Automatic generation of diverse equilibrium structures through shape grammars and graphic statics

This article presents a computational design methodology that integrates generative (architectural) and analytical (engineering) procedures into a simultaneous design process. By combining shape grammars and graphic statics, the proposed methodology enables the following: (1) rapid generation of diverse, yet statically equilibrated discrete structures; (2) exploration of various design alternatives without any biases toward pre-existing typologies; (3) customization of the framework for unique formulations of design problems and a wide range of applications; and (4) intuitive, bidirectional interaction between the form and forces of the structure through reciprocal diagrams. Design tests presented in this article illustrate the creative potential of the proposed approach and demonstrate the possibility for unbiased explorations of richer and broader design spaces during early stages of design, with much more trial and less error

Transition Probabilities Of Astrophysical Interest In The Niobium Ions Nb+ And Nb2+

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb II and Nb III and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture elements. Methods. We used the time-resolved laser-induced fluorescence technique to measure radiative lifetimes in Nb II. Branching fractions were measured from spectra recorded using Fourier transform spectroscopy. The radiative lifetimes and the branching fractions were combined yielding transition probabilities. In addition, we calculated lifetimes and transition probablities in Nb II and Nb III using a relativistic Hartree-Fock method that includes core polarization. Abundances of the sun and five metal-poor stars were derived using synthetic spectra calculated with the MOOG code, including hyperfine broadening of the lines. Results. We present laboratory measurements of 17 radiative lifetimes in Nb II. By combining these lifetimes with branching fractions for lines depopulating the levels, we derive the transition probabilities of 107 Nb II lines from 4d(3)5p configuration in the wavelength region 2240-4700 angstrom. For the first time, we present theoretical transition probabilities of 76 Nb III transitions with wavelengths in the range 1430-3140 angstrom. The derived solar photospheric niobium abundance log epsilon(circle dot) = 1.44 +/- 0.06 is in agreement with the meteoritic value. The stellar Nb/Eu abundance ratio determined for five metal-poor stars confirms that the r-process is a dominant production method for the n-capture elements in these stars.Integrated Initiative of Infrastructure RII3-CT-2003-506350Swedish Research CouncilKnut and Alice Wallenberg FoundationBelgian FRS-FNRSFRIAUS National Science Foundation AST-0607708, AST-0908978Astronom

HD 65949: Rosetta Stone or Red Herring

HD 65949 is a late B star with exceptionally strong Hg II at 3984[A], but it is not a typical HgMn star. The Re II spectrum is of extraordinary strength. Abundances, or upper limits are derived here for 58 elements based on a model with Teff = 13100K, and log(g) = 4.0. Even-Z elements through nickel show minor deviations from solar abundances. Anomalies among the odd-Z elements through copper are mostly small. Beyond the iron peak, a huge scatter is found. The abundance pattern of the heaviest elements resembles the N=126 r-process peak of solar material, though not in detail. We find a significant correlation of the abundance excesses with second ionization potentials for elements with Z > 30. This indicates the relevance of photospheric or near-photospheric processes. We explore a model with mass accretion of exotic material followed by the more commonly accepted differentiation by diffusion. That model leads to a number of predictions which challenge future work. Likely primary and secondary masses are near 3.3 and 1.6 M(solar), with a separation of ca. 0.25 AU. New atomic structure calculations are presented in two appendices.Comment: Accepted by MNRAS: 16 pages, 5 figure

Design of Load-Bearing Systems for Open-Ended Downstream Reuse

This paper discusses the design of load-bearing systems for buildings with regard to their current lack of open-ended reusability. The reason for dismantling load-bearing systems today tends to be less related to material degradation than to a loss of functional fit with an evolving building program. It can therefore be expected that load-bearing components are reused in other systems, which extends their service life and avoids the manufacture of other components. Common design strategies to ensure the actual reusability of components consist in guaranteeing that the assembly is durable, versatile, modular, reversible, and adaptable. This paper (a) reviews these features, (b) illustrates by means of case studies that, without minimum threshold, they do not guarantee the repurpose of components into different, unforeseen systems, and (c) describes opportunities and challenges related to the design of more open-ended sets of load-bearing elements, i.e. sets whose element types allow for a substantially large number of diverse assemblies, in terms of floor plans, spans, loads, support layouts, connection types, architectural language, and integration with other building systems

Constraint-Based Graphic Statics - A geometrical support for computer-aided structural equilibrium design

This thesis introduces “constraint-based graphic statics”, a geometrical support for computer-aided structural design. This support increases the freedom with which the designer interacts with the plane static equilibriums being shaped. Constraint-based graphic statics takes full advantage of geometry, both its visual expressiveness and its capacity to solve complex problems in simple terms. Accordingly, the approach builds on the two diagrams of classical graphic statics: a form diagram describing the geometry of a strut-and-tie network and a force diagram vectorially representing its inner static quilibrium. Two new devices improve the control of these diagrams: (1) nodes — considered as the only variables — are constrained within Boolean combinations of graphical regions; and (2) the user modifies these diagrams by means of successive operations whose geometric properties do not at any time jeopardise the static equilibrium of the strut-and-tie network. These two devices offer useful features, such as the ability to describe, constrain and modify any static equilibrium using purely geometric grammar, the ability to compute and handle multiple solutions to a problem at the same time, the ability to switch the hierarchy of constraint dependencies, the ability to execute dynamic conditional statements graphically, the ability to compute full interdependency and therefore the ability to remove significantly the limitations of compass-and-straightedge constructions and, finally the ability to propagate some solution domains symbolically. As a result, constraint-based graphic statics encourages the emergence of new structural design approaches that are highly interactive, precognitive and chronology-free: highly interactive because forces and geometries are simultaneously and dynamically steered by the designer; precognitive because the graphical region constraining each points marks out the set of available solutions before they are even explored by the user; and chronology-free because the deductive process undertaken by the designer can be switched whenever desired

Geometric Optimization of a Reciprocal Floor-Framing System with Self-Weight and Area-Loading Considerations

This paper explores the geometric optimization of a planar reciprocal frame (RF) floor framing structure, focusing on the triangular topology. The structural performance of the frames is computed and plotted against the geometric parameters for various load cases. The load cases modelled include both symmetric and asymmetric loading on a hypothetical surface supported by the frame, and the loads are distributed to the members based on tributary areas. The two key geometric parameters studied are the rotation angle of the members at the unit RF level which defines the geometry, and the total number of members in the grid which defines the grid density. The structural performance is deduced from the total strain energy in the grid. Results show that smaller rotation angles at the unit RF level produce more structurally efficient RF grids. Depending on the grid density and load case, the optimal angle lies between 4 and 8.2 degrees. To some extents, these values mean that optimum geometries for RF under area-loading considerations tend to reduce lever-arms to a minimum. It is also found that the optimal angle remains relatively unchanged for a given grid density between the symmetric and asymmetric load cases

Construction technology transfer in Shanghai in the nineteenth to twentieth centuries

Shanghai, in the early twentieth century, was a big construction site and attractive experimental field for Western designers. Because of its significant location and international role, the construction activities contributed to some landmarks of the world architecture history. In addition to famous architects, local builders played a crucial role in the realization of these edifices. Introduction and application of new technologies, digestion and diffusion of new knowledge, transportation and production of new materials, the magnification of pre-existing local concerns while dealing with the geological problem, as well as the training of the workers was already solved by the natives at this time. Based on a fresh study of the documents in the Historical Archives of Shanghai Library and in the Shanghai Local Chronicles, this particular context is here used as a case-study that aims at providing new insights on the shifts from traditional construction practices to industrialized dynamics. This paper reveals that the construction technology transfer that happened between Europe and East Asia in Shanghai in the nineteenth to twentieth centuries in a sense was a process of local desire to extract knowledge and technologies from numerous overseas sources for the construction of “Modern Shanghai”