1,721,032 research outputs found
Structural identification of a steel structure by forced vibrations
No full textIn the present paper, an application of a dynamic identification process in the frequencies domain, is presented. A steel structure 90 meters long, 22 meters high and simply supported by four pair of concrete piles is considered. The structure has been dynamically loaded by using a mechanical shaker, giving si-nusoidal excitation at prescribed frequency values. Experimental modal frequencies, deformations and damping ratios are evaluated starting from inertance function by using the MDOF Circle Fit Method. A finite element model of the structure has been developed and Modal Assurance Criterion (MAC) is, then, used to compare experimental and numerical vibration modes; good correlation is obtained both for global flexural modes, global torsional modes and longitudinal modes
Identificazione dinamica di una struttura di acciaio mediante vibrodina
No full textNella presente nota si riporta un esempio applicativo di una metodologia di identificazione basata su prove vi vibrazione forzata. Vengono descritti i risultati di una prova dinamica con vibrodina effetuata su una porzione dell’ampliamento del Politecnico di Torino a struttura metallica: dai dati sperimentali si sono calcolate le funzioni di risposta in frequenza che hanno fornito frequenze proprie e deformate modali. Successivamente si è confrontata la risposta con un modello agli elementi finiti correlando modi propri e frequenze
Influence of measurement and model errors in optimal sensor placement for SHM purposes
No full textIn this work, the influence of measurement and model errors in optimal sensor placement is investigated. The sensor placement procedure is based on the Information Entropy theory and the solution of the optimization problem is obtained maximizing the determinant of the so called Fisher Information Matrix (FIM). Results of placement process considerably depend on the so called covariance matrix of prediction error as well as on the definition of the correlation function. The paper thus investigates the role of the covariance matrix and the correlation function in optimal sensor placement. Different proposals on their definition are compared. A constant and an exponential correlation function depending on the distance between sensors are firstly assumed; then a new proposal depending from both the distance and modal vectors is presented. The method is finally applied to a benchmark case study and the effect of model and measurement error on results is described
Differential evolution algorithm in dynamic structural identification
No full textIn the present paper, a Differential Evolution algorithm is used to perform a structural identification of mass and stiffness properties of a frame structure. Identification is performed starting from exact data and, alternatively, from pseudo-experimental data, obtained by adding some statistic scattering to exact data. Different object functions are adopted and results are compared with those obtained adopting classical gradient method. Numerical results confirm that adopting both frequencies and modal shapes instead of fre-quencies only strongly increases the sensitivity of object function to identification parameters. Results ob-tained are then much less scattered, with coefficient of variation of the same order of magnitude of that of pseudo-experimental data
A surrogate-assisted evolutionary algorithm for dynamic structural identification
No full textIn the present paper, the performances of surrogate-assisted evolutionary algorithms for dynamic identification problems and damage detection are investigated. An improved algorithm is designed to limit the computational effort by introducing a proper infill sampling strategy in Differential Evolution (DE). The algorithm combines the robustness of DE with the computational efficiency due to a second-order surrogate approximation of the objective function. New individuals are selected trying to enhance both the accuracy in the region of the optimum predicted by the surrogate and the global exploration. The efficiency of the algorithm is tested by searching the global minimum of benchmark functions and by solving damage identifi-cation problems. Results are compared with those obtained adopting both the original DE algorithm and a previous proposal surrogate-based algorithm called DE-Q
Differential Evolution Algorithm for Dynamic Structural Identification
No full textIn the present paper, Differential Evolution algorithm is used to perform structural identification of mass and stiffness properties of civil structures from dynamic test results. Identification is performed initially starting from exact values of modal parameters (frequencies and mode shapes). Robustness of the algorithm is then tested by adopting pseudo-experimental input data, obtained by adding to exact data some statistic scattering, representing experimental measurement error. Different objective functions are adopted in identification procedure, and results are compared with those obtained adopting classical gradient method. The method is used to identify masses, elastic moduli and stiffnesses of external constraints of a RC frame structure and a steel – concrete bridge. Numerical results confirm that adopting both frequencies and mode shapes instead of frequencies only strongly increases sensitivity of objective function to identification parameters. Scattering of identified parameters is much smaller, with coefficient of variation of the same order of magnitude of that of pseudo-experimental data used as input values in dynamic identification procedure
A new denoising procedure based on empirical mode decomposition for SHM purpose
No full textIn this work, a signal processing method based on the Empirical Mode Decomposition (EMD) to denoise a recorded signal is proposed. EMD expresses the signal as an expansion of basis functions (Intrinsic Mode Functions - IMFs) that are signal dependent and are estimated via an iterative procedure.The decomposition of an "only noise" signal is first studied to define a Noise-Model in terms of energy and period. Then, the EMD is applied to a simulated measured signal, and the IMFs obtained are compared with the Noise-Model constructed before. Finally, an optimization procedure is performed to split the IMFs of the measured signal into 2 components: The denoised IMFs and the corresponding "Removed Noise" IMFs. The denoised IMFs are finally summed in order to reconstruct the denoised signal. The proposed algorithm is applied to a simple 3-floor shear-type frame and the ASCE 4-floor frame benchmark. The results are compared with those obtained by a standard denoising procedure based on a pass-band filter; the comparison confirmed the improvements obtained with the proposed method over classical procedures. © 2013 Taylor & Francis Group, London
Experimental Investigation on a Beam-Column Node of a Multi-Story Precast RC System
No full textThe results of an experimental program, devoted to the investigation of the structural behaviour of a precast RC beam-column node under cyclic loading, are described. The experimental activity is part of a research campaign developed to evaluate the seismic behaviour of a multi-story precast concrete system completed in situ. The experimental tests have been carried out by imposing cyclic quasi-static transverse displacements at the two end sections of the beams. An axial load on the column is also applied, simulating the vertical load given by the permanent actions. The seismic performance of the node is experimentally studied. The hysteresis response and the strain profiles of the steel bars (longitudinal reinforcement and stirrups) within the node are recorded. The ductility of the connection and the cyclic strength degradation at prescribed displacement values are also evaluated
Damage and collapses in industrial precast buildings after the 2012 Emilia earthquake
Full text linkThe present paper presents a complete and commented collection of cases of damage and collapse in reinforced concrete (RC) precast industrial buildings, observed by the authors during a series of field surveys after the 2012 Emilia earthquake in Northern Italy. They were selected among a total of about 2000 industrial RC precast buildings, whose structural characteristics and damage have been collected in a large database by the authors. The main causes of the collapses were vulnerabilities related to the structural characteristics of Italian precast buildings not designed with seismic criteria. In particular, these structures were typically built as an assembly of monolithic elements (roof elements, main and secondary beams, columns) in statically determinate configurations. The most common failure causes identified were: the absence of mechanical connectors between precast monolithic elements, the interaction of structural elements with non-structural walls, the insufficient column bending capacity, the rotation of pocket foundations, the inadequacy of connections of external precast cladding walls to bearing elements (columns and beams), the overturning of racks in buildings used as warehouses or in automated storage facilities
Inverse analysis for calibration of FRP-Concrete interface law
No full textInverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads for different bonding lengths and strains profiles along FRP plates are used. Parameter identification is performed by inverse analysis using a Direct Search technique. Considerations on well-posedness of inverse problem adopting different cost functions are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results
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