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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.
81

The Influence of Pile Shape and Pile Sleeves on Lateral Load Resistance

Russell, Dalin Newell 01 March 2016 (has links)
The lateral resistance of pile foundations is typically based on the performance of round piles even though other pile types are used. Due to lack of data there is a certain level of uncertainty when designing pile foundations other than round piles for lateral loading. Theoretical analyses have suggested that square sections will have more lateral resistance due to the increased side shear resistance, no test results have been available to substantiate the contention. Full-scale lateral load tests involving pile shapes such as circular, circular wrapped with high density polyethylene sheeting, square, H, and circular with a corrugated metal sleeve have been performed considering the influence of soil-pile interaction on lateral load resistance. The load test results, which can be summarized as a p-y curve, show higher soil resistance from the H and square sections after accounting for differences in the moment of inertia for the different pile sections. The increased soil resistance can generally be accounted for using a p-multiplier approach with a value of approximately 1.25 for square or 1.2 for H piles relative to circular piles. It has been determined that high density polyethylene sheeting provides little if any reduction in the lateral resistance when wrapped around a circular pile. Circular piles with a corrugated metal sleeve respond to lateral loading with higher values of lateral resistance than independent circular piles in the same soil.
82

Estudo de caso sobre tratamento de esgoto sanitário através de wetlands construídos em escala real no sudeste brasileiro: questões operacionais, eficiências de tratamento e interferências do tempo de operação e da sazonalidade / Case study about domestic wastewater through full scale constructed wetlands in the Brazilian Southeast: operational matters, treatment efficiency and interference of time of operation and seasonality

Abreu, Cauê Girão de 27 June 2019 (has links)
No Brasil, o modelo implantado de esgotamento sanitário é centralizado, baseado em grandes redes de coleta de esgoto para transporte até as estações de tratamento. No entanto, o atendimento para que uma maior parcela da população possa ser atendida, modelos e sistemas descentralizados devemser adotados. Os wetlands construídos são amplamente citados como soluções sustentáveis, com apelo natural e de custo competitivo para o tratamento de águas residuárias de diversas fontes e são ainda apontados como uma tecnologia adequada e viável para a implantação de sistemas descentralizados de esgotamento sanitário. Nesse contexto, o presente estudo buscou a partir de um estudo de caso compreender o comportamento de um wetlands construídos híbridos em escala real no tratamento de esgoto sanitário, com operação registrada de 50 meses. O estudo buscou compreender os problemas operacionais ocorridos e os efeitos sobre as eficiências de remoção de carga orgânica, as possíveis correlações entre o tempo de operação, dos wetlands construídos na eficiência de remoção de carga orgânica além da influência da temperatura do ar e pluviometria. A eficiência de remoção média ao longo dos 50 meses para DBO520 e DQO foi de 82% e 72% respectivamente. Nenhuma correlação de grande representatividade foi encontrada, mas correlações negativas fracas foram observadas entre a eficiência de remoção de carga orgânica e a temperatura ambiente e entre a mesma eficiência e o tempo de operação / The wastewater collection and treatment model adopted in Brazil is centralized, based on great networks and treatment plants; however, the provision to a large part of the population requires that models and systems be decentralized. The constructed wetlands are often mentioned as sustainable solutions, for its natural appeal and competitive cost for treating wastewater from several sources; they are also pointed out as a viable and adequate technology for the implementation of decentralized sanitation systems. In this scenario, this study aims at applying a scientific analysis, based on a case study, of a system of hybrid constructed wetlands for treating domestic sewage, in full-scale, whose operation was registered for 50 months. This dissertation aims at describing, in detail, the project criteria and the constructive methodologies used by reporting the advantages and problems created by these criteria, besides analyzing the efficiency in the removal of organic load affected by the wastewater system, testing if there is any correlation between time of operation of the wetland system and its efficiency to remove organic load, and between the variations of temperature in the region where the system is operating and the efficiency, and, finally, between pluviometry in the region where the system is operating and the efficiency. In conclusion, the study compares the results obtained from data of other full-scale systems in different locations, in full-scale. The study found average removal efficiency throughout the 50 months for BOD5 and COD of 82% and 72%, respectively. No major correlation was found, but weak negative correlations were observed between the organic load removal efficiency and room temperature, and between efficiency and time of operation
83

Development of the Design of Eccentrically Braced Frames with Replaceable Shear Links

Mansour, Nabil 23 February 2011 (has links)
In current design of steel eccentrically braced frames (EBFs), the yielding link is coupled with the floor beam. This often results in oversized link elements, which leads to over-designed structures and foundations. In addition, the beams are expected to sustain significant damage through repeated inelastic deformations under design level earthquakes, and thus the structure may require extensive repair or need to be replaced. These drawbacks can be mitigated by designing EBFs with replaceable shear links. Two different replaceable link types with alternate section profiles, connection configurations, welding details and intermediate stiffener spacing were tested. A total of 13 cyclic quasi-static full-scale cyclic tests were performed, which included tests on eccentrically braced frames with the replaceable shear links, to study their inelastic seismic performance. The links exhibited a very good ductile behaviour, developing stable and repeatable yielding. Additional inelastic rotation capacity can be achieved with bolted replaceable links when allowing bolt bearing deformations to occur. The on-site replaceability of the link sections is confirmed even in the presence of residual deformations of 0.5% drift.
84

Investigation of methods used to predict the heat release rate and enclosure temperatures during mattress fires

Threlfall, Todd 05 September 2005
Fires in buildings ranging in size from small residential houses to large office buildings and sports stadiums pose significant threats to human safety. Many advances have been made in the area of fire behaviour modeling and have lead to much safer, and more efficient fire protection engineering designs, saving countless lives. Fire, however, is still a difficult phenomenon to accurately model and the most important quantity used to describe a fire is the heat (energy) release rate (HRR). Predictions of the fire hazard posed by mattresses, using relatively simple modeling techniques, were investigated in this research work and compared to full-scale experimental results. Specifically, several common methods of predicting the HRR from a mattress fire were examined. Current spatial separation guidelines, which exist in order to mitigate fire spread between buildings, were used to predict radiation heat flux levels emitted by a burning building and compared to experimental results measured in the field. Enclosure ceiling temperatures, predicted using the Alpert temperature correlation, and average hot gas layer temperature predictions were also compared to experimental results. Results from this work indicate that the t-squared fire heat release rate modeling technique combined with the common Alpert ceiling temperature correlation, provide a reasonable prediction of real-life fire temperatures as results within 30% were obtained. The cone calorimeter was also found to be a useful tool in the prediction of full-scale fire behaviour and the guidelines used for spatial separation calculations were found to predict the radiant heat flux emitted by a burning building reasonably well.
85

Bond Of Lap-spliced Bars In Self-compacting Concrete

Ghasabeh, Mehran 01 February 2013 (has links) (PDF)
Self-compacting concrete is an innovative construction material / its priority to normal vibrated concrete is that there is not any vibration requirement. Bond strength of reinforcement is one of the key factors that ensures the usefulness of any reinforced concrete structure. In this study, 6 full-scale concrete beams spliced at the mid-span were tested under two-point symmetrical loading. Test variables were bottom cover, side cover, free spacing between longitudinal reinforcement, lap-splice length and presence of transverse reinforcements within the lap-splice region. Specimen SC_22_44_88_800 had cover dimensions close to the code limits and had 36db lap splice length. This specimen showed flexural failure. Specimen SC_44_44_44_710 had 32db lap splice and cover dimensions greater than code minimums. This specimen showed yielding primarily. With the increasing loading, however, bond failure occurred with side splitting. ACI 408 descriptive equation for normal vibrated concrete predicted bar stresses of the unconfined specimens produced with self-compacting concrete acceptably well. The predicted values were lower than the measured values to be on the safe side. The error varied between 3.4% and 6.5%. All predictions of the ACI408 descriptive equation was higher than the measured bar stresses of the confined specimens produced with SCC. All the calculated values were unsafe. The error varied between 10.6% and 34.5%. Specimen SC_44_22_22_530_T4 with 24db lap splice length had side cover and spacing between bars 63.3% and 56.7% less than the ACI 318 limits. The calculated bar stress was 21.6% higher than the measured value. The main reason of the deviation was inadequate cover dimensions. In specimen SC_44_22_22_530_T6, number transverse reinforcement was increased to 6 stirrups to overcome the small cover and spacing problem. However, increased number of stirrups inside a small side and face cover caused weak plane and measured bar stress decreased.
86

Development of the Design of Eccentrically Braced Frames with Replaceable Shear Links

Mansour, Nabil 23 February 2011 (has links)
In current design of steel eccentrically braced frames (EBFs), the yielding link is coupled with the floor beam. This often results in oversized link elements, which leads to over-designed structures and foundations. In addition, the beams are expected to sustain significant damage through repeated inelastic deformations under design level earthquakes, and thus the structure may require extensive repair or need to be replaced. These drawbacks can be mitigated by designing EBFs with replaceable shear links. Two different replaceable link types with alternate section profiles, connection configurations, welding details and intermediate stiffener spacing were tested. A total of 13 cyclic quasi-static full-scale cyclic tests were performed, which included tests on eccentrically braced frames with the replaceable shear links, to study their inelastic seismic performance. The links exhibited a very good ductile behaviour, developing stable and repeatable yielding. Additional inelastic rotation capacity can be achieved with bolted replaceable links when allowing bolt bearing deformations to occur. The on-site replaceability of the link sections is confirmed even in the presence of residual deformations of 0.5% drift.
87

Investigation of methods used to predict the heat release rate and enclosure temperatures during mattress fires

Threlfall, Todd 05 September 2005 (has links)
Fires in buildings ranging in size from small residential houses to large office buildings and sports stadiums pose significant threats to human safety. Many advances have been made in the area of fire behaviour modeling and have lead to much safer, and more efficient fire protection engineering designs, saving countless lives. Fire, however, is still a difficult phenomenon to accurately model and the most important quantity used to describe a fire is the heat (energy) release rate (HRR). Predictions of the fire hazard posed by mattresses, using relatively simple modeling techniques, were investigated in this research work and compared to full-scale experimental results. Specifically, several common methods of predicting the HRR from a mattress fire were examined. Current spatial separation guidelines, which exist in order to mitigate fire spread between buildings, were used to predict radiation heat flux levels emitted by a burning building and compared to experimental results measured in the field. Enclosure ceiling temperatures, predicted using the Alpert temperature correlation, and average hot gas layer temperature predictions were also compared to experimental results. Results from this work indicate that the t-squared fire heat release rate modeling technique combined with the common Alpert ceiling temperature correlation, provide a reasonable prediction of real-life fire temperatures as results within 30% were obtained. The cone calorimeter was also found to be a useful tool in the prediction of full-scale fire behaviour and the guidelines used for spatial separation calculations were found to predict the radiant heat flux emitted by a burning building reasonably well.
88

Shear and shear friction of ultra-high performance concrete bridge girders

Crane, Charles Kennan 06 July 2010 (has links)
Ultra-High Performance Concrete (UHPC) is a new class of concrete characterized by no coarse aggregate, steel fiber reinforcement, low w/c, low permeability, compressive strength exceeding 29,000 psi (200 MPa), tensile strength ranging from 1,200 to 2,500 psi (8 to 17 MPa), and very high toughness. These properties make prestressed precast UHPC bridge girders a very attractive replacement material for steel bridge girders, particularly when site demands require a comparable beam depth to steel and a 100+ year life span is desired. In order to efficiently utilize UHPC in bridge construction, it is necessary to create new design recommendations for its use. The interface between precast UHPC girder and cast-in-place concrete decks must be characterized in order to safely use composite design methods with this new material. Due to the lack of reinforcing bars, all shear forces in UHPC girders have to be carried by the concrete and steel fibers. Current U.S. codes do not consider fiber reinforcement in calculating shear capacity. Fiber contribution must be accurately accounted for in shear equations in order to use UHPC. Casting of UHPC may cause fibers to orient in the direction of casting. If fibers are preferentially oriented, physical properties of the concrete may also become anisotropic, which must be considered in design. The current research provides new understanding of shear and shear friction phenomena in UHPC including: *Current AASHTO codes provide a non-conservative estimate of interface shear performance of smooth UHPC interfaces with and without interface steel. *Fluted interfaces can be created by impressing formliners into the surface of plastic UHPC. AASHTO and ACI codes for roughened interfaces are conservative for design of fluted UHPC interfaces. *A new equation for the calculation of shear capacity of UHPC girders is presented which takes into account the contribution of steel fiber reinforcement. *Fibers are shown to preferentially align in the direction of casting, which significantly affects compressive behavior of the UHPC.
89

Experimental testing, analysis, and strengthening of reinforced concrete pier caps by exterior post tensioning

O'Malley, Curtis John 17 May 2011 (has links)
Condition assessment of existing concrete bridge pier caps using the general shear provisions of the AASHTO LRFD Bridge Design Specification has caused the Georgia Department of Transportation (GDOT) to post a large number of bridges in the State of Georgia. Posting of bridges disrupts the free flow of goods within the region served by the bridge and has a negative economic impact. To prevent structural deterioration, diagonal cracking or failure of concrete pier caps in shear, the GDOT employs an in-situ strengthening technique that utilizes an external vertical post-tensioning system. However, the fundamental mechanics of this system and its effectiveness under service load have not been examined previously. This research examines the behavior of reinforced concrete pier caps that utilize the above strengthening system in a combined analytical and experimental program. In the experimental part of the study, two groups of full-scale reinforced concrete deep beam specimens were tested. The first group consisted of six deep beams with shear span/depth ratios of approximately 1.0, which is typical of bridge pier caps; of these six, two included the external post-tensioning system. In the second group, nine deep beam specimens that included a segment of the column representing the pier were tested; four of those tests included the external post-tensioning system. The tests revealed that the shear capacity computed using the AASHTO LRFD Bridge Design Specifications provided a conservative estimate of the specimen capacity in all but one case when compared to the experimental results. However, the AASHTO strut and tie provisions were found to provide a much closer assessment of the load carrying mechanism in the pier cap than the general shear provisions, in that they were able to predict the load at which yielding of the tension reinforcement occurred as well as the angle of the compression strut. The presence of the column segment in the second group had a significant impact on the failure mechanism developed in the specimen near ultimate load. The stress concentration at the reentrant corner between the pier cap and column interface served as an attractor for the formation of diagonal shear cracks, a mechanism not observed in previous deep beam tests in shear. The research has led to recommendations for improving the design of pier caps and the external post-tensioning system, where required, based on mechanics which are consistent with the results of the experimental program.
90

Bayesian Spatial Modeling of Complex and High Dimensional Data

Konomi, Bledar 2011 December 1900 (has links)
The main objective of this dissertation is to apply Bayesian modeling to different complex and high-dimensional spatial data sets. I develop Bayesian hierarchical spatial models for both the observed location and the observation variable. Throughout this dissertation I execute the inference of the posterior distributions using Markov chain Monte Carlo by developing computational strategies that can reduce the computational cost. I start with a "high level" image analysis by modeling the pixels with a Gaussian process and the objects with a marked-point process. The proposed method is an automatic image segmentation and classification procedure which simultaneously detects the boundaries and classifies the objects in the image into one of the predetermined shape families. Next, I move my attention to the piecewise non-stationary Gaussian process models and their computational challenges for very large data sets. I simultaneously model the non-stationarity and reduce the computational cost by using the innovative technique of full-scale approximation. I successfully demonstrate the proposed reduction technique to the Total Ozone Matrix Spectrometer (TOMS) data. Furthermore, I extend the reduction method for the non-stationary Gaussian process models to a dynamic partition of the space by using a modified Treed Gaussian Model. This modification is based on the use of a non-stationary function and the full-scale approximation. The proposed model can deal with piecewise non-stationary geostatistical data with unknown partitions. Finally, I apply the method to the TOMS data to explore the non-stationary nature of the data.

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