Notched stringer segments spliced with metal connector plates (MCPs) and pallets with spliced stringer(s) were tested in static bending in order to determine the relative effectiveness of different stringer splicing methods and under what conditions the process is or is not effective. The species tested were oak, southern yellow pine, yellow-poplar, and two combined species - oak and yellow-poplar, and oak and southern yellow pine. The metal connector plates used were 3 x 4-inch, 3 x 6-inch truss plates, and a 3 x 4-inch plug plate. The splice methods tested were a vertical splice (VS), a 45° angle splice (AS), and a vertical splice with -inch gap between segments (VSG). The results of bending tests of these specimens were compared to non-spliced whole stringers and pallets containing whole stringers. Multiple comparison, statistical methods were used to analyze all test data. An analysis of the failure locations and types of specimens was also used to analyze test results. Vertical spliced stringers with 3 x 4 and 3 x 6 inch truss plates were the best designs of those tested. Spliced stringers were an average of 112% and 74% bending strength and stiffness of new non-spliced stringer. These plates were an average of 26% stronger and 13% stiffer than the 3 x 4 inch plug plate splice stringer. There was no difference between the performance stringers spliced with 3 x 6 and 3 x 4 inch truss plate. An angle splice design and the addition of 1.25 x 6 inch truss plate on the tension side of spliced stringer did not appear to improve the strength and stiffness. A gap between segments significantly reduces splice strength and stiffness by an average of 35% and 16% respectively. When mixing stringer segment species, the performance is determined by the weaker segment. The average strength and stiffness of pallets containing spliced stringers were similar to that of pallets with whole stringers, however the variation in performance was greater when notched stringer pallets contain splices. / Master of Science

This study highlights the aeroelastic behavior of very flexible truss-braced wing (TBW) aircraft designs obtained through a multidisciplinary design optimization (MDO) framework. Several improvements to previous analysis methods were developed and validated. Firstly, a flutter constraint was developed and the effects of the constraint on the MDO of TBW transport aircraft for both medium-range and long-range missions were studied while minimizing the take-off gross weight (TOGW) and the fuel burn as the objective functions. Results show that when the flutter constraint is applied at 1.15 times the dive speed, it imposes a 1.5% penalty on the take-off weight and a 5% penalty on the fuel consumption while minimizing these two objective functions for the medium-range mission. For the long-range mission, the penalties imposed by the similar constraint on the minimum TOGW and minimum fuel burn designs are 3.5% and 7.5%, respectively. Importantly, the resulting TBW designs are still superior to equivalent cantilever designs for both of the missions as they have both lower TOGW and fuel burn. However, a relaxed flutter constraint applied at 1.05 times the dive speed can restrict the penalty on the TOGW to only 0.3% and that on the fuel burn to 2% for minimizing both the objectives, for the medium-range mission. For the long-range mission, a similar relaxed constraint can reduce the penalty on fuel burn to 2.9%. These observations suggest further investigation into active flutter suppression mechanisms for the TBW aircraft to further reduce either the TOGW or the fuel burn. Secondly, the effects of a variable-geometry raked wingtip (VGRWT) on the maneuverability and aeroelastic behavior of passenger aircraft with very flexible truss-braced wings (TBW) were investigated. These TBW designs obtained from the MDO environment while minimizing fuel burn resemble a Boeing 777-200 Long Range (LR) aircraft both in terms of flight mission and aircraft configuration. The VGRWT can sweep forward and aft relative to the wing with the aid of a Novel Control Effector (NCE) mechanism. Results show that the VGRWT can be swept judiciously to alter the bending-torsion coupling and the movement of the center of pressure of wing. Such behavior of the VGRWT is applied to both achieve the required roll control as well as to increase flutter speed, and thus, enable the operation of TBW configurations which have up to 10% lower fuel burn than comparable optimized cantilever wing designs. Finally, a transonic aeroelastic analysis tool was developed which can be used for conceptual design in an MDO environment. Routine transonic aeroelastic analysis require expensive CFD simulations, hence they cannot be performed in an MDO environment. The present approach utilizes the results of a companion study of CFD simulations performed offline for the steady Reynolds Averaged Navier Stokes equations for a variety of airfoil parameters. The CFD results are used to develop a response surface which can be used in the MDO environment to perform a Leishman-Beddoes (LB) indicial functions based flutter analysis. A reduced-order model (ROM) is also developed for the unsteady aerodynamic system. Validation of the strip theory based aeroelastic analysis with LB unsteady aerodynamics and the computational efficiency and accuracy of the ROM is demonstrated. Finally, transonic aeroelastic analysis of a TBW aircraft designed for the medium-range flight mission similar to a Boeing 737 next generation (NG) with a cruise Mach number of 0.8 is presented. The results show the potential of the present approach to perform a more accurate, yet inexpensive, flutter analysis for MDO studies of transonic transport aircraft which are expected to undergo flutter at transonic conditions. / Ph. D.

Non-ductile Reinforced Concrete Frames (RCF) with and without Unreinforced Masonry (URM) infills can be found in many places around the world including the Western United States, Eastern Europe, Asia and Latin America. These structures can have an unsatisfactory seismic performance which may even lead to collapse due to brittle failure modes. Furthermore, the effect of the infills on the seismic response of the structural system is not always accounted for in analysis and design. At present, there is no consensus on whether masonry infills are beneficial (by increasing the resistance of the system) or detrimental (by leading to brittle failure modes) for RCF construction. This study focuses on the development of a simplified modeling approach for non-ductile RCF with URMI that combines the simplicity of strut-and-tie models with the accuracy of Nonlinear Finite Element Analysis (NLFEA). Despite the fact that NLFEA procedures are the most advanced way to address the structural analysis of RCF with URM infills, their conceptual complexity and computational cost may hinder their widespread adoption as an analysis and design tool. At the same time, simplified methods, such as those based on the equivalent strut concept, may be overly crude and neglect essential aspects of the nonlinear response. To address the need for an adequately accurate, but computationally and conceptually efficient analysis method, this study establishes a novel method for planar RCF with URM infills subjected to lateral loads. The method, which is based on the Nonlinear Truss Analogy (NLTA) is shown to have an accuracy comparable to that of NLFEA. Specifically, the method is shown to adequately capture the strength and stiffness degradation and the damage patterns while entailing a reduced computational cost (compared to that of NLFEA). The proposed method is expected to bridge the gap between overly crude equivalent strut models and computationally expensive NLFEA. / Ph. D.

This study utilizes Multidisciplinary Design Optimization (MDO) techniques to explore the effectiveness of the truss-braced (TBW) and strut-braced (SBW) wing configurations in enhancing the performance of medium range, transonic transport aircraft. The truss and strut-braced wing concepts synergize structures and aerodynamics to create a planform with decreased weight and drag. Past studies at Virginia Tech have found that these configurations can achieve significant performance benefits when compared to a cantilever aircraft with a long range, Boeing 777-200ER-like mission. The objective of this study is to explore these benefits when applied to a medium range Boeing 737-800NG-like aircraft with a cruise Mach number of 0.78, a 3,115 nautical mile range, and 162 passengers. Results demonstrate the significant performance benefits of the SBW and TBW configurations. Both configurations exhibit reduced weight and fuel consumption. Configurations are also optimized for 1990's or advanced technology aerodynamics. For the 1990's technology minimum TOGW cases, the SBW and TBW configurations achieve reductions in the TOGW of as much as 6% with 20% less fuel weight than the comparable cantilever configurations. The 1990's technology minimum fuel cases offer fuel weight reductions of about 13% compared to the 1990's technology minimum TOGW configurations and 11% when compared to the 1990's minimum fuel optimized cantilever configurations. The advanced aerodynamics technology minimum TOGW configurations feature an additional 4% weight savings over the comparable 1990's technology results while the advanced technology minimum fuel cases show fuel savings of 12% over the 1990's minimum fuel results. This translates to a 15% reduction in TOGW for the advanced technology minimum TOGW cases and a 47% reduction in fuel consumption for the advanced technology minimum fuel cases when compared to the simulated Boeing 737-800NG. It is found that the TBW configurations do not offer significant performance benefits over the comparable SBW designs. / Master of Science

The objectives of this research were twofold: a) to define the relationship between tooth withdrawal and specific gravity for southern pine lumber and four different plate-to-wood load orientations, and b) to demonstrate how these relationships could be applied to new lumber grades to predict tooth withdrawal performance so that additional testing would not be necessary. The four orientations investigated were: a.) LRAA - plate axis parallel to load and wood grain parallel to load. b.) LREA - plate axis perpendicular to load and wood grain parallel to load. c.) LRAE - plate axis parallel to load and wood grain perpendicular to load. d.) LREE - plate axis perpendicular to load and wood grain perpendicular to load. For the LRAA, LREA, LRAE, LREE orientations, the following sample sizes were respectively: 27, 22, 27, and 29. Results showed specific gravity and embedment gap were excellent predictors of ultimate tooth withdrawal stress for the LRAA orientation. However, neither specific gravity nor percentage of latewood significantly influenced the location of tooth withdrawal. For the LREA orientation, specific gravity alone was a good predictor of ultimate tooth withdrawal stress. Furthermore, the side of the joint test specimen where tooth withdrawal initiated was dependent on the wood piece with the lowest mean specific gravity. For the LRAE orientation, specific gravity was a marginal predictor of ultimate tooth withdrawal stress. For the LREE orientation, specific gravity was a decent predictor of ultimate tooth-withdrawal stress. / Master of Science

Reinforced masonry (RM) shear walls are a common lateral load-resisting system for building structures. The seismic design guidelines for such systems are based on relatively limited experimental data. Given the restrictions imposed by the capabilities of available experimental equipment, analytical modeling is the only means to conduct systematic parametric studies for prototype RM wall systems and quantify the seismic safety offered by current design standards. A number of modeling approaches, with varying levels of complexity, have been used for the analysis of reinforced concrete (RC) and masonry wall structures. Among the various methods, the truss analogy is deemed attractive for its conceptual simplicity and excellent accuracy, as indicated by recent studies focusing on RC walls. This thesis uses an existing modeling method, based on nonlinear truss models, to simulate the behavior of fully grouted reinforced masonry shear walls. The modeling method, which was originally created and used for RC walls, is enhanced to capture the effect of localized sliding along the base of a wall, which may be the dominant mode of damage for several types of RM walls. The truss modeling approach is validated with the results of quasi-static cyclic tests on single-story isolated walls and dynamic tests on a multi-story, three-dimensional wall system. For the latter, the truss model is found to give similar results to those obtained using a much more refined, three-dimensional finite element model, while requiring a significantly smaller amount of time for the analysis. Finally, truss models are used for the nonlinear static analysis of prototype low-rise walls, which had been analyzed with nonlinear beam models during a previous research project. The comparison of the results obtained with the two modeling methods indicates that the previously employed beam models may significantly overestimate the ductility capacity of RM squat walls, due to their inability to accurately capture the shear-flexure interaction and the effect of shear damage on the strength of a wall. / Master of Science

This thesis presents the methods utilized to model a steel deck truss bridge over the New River in Hillsville, Virginia. These methods were evaluated by comparing analytical results with data recorded from 14 members during live load testing. The research presented herein is part of a larger endeavor to understand the structural behavior and collapse mechanism of the erstwhile I-35W bridge in Minneapolis, MN. Objectives accomplished toward this end include investigation of lacing effects on built up member strain detection, live load testing of a steel truss bridge, and evaluating modeling techniques in comparison to recorded data. Before any live load testing could be performed, it was necessary to confirm an acceptable strain gage layout for measuring member strains. The effect of riveted lacing in built-up members was investigated by constructing a two-thirds mockup of a typical bridge member. The mockup was then instrumented with strain gages and subjected to known strains in order to determine the most effective strain gage arrangement. Testing analysis concluded that for a built up member consisting of laced channels, one strain gage installed on the middle of the extreme fiber of each channel's flanges was sufficient. Thus, laced members on the bridge were mounted with four strain gages each. Data from live loads were obtained by loading two trucks to 25 tons each. Trucks were positioned at eight locations on the bridge in four different relative truck positions. Data were recorded continuously and reduced to member forces for model validation comparisons. Deflections at selected truss nodes were also recorded for model validation purposes. The model validation process began by developing four simple truss models, each reflecting different expected restraint conditions, in the hopes of bracketing data from recorded results. Models were refined to frames, and then frames including floor beams and stringers for greater accuracy. The final, most accurate model was selected and used for a failure analysis. This model showed where the minimum amount of load could be applied in order to learn about the bridge's failure behavior, for a test to be conducted at a later time. / Master of Science

This study presents a new Python-based novel framework, in a distributed computing environment for multidisciplinary design optimization (MDO) called DELWARX. DELWARX also includes a transonic flutter analysis approach that is computationally very efficient, yet accurate enough for conceptual design and optimization studies. This transonic flutter analysis approach is designed for large aspect-ratio wings and attached flow. The framework employs particle swarm optimization with penalty functions for exploring optimal Transonic Truss Braced Wing (TTBW) aircraft design, similar to the Boeing 737-800 type of mission with a cruise Mach of 0.8, a range of 3115 n miles, and 162 passengers, with two different objective functions, the fuel weight and the maximum take-off gross weight, while satisfying all the required constraints. Proper memory management is applied to effectively address memory-related issues, which are often a limiting factor in distributed computing. The parallel implementation in MDO using 60 processors allowed a reduction in the wall-clock time by 96% which is around 24 times faster than the optimization using a single processor. The results include a comparison of the TTBW designs for the medium-range missions with and without the flutter constraint. Importantly, the framework achieves extremely low computation times due to its parallel optimization capability, retains all the previous functionalities of the previous Virginia Tech MDO framework, and replaces the previously employed linear flutter analysis with a more accurate nonlinear transonic flutter computation. These features of DELWARX are expected to facilitate a more accurate MDO study for innovative transport aircraft configurations operating in the transonic flight regime. High-fidelity CFD simulation is performed to verify the result obtained from extended Strip theory based aerodynamic analysis method. An approach is presented to develop a deep neural network (DNN)-based surrogate model for fast and accurate prediction of flutter constraints in multidisciplinary design optimization (MDO) of Transonic Truss Braced Wing (TTBW) aircraft in the transonic region. The integration of the surrogate model in the MDO framework shows lower computation times than the MDO with nonlinear flutter analysis. The developed surrogate models can predict the optimum design. The wall-clock time of the design analysis method was reduced by 1500 times as compared to the result implemented in the previous framework, DELWARX. / Doctor of Philosophy / The current study presents DELWARX, a novel Python-based framework specifically engineered for the optimization of aircraft designs, with a primary focus on enhancing the performance of aircraft wings under transonic conditions (speeds approaching the speed of sound). This advancement is particularly pertinent for aircraft with a mission analogous to the Boeing 737-800, which necessitates a harmonious balance between speed, range, passenger capacity, and fuel efficiency. A salient feature of DELWARX is its adeptness in analyzing and optimizing wing flutter, a critical issue where wings may experience hazardous vibrations at certain velocities. This is particularly vital for wings characterized by a high aspect ratio (wings that are long and narrow), presenting a substantial challenge in the domain of aircraft design. DELWARX surpasses preceding methodologies by implementing a sophisticated computational technique known as particle swarm optimization, analogous to the collective movement observed in bird flocks, integrated with penalty functions that serve to exclude design solutions that fail to meet predefined standards. This approach is akin to navigating through a maze with specific pathways rendered inaccessible due to certain constraints. The efficiency of DELWARX is markedly enhanced by its ability to distribute computational tasks across 60 processors, achieving a computation speed that is 24 times faster than that of a single-processor operation. This distribution results in a significant reduction of overall computation time by 96%, representing a substantial advancement in processing efficiency. Further, DELWARX introduces an enhanced level of precision in its operations. It supplants former methods of flutter analysis with a more sophisticated, nonlinear approach tailored for transonic speeds. Consequently, the framework's predictions and optimization strategies for aircraft wing designs are imbued with increased reliability and accuracy. Moreover, DELWARX also integrates a Deep Neural Network (DNN), an advanced form of artificial intelligence, to swiftly and precisely predict flutter constraints. This integration manifests as a highly intelligent system capable of instantaneously estimating the performance of various designs, thereby expediting the optimization process. DELWARX employs high-fidelity Computational Fluid Dynamics (CFD) simulations to verify its findings. These simulations utilize intricate models to simulate the aerodynamics of air flow over aircraft wings, thereby ensuring that the optimized designs are not only theoretically sound but also pragmatically effective. In conclusion, DELWARX represents a significant leap in the field of multidisciplinary design optimization. It offers a robust and efficient tool for the design of aircraft wings, especially in the context of transonic flight. This framework heralds a new era in the optimization of aircraft designs, enabling more innovative and efficient solutions in the aerospace industry.

In recent years, research has been conducted for alternative commercial transonic aircraft design configurations, such as the strut- braced wing and the truss-braced wing aircraft designs, in order to improve aircraft performance and reduce the impact of aircraft emissions as compared to a typical cantilever wing design. Research performed by Virginia Tech in conjunction with NASA Langley Research Center shows that these alternative configurations result in 20% or more reduction in fuel consumption, and thus emissions. Another option to reduce the impact of emissions on the environment is to reduce the aircraft cruise altitude, where less nitrous oxides are released into the atmosphere and contrail formation is less likely. The following study was performed using multidisciplinary design optimization (MDO) in ModelCenterTM for cantilever wing, strut-braced wing, and truss-braced wing designs and optimized for minimum takeoff gross weight at 7730 NM range and minimum fuel weight for 7730 and 4000 NM range at the following cruise altitudes: 25,000; 30,000; and 35,000 ft. For the longer range, both objective functions exhibit a large penalty in fuel weight and takeoff gross weight due to the increased drag from the fixed fuselage when reducing cruise altitude. For the shorter range, there was a slight increase in takeoff gross weight even though there was a large increase in fuel weight for decreased cruise altitudes. Thus, the benefits of reducing cruise altitude were offset by increased fuel weight. Either a two-jury truss-braced wing or telescopic strut could be studied to reduce the fuel penalty. / Master of Science

This research focuses on the development of the semantic and fiducial aided graph simultaneous localization and mapping (SF-GraphSLAM) method that is tailored for robotic assembly and servicing of large truss structures. SF-GraphSLAM contributes to the state of the art by creating a novel way to add associations between map landmarks, in this scenario fiducials, by pre-generating a semantic map of expected relations based on the truss module known models, kinematic information about deployable modules, and hardware constraints for assembled modules. This additional information about the expected fiducial relations, and therefore truss module relative poses, can be used to add robustness to camera pose and measurement error. In parallel, the concept of a mixed assembly truss structure paradigm was created and analyzed. This mixed assembly method focuses on reducing the number of modules required to construct large truss structures by using a mixture of deployable and assembled truss modules to create a checkerboard array that is scalable to various dimensions and shapes while still minimizing the number of modules compared to a strut-by-strut method. Leveraging this paradigm SF-GraphSLAM is able to start at an advantage in terms of minimizing the state vector for the assembly testing. In addition, due to the added knowledge of the structure and the choice to utilize fiducial markers, SF-GraphSLAM is able to minimize the number of fiducials used to define the structure and therefore have the minimum state space to solve the assembly scenario, greatly improving the real-time estimation process between assembly steps. These optimizations will have a larger effect as the size of the scaled end structure increases. SF-GraphSLAM is derived in mathematical form following the same core process used for the pose and measurement components used in the base GraphSLAM. SF-GraphSLAM is evaluated against the state of the art example of GraphSLAM through simulation using an example 3x3x3 mixed assembly truss structure, known as the Built On-orbit Robotically-assembled Gigatruss (BORG). A physical BORG test truss was constructed to enable hardware trials of the SF-GraphSLAM algorithm. Although this ground hardware is not ideal for the high precision application of space structures it allows for rapid experimental robotic testing. This tailored SF-GraphSLAM approach will contribute to the state of the art of robotic in-space servicing, assembly, and manufacturing (ISAM) by providing progress on a method for dealing with the autonomous robotic assembly of movable modules to create larger structures. This will be critical for missions such as robotically assembling a large antenna structure or space telescope. Furthermore, the core methodology will study into how to best utilize information in a large-scale structure environment, including non-static flexible or deployable modules, to adequately map it which is also applicable to the larger field of robotic operations dealing with structures such as bridge surveying. / Doctor of Philosophy / The goal of this research is to enable in-space assembly of large truss structures by advancing the state of the art of how a robot can map the structure it is actively assembling. The concept of having a robot create a map of the landmarks, or in this case truss elements, it sees while keeping track of it's own movement is known as simultaneous localization and mapping (SLAM). This research focuses on the creation of a method called semantic and fiducial aided graph simultaneous localization and mapping (SF-GraphSLAM). The added semantic information is the model knowledge of the truss structure the robot is assembling, including what kind of modules are within and their desired relationships to each other. Fiducials are optical markers that can be used to provide identification, position, and orientation of what they are mounted to. Combining these concepts SF-GraphSLAM can use easily identifiable fiducials to mark components of the truss structure and use knowledge of how the truss structure should be assembled to help in estimating where the actual physical components are at different stages of the assembly process. This method is used to check if a truss module is assembled correctly after each step to ensure the final structure is within the requirements desired. This concept can be likened to when assembling a LEGO model, a person verifies they are using the correct brick for the next assembly step and then compared the state of the model with the reference photo before proceeding with the building. An incorrectly assembled module in an early step could result in a module down the line not being able to be properly placed or the final assembled structure not being within operational tolerances. This research shows how SF-GraphSLAM can be implemented for the application of assembling a truss structure out of both deployable and assembled modules. Mathematical analysis, simulations, and hardware testing were completed to compare this new method to the state of the art approach. SF-GraphSLAM is a critical step in the development required to make autonomous robotic assembly of larger structures in space feasible.