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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
641

Development of a Performance-Based Procedure for Assessment of Liquefaction-Induced Free-Field Settlements

Peterson, Brian David 01 December 2016 (has links)
Liquefaction-induced settlement can cause significant damage to structures and infrastructure in the wake of a seismic event. Predicting settlement is an essential component of a comprehensive seismic design. The inherent uncertainty associated with seismic events makes the accurate prediction of settlement difficult. While several methods of assessing seismic hazards exist, perhaps the most promising is performance-based earthquake engineering, a framework presented by the Pacific Earthquake Engineering Research (PEER) Center. The PEER framework incorporates probability theory to generate a comprehensive seismic hazard analysis. Two settlement estimation methods are incorporated into the PEER framework to create a fully probabilistic settlement estimation procedure. A seismic hazard analysis tool known as PBLiquefY was updated to include the fully probabilistic method described above. The goal of the additions to PBLiquefY is to facilitate the development of a simplified performance-based procedure for the prediction of liquefaction-induced free-field settlements. Settlement estimations are computed using conventional deterministic methods and the fully probabilistic procedure for five theoretical soil profiles in 10 cities of varying seismicity levels. A comparison of these results suggests that deterministic methods are adequate when considering events of low seismicity but may result in a considerable under-estimation of seismic hazard when considering events of mid to high seismicity.
642

Scale Model Shake Table Testing of Underground Structures in Soft Clay

Crosariol, Victor A 01 June 2010 (has links)
Underground structures perform an important role in transportation systems in many seismically active regions around the world, but empirical data regarding the seismic behavior of these structures is limited. This research works towards filling that empirical gap through the use of scale model shake table testing. Underground seismic soil-structure interaction (USSSI) effects were investigated for a stiff rectangular tunnel cross-section embedded within soft clay. San Francisco Young Bay Mud was used as a prototype soil for developing a scale model soil mixture consisting of kaolinite, bentonite, class C fly ash, and water. A single cell Bay Area Rapid Transit (BART) cut-and-cover subway tunnel was used as the prototype for the 10th scale model subway cross-section. A flexible walled test container originally developed for a pile study at UC Berkeley was modified for use at Cal Poly, San Luis Obispo. The flexible container allows for close approximation of one-dimensional (1D) free-field site response by significantly limiting the rigidity of the boundary conditions and allowing the soil to deform under simple shear. The study was conducted over two shake table testing phases: Phase I consisted of shaking a model soil column to evaluate the ability of the test container to produce adequate 1D free-field site response, and Phase II tests explored the horizontal racking distortion of a shallow rectangular tunnel cross-section subjected to strong transverse ground shaking. Phase I test results and comparison with SHAKE models indicate that the test container can sufficiently mimic 1D free-field conditions, specifically for the primary shear deformation mode. Similarly, the equivalent linear soil-structure interaction code FLUSH was found to adequately model site response for the Phase II soil-structure system. Comparison of recorded horizontal racking distortions of the model structure with those from numerical modeling suggest that current simplified design methods may overestimate distortions to some degree for cases similar to those examined in this research. Overall, the flexible wall testing container shows promise as a viable means for gaining further insight into USSSI topics, as well as various other geotechnical and soil-structure interaction problems.
643

Design and Experimental Investigation of 500kV Current Transformer Seismic Retrofit Utilizing Structure Rocking and Supplemental Damping with Self-Centering

Palnikov, Ilya S. 10 July 2017 (has links)
Electrical substations perform a key role in electrical transmission and distribution; the ability for a substation to remain functional during and after a seismic event contributes significantly to the resilience of the clients supplied. Many legacy components currently installed in the main grid substations were designed with minimal consideration of lateral loads and are not qualified per IEEE693. One of the more critical high-voltage substation components that are vulnerable to earthquake damage is the 500kV freestanding current transformer (CT). The CT is particularly vulnerable due to the slenderness and mass distribution of the component. Current transformers are typically constructed from a combination of aluminum and brittle porcelain. Two novel retrofit measures were investigated utilizing base rocking and supplemental damping to reduce the seismic amplification in the CT while also potentially providing post-earthquake self-centering capability. The retrofit measures utilize both shift in system frequency and energy dissipation through supplemental damping to reduce seismic demands on the CT. The purpose of the research was to conceptually develop, detail design, analyze and experimentally validate the retrofit measures. A desired feature of the retrofit measures was for minimal or no residual displacement following the seismic event, which was implemented in the retrofit through a preloaded centering mechanism. Based on the analyses and experiments, the proposed retrofit measures exhibited significantly decreased demands on the CT and true self-centering.
644

Development of a Design Guideline for Bridge Pile Foundations Subjected to Liquefaction Induced Lateral Spreading

Nasr, Jonathan A. 11 January 2018 (has links)
Effective-stress nonlinear dynamic analyses (NDA) were performed for piles in liquefiable sloped ground to assess how inertia and liquefaction-induced lateral spreading combine in long-duration vs. short-duration earthquakes. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of earthquake durations. The NDA results were used to evaluate the accuracy of the equivalent static analysis (ESA) recommended by Caltrans/ODOT for estimating pile demands. Finally, the NDA results were used to develop new ESA methods to combine inertial and lateral spreading loads for estimating elastic and inelastic pile demands. The NDA results showed that pile demands increase in liquefied conditions compared to nonliquefied conditions due to the interaction of inertia (from superstructure) and kinematics (from liquefaction-induced lateral spreading). Comparing pile demands estimated from ESA recommended by Caltrans/ODOT with those computed from NDA showed that the guidelines by Caltrans/ODOT (100% kinematic combined with 50% inertia) slightly underestimates demands for subduction earthquakes with long durations. A revised ESA method was developed to extend the application of the Caltrans/ODOT method to subduction earthquakes. The inertia multiplier was back-calculated from the NDA results and new multipliers were proposed: 100% Kinematic + 60% Inertia for crustal earthquakes and 100% Kinematic + 75% Inertia for subduction earthquakes. The proposed ESA compared reasonably well against the NDA results for elastic piles. The revised method also made it possible to estimate demands in piles that performed well in the dynamic analyses but could not be analyzed using Caltrans/ODOT method (i.e. inelastic piles that remained below Fult on the liq pushover curve). However, it was observed that the pile demands became unpredictable for cases where the pile head displacement exceeded the displacement corresponding to the ultimate pushover force in liquefied conditions. Nonlinear dynamic analysis is required for these cases to adequately estimate pile demands.
645

Strength Tuned Steel Eccentric Braced Frames

Al-Azzawi, Hosam Abdullah 05 June 2019 (has links)
The primary component in eccentrically braced frames (EBF) is the link as its plastic strength controls the design of the frame as well as the entire building within which it is installed. EBFs are the first part of building design and every other component is sized based on the forces developed in the link. Oversized link elements lead to the use of unnecessary materials and can increase construction costs. Additionally, the advantages of using a continuous member of the same depth for both the link and the controller beam (in terms of the cost and the time) motivates researchers to find a way to control the link strength in conventional EBFs. Previous studies on the link-to-column connections in EBF have shown that the links are likely to fail before reaching the required rotation due to fractures at low drift level. Moreover, improving the strength of the links in EBF depends primarily on their ability to achieve target inelastic deformation and to provide high ductility during earthquakes. Therefore, in this study, the concept of tuned link strength properties in EBF, T-EBF, is experimentally introduced as a solution to improve the performance of the link in conventional EBF by cutting out an opening in the link web. Furthermore, a new brace-to-link connection is proposed to bolt the brace member with the link in contrast to the conventional method of welding them. This new idea in continuous beam design was investigated to verify the stability of the tuned eccentrically braced frame, either welded or bolted, with a bracing member. A total of four full-scale cyclic tests were conducted to study the ability of T-EBF to achieve inelastic deformation. The specimens have two different cross sections: W18x76 and W16x67, two different sections where the brace was welded to the link, and two other specimens at different sections where the brace was bolted to the link were examined. The experimental results indicate that the link in T-EBF can achieve high rotation, exceeding 0.15 rad, and an overstrength factor equal to 1.5. Failure involved included web buckling at very high rotation. The T-EBF displayed a very good, non-replaceable ductile link. The experiments were followed by an isotropic kinematic-combined hardening model in the finite element analyses (FEA). The FEA analysis is developed to predict the effect of web opening configuration on the local section stresses and strains and global characteristics of the frame. FEA exhibits good agreement with the experimental results and can capture the inelastic buckling behavior of the sections. The link configuration parameters of the T-EBF were studied extensively on a W18x76 shear link subjected to the 2016 AISC seismic design provisions loading protocol (ANSI/AISC 341-16, 2016). The parametric study also included the performance of a range of wide flange sections. The analysis shows that the reduced web section has effect on the plastic strain in which low plastic strain observed near ends and connections and high at the center of the web. Results also demonstrate that if the shear link is appropriately sized with web opening and intermediate web stiffeners provided, an excellent shear link with high ductility under cyclic loads can be obtained. Changing the configuration of the opening cutout also had a significant effect on reducing the transition zone cracks.
646

Disaster recovery modeling for multi-damage state scenarios across infrastructure sectors

Deelstra, Andrew 18 September 2019 (has links)
Residents in urban areas depend on infrastructure systems to return to functionality quickly after disruptions from natural and man-made disasters to support their livelihood and well-being. This work seeks to improve the accuracy of infrastructure recovery time estimates by introducing mutually exclusive damage state modeling into the Graph Model for Operational Resilience (GMOR) and utilizing this capability for road recovery assessment in two case studies in the District of North Vancouver, British Columbia. The first case study also explores the recovery of water, wastewater, and power networks in the District, and demonstrates that power and road systems recover more slowly and are more variable in their recovery time than water distribution and wastewater collection systems. The second study specifically addresses important sections of road within the District and shows that intelligent prioritization of resource allocation for road repairs can improve recovery times by up to 37% compared to random ordering. / Graduate
647

Geometry and Physical Properties of the Chelungpu Fault, Taiwan, and Their Effect on Fault Rupture

Heermance, Richard V. 01 May 2002 (has links)
Rupture of the Chelungpu fault during the September 21, 1999, 7.6 Mwearthquake in Taiwan caused a 90-Jr,m-long surface rupture with variable displacement along strike. Analysis of core from two holes drilled through the fault zone, combined with geologic mapping and detailed investigation from three outcrops, define the fault geometry and physical properties of the Chelungpu fault in its northern and southern regions. In the northern region, the fault dips 45-60° east parallel to bedding and consists of a narrow (1-20 cm) core of dark-gray, sheared clay gouge at the base of a 30-50 m zone of increased fracture density that is confined asymmetrically to the hanging wall. Microstructural analysis of the fault gouge indicates the presence of extremely narrow clay zones (50-300 μm thick) that are interpreted as the fault rupture surfaces. Few shear indicators are observed outside of the fault gouge, which implies that slip was localized in the gouge in the northern region. Slip localization along a bed-parallel surface resulted in less high-frequency ground motion and larger displacements during the earthquake than in the southern region. Observations from the southern region indicate that the fault dips 20-30° at the surface and consists of a wide (20- 70 m-thick) zone of sheared, foliated shale with numerous gouge zones. A footwall-ramp geometry juxtaposes 2000-3000 m of flat-lying Quaternary Toukoshan Formation in the footwall with Pliocene and Miocene, east-dipping siltstone and muds tone in the hanging wall. The wide, diffuse fault zone contributed to the lower displacement and higher frequency ground motion in the southern region during the 1999 earthquake. The structure in the northern region is the result of the fault being a very young (<50 >ka) fault segment in the hanging wall of an older segment of the Chelungpu fault, buried in the Taichung basin. The fault in the southern region is located on an older (~1 Ma) fault trace. The contrasting fault properties in the different regions are responsible for the variability in strong-motion and displacement observed during the 1999 earthquake.
648

The 2010 Earthquake And Media In Haiti: Journalistic Transformations, Democracy And The Politics Of Disaster.

January 2014 (has links)
This dissertation explains the role that Haiti's leading mainstream and alternative news outlets have played in the aftermath of the 2010 earthquake that devastated the island nation of Haiti. The role of the media as a civic institution that acts on behalf of and in alliance with civil society in times of crisis is the central theme of this dissertation. Prior research has demonstrated that Haiti's media has been at the heart of such a role in civic society throughout the country's two hundred plus years of independent existence. This dissertation argues that this media tradition has been revitalized, strengthened and put to the test by the current crisis the country faces in physical reconstruction from natural disaster, political reconstruction from fragile early attempts at democracy, and social reconstruction from decades of economic stagnation that have exacerbated poverty and living conditions of the average Haitian. This project uses a mixed methodological approach of qualitative methods and basic quantitative methods to analyze how Haitian journalists have covered the aftermath of the disaster. This research addressed three key elements: (1) the impact of the disaster on the fractions that existed within the leading news media outlets during the nation's ongoing experiment with democracy (2) the impact of the disaster on how journalists view and practice their profession (3) the impact of the disaster on the quality of news being produced in Haiti. Findings indicate that there was an initial solidarity reborn among key Haitian news outlets that has sustained itself four years into the crisis. The solidarity born out of this most recent crisis has resulted in changes in how journalists approach their civic duty, despite commercial strains, and how they cooperate through sharing of news content and resources. These changes are seen across all media platforms. Additionally, Haitian media outlets have taken joint stances on developments in the country since the 2010 disaster that has resulted in news content that is more critical of those who hold power, and more concerned with advocacy on behalf of the Haitian people in general. At a time when the Haitian people are searching for a path forward, Haiti's media is providing a powerful platform to debate the course of the country's future. / acase@tulane.edu
649

Discovery of Possible Paleotsunami Deposits in Pangandaran and Adipala, Java, Indonesia Using Grain Size, XRD, and <sup>14</sup>C Analyses

Stuart, Kevin L. 01 March 2018 (has links)
Grain size, 14C age, and X-ray diffraction (XRD) analyses of sediments indicate possible tsunami deposits on the southern coast of Java near Pangandaran and Adipala. Previous studies that have described known recent and paleotsunami deposits were used for comparison. Fining-upward grain size trends, interbedded sand and mud, sediment composition, and trends in heavy mineral abundances are among the characteristics used for tsunami deposit identification. At Batu Kalde, an archaeological site south of Pangandaran, a layer of aragonitic sand with marine fossils was found atop a layer of archaeological fragments at an elevation of ~2-5 m. It is likely this layer was deposited by a tsunami, potentially generated by a mega-thrust earthquake. Archaeological material remains suggest that the tsunami occurred ~1300 years ago. A bivalve with an age of 5584-5456 cal YBP was buried within the deposit, perhaps long after its death. At Goa Panggung, a cave east of Batu Kalde, fining-upward grain size trends, composition of sediments, and radiocarbon ages suggest the presence of at least one tsunami deposit. A 5040-4864 cal YBP piece of charcoal overlying modern organic matter suggest that the tsunami first scoured the cave floor, reworking existing material and making interpretation difficult. At Adipala, in western Central Java, fining-upward grain size, upward decrease in heavy mineral abundances, and lateral continuity of sand layers revealed the existence of two possible tsunami deposits buried within the sediments in a swale ~1.6 km from the ocean. Age of the deposits is undetermined.
650

The Taiwanese Residential Construction Peak of the 1990's: Interpreting industry and Developer Behaviour

Hsieh, Hui-Yuan (Henry), n/a January 2003 (has links)
Taiwanese residential construction experienced a massive rise and then fall in residential unit completions during the period 1992-1997. Completions rose nearly 200 per cent between 1992 and 1994 alone. A series of questions arise in relation to this phenomenon (referred to here as 'the Peak'): Why did it occur? How was this increase in construction achieved in such a short time? What were its impacts? Was it a supply-side or a demand-side phenomenon? And what are the significance and implications of the Peak? This thesis adopts a distinct methodological stance, being explanatory and interpretative rather than concerned with theory construction and testing. It is argued that this is appropriate as the Peak was a singular phenomenon, and not part of the regular fluctuations in a residential market cycle. Consequently, it is treated as an event and event-triggered, rather than as part of a continuing time-series. In addition, given that it was influenced by an enormous array of exogenous factors, including politics, the economy, and government regulations and policy, as well as by demographic, historical and geographical factors, a holistic approach is employed, as opposed to a reductionist one. The purpose is to build as complete an interpretation as possible. A major trigger for the Peak was the announcement of a residential density regulation (vohme control) in early 1992. This regulation, which threatened to dramatically reduce the profitability of development land, caused a massive acceleration in the rate of residential development approvals and ensuing completions. The regulation is viewed as interacting with a loosening of development and construction credit restrictions in late 1990 to precipitate a massive Peak in residential construction. This took glace over a very short period of time. This is analysed for each city and county in Taiwan as well as for Taiwan as a whole, the same factors applying throughout the country with the exception of Taipei City. In Taipei City, the peak occurred in a milder form in the 1980s rather than in the 1990s, due to an earlier implementation of volume control. This provides support for the overall interpretation of the thesis. After its announcement a grace period before the regulation was to come into effect allowed existing developers and landowners to propose and execute land development and construction under the old regulation. This period also induced new developers into the market, in part based on an expectation of higher unit prices resulting from volume control. This created a huge new stock of smaller-size apartments. Accompanied by falling prices, this outcome is consistent with the supply-side explanation of the Peak. Additional evidence of a supply-side phenomenon includes the high vacancies and unsold developer inventories that resulted. The rush to construction under the old regulation meant that the demand and supply market feedback loop could not effectively operate. The presence of simultaneous production peaks in all cities and counties is just one piece of evidence that this feedback loop was ineffective. A pooled cross-sectional time-series model, based on supply and demand factors of all cities and counties during 1982-1998, was used to further analyse this model of the Peak. Again the results are consistent with the supply- side interpretation. While credit loosening and volume control triggered the Peak, it is the existence of huge production flexibilities in the residential construction industry that enabled such a massive and rapid increase in construction. These flexibilities flowed, in part, from a dominant reinforced concrete construction method, as well as the Taiwanese subcontracting system, and residential construction industry networks. It is argued that these networks provided a form of quasi-public good that could be exploited. These same factors also facilitated the rapid entry of new developers into the industry. Conversely, this was associated with a decline in construction quality, as the limits of flexibility were reached. Some evidence for this was revealed by the 1999 earthquake. Imputed construction costs rose enormously during the Peak, with profits necessarily declining under the combined pressures of falling prices and rising costs. This resulted in bankruptcies and other exits from the industry. The impacts of oversupply -such as a high vacancy rate, growing developer inventories and falling prices -are expected to be long-term. The vacant stock is calculated as equivalent to ten to twelve years of pre- Peak construction. This thesis concludes that the Peak was a discontinuity phenomenon. It was triggered by a unique set of events, rather than being part of a continuous historical development. While developer behaviour was individually rational, collectively their decisions were disastrous for themselves and the industry

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