Topology Optimized Reinforced Concrete Walls Constructed with 3D Printed Formwork

The construction industry continually evolves to adapt to gains in knowledge, market pressures and new technologies. However, two promising new technologies, 3D printing and computational topology optimization, have not yet penetrated the civil engineering industry despite being important drivers of change in other fields. The aim of this study was the potential to overcome the major barriers to adoption of both technologies by using them in combination. Both theoretical and practical problems must still be addressed, but the potential impacts are significant: lightweight, architecturally pleasing, reduced volume structures. Two small-scale specimens were constructed and tested to demonstrate the feasibility of using additively manufactured (3D printed) formwork to construct complex reinforced concrete (RC) structures. The concept was shown to be viable. Areas were identified where further development is necessary before 3D printing can be used for large-scale cost-competitive formwork. An approach, based on the rule of mixtures, was proposed for applying computational topology optimization to RC structures. This was necessary because the computational topology optimization algorithm employed in this study assumes a structure is homogenous but RC structures are not. The approach was shown to work for optimizing an RC wall for force demands within the linear-elastic range of response. The sensitivity of optimization outputs to modeling parameters was investigated. The effects and interdependencies of mesh size, element type, number of optimization cycles, and target volume ratio on optimization outcome were demonstrated. The importance of ISO and “percent reduction” parameters on the process of importing the optimized geometry to ABAQUS was also demonstrated. Finally, a parametric study was conducted to examine the relationships between volume ratio and member strength and stiffness (volume ratio refers to the volume of the optimized structure divided by the volume of the original structure). The study used finite element models of topology optimized slender structural walls subjected to pseudo-static lateral force. It was shown that reductions in volume are not proportional to reductions in stiffness, as expected for slender walls that are flexure-dominated. Reductions in volume of 10 to 20% cause only approximately 3 to 7% reductions in uncracked member stiffness. These reductions in stiffness can be compensated for with use of modestly higher-strength concrete

A Moving Boundary Flux Stabilization Method for Cartesian Cut-Cell Grids using Directional Operator Splitting

An explicit moving boundary method for the numerical solution of time-dependent hyperbolic conservation laws on grids produced by the intersection of complex geometries with a regular Cartesian grid is presented. As it employs directional operator splitting, implementation of the scheme is rather straightforward. Extending the method for static walls from Klein et al., Phil. Trans. Roy. Soc., A367, no. 1907, 4559-4575 (2009), the scheme calculates fluxes needed for a conservative update of the near-wall cut-cells as linear combinations of standard fluxes from a one-dimensional extended stencil. Here the standard fluxes are those obtained without regard to the small sub-cell problem, and the linear combination weights involve detailed information regarding the cut-cell geometry. This linear combination of standard fluxes stabilizes the updates such that the time-step yielding marginal stability for arbitrarily small cut-cells is of the same order as that for regular cells. Moreover, it renders the approach compatible with a wide range of existing numerical flux-approximation methods. The scheme is extended here to time dependent rigid boundaries by reformulating the linear combination weights of the stabilizing flux stencil to account for the time dependence of cut-cell volume and interface area fractions. The two-dimensional tests discussed include advection in a channel oriented at an oblique angle to the Cartesian computational mesh, cylinders with circular and triangular cross-section passing through a stationary shock wave, a piston moving through an open-ended shock tube, and the flow around an oscillating NACA 0012 aerofoil profile.Comment: 30 pages, 27 figures, 3 table

Mechanistic and pathological study of the genesis, growth, and rupture of abdominal aortic aneurysms

Postprint (published version

A computational framework for the morpho-elastic development of molluskan shells by surface and volume growth

Mollusk shells are an ideal model system for understanding the morpho-elastic basis of morphological evolution of invertebrates' exoskeletons. During the formation of the shell, the mantle tissue secretes proteins and minerals that calcify to form a new incremental layer of the exoskeleton. Most of the existing literature on the morphology of mollusks is descriptive. The mathematical understanding of the underlying coupling between pre-existing shell morphology, de novo surface deposition and morpho-elastic volume growth is at a nascent stage, primarily limited to reduced geometric representations. Here, we propose a general, three-dimensional computational framework coupling pre-existing morphology, incremental surface growth by accretion, and morpho-elastic volume growth. We exercise this framework by applying it to explain the stepwise morphogenesis of seashells during growth: new material surfaces are laid down by accretive growth on the mantle whose form is determined by its morpho-elastic growth. Calcification of the newest surfaces extends the shell as well as creates a new scaffold that constrains the next growth step. We study the effects of surface and volumetric growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and therefore of the developing shell's morphology. Connections are made to a range of complex shells ornamentations.Comment: Main article is 20 pages long with 15 figures. Supplementary material is 4 pages long with 6 figures and 6 attached movies. To be published in PLOS Computational Biolog