No description available.

This dissertation is intended to explore the design of a dual connection skeleton (DCS), which facilitates effective and efficient exploitation of Internet-centric collaborative workgroup and high performance metacomputing applications. The predominant difference between DCS and conventional frameworks is that DCS administers a network of brokers that are grouped into a logical ring. New mechanisms for group collaboration, load distribution, and fault tolerance, which are three crucial issues in Internet-based computing, are proposed and integrated into the dual connection skeleton. Collaborative workgroup becomes a significant common issue when we attempt to develop wide area applications supporting computer-supported cooperative work (CSCW). For group collaboration, DCS therefore offers a strategy for concurrency control that ensures the consistency of shared resources. By using the strategy, multiple users in a collaborative group are able to simultaneously access shared data without violating its consistency. With respect to load distribution, additionally, DCS applies an adaptive highest response ratio next (AHRRN) algorithm to job scheduling. Performance evaluations on competing algorithms, such as shortest job first (SJF), highest response ratio next (HRRN), and first come, first served (FCFS) are conducted. Simulation results demonstrate that AHRRN is not only an efficient algorithm, but also is able to prevent the well-known job starvation problem. In a parallel computational application, one can further decompose a composite job into constituent tasks such that these tasks can be assigned to different PEs for concurrent execution. The dual connection skeleton thus makes use of a proposed dynamic grouping scheduling (DGS), to undertake task scheduling for performance improvement. The DGS algorithm employs a task grouping strategy to determine computational costs of tasks. It re-prioritizes unscheduled tasks at each scheduling step to explore an appropriate task allocation decision. In terms of the schedule length, the performance of DGS has been evaluated by comparing with some existing algorithms, such as Heavy Node First (HNF), Critical Path Method (CPM), Weight Length (WL), Dynamic Level Scheduling (DLS), and Dynamic Priority Scheduling (DPS). Simulation results show that DGS outperforms these competing algorithms. Moreover, as for fault tolerance, DCS utilizes a dual connection mechanism for computational reliability enhancement. For the sake of constructing dual connection, we examine five approaches: RANDOM, NEXT, ROTARY, MINNUM, and WEIGHT. Each one of these approaches can be incorporated into DCS-based wide-area metacomputing systems. Performance simulation shows that WEIGHT benefits the dual connection the most. A DCS-based scientific computational application named the motion correction is used to demonstrate the fault tolerant ability of DCS. Putting the group collaboration, load distribution, and fault tolerance issues together, the dual connection skeleton forms a seamless and integrated framework for Internet-centric computing.

No description available.

No description available.

Studies have shown that over 30 percent of the bridges in the United States are structurally deficient, and/or over 50 years old. The majority of the highway bridges have reinforced concrete decks supported on steel or concrete girders. Over the years, weathering and deicing chemicals have caused spalling of the concrete surrounding the reinforcing steel, deteriorating many bridges to levels that often result in closure. Repairing or reconstructing the reinforced concrete deck to meet current design specifications is often not possible or feasible, and at times seems illogical due to the possibility of reoccurrence. Because of reinforced concrete's downfalls, there is a move toward alternative materials and designs for bridge deck replacements. In particular, Reynolds Metals Company has lead the movement toward the use of a shop-extruded aluminum deck system known as ALUMADECKTM. The purpose of this research is to evaluate data collected from full-scale testing under test truck loading of an in-service ALUMADECK bridge system. The bridge is known as the Little Buffalo Creek Bridge and is located in Mecklenburg County, VA. The topics researched from the load tests are the composite action amongst the deck and supporting members, the load distribution amongst supporting members, the dynamic load allowance for supporting members, and the developed deck stresses due to test truck loads. Evaluations of the research topics include comparisons to the methods employed in the design calculations provided by VDOT and to those of the American Association of State Highway and Transportation Officials (AASHTO) design specifications. / Master of Science

This dissertation investigates how to optimize flow-level performance in interference dominated wireless networks serving dynamic traffic loads. The schemes presented in this dissertation adapt to long-term (hours) spatial load variations, and the main metrics of interest are the file transfer delay or average flow throughput and the mean power expended by the transmitters. The first part presents a system level approach to interference management in an infrastructure based wireless network with full frequency reuse. The key idea is to use loose base station coordination that is tailored to the spatial load distribution and the propagation environment to exploit the diversity in a user population's sensitivity to interference. System architecture and abstractions to enable such coordination are developed for both the downlink and the uplink cases, which present differing interference characteristics. The basis for the approach is clustering and aggregation of traffic loads into classes of users with similar interference sensitivities that enable coarse grained information exchange among base stations with greatly reduced communication overheads. The dissertation explores ways to model and optimize the system under dynamic traffic loads where users come and go resulting in interference induced performance coupling across base stations. Based on extensive system-level simulations, I demonstrate load-dependent reductions in file transfer delay ranging from 20-80% as compared to a simple baseline not unlike systems used in the field today, while simultaneously providing more uniform coverage. Average savings in user power consumption of up to 75% are achieved. Performance results under heterogeneous spatial loads illustrate the importance of being traffic and environment aware. The second part studies the impact of policies to associate users with base stations/access points on flow-level performance in interference limited wireless networks. Most research in this area has used static interference models (i.e., neighboring base stations are always active) and resorted to intuitive objectives such as load balancing. In this dissertation, it is shown that this can be counter productive, and that asymmetries in load can lead to significantly better performance in the presence of dynamic interference which couples the transmission rates experienced by users at various base stations. A methodology that can be used to optimize the performance of a class of coupled systems is proposed, and applied to study the user association problem. It is demonstrated that by properly inducing load asymmetries, substantial performance gains can be achieved relative to a load balancing policy (e.g., 15 times reduction in mean delay). A novel measurement based, interference-aware association policy is presented that infers the degree of interference induced coupling and adapts to it. Systematic simulations establish that both the optimized static and interference-sensitive, adaptive association policies substantially outperform various proposed dynamic policies and that these results are robust to changes in file size distributions, channel parameters, and spatial load distributions. / text

This thesis presents the results of an investigation into the evaluation of a selected test bridge using instrumentation to obtain site-specific factors contributing to the evaluation, with the ultimate objective of improving the estimate of the bridges reliability in order to assess allowable loading more accurately. The experimental portion of the research program involved instrumenting the test bridge with strain gauges, and recording field measurements using two forms of loading. The analytical portion of the research program involved the analysis of the bridge in the as-designed state, based on the design drawings and specification, followed by a re-analysis of the bridge using the site-specific factors measured on-site. The bridge was evaluated using methods outlined in the Canadian Highway Bridge Design Code CAN/CSA-S6-00 (CSA 2000). <p>The test bridge is located near the community of Hudson Bay, Saskatchewan. The bridge is constructed of steel-reinforced concrete, and there are three, three-span arch-shaped girders. There are also external steel bars added after initial construction to increase the midspan bending moment resistance. In total, 45 strain gauges were placed on the middle spans of the three girders to record strain induced by two forms of loading: controlled loading, in which a truck of known weight and dimensions was driven over the bridge in a number of pre-determined configurations, and in-situ loading, in which normal truck traffic was used. The current allowable loading on the bridge is a gross vehicle weight of 62.5 t, although increasing the allowable loading to 110 t has been proposed, along with two strengthening alternatives to make this increased loading feasible. <p>To provide a base-line analysis for comparison purposes, the bridge was first evaluated based strictly on information taken from the design drawings and specifications. The evaluation was performed using the load and resistance factor method, in which load and resistance factors were used to account for uncertainty, as well as by the mean load method, in which statistical properties of the variables parameters included in the design were used to account for uncertainty. The result of the load and resistance factor method was a live load capacity factor, indicating the overall rating of the bridge. In addition to the live load capacity factor, the mean load method was also used to determine the reliability index. The results of the as-designed analysis showed that the mean load method gave more conservative estimates of the bridge capacity. Furthermore, it was determined that, based on these assessments, the bridge would not have sufficient capacity to carry the proposed 110 t truck loads.<p>The bridge was re-evaluated using site-specific factors with the mean load method. Using the measured strains, statistical parameters were determined for live load effects, distribution factors, dynamic load allowance, and resistance. Statistical parameters that could not be obtained readily through testing were obtained from the literature. The results indicated that code-predicted estimates of a number of factors were highly conservative. Flexural and shear load effects in the girders were found to be less than 15% of the theoretical predictions, as a result of apparent arching action in the girders, generating significant axial forces. For this arching action to occur, horizontal restraint was required at the supports, either through unanticipated restraint in the bearings, or tension tie action of the tensile girder reinforcement. Furthermore, the dynamic amplification was found to be less than 1.0. The resulting reliability indices indicated that the bridge would be safe under the proposed increased allowable loading (110 t). <p>Finite element models were used to confirm the dynamic amplification observations and examine the effects of different degrees of bearing restraint. The model showed results similar to those measured for dynamic amplification. It was found that if the bearings were to become completely fixed against horizontal translation, the bridge would become overloaded as a result of increased shear effects, demonstrating the need for proper bearing maintenance. <p>An analysis of relative costs was completed to determine the most cost-effective solution for hauling logs. Assumptions were made regarding truck and maintenance and operating costs. The results indicated that the most economic solution was to use the method outlined in the research to increase the allowable loading on the bridge to 110 t, over the strengthening alternatives and simply leaving the bridge in the current state.

This paper presents the development of a finite element method for modeling fastener joints in aircraft structures. By using connector element in commercial software Abaqus, the finite element method can handle multi-bolt joints and secondary bending. The plates in the joints are modeled with shell elements or solid elements. First, a pre-study with linear elastic analyses is performed. The study is focused on the influence of using different connector element stiffness predicted by semi-empirical flexibility equations from the aircraft industry. The influence of using a surface coupling tool is also investigated, and proved to work well for solid models and not so well for shell models, according to a comparison with a benchmark model. Second, also in the pre-study, an elasto-plastic analysis and a damage analysis are performed. The elasto-plastic analysis is compared to experiment, but the damage analysis is not compared to any experiment. The damage analysis is only performed to gain more knowledge of the method of modeling finite element damage behavior. Finally, the best working FE method developed in the pre-study is used in an analysis of an I-beam with multi-bolt structure and compared to experiments to prove the abilities with the method. One global and one local model of the I-beam structure are used in the analysis, and with the advantage that force-displacement characteristic are taken from the experiment of the local model and assigned as a constitutive behavior to connector elements in the analysis of the global model.

This thesis presents the results of an investigation into the evaluation of a selected test bridge using instrumentation to obtain site-specific factors contributing to the evaluation, with the ultimate objective of improving the estimate of the bridges reliability in order to assess allowable loading more accurately. The experimental portion of the research program involved instrumenting the test bridge with strain gauges, and recording field measurements using two forms of loading. The analytical portion of the research program involved the analysis of the bridge in the as-designed state, based on the design drawings and specification, followed by a re-analysis of the bridge using the site-specific factors measured on-site. The bridge was evaluated using methods outlined in the Canadian Highway Bridge Design Code CAN/CSA-S6-00 (CSA 2000). <p>The test bridge is located near the community of Hudson Bay, Saskatchewan. The bridge is constructed of steel-reinforced concrete, and there are three, three-span arch-shaped girders. There are also external steel bars added after initial construction to increase the midspan bending moment resistance. In total, 45 strain gauges were placed on the middle spans of the three girders to record strain induced by two forms of loading: controlled loading, in which a truck of known weight and dimensions was driven over the bridge in a number of pre-determined configurations, and in-situ loading, in which normal truck traffic was used. The current allowable loading on the bridge is a gross vehicle weight of 62.5 t, although increasing the allowable loading to 110 t has been proposed, along with two strengthening alternatives to make this increased loading feasible. <p>To provide a base-line analysis for comparison purposes, the bridge was first evaluated based strictly on information taken from the design drawings and specifications. The evaluation was performed using the load and resistance factor method, in which load and resistance factors were used to account for uncertainty, as well as by the mean load method, in which statistical properties of the variables parameters included in the design were used to account for uncertainty. The result of the load and resistance factor method was a live load capacity factor, indicating the overall rating of the bridge. In addition to the live load capacity factor, the mean load method was also used to determine the reliability index. The results of the as-designed analysis showed that the mean load method gave more conservative estimates of the bridge capacity. Furthermore, it was determined that, based on these assessments, the bridge would not have sufficient capacity to carry the proposed 110 t truck loads.<p>The bridge was re-evaluated using site-specific factors with the mean load method. Using the measured strains, statistical parameters were determined for live load effects, distribution factors, dynamic load allowance, and resistance. Statistical parameters that could not be obtained readily through testing were obtained from the literature. The results indicated that code-predicted estimates of a number of factors were highly conservative. Flexural and shear load effects in the girders were found to be less than 15% of the theoretical predictions, as a result of apparent arching action in the girders, generating significant axial forces. For this arching action to occur, horizontal restraint was required at the supports, either through unanticipated restraint in the bearings, or tension tie action of the tensile girder reinforcement. Furthermore, the dynamic amplification was found to be less than 1.0. The resulting reliability indices indicated that the bridge would be safe under the proposed increased allowable loading (110 t). <p>Finite element models were used to confirm the dynamic amplification observations and examine the effects of different degrees of bearing restraint. The model showed results similar to those measured for dynamic amplification. It was found that if the bearings were to become completely fixed against horizontal translation, the bridge would become overloaded as a result of increased shear effects, demonstrating the need for proper bearing maintenance. <p>An analysis of relative costs was completed to determine the most cost-effective solution for hauling logs. Assumptions were made regarding truck and maintenance and operating costs. The results indicated that the most economic solution was to use the method outlined in the research to increase the allowable loading on the bridge to 110 t, over the strengthening alternatives and simply leaving the bridge in the current state.

Transverse load distribution behavior amongst bridge girders is influenced by many parameters including girder material properties, spacing, skew, deck design, and stiffening element interactions. In order to simply and conservatively approximate the bridge superstructure load distribution between girders, the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications contain load distribution factor (LDF) equations for many common bridge types. The Texas Department of Transportation (TxDOT) had recently developed a new design for bridge superstructures that utilizes a spread configuration of prestressed concrete slab beams. AASHTO does not contain LDFs for this type of bridge so the load sharing behavior of this superstructure must be investigated further. TxDOT has funded the Texas A&M University Transportation Institute (TTI) to design, model, construct, test, and analyze a full scale spread slab beam bridge. In addition to this testing, an existing slab beam bridge in Denison, Texas will be instrumented and observed for supplementary slab beam behavior data. To predict bridge behavior, computer models of the Riverside experimental bridge and of the Denison field bridge were developed using both the grillage and finite element methods of analysis. The experimental results from the Riverside and Denison bridges will not be collected by the conclusion of this thesis so a third bridge with existing experimental data, the Drehersville, Pennsylvania bridge, was also modeled for calibration purposes. The work presented by this thesis focuses on how to accurately model transverse load distribution relationships and LDFs for use in bridge design. The analysis covered is concentrated primarily on the grillage method, with the finite element analysis as part of the larger project scope. From this analysis it was determined that the grillage method was able to accurately model bridge LDFs as compared to FEM modeling and experimental results, for spread slab beam and spread box beam bridges. The critical loading configurations for all bridges placed two trucks side by side and as far to one edge of the bridge as possible. It was also determined that at an ultimate loading case, the load is distributed much more evenly across the deck than at service loading.