Antolino Gallego

An acoustic emission energy index for damage evaluation of reinforced concrete slabs under seismic loads

This article presents the results and analysis of Acoustic Emission (AE) as recorded in a reinforced concrete (RC) slab supported by four steel columns and subjected to earthquake-type dynamic loading on a shake table. Fifteen seismic simulations were conducted using an accelerogram registered during the Campano-Lucano earthquake (Italy, 1980). The peak acceleration applied to the shake table was increased until the slab reinforcement was on the brink of yielding and slippage of the bars within the concrete occurred. This limit state is commonly associated with low-to-moderate intensity earthquakes in earthquake-prone regions. The evolution of damage to the slab was monitored in terms of AE energy and the history of plastic strain energy was calculated from the acceleration and displacement measurements. A good correlation was found between the energy dissipated by the concrete through plastic deformations and the AE energy associated with concrete cracking and friction. On this basis, a tentative formula is proposed for predicting the level of damage to RC slabs, based on the AE energy recorded by sensors located near the region of expected damage concentration under lateral loads.

Parameter estimation of exponentially damped sinusoids using a higher order correlation-based approach

A very common problem in signal processing is parameter estimation of exponentially damped sinusoids from a finite subset of noisy observations. When the signal is contaminated with colored noise of unknown power spectral density, a cumulant-based approach provides an appropriate solution to this problem. We propose a new class of estimator, namely, a covariance-type estimator, which reduces the deterministic errors associated with imperfect estimation of higher order correlations from finite-data length. This estimator allows a higher order correlation sequence to be modeled as a damped exponential model in certain slices of the moments plane. This result shows a useful link with well-known linear-prediction-based methods, such as the minimum-norm principal-eigenvector method of Kumaresan and Tufts (1982), which can be subsequently applied to extracting frequencies and damping coefficients from the 1-D correlation sequence. This paper discusses the slices allowed in the moments plane, the uses and limitations of this estimator using multiple realizations, and a single record in a noisy environment. Monte Carlo simulations applied to standard examples are also performed, and the results are compared with the KT method and the standard biased-estimator-based approach. The comparison shows the effectiveness of the proposed estimator in terms of bias and mean-square error when the signals are contaminated with additive Gaussian noise and a single data record with short data length is available.

Subsectional-polynomial E-pulse synthesis and application to radar target discrimination

A new family of extinction-pulses (E-pulses), called subsectional-polynomial E-pulses, is presented. This new type of E-pulse is constructed by choosing polynomials of degree Q as subsectional basis-functions in the E-pulse expansion. The main feature of this family of E-pulses is that the waveforms are continuous and smooth. Several topics concerning the E-pulse technique are investigated, such as: insensitivity to the exact number of natural modes present in the target response; aspect-angle independence; and effects of additive white Gaussian noise. Numerical results, using the response of a thin cylinder and a sphere, show that the subsectional-polynomial E-pulses improve the results obtained using subsectional-rectangular E-pulses. >

AE Monitoring for Damage Assessment of RC Exterior Beam-column Subassemblages Subjected to Cyclic Loading

This paper ascertains that Acoustic Emission (AE) monitoring is very effective for assessing the damage of reinforced concrete wide beam-column connections subjected to earthquake-type loadings. A cyclic test is conducted on an exterior connection until its failure. The experimental results show a strong correlation between the hysteretic strain energy and the AE energy histories. For this reason, a tentative formula is proposed, to predict the level of damage and the closeness to failure of the connection on the basis of the AE recorded by one piezoelectric sensor located near the critical zone (i.e., the beam-end and beam-column joint).

Concrete-Galvanized Steel Pull-Out Bond Assessed by Acoustic Emission

AbstractThis paper experimentally investigates the steel-to-concrete bond phenomenon in two kinds of deformed bars: black steel and hot-dip galvanized steel. The differences in the steel-to-concrete bond behavior are identified in terms of the load-slip curves and the acoustic emission (AE) patterns measured during pull-out tests. Test results show that the bond capacity and the initial stiffness of the bond stress–slip curve of black steel are approximately 20 and 50% greater, respectively, than those of galvanized steel, and the slip corresponding to the maximum bond stress is approximately 20% times larger in the latter. By measuring the AE activity, it is possible to identify the transitional points between the four stages characterizing interaction between the concrete and the bar subjected to pull-out force. Each transition coincides with a sudden drop in the AE activity.

The relationship between AR-modelling bispectral estimation and the theory of linear prediction

Abstract In this paper, a relationship between bispectrum estimation by means of autoregressive modelling and the theory of linear prediction is presented. It is demonstrated that the ‘third-order recursion’ equations for a causal and an anticausal model can be derived via minimization of a set of forward- and backward-prediction squared errors, respectively.

Experimental Comparison of Different Carbon Fiber Composites in Reinforcement Layouts for Wooden Beams of Historical Buildings

This paper offers a detailed, quantitative and exhaustive experimental comparison in terms of mechanical properties of three different layouts of carbon composite materials (CFRP) used to strengthen existing old timber beams highly affected by diverse natural defects and biological attacks, testing the use of pultruded laminate attached on the tension side of the element (LR), CFRP fabrics totally U-shape wrapping the timber element (UR), and the combined use of both reinforcement solutions (UR-P). Moreover, unidirectional and bidirectional fabrics were considered and compared. Timber elements used for the experimental program were extracted from a recent rehabilitation of the roof of the current Faculty of Law building, University of Granada (Spain), catalogued as a historical edifice. Experimental results from bending tests show that in all cases reinforcement provides a clear improvement in terms of bending capacity and stiffness as compared with the control specimens (without reinforcement). However, improvements in terms of ductility differ considerably depending on the kind of layout.

Health monitoring of web plastifying dampers subjected to cyclic loading through vibration tests

This article investigates experimentally the application of health monitoring techniques to assess the damage on a particular kind of hysteretic (metallic) damper called web plastifying dampers, which are subjected to cyclic loading. In general terms, hysteretic dampers are increasingly used as passive control systems in advanced earthquake-resistant structures. Nonparametric statistical processing of the signals obtained from simple vibration tests of the web plastifying damper is used here to propose an area index damage. This area index damage is compared with an alternative energy-based index of damage proposed in past research that is based on the decomposition of the load–displacement curve experienced by the damper. Index of damage has been proven to accurately predict the level of damage and the proximity to failure of web plastifying damper, but obtaining the load–displacement curve for its direct calculation requires the use of costly instrumentation. For this reason, the aim of this study is to estimate index of damage indirectly from simple vibration tests, calling for much simpler and cheaper instrumentation, through an auxiliary index called area index damage. Web plastifying damper is a particular type of hysteretic damper that uses the out-of-plane plastic deformation of the web of I-section steel segments as a source of energy dissipation. Four I-section steel segments with similar geometry were subjected to the same pattern of cyclic loading, and the damage was evaluated with the index of damage and area index damage indexes at several stages of the loading process. A good correlation was found between area index damage and index of damage. Based on this correlation, simple formulae are proposed to estimate index of damage from the area index damage.

Extinction pulse and resonance annihilation filter: Two methods for radar target discrimination

A comparison of the resonance annihilation filter (RAF) method and the extinction pulse (E-pulse) technique for radar target discrimination is presented in this paper. It is theoretically demonstrated that the RAF synthesized using finite impulse-response digital filters is a particular forced E-pulse waveform expanded using impulse-basis functions. This fact reveals the RAF method to be a very poor technique for discrimination in a noisy environment. Improvement is possible with suitable data windowing equivalent to using E-pulse waveforms synthesized with continuous and smooth basis functions. Numerical simulations are employed to compare the two techniques when different levels of additive white Gaussian noise are present in the target response. This comparison shows that the use of the Gaussian window originally proposed in the RAF method produces results comparable to rectangular E-pulses. However, these results can be improved by the introduction of alternative smoothing windows or subsectional-polynomial E-pulses.

A block-data recursive-in-order method based on reflection coefficients for bispectrum estimation using AR-modeling

Abstract The paper proposes a new method for bispectrum estimation of random processes by means of autoregressive (AR) modeling. First, it is demonstrated that the Third-Order Recursion (TOR) equations, which relate the AR parameters with the third moments, can be derived by minimizing a set of forward (for a causal model) or backward (for an anticausal model) squared errors with respect to the parameters of an AR model of order p . When third moments over the straight line m = n of the m−n plane of moments are used, these equations exhibit a Toeplitz but nonsymmetric structure. Consequently, Levinsons recursive-in-order algorithm can be used for their resolution. Thus, the causal and anticausal parameters for orders lower than p can also be obtained. This algorithm also introduces the so-called reflection coefficients. The proposed method is based on the recursive-in-order minimization of the forward- and backward-squared errors with respect to the reflection coefficients instead of the fixed-order AR parameters. By means of several simulations, it is shown that this method improves the TOR and CTOM methods, most of all if few data are assumed. The method also has the advantage of providing, without additional computational cost, the AR parameters of models of an order lower than p . Finally, a comparative study of the performance of the TOR, CTOM, and the new method in the presence of additive random Gaussian noise, white and colored, is presented.