Samit Ray Chaudhuri

Simplified expression for seismic fragility estimation of sliding-dominated equipment and contents

Damage to small equipment and contents during seismic events has gained considerable attention following recent earthquakes, largely due to the potential for operational downtime, which results in significant economic losses. The estimation of losses from this interior building damage is a daunting task, due to the complexity of types of equipment and the randomness of their location within the structure. Nonetheless, a precursor to calculating such losses is a reasonable association between structural and nonstructural (equipment or contents) demands. Cast in a probabilistic framework, such an association is best represented through the use of seismic fragility curves, where the probabilities of exceeding a given damage state is correlated with an input parameter. In this paper, analytically developed seismic fragility curves for various unattached equipment and contents are calculated and presented. The emphasis of the study is on rigid scientific equipment and contents, which are often placed on the surface of ceramic laboratory benches in science laboratories or other buildings. Only uniaxial seismic excitation is considered to provide insight into the form of the fragility function. Generalized fragility curves are then developed and a simple expression is presented, which is envisioned to be very useful from a design perspective. The usefulness of the proposed expression is illustrated via a simple numerical example coupled with a design code-specified horizontal acceleration distribution profile for an example building structure.

Performance Evaluation of Pile-Supported Wharf under Seismic Loading

Past earthquakes have demonstrated that port facilities suffer extensive seismically induced damage due to poor foundation and backfill soil that are common in waterfront environments. Focusing on pile-supported wharves, this study evaluates seismic behavior of port structures recognizing that most of the parameters controlling the properties of soil are of a random nature. The response of such structures inherently presents a complex soil-structure interaction (SSI) problem involving ground shaking, pile-failure mechanism, and liquefaction and lateral spreading in backfill and sand layers. In this study, using a representative model of a typical pile-supported wharf in the west coast of United States and considering an ensemble of ground motions with different hazard levels, effect of soil parameter uncertainty on seismic response is evaluated. For numerical simulations, an effective stress analysis method has been utilized. In order to investigate the effect of soil parameter uncertainty on seismic response, random samples are generated using Latin Hypercube Sampling and nonlinear time history analysis is carried out repeatedly for each realized sample. Finally, the effect of parameter uncertainty is demonstrated in terms of seismic fragility curves. The results of this study can be utilized to evaluate the seismic vulnerability of similar pile supported wharves.

Development and Evaluation of a Seismic Monitoring System for Building Interiors—Part I: Experiment Design and Results

The advent of high-speed, lightweight, and durable sensor technologies opens new possibilities for field monitoring applications. In particular, under natural or man-made loading conditions, applying these new technologies to the monitoring of building interiors may substantially help rescue and reconnaissance crews during postevent evaluations. To test such a methodology, in this paper, we develop a specialized network of conventional analog and digital (camera) sensors and use them in monitoring nonstructural components subjected to vibration loading within a demonstration building structure. A full-scale vibration experiment is conducted with a research team from the University of California, Los Angeles, on a vacant structure damaged during the 1994 Northridge Earthquake. The building of interest is a four-story office building located in Sherman Oaks, CA. The investigation has two primary objectives: (1) to characterize the seismic response of an important class of equipment and building contents and (2) to study the applicability of tracking the response of these equipment and contents using arrays of image-based monitoring systems. In this paper, we describe the experimental field setup, including the analog and camera sensor systems and the networking hardware used to collect data, present the testing matrix, and sample the processed analog data results. We summarize the difficulties encountered in the field implementation of these types of monitoring systems while highlighting their potential benefits. In a companion paper, we present the analysis methodology applied to the image sequences collected and summarize needs for future work if such systems are to be robustly employed in the field.

Spectral characterization of the stochastically simulated vehicle queue on bridges

Monte Carlo simulation in conjunction with Fourier transform based spectral windowing is used to model the live load on bridges. Vehicles are classified into a few groups and the probability distributions of axle weight and length associated with each group are estimated. The vehicle arriving at an instant is determined through Monte Carlo simulation, which uses a vehicle group density function derived from measurement data on the relative contribution of each group in total vehicles. The weight and length of the arriving vehicle is also simulated by Monte Carlo using the distribution function for the corresponding group. Vehicle arrivals are modeled by the Poisson distribution. The vehicle velocities are realized through spectral simulation based on decaying power spectra of the velocity time series. The simulations are performed for a sufficient time interval in several lanes, thus the ensemble sampling of load is obtained. Fourier transform based windowing is used to characterize the power spectra of mechanical load on the bridge. The study shows the white noise nature of the load spectral density, which is in agreement with the assumptions of previous investigators. Parametric sensitivity of the spectra is also performed and recommendations are made to include site-specific parameters in the model. Finally, applications are illustrated for frequency domain random vibration analysis of a simple model of bridge structures.

Monitoring earthquake-induced loading with camera networks: case study in Sherman Oaks, California

The advent of high speed, CCD-based camera technologies opens new possibilities for field monitoring applications. In particular, under natural or man-made loading conditions, applying these new technologies towards the monitoring of building interiors may substantially help rescue and reconnaissance crews during post-event evaluations. To test such a methodology, we have developed a specialized network of high-speed cameras and supporting hardware for monitoring and tracking nonstructural elements subjected to vibration loading, within building structures. Teamed with the University of California, Los Angeles, a full-scale vibration experiment is conducted on a vacant structure damaged during the 1994 Northridge Earthquake. The building of interest is a four-story office building located in Sherman Oaks, California. The investigation has two primary objectives: (1) to characterize the seismic response of an important class of equipment and building contents and (2) to study the applicability of tracking the response of these equipment and contents using arrays of image-based monitoring systems. In this paper, we describe the image acquisition (hardware and software) system and the experimental field set-up are described. In addition, the underlying communication, networking and synchronization of the camera sensor system are discussed.