Eric Hernandez

• PhD
• Professor (Associate) at University of Vermont

This paper presents the application of Bayesian filtering for the estimation and uncertainty quantification of interstory drifts and shears in partially instrumented buildings. We investigate the performance of four Bayesian filters: the extended, unscented, and ensemble Kalman filters, and the particle filter. The filters were compared in a simula...

SUMMARY The use of sparse-measured response as a means to monitor stresses and fatigue damage throughout metal structures has been the subject of recent work by researchers in the field of vibration-based structural health monitoring. The basic premise is that by using measured structural response, one can improve upon purely stochastic estimates....

This paper derives exact expressions to compute the lowest achievable variance by any unbiased estimator of modal frequency and damping ratio from free vibration and forced vibration signals contaminated by additive zero-mean Gaussian white noise. These limits are found through the Cramer–Rao lower bound theory. The paper presents simulated system...

This paper presents a methodology to reconstruct the complete dynamic response of a nonlinear structural system by blending a nominal model with partial measurements of the response. The method is implemented by extending to the nonlinear case an observer originally derived by the authors for linear systems. The methodology assumes that the main so...

This paper presents a methodology to minimally modify a ground motion time history to induce collapse in nonlinear single‐degree‐of‐freedom systems (SDOF). The metric used to characterize the modification is the Arias intensity. The proposed procedure is a heuristic extension of a closed‐form solution derived to achieve a target maximum response in...

This paper examines the effect of structural damage on the practical/computational identifiability of the parameters that define nonlinear models of building structures subjected to earthquake‐induced base motions. The objective is to determine the level of physical damage expected to successfully estimate the nonlinear parameters of restoring forc...

This paper presents a new concept for performance-based monitoring (PBM) of instrumented buildings subject to earthquakes. This concept is achieved by simultaneously combining and advancing existing knowledge from structural mechanics, signal processing, and performance-based earthquake engineering paradigms. The PBM concept consists of 1) measurem...

This paper proposes a high-resolution seismic monitoring framework that employs dissipated energy as a feature for damage detection and localization in instrumented building structures. The methodology consists of (1) implementing a nonlinear state observer to reconstruct the dynamic response at all degrees of freedom (DoF) of a structural model, (...

Explicit multihazard analysis of structures, especially bridges, has attracted significant attention from researchers and practitioners. Depending on the number of hazards considered and the length of the time interval, such analysis can be time-consuming and cumbersome for practical purposes. Therefore it would be beneficial to determine under wha...

The l1-norm regularized inverse methods have been suggested as a means to quantify and localize spatially sparse damage from a set of identified natural frequencies. Thus far, damage has been interpreted as changes in stiffness without any appreciable associated changes in mass. In seeking to generalize l1-norm-based inverse methods to encompass da...

Estimation of ground reaction forces in runners has been limited to laboratory environments by means of instrumented treadmills, in-ground force plates and optoelectronic systems. Recent advances in estimation techniques using wearable sensors for kinematic analysis and sports performance could enable estimation outside the laboratory. This paper p...

This paper develops a decision making framework for post-earthquake assessment of instrumented buildings in a manner consistent with performance-based design criteria. This framework is achieved by simultaneously combining and advancing existing knowledge from seismic structural health monitoring and performance-based earthquake engineering paradig...

The authors propose a seismic monitoring framework for instrumented buildings that employs dissipated energy as a feature for damage detection and localization. The proposed framework employs a nonlinear model-based state observer that combines a nonlinear finite element model of a building and global acceleration measurements to estimate the time...

Cascading blackouts typically occur when nearly simultaneous outages occur in k out of N components in a power system, triggering subsequent failures that propagate through the network and cause significant load shedding. While large cascades are rare, their impact can be catastrophic, so quantifying their risk is important for grid planning and op...

Non-negative constrained least squares and l1-norm optimization are sometimes viable inverse-based methods used to quantify and locate damage described by local stiffness reductions using measured changes in natural frequencies. Although the two methods provide meaningful solutions to the associated underdetermined inverse problem when the physical...

This paper presents a framework for decision-making regarding post-earthquake assessment of instrumented buildings in a manner consistent with performance-based design criteria. This framework is achieved by simultaneously combining and advancing existing knowledge from seismic structural health monitoring and performance-based earthquake engineeri...

The authors propose a seismic monitoring framework for instrumented buildings that employs dissipated energy as a feature for damage detection and localization. The proposed framework employs a nonlinear model-based state observer, which combines a nonlinear finite element model of a building and global acceleration measurements to estimate the tim...

The authors present a methodology to reconstruct nonlinear seismic response and assess seismic performance of instrumented wood-frame buildings subjected to earthquakes. The paper proposes the use of a nonlinear model-based state observer that combines global acceleration measurements and a nonlinear structural model of the building to estimate the...

The paper derives a Lyapunov equation whose solution is the sensitivity of the Kalman filter state error covariance matrix to structured and parametric model errors in the stiffness and damping of structural systems. This result is utilized to propose an expression to balance optimality and robustness for sensor placement in the presence of paramet...

The authors propose a methodology to perform seismic damage assessment of instrumented wood-frame buildings using response measurements. The proposed methodology employs a nonlinear model-based state observer that combines sparse acceleration measurements and a nonlinear structural model of a building to estimate the complete seismic response inclu...

Cascading blackouts typically occur when nearly simultaneous outages occur in k out of N components in a power system, triggering subsequent failures that propagate through the network and cause significant load shedding. While large cascades are rare, their impact can be catastrophic, so quantifying their risk is important for grid planning and op...

This paper presents a methodology to estimate element‐by‐element demand‐to‐capacity ratios in instrumented steel moment‐resisting frames subject to earthquakes. The methodology combines a finite element model and acceleration measurements at various points throughout the building to estimate time history of displacements and internal force demands...

This paper presents an impulse response sensitivity approach enhanced with a least absolute shrinkage and selection operator regularization in order to detect spatially sparse (localized) damage. The analytical expression for impulse response sensitivity was derived using Vetter calculus. The proposed algorithm exploits the fact that when damage is...

One of the main limitations traditionally encountered in vibration-based structural health monitoring (SHM) is detecting, localizing and quantifying localized damage using global response measurements. This paper presents an impulse response sensitivity approach enhanced with a LASSO regularization in order to detect spatially sparse (localized) da...

This paper presents a methodology to estimate member-by-member demand-to-capacity ratio for instrumented buildings whose lateral-force resisting system consists in steel moment-resisting frames. The methodology estimates internal forces and displacements in all members by combining a model and acceleration measurements using a model-based observer....

One of the main limitations traditionally encountered in vibration-based structural health monitoring (SHM) is detecting, localizing and quantifying localized damage using global response measurements. This paper presents an impulse response sensitivity approach enhanced with a LASSO regularization in order to detect spatially sparse (localized) da...

This paper derives a computationally efficient algorithm to determine optimal sequential sensor placement for state estimation in linear structural systems subjected to unmeasured excitations and noise contaminated measurements. The proposed algorithm is developed within the context of the Kalman filter and it minimizes the variance of the state es...

Composite bridge decks provide higher flexural moment capacity and stiffness compared to their non-composite counterparts. In order to achieve composite behavior, differential slip between the steel member and the concrete slab must be restrained by means of shear connectors. In older bridge decks composite behavior is uncertain. Uncertainty arises...

This paper proposes a model-based state observer to perform high-definition response estimation in partially instrumented building structures. The proposed estimator is verified in a simulated five-story shear-building structure and validated using measurements from a seven-story reinforced concrete building slice tested at the NEES-University of C...

This paper presents a probabilistic framework for estimating seismic-induced damage in partially instrumented buildings. The proposed framework uses acceleration measurements at a limited number of stories and Bayesian filtering to estimate the response at all stories. The paper compares four Bayesian filters: the extended, unscented, and ensemble...

The paper presents a methodology for identification of localized structural damage using highly incomplete modal information, such as a subset of modal frequencies. The proposed methodology is based on linearized modal sensitivities and ℓ1-norm minimization of the algebraic difference between identified frequencies in damaged and undamaged states....

This paper presents a finite element model-based state observer, which allows for accurate real time monitoring of stress, strain and their resultants at any location within an instrumented structure. The input to the proposed observer is: a finite element model of the structure, the spectral density matrix of the random field representing the load...

This paper presents the application of state estimators in nonlinear structural systems. The objective is to provide a comparison of the effectiveness to reconstruct the state time history in nonlinear building-type structures of four existing algorithms - namely, extended Kalman filter, unscented Kalman filter, ensemble Kalman filter and the parti...

This paper derives exact results for the maximum achievable accuracy when estimating modal parameters from free vibration and forced vibration signals contaminated by Gaussian white noise. These limits are found through the Cramer-Rao lower bound. The paper proposes a simple yet accurate expression to determine the ratio between the coefficient of...

This paper presents the application of state estimators in nonlinear structural systems. The objective is the estimation of earthquake induced damage in building-type structures. The paper compares the effectiveness of four existing methods, namely, Extended Kalman filter, Unscented Kalman filter, Ensemble Kalman filter and the Particle filter. Ove...

The objective of this paper is to provide a new theoretical basis to localize and quantify sparse damage in a structure based on highly incomplete modal information. Although a large number of papers have been written on the subject, this paper offers a new perspective on the problem by proposing the L-1 norm minimization criteria, in contrast to t...

The paper proposes an energy-based damage feature to detect the presence of earthquake-induced structural damage in instrumented buildings. The proposed feature is a function of the ratio between the hysteretic dissipated energy and the total dissipated energy. The main contribution of the paper consists in deriving an expression to estimate the di...

The use of output feedback as a means to monitor stresses at critical locations in instrumented structures has been the subject of recent work by researchers in the field of vibration based structural health monitoring. In the present paper we propose an model-based state estimator that can be implemented as a modified finite element model of the s...

This paper derives exact results for the maximum achievable accuracy when estimating modal parameters from free vibration signals contaminated by Gaussian white noise. These limits are found through the Cramer-Rao lower bound. The paper compares the exact findings with previous approximate results found in the literature. Comparisons are drawn with...

The objective of this paper is to present the results of an experimental study aimed at verifying the performance of an algorithm developed by one of the authors for state estimation in structural and mechanical systems subject to unmeasured excitations realizations of random processes with known spectral density matrix. The proposed algorithm oper...

SUMMARY In many applications, such as control, monitoring, assessment, and failure detection in mechanical and structural systems, the state of the system is sought. However, in almost all cases, the full state vector is not directly measured, and it must be reconstructed from sparse measurements contaminated by noise. If in addition, the excitatio...

The University of Vermont Structural Monitoring and Diagnostics Lab is collaborating with the Vermont Agency of Transportation to instrument and monitor traffic induced vibrations in bridge 58N on interstate 89 in the town of Richmond, VT. The bridge consists of an unorthodox concrete and steel deck supported on reinforced concrete piers. A critica...

An iterative time domain formulation for finite element model updating in structural dynamics is presented. The approach is supported on a derivation showing that the discrepancy between observations and model predictions can be expressed as a convolution between the state of the system and a sequence of pseudo-Markov parameters which are linear in...

This paper proposes a real-time methodology estimate earthquake induced structural damage in instrumented buildings. The methodology relies on model-based state estimation to perform the assessment throughout the complete structure. In a similar fashion to existing data assimilation methods for nonlinear systems, the proposed observer uses sparse n...

The use of output feedback as a means to monitor stresses and fatigue in metal structures has been the subject of recent work by researchers in the field of vibration based structural health monitoring. The methodologies that have been proposed in the literature employ the Kalman filter as an estimator and operate under the premise that excitations...

The paper proposes an energy based damage function to estimate earthquake induced structural damage in building-type structures. The proposed damage function depends on the ratio of the dissipated energy by means of hysteresis and the total dissipated energy. The main contribution of the paper consists in presenting a method to estimate both quanti...

A state observer for mechanical and structural systems is derived in the context of the second order differential equation of motion of linear structural systems. The proposed observer possesses similar characteristics to the Kalman filter in the sense that it minimizes the trace of the state error covariance matrix within the predefined structure...

A data-driven approach for post-earthquake posting of buildings is presented. The approach is based on the analysis of residuals obtained as differences between measured responses and reference signals computed using a set of observers. The observers are particular to every output channel and can be described as mathematical structures that offer a...

An approach for detection of earthquake-induced damage in buildings is presented. The method is based on contrasting the response measured at all available channels with that predicted by a partial observer model formulated using data from prior small events. It is shown that the approach can discriminate between structures that undergo significant...

A data driven methodology for the evaluation of earthquake induced damage on civil engineering structures in presented. The main features of the approach are: (1) identification of a collection of mappings containing transmissibility between sets of channels for the nominally healthy state of the system and (2) computation of differences between th...