Mariano Modano

ON THE FORCED VIBRATION TEST BY VIBRODYNE

Abstract. In civil engineering, Experimental Modal Analysis (EMA) dynamic tests are powerful aids to the seismic design of new structures, and useful tools for the structural identification of existing structures. EMA tests require to accurately evaluate the harmonic forcing function that is applied to the structure under testing, in order to correctly apply “model updating” procedures. The present work experimentally investigates on the nature of the forcing function applied by a vibrodyne, and its influence on the results of simulations on the dynamics of a single degree of freedom system . By using wireless accelerometers attached to a vibrodyne, we were able to measure the applied accelerations in the time domain, and the applied forcing function under different frequencies. Such an identification procedure was applied both in presence of 3+3 keyed masses, and in presence of 5+5 keyed masses, considering different angular speeds. In both cases, the forcing function applied by the vibrodyne was accurately determined as a function of time. We found out that the actual forcing function is slightly different from the theoretical sinusoidal profile, featuring marked oscillations.The work is completed by the analysis of the dynamic response a simple degree of freedom system under the action of smooth and oscillating sinusoidal forcing functions. A comparison between the results of the analyzed systems highlights marked mismatches in terms of predicted displacements, velocities, and accelerations. We therefore conclude that an accurate knowledge of the applied forcing function in EMA tests is essential in order to correctly identify the properties of the tested structures.

Theoretical Models and Experimental Techniques in Nondestructive Evaluation of Concrete

When evaluating concrete strength, common opinion is that adequate precisions can be achieved only by a particular or even total destruction. However, such methods are not always applied, besides they are very laborious. The NDE methods have a number of merits, when compared with destructive ones: a possibility to find cracks and hidden flaws in concrete; besides, they show good results in testing materials of other types, such as metals and composites. At the same time, application of NDE methods to concretes is difficult because of their complex internal structure. No existing theory can predict these properties of the transmitted wave. Therefore, the main goal of the present work is to propose a theoretical model enabling the wave penetration of ultrasonic wave through a medium with multiple internal obstacles to be described adequately. Practical applications of this ultrasonic method is toward the evaluation of mechanical properties of concrete, where the influence of internal dislocations, such as pores and cracks, is of significant importance.

Numerical and Analytical Approaches to the Self-Equilibrium Problem of Class θ = 1 Tensegrity Metamaterials

This study formulates numerical and analytical approaches to the self-equilibrium problem of novel units of tensegrity metamaterials composed of class theta=1 tensegrity prisms. The freestanding placements of the examined structures are determined for varying geometries, and it is shown that such configurations exhibit a large number of infinitesimal mechanisms. The latter can be effectively stabilized by applying self-equilibrated systems of internal forces induced by cable prestretching. The equilibrium equations of class theta=1 tensegrity prisms are studied for varying values of two aspect parameters, and local solutions to the self-equilibrium problem are determined by recourse to Newton-Raphson iterations. Such a numerical approach to the form-finding problem can be easily generalized to arbitrary tensegrity systems. An analytical approach is also proposed for the class

ON THE OPTIMAL DESIGN OF CABLE-STAYED BRIDGES

\theta=1

M-N Interaction Effect on the Frames Failure Mechanisms

units analyzed in the present work. The potential of such structures for development of novel mechanical metamaterials is discussed, in the light of recent findings concerned with structural lattices alternating lumped masses and tensegrity units.

A Finite Element Analysis of the Stability of Composite Beams With Arbitrary Curvature

This paper studies cable-stayed bridges (CBSs), with special focus on the initial force distributions in cables during construction phases. An algorithm for the optimal design of the pre-tensioning sequence of cables is presented. A procedure for the optimization of cable forces is developed, according to a given objective function. Particular attention is given to the choice of the parameters to be optimized, and numeric examples are provided. The proposed method is employed to study the At Tannumah bridge in Basrah, Iraq; and is suitable for the optimization of the pre-tensioning sequence of arbitrary cable-stayed bridges. We show in the rest of the paper that an initial design (named S0 configuration) that does not include any pre-tensioning forces in cables can lead to a highly non uniform bending moment distribution over the deck; which is not ideal for an optimal structure. Fort that reason we develop an “optimal design” (named Sd configuration), that corresponds to pre-tensioning forces inducing an “optimal” bending moment distribution over the deck.

Innovative Strategy to Reduce the Seismic Vulnerability of a RC Existing Building: Assessment and Retrofitting

The collapse factor is a significant parameter in the framework of the safety assessment and economical design of ductile structures. This fact draws attention to the necessity of a careful assessment of the limit analysis approaches. The kinematics in these structures arises in fact from the actual rotation of the plastic hinges under axial force and bending moment. It can be shown that it is possible to obtain a reliable tool capable of competing with computationally expensive methodologies. The application of the methods of limit analysis involves a simplified and idealised model of the structure and, notwithstanding the fact that hundreds of papers have been devoted to the topic, some consequences of apparently unimportant simplifications still seem to have not been properly and firmly highlighted. This paper investigates the ultimate load and collapse modes of steel frames under combined vertical and horizontal forces through limit analysis.

Numerical issues in the plastic behavior of solids

A finite element approximation of a theory recently proposed for the geometrically nonlinear analysis of laminated curved beams is developed. The application of the given finite element model to the computation of stability points and post-buckling behavior of beams with arbitrary curvature is also carried out, on taking into account the influences of shear deformation and warping effects on the in-plane and out-plane responses of the beam. The stability analysis is performed through a path-following procedure and a bordering algorithm. Several numerical results are given and comparisons with classical beam theories and other theories available in the relevant literature are established. The given results highlight that the proposed finite element model is well suited to study the stability of structures that incorporate laminated composite beams, such as, e.g., light-weight roof structures and arch bridges.

On the reinforcement of cement mortars through 3D printed polymeric and metallic fibers

In the present paper we have evaluated the seismic response of a Reinforced Concrete (RC) existing building located in an area classified as high seismicity zone and designed, in the past, only for gravitational loads. We have compared traditional and innovative steel braces for the seismic retrofitting by using a Displacement Based Approach. The innovative steel braces allow a significant improvement of the seismic behavior of the building by providing a better dissipation of the seismic input energy in the structure and thus ensuring a better performance of the RC structure in the elastoplastic range. Unlike the traditional retrofitting, the innovative strategy allows to significantly reduce the plasticization of the structural frame at the ultimate limit state, in order to minimize the post-seismic actions on the structure.

A tensegrity approach to the optimal reinforcement of masonry domes and vaults through fiber-reinforced composite materials

In the present paper numerical issues and computational procedures are described with reference to the evolutive problem in plasticity. A fully implicit integration scheme is assumed. An appropriate consistent tangent operator is applied which is suitable to be adopted for general numerical schemes. Numerical examples and computational results are illustrated which describe the effectiveness of the numerical procedure.