selection was limited only to the Mooney-Rivlin (M-R) material models available in the MSC.Marc/Mentat system. The selection of the most appropriate material model was based on the most accurate approximation of the experimental results, considering also CPU time, the stability of the material model, and convergence of the FE analyses. The current study was limited to static analysis without cyclical deformation modes. The conclusions reached and the observations from the conducted analyses should not be generalized to the whole group of hyper-elastic materials, as they relate only to the specific material under consideration. However, the results may provide a foundation for researchers involved in the analysis of such types of engineering materials.

Resumo em Inglês:

Abstract In this study, finite element analysis was performed to investigate the feasibility of multi-layered pyramidal truss structures as a filler material of energy absorbing tubes. Rectangular tubes with the filler and empty tubes were compressed at a constant velocity of 10km/h and their energy absorbing capabilities were compared to demonstrate the structural benefit of filling materials in the tubes. Additionally, the compressive response of the multi-layered pyramidal truss structures without tube wall constraint were observed. The investigations included three tube wall thicknesses and three pyramidal truss structures with three relative densities by varying the inclination angle of the pyramidal truss strut. Those were made of Al6063T5 and 304 stainless steel (SS304) for tube wall and pyramidal truss structure, respectively. The results indicate that the energy absorption capability of the tube with the filling exceeds the simple sum of that of tube and that of the filler, and this is due to the interaction effect between outer tubes and pyramidal truss struts near the tube wall. Furthermore, the inclination angle of pyramidal truss struts influences energy absorption. Thus, the pyramidal truss structures can be potentially applied as a filler material for energy absorbing structures.

Resumo em Inglês:

Abstract Cold-formed steel (CFS) construction is widely recognised as an important contributor to sustainability and green construction. Thus, the use of CFS construction is encouraged and had been advanced by innovations in its structural applications. One such innovation that has recently gained popularity is the use of CFS sections in composite construction. The researchers assembled two CFS C-lipped channels back to back to construct I-beam sections for testing. Innovative bracket shear connectors were also developed and inserted between concrete slabs and steel beams in order to provide composite action. The composite beams were drastically stronger and stiffer than non-composite beams. The experimental results were validated theoretically with a high level of correspondence. The proposed composite beams with CFS sections were found to be strong and stiff enough to be used in the construction industry.

Resumo em Inglês:

Abstract This report presents a computational research on Eurocode 2 (EC2) tension lap lengths (lo) design in a normally reinforced concrete beam, using ANSYS Workbench simulation software program by simulating a laboratory 4-point beam loading test system under static loading(discrete model approach). A typical 4-point laboratory setup loading system was modelled using an innovative and sustainable Finite Element Analysis (FEA) approach. In order to investigate the EC2 tension lap lengths (lo) design recommendation, a total of 100 analysis cases of lap lengths were considered for different reinforcement bar diameters of 10mm, 12mm, 16mm, 20mm and 25mm. The study has considered beam failure types, effects of failure load on the various lap length reduction cases and effects of steel reinforcement bar size changes on the design lap lengths. The analysis of results revealed that the yield strength of steel (fyk), diameter of tension reinforcement bar, (db), tensile strength of concrete (fctd) and concrete cover (cd) are the main parameters for a tension lap length design according to EC2. While a linear relationship exists between tension steel reinforcement bar sizes (db) and the obtained lap lengths (lo). The study reveals a potential use of 15% and 20% reduction in lap length (lo) for tension steel reinforcement bar sizes of 10mm, 16mm and 12mm and 20mm in comparison with the recommended design lap length of EC2. It was concluded that EC2 tension lap length design recommendation is conservative.

Resumo em Inglês:

Abstract In this paper, a new type of structure was introduced. The spatial steel grid structure was composed of the top layer, lower layer H-shaped steel ribs and square steel tubes. The shear key is the key part of the structure.Based on the real dimensions of a practical prototype,two sets of full-scale shear key specimens were made, one of which has vertical stiffening ribs. The loading tests of two groups of specimens were carried out to simulate cases under pure shears and the experimental results were compared with the simulations from the finite element analysis. The effects of vertical stiffeners on failure modes, ultimate loads, strength-yield ratio and ductility of shear key were studied through experiments. By parametric analyses in the present article, relations of the stiffening plates width and thickness was recommended.

Resumo em Inglês:

Abstract For offshore structures, especially jacket supported structure such as fixed platform and offshore wind turbine, the underwater area provides an ideal site for corrosion formation and marine fouling. In this marine environment, the structures are exposed to particularly aggressive corrosion and colonized by marine organisms involving a diversity of species. In this paper, a number of cases are conducted where an existing fixed platform is subjected to uniform corrosion. Furthermore, the platform is also subjected to marine fouling. The platform is assessed to investigate the effects of corrosion and marine fouling on its structural strength by determining the Reserve Strength Ratio (RSR) value. It is found the platform is limited to at least 50 years of service life when subjected to average corrosion. However, the platform is no longer considered as safe after 37 years when subjected to severe corrosion. Moreover, there is an RSR loss of 38% when marine fouling is introduced at the first 5 years which is detrimental to the overall safety of the platform. On the other hand, there is minimum RSR loss of only 5% for most cases when marine fouling is introduced but still detrimental to the overall safety of the platform. The obtained outcomes were documented and will be useful information to conduct condition assessment (or structural health monitoring) of aged fixed jacket structures.

Resumo em Inglês:

Abstract This study focused on improving the design of slender structures with reinforced concrete (RC) telecommunication towers as the main application. Analytical procedure based on Rayleigh’s method to compute the first natural vibration frequency and the critical buckling load was development. All the nonlinearities present in the system were considered, in addition to the soil-structure interaction and the variation of the geometric properties along the length of the structure. The geometric nonlinearity and imperfections of the tower structure were computed as functions of the axial load using a geometric stiffness matrix. Further, the material nonlinearity was accounted for by reducing the flexural stiffness. As concrete structures exhibit viscoelasticity, creep was calculated using the Eurocode 2 model. The soil-structure interaction was modeled as a set of distributed springs. To validate the proposed method, the first frequency and critical buckling load were compared with those yielded by FEM simulations. The frequency results were in good agreement with those of the FEM simulations, indicating that the proposed method is sufficiently accurate for use in engineering design applications and easy to implement. On the other hand, the buckling load results obtained using the proposed method and FEM differed significantly, motivating further investigation.