Vibration and buckling of open TWBs with local weakening

Free vibration and Ljapounov stability of compressed open thin-walled beams with a cross-section reduction are studied by a in-house finite differences numerical code, based on a refined direct beam model and allowing for investigating elastic stability of non-trivial equilibrium paths in a dynamic setting. The benchmark is a beam with doubly symmetric cross-section and non-zero warping rigidity, under free, semi-, and fully restrained warping at its ends. In all cases, the results of the direct model are compared to finite element and/or experimental ones. The reduction in the cross-section rigidity induces a weakening that may model a local damage; thus, the present investigation may be useful with an outlook to damage monitoring and identification

Structural Analysis of High-rise Buildings under Horizontal Loads: A Study on the Piedmont Region Headquarters Tower in Turin

Background: When a high-rise building is designed, the main aim is to limit transversal displacements. In addition, when vertical bracings, made up of thin open sections, are subjected to external torsion, warping and secondary torsional moment stresses arise which need to be evaluated using Vlasov’s Theory. Objective: This work analyzes the Piedmont Region Headquarters Tower, using an analytical formulation which enables the calculation of structural displacements and stresses. Methods: The analytical formulation used in the static and dynamic analysis of the structure was implemented using Matlab computation code. A computational model was also created using a commercial Finite Element Code to validate the results. Results: The results obtained with the analytical model were compared with those obtained with the FEM model. The transversal displacements, bending, torsional, and axial stresses in the vertical bracings were calculated, along with the principal natural frequencies of the structure. Conclusion: It has been proved that analytical calculation codes are a good tool for the preliminary design of a high-rise building. In particular, the proposed formulation, which has only three degrees of freedom per floor, provided results similar to those obtained using a FEM model. The great advantage of this analytical code is to speed up the computation time, which is proportional to the square of the degrees of freedom. In a FEM model, these have orders of magnitude greater than in the analytical model. Moreover, the proposed formulation allows the load distribution between the structural elements to be determined

Optimization of diagrid geometry based on the desirability function approach

Abstract Diagrids represent one of the emerging structural systems employed worldwide for the construction of high-rise buildings. Their potential relies on the peculiar architectural effect and their great lateral stiffness. Because of the modular nature of the diagrid triangular element, optimization processes are usually carried out to assess the best arrangement of the external diagonals in order to enhance the structural performance while using the lowest amount of structural material. In this contribution, we make use for the first time of the desirability function approach to investigate the optimal geometry of the dia-grid system. A 168-meter tall building, with four different floor shapes, is analyzed, and the inclination of the external diagonals is varied between 35° and 84°. The desirability function approach is applied to find the most desirable geometry to limit both the lateral and torsional deformability, the amount of employed material as well as the construction complexity of the building. A sensitivity analysis is also carried out to investigate the influence of the individual desirability weight on the obtained optimal geometry. The effect of the building height is finally evaluated, through the investigation of sets of 124-, 210- and 252-meter tall diagrid structures

Geometrically nonlinear behavior of lattice domes coupled with local Eulerian instability

Abstract Structural analysis is an intricate subject when nonlinearities occur. They make the structural behavior complex and may have important consequences in the design choice as well. Especially for lattice domes, as snap-through phenomena and local Eulerian instabilities generally affect the structural response, linear analysis is not enough. In this paper, a semi-analytical formulation is used in order to study the geometrically nonlinear behavior of lattice domes subject to vertical loads. The formulation is derived from the equilibrium equations written in the deformed configuration, considering large displacements and taking also into account local buckling conditions. The resulted system of equations, being strongly nonlinear, has been solved by means of a numerical procedure, based on a mixed load-displacement control scheme, leading to the evaluation of the complete equilibrium path. The influence of geometrical parameters on the critical load multiplier and shape of the load-displacement curve is also discussed. In particular, a complex equilibrium path for a sixteen-member five-node lattice structure is analyzed, which is characterized by several branches which can generate 'snapping' conditions

Analytical Stress Intensity Factors for cracks at blunted V-notches

AbstractAn analytical expression for the Stress Intensity Factor (SIF) related to a crack emanating from a blunted V-notch root is put forward. Different notch amplitudes, ranging from 0° to 180°, and different crack length to root radius ratios, ranging from 0 to 10, are taken into account. The analysis is limited to mode I loading conditions, as long as the crack length is sufficiently small with respect to the notch depth. The proposed formula improves significantly the predictions of the relationships available in the Literature, by considering a notch amplitude dependent parameter: its values are estimated through a finite element analysis (FEA)