Tara C. Hutchinson

Inelastic Seismic Response of Extended Pile-Shaft-Supported Bridge Structures

Nonlinear static and dynamic analyses were used to evaluate the inelastic seismic response of bridge and viaduct structures supported on extended cast-in-drilled-hole (CIDH) pile shafts. The nonlinear dynamic analyses used a beam-on-nonlinear-Winkler foundation (BNWF) framework to model the soil-pile interaction, nonlinear fiber beam-column elements to model the reinforced concrete sections, and one-dimensional site response analyses for the free-field soil profile response. The study included consideration of ground motion characteristics, site response, lateral soil resistance, structural parameters, geometric nonlinearity (P-Δ effects), and performance measures. Results described herein focus on how the ground motion characteristics and variations in structural configurations affect the performance measures important for evaluating the inelastic seismic response of these structures. Presented results focus on a representative dense soil profile and thus are not widely applicable to dramatically different soil sites.

INVESTIGATION INTO THE EFFECTS OF FOUNDATION UPLIFT ON SIMPLIFIED SEISMIC DESIGN PROCEDURES

Uplifting of and yielding below shallow foundations supporting rigid lateral force–resisting elements can provide additional nonlinearity into a systems overall force-deformation behavior. While this nonlinearity may be advantageous, potentially reducing seismic demands, displacement compatibility may result in overstress of lateral and/or gravity-resisting elements. Incorporating this balance of benefit versus consequence in structural design is one goal of performance-based earthquake engineering (PBEE). There are a variety of approaches in design codes for estimating seismic demands and incorporating “performance” as a design goal. Such methods generally account for the displacement of an equivalent SDOF system by reducing the design strength, however, not explicitly for the case of foundation uplift. To address this shortcoming, this paper investigates the relationship between the strength ratio R and the displacement ratio C1 using the beam on nonlinear Winkler foundation (BNWF) concept. Numerical models were constructed considering a range of soil-structure natural periods and a range of design R values. Nineteen ground motions with a broad range of characteristics are used to conduct nonlinear time-history analyses. Results from these simulations indicate that current suggestions for C1-R relations are highly unconservative when uplifting foundations are anticipated. Revised C1-R relations for uplifting foundations are presented and an example numerical comparison provided.

Optimal hardware and software design of an image-based system for capturing dynamic movements

In contrast to conventional image-capture systems, which attempt to minimize the amount of data collected during capture, typically by using hardware filters, the more general condition of using all information captured on a camera sensor is much more challenging and requires rigorous consideration of the hardware and software pipelines to obtain accurate tracking results. In this paper, this issue is specifically addressed by describing a unique hardware and software design implemented for use as a fully image-based capture system. An attempt is made to minimize the cost of this system by maximizing hardware control through software implementation. The hardware and software requirements are described in the context of the desired high-speed capture suitable for earthquake motions or other dynamic movements in a scene. Experiments are conducted and presented illustrating the good performance and stability of the system. This system is deemed suitable for the general condition of a building interior.

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.

Monitoring global earthquake-induced demands using vision-based sensors

A vision-based approach is evaluated for its applicability as a new sensing technology for measuring earthquake-induced motions. The approach evaluated in this paper is advantageous since it requires very limited physical attachment to the structure of interest, is high-speed, high-resolution, and does not introduce additional mass or otherwise modify the properties of the structure. A demonstration experiment is described in which four digital high-speed, high-resolution, charge-coupled-device cameras outfitted with red light-emitting diodes are used to track 21 reflective (nearly) mass less spherical elements discretely mounted on a scale five-story steel frame structure. The structure is mounted on a large bi-axial shake table and subjected to different earthquake motions. A total of eleven conventional (wired) transducers [linear variable displacement transducers and accelerometers] are also discretely mounted on the structure, providing a unique comparison with the vision-based approach. Results from these experiments show that the nonintrusive vision-based approach is extremely promising in terms of its ability to capture inter-story drift, floor level velocities, and accelerations, provided proper post-processing of the dynamic data occurs.

Hardware architecture for a visualization classroom: VizClass

Interactive learning, critical thinking, creative problem‐solving, and problem‐based learning are all critical elements for enhancing engineering education. Visualization can provide the much needed computer‐assisted design and analysis environment to foster problem‐based learning, while virtual reality (VR) can provide the environment for hands‐on manipulation, stimulating interactive learning in the engineering classroom. To provide such a space, at the University of California, Irvine a new interactive, spatially balanced learning environment, termed VizClass, has been developed. VizClass incorporates a specially designed lecture room and laboratory integrating both 2‐ and 3‐dimensional spatial learning by coupling a series of interactive projection display boards (touch sensitive whiteboards) and a semi‐immersive 3D wall display. Control of devices integrated with VizClass is supported via a centrally located, easy to activate, touch‐sensitive display. Digital material, including slides, web content, video clips, sound files, numerical simulations, or animations may be loaded and presented by instructors using either 2D or 3D modalities. This environment has already been integrated into both undergraduate and graduate level courses, providing a balanced spatial learning environment for students. This article describes the unique hardware architecture developed to support this new environment and presents the first course activities conducted within the space.

A hybrid reality environment and its application to the study of earthquake engineering

Visualization can provide the much needed computer-assisted design and analysis environment to foster problem-based learning, while Virtual Reality (VR) can provide the environment for hands-on manipulation, stimulating interactive learning in engineering and the sciences. In this paper, an interactive 2D and 3D (hybrid) environment is described, which facilitates collaborative learning and research and utilizes techniques in visualization and VR, therefore enhancing the interpretation of physical problems within these fields. The environment described, termed VizClass, incorporates a specially designed lecture room and laboratory integrating both 2-D and 3-D spatial activities by coupling a series of interactive projection display boards (touch-sensitive whiteboards) and a semi-immersive 3D wall display. The environment is particularly appealing for studying critical, complex engineering problems, for example, where time-varying feature modifications and coupling between multiple modes of movement are occurring. This paper describes the hardware architecture designed for this new hybrid environment as well as an initial application within the environment to the study of a real case history building subjected to a variety of earthquakes. The example simulation uses field measured seismic data sources, and illustrations of simple visual paradigms to provide an enhanced understanding of the physical model, the damage accumulated by the model, and the association between the measured and observed data. A detailed evaluation survey was also conducted to determine the merits of the presented environment and the techniques implemented. Results substantiate the plausibility of using these techniques for more general, everyday users. Over 70% of the survey participants believed that the techniques implemented were valuable for engineers.

Urban Damage Estimation Using Statistical Processing of Satellite Images: 2003 Bam, Iran Earthquake

Remotely sensed satellite imagery of an earthquake-affected area can significantly assist in estimating the severity of infrastructure damage. Modern high-resolution satellite systems have been launched to provide users optical or Synthetic Aperture radar (SAR) data with sub-meter accuracy, which enable the possibility of sensing damage for individual infrastructure by means of pre- and post-event imagery. Herein, we focus our study on the region of Bam, Iran, which was devastated by a moment magnitude Mw = 6.6 earthquake on December 26, 2003, causing approximately 43,200 lives lost. To recognize houses within the Bam region before the earthquake, the boundary of houses are located using a combination of morphological gray-level open and intensity threshold operators. The unique aspect of this paper, as demonstrated with satellite imagery data from this event, is the use of an probabilistic framework for determining the optimal combination of morphological and intensity threshold parameters, which results in an estimated ground truth (EGT). By overlaying the EGT obtained from images before the earthquake with images of the same region after the earthquake, two statistical damage indices, including a new boundary-compactness based index proposed in this study, are compared. This comparison is presented using easily interpretable damage maps, where individual houses are rendered with colors representing the severity of damage.

A METHODOLOGY FOR IMAGE-BASED TRACKING OF SEISMIC-INDUCED MOTIONS

Previous experiences during earthquake events emphasize the need for new technologies for real-time monitoring and assessment of facilities with high value nonstructural elements such as equipment or other contents. Moreover, there are substantial limitations to our ability to rapidly evaluate and identify potential hazard zones within a structure, exposing rescue workers, society and the environment to unnecessary risks. A real-time monitoring system, integrated with critical warning systems, would allow for improved channeling of resources. Ideally such a system would acquire all relevant data non-intrusively, at high rates and resolution and disseminate it with low latency over a trusted network to a central repository. This repository can then be used by the building owner and rescue workers to make informed decisions. In recognition of these issues, in this paper, we describe a methodology for image-based tracking of seismically induced motions. The methodology includes calibration, acquisition, processing, and analysis tools geared towards seismic assessment. We present sample waveforms extracted considering pixel-based algorithms applied to images collected from an array of high speed, high-resolution charged-couple-device (CCD) cameras. This work includes use of a unique hardware and software design involving a multi-threaded process, which bypasses conventional hardware frame grabbers and uses a software-based approach to acquire, synchronize and time stamp image data.

Technical section: Image centric finite element simulation

Images have played a substantial role in documenting historical structures and structural systems. As a result, extensive archives are now available to reconstruct both modern and ancient buildings, bridges and other structures for subsequent analysis and visualization. While common approaches require the creation of complex three-dimensional models to facilitate the study of response to anticipated loading of a target system or subsystem, faster techniques are required for preliminary data analysis. This paper presents an image-based approach that allows users to sketch structural systems over a reference image while using standard engineering symbols and nomenclature. Within the presented framework, the response of the sketched system is analyzed and presented using an image-centric finite element analysis approach. Finite element models of the sketched structural system and image are constructed and simulation results fused into a final visual encoding, using deformation patterns and image warping. Results for two example structures illustrate the intuitive modeling capability that the system provides to the user. The presented system is particularly beneficial in educational environments, where fundamental behavioral characteristics of structural systems are studied.