Alessio Bonelli

EXPLICIT PREDICTOR–MULTICORRECTOR TIME DISCONTINUOUS GALERKIN METHODS FOR LINEAR DYNAMICS

Abstract This paper focuses on the formulation and implementation of explicit predictor– multicorrector Time Discontinuous Galerkin methods for linear structural dynamics. The formulation of the schemes is based on piecewise linear functions in time that approximate displacements and momenta. Both the predictors and correctors are designed to inherit third order accuracy from the exact parent implicit Time Discontinuous Galerkin method. Moreover, they are endowed with large stability limits and controllable numerical dissipation by means of an algorithmic parameter. Thereby, the resulting algorithms appear to be competitive with standard explicit algorithms for structural dynamics. Representative numerical simulations are presented illustrating the performance of the proposed numerical schemes and confirming the analytical results.

Capabilities of a Fiber Bragg Grating Sensor System to Monitor the Inelastic Response of Concrete Sections in New Tunnel Linings Subjected to Earthquake Loading

In a comprehensive experimental campaign, we investigated the capabilities of Fiber Bragg Grating (FBG) sensors in monitoring the inelastic response of new circular concrete tunnel linings, subjected to seismic events. The FBG sensors measured the strains of steel reinforcement to be treated by a decision support system (DSS). First, a set of four-point bending tests was performed on tunnel substructures, with the aim of characterizing the cross-section under cyclic loading and of designing an FBG sensor package for use in a unique full-scale test on a structure, which represented a complete circular section of the tunnel lining. Several types of FBG packages, to be embedded in and applied externally to the tunnel section, were tested to find the best solution. For comparison purposes, some standard devices were also used. The results of the experimental campaign are presented in detail, highlighting the performance of FBG sensors in reliable inelastic strain measurement of ductile concrete sections in seismic zones. Finally, the use of these data by a DSS allowed for the estimate of current structural conditions and damage at the monitored sections.

Linearly Implicit Time Integration Methods for Real-Time Dynamic Substructure Testing

The simulation in real time of heterogeneous systems has to guarantee that the time integration of the equations of motion is always successfully completed within an a priori fixed sampling time interval. Therefore, numerical and/or physical substructures as well as numerical solution methods have to be adapted to the needs of real-time simulations. Monolithic stable numerical methods are implicit and cannot be easily used in real-time applications because of their iterative strategies necessary to solve the nonlinear corrector equations. As an alternative, in the present paper, we consider linearly implicit Rosenbrock-based L-stable real-time (LSRT) compatible algorithms with both two-stage and three-stage. Moreover, other linearly implicit structural integrators used nowadays to perform coupled simulations in real time are introduced too. Successively, typical properties of monolithic algorithms are shown when large time steps are employed. The loss of stability and the reduction of accuracy of these algorithms, when applied to coupled systems caused by kinematically closed loops, are analyzed in-depth through a split-inertia substructured system. In this respect, the benefits of the L-stability property are shown. Finally, the performance of the algorithms under investigation appears in a number of more realistic tests considering both nonstiff and stiff substructures.

Predictor‐corrector procedures for pseudo‐dynamic tests

Purpose – To propose novel predictor‐corrector time‐integration algorithms for pseudo‐dynamic testing.Design/methodology/approach – The novel predictor‐corrector time‐integration algorithms are based on both the implicit and the explicit version of the generalized‐α method. In the non‐linear unforced case second‐order accuracy, stability in energy, energy decay in the high‐frequency range as well as asymptotic annihilation are distinctive properties of the generalized‐α scheme; while in the non‐linear forced case they are the limited error near the resonance in terms of frequency location and intensity of the resonant peak. The implicit generalized‐α algorithm has been implemented in a predictor‐one corrector form giving rise to the implicit IPC‐ρ∞ method, able to avoid iterative corrections which are expensive from an experimental standpoint and load oscillations of numerical origin. Moreover, the scheme embodies a secant stiffness formula able to approximate closely the actual stiffness of a structure. ...

Pseudo-Dynamic Heterogeneous Testing With Dynamic Substructuring of a Piping System Under Earthquake Loading

In recent years, both pseudo-dynamic and real time heterogeneous testing with dynamic substructuring — hybrid testing — have gained significant popularity for their applicability to testing several types of nonlinear structures/systems. In a hybrid test, a heterogeneous model of the emulated system is created by combining a Physical Substructure (PS) with a Numerical Substructure (NS) that describes the remainder of the system. Nevertheless, an efficient implementation of this technique requires overcoming certain problems, e. g., proper dynamic substructuring, reduction of external forces and actuator delay compensation. This paper presents a pseudo-dynamic test campaign undertaken by the University of Trento, Italy, on a typical full-scale industrial piping system subjected to earthquake loading in order to investigate its seismic performance. Some challenges faced during the implementation are shown and strategies adopted to overcome these problems are illustrated. Experimental activities will be described and performances of different components of the piping system, i.e., elbows, tee-joints, bolted flange joints and straight pipes under earthquake loading with the presence of an internal pressure of 3.2 MPa will be presented and commented.Copyright

Hybrid Simulations of a Piping System Based on Model Reduction Techniques

The deficiency of seismic design standards for piping systems, their components and support structures necessitates experimental investigations of such structures under earthquake loading to extract valuable information for the amendments/development of relevant design guidelines. This paper describes an experimental test campaign carried out at the University of Trento, Italy, on a full-scale piping system in order to evaluate its seismic performance. In particular, a typical industrial piping system containing several critical components, such as elbows, a bolted flange joint and a Tee joint, was tested under different levels of earthquake loading corresponding to serviceability and ultimate limit states suggested by performance-based earthquake engineering standards. Hybrid Simulations with Dynamic Substructuring (HSDS) in both pseudo- and real-time were adopted to conduct seismic tests. Experimental results displayed a favorable performance of the piping system and its components; they remained below their yield limits without any leakage even for the Collapse Limit State. As a result, the proposed model reduction techniques were fully justified.

Modeling and Optimal Semi Active Control Strategies for adaptive MR- TMD

In recent years the evolution of construction techniques and design of pedestrian bridges led to structures more and more slender and light. This process entailed the development of unexpected interaction phenomena owing to pedestrian and wind loads. The impact of wind or pedestrians loads on low stiffness structures resulted in including, in the design phase, the concept of vibrations control and design of structural damping devices. These aspects are the one that we tackled on the Nomi-Calliano footbridge located in the northern part of Italy (near Trento). Semi-active control systems, coupled with smart materials such as magnetorheological fluids, became more and more attractive. In this respect, the University of Trento, in cooperation with the Autonomous Province of Trento, decided to use a Magneto-Rheological Tuned Mass Damper (MR-TMD), in order to limit discomfort on the aforementioned footbridge. This paper presents the main dynamic characteristics of the footbridge and the preliminary experimental program devoted to the MR fluid characterization. Finally, the optimal clipped control strategy for the control of the MR-damper is outlined.