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The presence of cemented soils pose significant challenges in drilled shaft design and may prevent accurate estimates of the service limit state if traditional analytical techniques are employed. Thus, an Artificial Neural Network (ANN)... more
The presence of cemented soils pose significant challenges in drilled shaft design and may prevent accurate estimates of the service limit state if traditional analytical techniques are employed. Thus, an Artificial Neural Network (ANN) is developed and tested as an alternative method for predicting settlement induced by axial loads. Training is carried out using the results of 31 field load tests performed in Las Vegas, USA, where cemented soils are common, and an automated process is employed to determine the optimal network architecture. Ultimately, a cascaded feed-forward ANN with one hidden layer consisting of six artificial neurons produced the highest quality generalization. Ten additional load tests not included in the original training, testing, or validation datasets are reserved to evaluate performance. It is observed that the ANN produces similarly accurate estimates of load-settlement on average as compared to two more traditional t-z style approaches.
The development of the drilled shafts component a deep foundation load test database for the state of Nevada is presented. Preliminary analyses aimed at deriving region-specific resistance factors for Load and Resistance Factor Design... more
The development of the drilled shafts component a deep foundation load test database for the state of Nevada is presented. Preliminary analyses aimed at deriving region-specific resistance factors for Load and Resistance Factor Design (LRFD) of drilled shafts in Las Vegas have provided insight concerning the necessary components of a useful load test database. Specific recommendations are given concerning the information needed to make full use of both traditional top-down and bi-axial load tests on drilled shafts. A framework for classifying the quality of an axial load test for research and practical applications is proposed as well as a methodology for defining drilled shaft axial nominal resistance based on load test data.
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AbstractResistance factors for load and resistance factor design (LRFD) of axially loaded drilled shafts in the Las Vegas Valley are calibrated using data from 41 field load tests. In addition to t...
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A nonlinear ground response analysis is conducted for the Niigata-ken Chuetsu-oki earthquake recorded at a free-field vertical array near the Kashiwazaki-Kariwa Nuclear Power Plant in Japan. A bidirectional site response analysis is... more
A nonlinear ground response analysis is conducted for the Niigata-ken Chuetsu-oki earthquake recorded at a free-field vertical array near the Kashiwazaki-Kariwa Nuclear Power Plant in Japan. A bidirectional site response analysis is carried out using LS-DYNA which allows user defined stress-strain relationships to dictate soil behavior subjected to dynamic loading. Dynamic soil behavior is characterized using a two-stage hyperbolic backbone curve implemented with modifications to consider the peak strength of soil layers as well as the strain at which the peak strength is fully mobilized. The effects of bidirectional input motions, strain rate, and the shape of the shear modulus degradation curves are investigated, and it is demonstrated that each factor can have a significant influence on the results.
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A methodology is presented for employing the Deep Foundation System Analysis Program (DFSAP) to predict the performance of an axially loaded drilled shaft. The methodology is evaluated with respect to the outcomes of calculations... more
A methodology is presented for employing the Deep Foundation System Analysis Program (DFSAP) to predict the performance of an axially loaded drilled shaft. The methodology is evaluated with respect to the outcomes of calculations following the AASHTO LRFD Bridge Design Specification (AASHTO 2012), Brown et al., (2010) as well as from Osterberg Cell (O-Cell) load test data. While the AASHTO based design method can be carried out by hand and tends to be conservative, the DFSAP projections are established using the t-z method for axial settlement analysis and have the potential to be more accurate and precise. The procedure presented herein is developed based on an approach used for blind prediction of an O-Cell load test conducted on a 7-ft diameter, 116-ft long drilled shaft in Washoe County, Nevada. The test shaft was a part of the foundation system of a ten-span bridge over the Truckee River in the Reno area. Although the preliminary model achieved an adequate prediction, the formal procedure from this analysis employs updated information about the test shaft as well as a more detailed soil profile to generate a significantly closer fit to the published O-Cell test data.
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In this chapter, we provide a comprehensive overview of timing. We describe the underlying concepts that comprise timing through examples and then present a range of mature, standardised and evolving techniques to improve the so-called... more
In this chapter, we provide a comprehensive overview of timing. We describe the underlying concepts that comprise timing through examples and then present a range of mature, standardised and evolving techniques to improve the so-called time awareness across the full Information and Communications Technology (ICT) infrastructure over which multimedia applications operate. Although the media synchronisation community is already acutely aware of timing issues, this chapter offers some valuable insights through its holistic approach to timing.
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Research Interests:
Time is a foundational aspect of Cyber-Physical Systems (CPS). Correct time and timing of system events are critical to optimized responsiveness to the environment, in terms of timeliness, accuracy, and precision in the knowledge,... more
Time is a foundational aspect of Cyber-Physical Systems (CPS). Correct time and timing of system events are critical to optimized responsiveness to the environment, in terms of timeliness, accuracy, and precision in the knowledge, measurement, prediction, and control of CPS behavior. However, both the specification and verification of timing requirements of the CPS are typically done in an ad-hoc manner. While feasible, the system can become costly and difficult to analyze and maintain, and the process of implementing and verifying correct timing behavior can be errorprone. Towards the development of a verification testbed for testing timing behavior in tools and platforms with explicit time support, this paper first describes a way to express the various kinds of timing constraints in distributed CPS. Then, we outline the design and initial implementation of a distributed testbed to verify the timing of a distributed CPS analytically through a systematic framework. Finally, we illu...
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A new economy built on the massive growth of endpoints on the internet will require precise and verifiable timing in ways that current systems do not support. Applications, computers, and communications systems have been developed with... more
A new economy built on the massive growth of endpoints on the internet will require precise and verifiable timing in ways that current systems do not support. Applications, computers, and communications systems have been developed with modules and layers that optimize data processing but degrade accurate timing. State-of-the-art systems now use timing only as a performance metric. Correctness of timing as a metric cannot currently be designed into systems independent of hardware and/or software implementations. To enable the massive growth predicted, accurate timing needs cross-disciplinary research to be integrated into these existing systems. This paper reviews the state of the art in six crucial areas central to the use of timing signals in these systems. Each area is shown to have critical issues requiring accuracy or integrity levels of timing, that need research contributions from a range of disciplines to solve.
Research Interests: Computer Science and NIST
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A DetNet (deterministic network) provides specific performance guarantees to its data flows, such as extremely low data loss rates and bounded latency. As a result, securing a DetNet requires that in addition to the best practice security... more
A DetNet (deterministic network) provides specific performance guarantees to its data flows, such as extremely low data loss rates and bounded latency. As a result, securing a DetNet requires that in addition to the best practice security measures taken for any mission- critical network, additional security measures may be needed to secure the intended operation of these novel service properties. This document addresses DetNet-specific security considerations from the perspectives of both the DetNet system-level designer and component designer. System considerations include a threat model, taxonomy of relevant attacks, and associations of threats versus use cases and service properties. Component-level considerations include ingress filtering and packet arrival time violation detection. This document also addresses DetNet security considerations specific to the IP and MPLS data plane technologies thereby complementing the Security Considerations sections of the various DetNet Data Plane (and other) DetNet documents.
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Research Interests:
Time is a foundational aspect of Cyber-Physical Systems (CPS). Correct time and timing of system events are critical to optimized responsiveness to the environment, in terms of timeliness, accuracy, and precision in the knowledge,... more
Time is a foundational aspect of Cyber-Physical Systems (CPS). Correct time and timing of system events are critical to optimized responsiveness to the environment, in terms of timeliness, accuracy, and precision in the knowledge, measurement, prediction, and control of CPS behavior. However, both the specification and verification of timing requirements of the CPS are typically done in an ad-hoc manner. While feasible, the system can become costly and difficult to analyze and maintain, and the process of implementing and verifying correct timing behavior can be error-prone. Towards the development of a verification testbed for testing timing behavior in tools and platforms with explicit time support, this paper first describes a way to express the various kinds of timing constraints in distributed CPS. Then, we outline the design and initial implementation of a distributed testbed to verify the timing of a distributed CPS analytically through a systematic framework. Finally, we illustrate the use of the verified timing testbed on two distributed CPS case studies.