Ashley P. Thrall

Portable and Rapidly Deployable Bridges: Historical Perspective and Recent Technology Developments

AbstractPortable and rapidly deployable bridges are critical for providing access routes for troops during military operations and for restoring vital lifelines for communities affected by large-scale disasters. This paper reviews the history and the state of the art in portable and rapidly deployable bridge technology, primarily for U.S. systems. Four types of deployable systems are presented, including (1) rapidly erectable gap-crossing bridges (e.g., Bailey Bridge, Medium Girder Bridge), (2) vehicle-launched bridges (e.g., Armored Vehicle–Launched Bridge, Dry Support Bridge), (3) river-crossing solutions (e.g., M4T6, Improved Ribbon Bridge), and (4) causeways (e.g., Navy Elevated Causeway System, Lightweight Modular Causeway System). Discussion of each design emphasizes the technology itself, its application throughout history, and the evolution of the forms in relation to one another. The paper concludes with a discussion of the future of these technologies. The paper provides the first review of port...

Modelling collision products of triple‐star mergers

In dense stellar clusters, binary-single and binary-binary encounters can ultimately lead to collisions involving two or more stars during a resonant interaction. A comprehensive survey of multistar collisions would needto explore an enormous amount of parameter space, but here we focus on a number of representative cases involving low-mass (0.4-, 0.6- and 0.8-M O .) main-sequence stars. Using both smoothed particle hydrodynamics (SPH) calculations and a much faster fluid sorting software package (MMAS), we study scenarios in which a newly formed product from an initial collision collides with a third parent star. By varying the order in which the parent stars collide, as well as the orbital parameters of the collision trajectories, we investigate how factors such as shock heating affect the chemical composition and structure profiles of the collision product. Our simulations and models indicate that the distribution of most chemical elements within the final product is not significantly affected by the order in which the stars collide, the direction of approach of the third parent star, or the periastron separations of the collisions. Although the exact surface abundances of beryllium and lithium in the product do depend on the details of the dynamics, these elements are always severely depleted due to mass loss during the collisions. We find that the sizes of the products, and hence their collisional cross-sections for subsequent encounters, can be sensitive to the order and geometry of the collisions. For the cases that we consider, the radius of the product formed in the first (single-single star) collision ranges anywhere from roughly 2-30 times the sum of the radii of its parent stars. The size of the final product formed in our triple-star collisions is more difficult to determine, but it can easily be as large or larger than a typical red giant. Although the vast majority of the volume in such a product contains diffuse gas that could be readily stripped in subsequent interactions, we nevertheless expect the collisional cross-section of a newly formed product to be greatly enhanced over that of a thermally relaxed star of the same mass. Our results also help establish that the algorithms of MMAS can quickly reproduce the important features of our SPH models for these collisions, even when one of the parent stars is itself a former product.

Structural Optimization of Deploying Structures Composed of Linkages

AbstractDetermining the global shape of a deploying structure and the section profiles of its members is a challenging design problem. Geometry, meaning the lengths and relative angles of members, is critical to achieving stable deployment to a desired span, while the design must also satisfy structural capacity demands at each stage of deployment. This paper explores the potential role of formal structural optimization in designing feasible and structurally efficient deploying steel structures composed of linkage elements. Both stochastic search and gradient-based algorithms are used to explore the design space and identify minimum weight solutions that satisfy kinematic and structural constraints. The proposed methodology is tested on the case study of a deploying pantograph. This strategy has the potential to be implemented for a wide range of deploying structures, including retractable roofs, rapidly expandable shelters, deploying space structures, and movable bridges.

New Bridge Forms Composed of Modular Bridge Panels

AbstractPanelized bridge systems (e.g., Bailey, Mabey Johnson, Acrow) are intended for girder-type bridges and have been implemented for military, civilian, and disaster relief applications. Design challenges, however, include material efficiency (span squared per number of panels), lateral bracing, and achieving longer spans. These challenges are addressed by investigating the promise of implementing panels in new configurations with longer spans and evaluating bracing strategies. Three new forms (Pratt truss, bowstring truss, and network tied arch) composed of standard length panels, with shapes determined based on geometric considerations and structural performance (resistance to buckling), are presented. A parametric study evaluates lateral bracing strategies for girder-like and column-like configurations. The promise of the new forms, also incorporating the developed bracing strategy, is demonstrated through finite element analyses. Following this investigation using a standard length panel, an optim...

The universal scissor component: Optimization of a reconfigurable component for deployable scissor structures

Deployable scissor structures are well equipped for temporary and mobile applications since they are able to change their form and functionality. They are structural mechanisms that transform from a compact state to an expanded, fully deployed configuration. A barrier to the current design and reuse of scissor structures, however, is that they are traditionally designed for a single purpose. Alternatively, a universal scissor component (USC)—a generalized element which can achieve all traditional scissor types—introduces an opportunity for reuse in which the same component can be utilized for different configurations and spans. In this article, the USC is optimized for structural performance. First, an optimized length for the USC is determined based on a trade-off between component weight and structural performance (measured by deflections). Then, topology optimization, using the simulated annealing algorithm, is implemented to determine a minimum weight layout of beams within a single USC component.

Impact of Hinged Connectors on Sandwich Panel Behavior

AbstractThis paper discusses the impact of hinged connectors (a common connection in folding structures) on the behavior of sandwich panels (with fiber-reinforced polymer faces and foam core). A sandwich panel is subjected to uniform loading and tested when restrained by hinged connectors in compression and in tension. The measured results are compared to finite-element numerical models, focusing on global behavior (displacements and strains at center) and local behavior (strains near connectors). Parametric studies using these validated numerical models investigate the impact of the number, size, and relative placement of hinged connectors. These studies culminate in guidelines for the design of structures comprised of hinged, folding panels. Ultimately, this paper addresses a research gap in understanding the behavior of sandwich panels connected by hinges.

Reconceptualization and Optimization of a Rapidly Deployable Floating Causeway

There is an increasing demand for rapidly deployable causeways that can provide access from ship-to-shore for military and disaster relief operations. Existing systems have major limitations including only being transportable and emplaceable by large strategic sealift vessels, having high weight and packaged volumes, and requiring intensive on-site assembly. In response to the demand for a lightweight, air-liftable, quickly emplaceable causeway, the Engineer Research and Development Center (Vicksburg, Mississippi) developed a prototype comprised of aluminum modules joined by compliant connections and supported by pneumatic floats. As research and development progressed and experience was gained, eliminating the heavy and complex compliant connections was identified as a potential improvement. To eliminate these compliant connections, this paper shows how this design can be reconceptualized so a desired superstructure flexibility (that takes advantage of buoyancy while meeting deflection limits) is achieved. The superstructure has been designed for a target stiffness to permit a desired curvature under a design moment. This paper will review existing causeways, present this reconceptualization, and discuss the optimization implemented to achieve this new design.

Parametric Study of the Effect of Hinged Connectors on the Behavior of Origami-Inspired Structures Comprised of Sandwich Panels

Origami can be a source of inspiration for rapidly deployable, rigid wall shelters. Folding panels comprised of sandwich panels will result in a lightweight, transportable design. The design of connections between panels is critical to the overall structural performance, but can pose a major design challenge. This paper investigates the implementation of hinges for connections between panels. A single panel, comprised of fiber-reinforced polymer faces and a foam core, is restrained by aluminum hinged connectors and subjected to a uniform load. An exhaustive parametric study is performed using a numerical model previously validated by experimental data. The numerical study will facilitate better understanding of the impact of the 1) number, 2) size, and 3) relative placement of connectors on panel behavior, with data comparisons focusing on the longitudinal surface strains and displacements of the panel. This investigation culminates in a set of guidelines for hinged connectors in origami-inspired structures.Copyright

Behavior of an Adjustable Bolted Steel Plate Connection during Field Installation

AbstractThis paper presents a bolted steel plate connection to join steel members at a range of angles with the capability of adjusting in situ to accommodate additional angles or tolerances throug...

Economic Evaluation of High-Strength Materials in Stocky Reinforced Concrete Shear Walls

AbstractPrevious numerical research has shown that high-strength steel reinforcing bars (rebar) combined with high-strength concrete can increase the lateral strength of stocky (i.e., low height-to...