Publications

Real-time close-up imaging (filming or video surveillance) of structures is used to automate detection of local component-level damage by exploiting the spatiotemporal data structure of the multiple temporal frames of structures. Specifically, the multiple frames are decomposed into a superposition of a low-rank background component and a sparse innovation (dynamic) component by a technique called principal component pursuit (PCP, or robust principal component analysis). The low-rank component represents the irrelevant, temporally correlated background of the multiple frames, whereas the sparse innovation component indicates the salient, evolutionary damage-induced information. The sparse innovation component is then quantitatively measured for continuous alert and indication of the damage evolution. It is a data-driven and unsupervised (blind) approach that requires no parametric model or prior structural information for calibration. In addition, PCP has an overwhelming probability of success under broad conditions and can be implemented by an efficient convex optimization program without tuning parameters. Laboratory experiments on concrete structures demonstrate that the proposed dynamic imaging method can efficiently and effectively track and indicate the evolution of small or severe damage by the recovered outstanding sparse innovation component (with the low-rank background subtracted from the original images). The proposed method has the potential to benefit real-time automated local damage surveillance and diagnosis of structures where experts' visual inspection is not needed or not possible.

Real-time automatic detection of multiple cracks from a video stream of a concrete surface is addressed in this paper. Robust principal component analysis is used to detect multiple cracks forming at different instances of time in an unsupervised manner using the Gini index as a metric to quantify the presence of an observable crack. The relative positions of the relevant pixels around the crack are monitored using the Kanade Lucas Tomasi feature tracking algorithm. Further, Hu's invariant moments of those pixel positions are computed which acts as a robust damage indicator even for breathing cracks under time-varying service loads. The proposed method is experimentally validated using two small scale under-reinforced beams undergoing three-point bending tests. The method successfully detects the onset of multiple cracks, at varied locations, at different time instants and further tracks their propagations.

A = system state transmission matrix with dimension n n Bd = noise input influence matrix with dimension n nd Bu = input influence matrix with dimension n r C = output influence matrix with dimension m n Dd = noise direct transmission matrix with dimension m nd Fi = ith force direction vector H = projection matrix I = identity matrix L = observer gain with dimension n m m = number of outputs mi = arbitrary scalar function of time with respect to the ith fault direction n = number of states nd = number of disturbance inputs q = number of faults r = number of inputs

This paper proposes a multiresolution based wavelet controller for the control of linear time varying systems consisting of a time invariant component and a component with zero mean slowly time varying parameters. The real time discrete wavelet transform controller is based on a time interval from the initial until the current time and is updated at regular time steps. By casting a modified optimal control problem in a linear quadratic regulator (LQR) form constrained to a band of frequency in the wavelet domain, frequency band dependent control gain matrices are obtained. The weighting matrices are varied for different bands of frequencies depending on the emphasis to be placed on the response energy or the control effort in minimizing the cost functional, for the particular band of frequency leading to frequency dependent gains. The frequency dependent control gain matrices of the developed controller are applied to multiresolution analysis (MRA) based filtered time signals obtained until the current time. The use of MRA ensures perfect decomposition to obtain filtered time signals over the finite interval considered, with a fast numerical implementation for control application. The proposed controller developed using the Daubechies wavelet is shown to work effectively for the control of free and forced vibration (both under harmonic and random excitations) responses of linear time varying single-degree-of-freedom and multidegree-of-freedom systems. Even for the cases where the conventional LQR or addition of viscous damping fails to control the vibration response, the proposed controller effectively suppresses the instabilities in the linear time varying systems.

<p><strong>Title:</strong> Development of Next Generation Adaptive Seismic Protection Systems (NEES-2008-0653)</p> <p><strong>Year Of Curation: </strong>2014</p> <p><strong>Description: </strong>Design of conventional structures specified by the codes is based on the philosophy that the structure should withstand seismic loads while sustaining an acceptable level of damage. Structures are designed to prevent collapse but their serviceability and functionality in the aftermath of strong earthquake ground motion are not taken into consideration. This is achieved by designing structures to be ductile and letting them yield when subjected to strong earthquake ground motions. Yielding leads to stiffness and strength degradation, increased interstory drifts, and damage with permanent drifts, which render the structure non-functional.</p> <p><strong>Award: </strong>http://www.nsf.gov/awardsearch/showAward?AWD_ID=0830391</p> <p><strong>PIs & CoPIs: </strong>Satish Nagarajaiah, Michael Constantinou, Andrei Reinhorn, Michael Symans, Douglas Taylor, Jian Zhang</p> <p><strong>Dates: </strong>September 01, 2008 - August 31, 2013</p> <p><strong>Organizations: </strong>Rensselaer Polytechnic Institute, Troy, NY, United States, Rice University, TX, United States, State University of New York at Buffalo, NY, United States, University of California, Los Angeles, CA, United States</p> <p><strong>Facilities: </strong>State University of New York at Buffalo, NY, United States</p> <p><strong>Sponsor: </strong>NSF - CMMI - 0830391</p> <p><strong>Keywords: </strong>Adaptive seismic protection systems, Negative Stiffness Device, Shake table testing, Apparent Weakening, Apparent yielding, base isolated building, Adaptive Stiffness Structures</p> <p><strong>Publications: </strong></p> <p>"Performance Assessment of a Highway Bridge Structure employing Adaptive Negative Stiffness for Seismic Protection"</p> <p>"Seismic Responses and Protection of Building Systems Using PBEE Methodology"</p> <p>"Negative Stiffness Device for Seismic Protection of Base Isolated Structures - Shake Table Testing"</p> <nb:citations></nb:citations>

Column forces, displacements and accelerations experienced by the structure during strong ground motions can be reduced by weakening and (or) softening the structure and adding a supplemental damper. Although this approach proved to be promising analytically, the concept of "structural strength reduction" leads to inelastic behavior and large permanent deformations in the main structural system. In this paper a new concept is developed to emulate weakening in a structural system by adding an "adaptive negative stiffness device" (NSD) and shifting the "yielding" away from the main structural system; leading, to the new idea of "apparent weakening" with reduced inelastic excursions in the main structural system. This is achieved through an adaptive negative stiffness system (ANSS), which is a combination of NSD and a damper. Engaging the NSD at an appropriate displacement (simulated yield displacement), that is well below the actual yield displacement of the structural system, will result in a composite structure-device assembly that behaves like a yielding structure. The NSD has a re-centering mechanism thereby avoiding permanent deformation in the composite structuredevice assembly unless, the main structure itself yields. Essentially, a yielding-structure is "mimicked" without any, or with minimum yielding and permanent deformation in the main structure. In summary, the main structural system undergoes less acceleration, less displacements and less base shear, while the ANSS "absorbs" them. This paper presents the working principle and details on development and study of the ANSS/NSD. Through numerical simulations, the effectiveness and the superior performance of the ANSS/NSD as compared to a structural system with supplemental passive dampers is presented.

This paper presents a novel negative stiffness device (NSD) for the seismic protection of the base isolated benchmark building in near fault earthquake. The benchmark structure has eight stories and irregular plan, and the superstructure is considered to be a linear elastic system with lateral torsional behavior. Furthermore, it is equipped with low damping elastomeric rubber bearings and viscous dampers for seismic protection. The proposed NSD can change the stiffness of composite structure-device assembly, emulate "apparent yielding" of the structure system without permanent deformations. It consists of a highly compressed spring, a wheel and a curved template that the wheel can roll on. The device can achieve any force-displacement behavior within its designed range. Experimental results are presented to verify the analytical model of the NSD. Numerical simulation results under seven earthquake inputs show that the proposed device is effective in reducing the response of the base and superstructure in comparison with a sample clipped optimal controller and an H2/LQG sample controller.

The lateral‐torsional response of base‐isolated structures, with sliding isolation system due to bidirectional lateral ground motion, is studied. The objective of the study is to identify the key system parameters that lead to significant torsional coupling in sliding base‐isolated structures. The analysis procedure adopted can capture the highly nonlinear behavior of sliding systems in plane motion. The nonlinear biaxial stick‐slip characteristics of sliding bearings and the velocity dependence of coefficient of friction are accounted for. The study considers multistoried structures with variable number of bearings subjected to the effects of earthquakes with various frequency content and different peak ground accelerations. It is shown that, although the total superstructure response is reduced significantly due to the effects of sliding base isolation, torsional coupling can be significant depending on the superstructure eccentricity and the lateral‐torsional flexibility of the superstructure and the base.