Oded Amir

Towards realistic minimum-cost optimization of viscous fluid dampers for seismic retrofitting

This paper presents an effective approach for achieving minimum cost designs for seismic retrofitting using viscous fluid dampers. A new and realistic retrofitting cost function is formulated and minimized subject to constraints on inter-story drifts at the peripheries of frame structures. The components of the new cost function are related to both the topology and to the sizes of the dampers. This constitutes an important step forward towards a realistic definition of the optimal retrofitting problem. The optimization problem is first posed and solved as a mixed-integer problem. To improve the efficiency of the solution scheme, the problem is then re-formulated and solved by nonlinear programming using only continuous variables. Material interpolation techniques, that have been successfully applied in topology optimization and in multi-material optimization, play a key role in achieving practical final design solutions with a reasonable computational effort. Promising results attained for 3-D irregular frames are presented and compared with those achieved using genetic algorithms.

Topology Optimization and Robotic Fabrication of Advanced Timber Space-Frame Structures

This paper presents a novel method for integrated topology optimization and fabrication of advanced timber space-frame structures. The method, developed in research collaboration between ETH Zurich, Aarhus School of Architecture and Israel Institute of Technology, entails the coupling of truss-based topology optimization with digital procedures for rationalization and robotic assembly of bespoke timber members, through a procedural, cross-application workflow. Through this, a direct chaining of optimization and robotic fabrication is established, in which optimization data is driving subsequent processes solving timber joint intersections, robotically controlling member prefabrication, and spatial robotic assembly of the optimized timber structures. The implication of this concept is studied through pilot fabrication and load-testing of a full scale prototype structure.

Advanced Topology Optimization Methods for Conceptual Architectural Design

This paper presents a series of new, advanced topology optimization methods, developed specifically for conceptual architectural design of structures. The proposed computational procedures are implemented as components in the framework of a Grasshopper plugin, providing novel capacities in topological optimization: Interactive control and continuous visualization; embedding flexible voids within the design space; consideration of distinct tension / compression properties; and optimization of dual material systems. In extension, optimization procedures for skeletal structures such as trusses and frames are implemented. The developed procedures allow for the exploration of new territories in optimization of architectural structures, and offer new methodological strategies for bridging conceptual gaps between optimization and architectural practice.

Topology Optimization with Stress Constraints Using Isotropic Damage with Strain Softening

Considering stress constraints in continuum topology optimization is challenging because the optimization involves a large number of design variables as well as large number of constraints. The most common approach is to aggregate the constraints into a single or a few global approximate functions. A different approach was proposed recently in which elasto-plastic response is considered and plastic strains are minimized, so that the yield conditions can be enforced implicitly. The main drawback of this approach is the added computational cost due to the nonlinear analysis. In the current work we aim to reduce the computational burden by using a simpler, yet effective, nonlinear material law. In the proposed approach, the continuum domain is modeled with isotropic damage and strain softening. The optimization problem involves only compliance and volume that can play the roles of either the objective or the constraint. An attractive aspect of this formulation is that no actual stress constraint is necessary. Once strain softening is considered, material that is strained beyond the yield strain becomes uneconomical in terms of strength. Therefore, the design is driven toward the utilization of material up to the yield strain and not beyond it – meaning that the stress constraint is imposed implicitly by the model. Numerical experiments show promising results: the proposed procedure is capable of generating stress constrained topological layouts that match results achieved by various other approaches.

Intricate Interrelation Between Robustness and Probability in the Context of Structural Optimization

In this study, we deal with the problem of structural optimization under uncertainty. In previous studies, either of three philosophies were adopted: (a) probabilistic methodology, (b) fuzzy-sets-based design, or (c) nonprobabilistic approach in the form of given bounds of variation of uncertain quantities. In these works, authors are postulating knowledge of either involved probability densities, membership functions, or bounds in the form of boxes or ellipsoids, where the uncertainty is assumed to vary. Here, we consider the problem in its apparently pristine setting, when the initial raw data are available and the uncertainty model in the form of bounds must be constructed. We treat the often-encountered case when scarce data are available and the unknown-but-bounded uncertainty is dealt with. We show that the probability concepts ought to be invoked for predicting the worst- and best-possible designs. The Chebyshev inequality, applied to the raw data, is superimposed with the study of the robustness o...

Optimal Design of Skeletal Structures Exhibiting Nonlinear Response

A unified approach that accounts for buckling and stress limitations in optimization of skeletal structures is presented. Global buckling, local buckling and exceptions from allowed stresses in frame members are considered by optimizing the geometric and material nonlinear response instead of by imposing a large number of constraints. In the proposed approach, each frame member is modeled as a sequence of co-rotational beam elements with hyperelastic material behavior. Design variables are cross-section properties so that both topology and sizes can be optimized, and to node coordinates so that shape optimization can be pursued. Sensitivity analysis follows the adjoint method and optimization is solved using well-established first-order methods. We show that the procedure leads to a buckling-resistant and stress-constrained design by maximizing the sustained load for a given prescribed displacement. A detailed discussion on key aspects of the proposed approach is presented.

Topological interlocking in architecture: A new design method and computational tool for designing building floors

This article presents a framework for the design process of structural systems based on the notion of topological interlocking. A new design method and a computational tool for generating valid architectural topological interlocking geometries are discussed. In the heart of the method are an algorithm for automatically generating valid two-dimensional patterns and a set of procedures for creating several types of volumetric blocks based on the two-dimensional patterns. Additionally, the computational tool can convert custom sets of closed planar curves into structural elements based on the topological interlocking principle. The method is examined in a case study of a building floor. The article concludes with discussions on the potential advantages of using the method for architectural design, as well as on challenging aspects of further development of this method toward implementation in practice.