Exploring the application domain of adaptive structures

Using a previously developed design methodology it was shown that optimal material distribution in combination with strategic integration of the actuation system lead to significant whole-life energy savings when the design is governed by rare but strong loading events. The whole-life energy of the structure is made of an embodied part in the material and an operational part for structural adaptation. Instead of using more material to cope with the effect of loads, the actuation system redirects the internal load-path to homogenise the stresses and change the shape of the structure to keep deflections within limits. This paper presents a systematic exploration of the domain in which adaptive two-dimensional pin-jointed structures are beneficial in terms of whole-life energy and monetary costs savings. Two case studies are considered: a vertical cantilever truss representative of a multi-storey building supported by an exoskeleton structure and a simply supported truss beam which is part of a roof system. This exploration takes five directions studying the influence of: (1) the structural topology (2) the characteristics of the load probability distribution (3) the ratio of live load over dead load (4) the aspect ratio of the structure (e.g. height-to-depth) (5) the material energy intensity factor. Results from the main five strands are combined with those from the monetary cost analysis to identify an optimal region where adaptive structures are most effective in terms of both energy and monetary savings. It was found that the optimal region is broadly that of stiffness-governed structures. For the cantilever case, the optimal region covers most of the application domain and it is not very sensitive to either live-to-dead-load or height-to-depth ratios thus showing a wide range of applicability, including ordinary loading scenarios and relatively deep structures

Energy and Cost Assessment of Adaptive Structures: Case Studies

This paper demonstrates how adaptive design (details published elsewhere) can be employed to save, on average, 70% of whole-life energy on a range of spatial structures, the whole-life energy deriving from an embodied part in the material and an operational part for structural adaptation. Assuming some statistical distribution for the probability of occurrence of the loads, whole-life energy is minimized by combining optimal material distribution and strategic integration of the actuation system, which is only used when loading events exceed a certain threshold. Instead of using more material to cope with the effect of the loads, the active elements change the shape of the structure in order to homogenize the stresses and keep deflections within limits. Five case studies are investigated here: a tall building core, a trussed portal frame, a long-span arch bridge, a 3-pin roof arch, a double-curved shell, and an office tower supported by an exoskeleton structural system. The purpose of the case studies described in this paper is to study (1) adaptive structure performance in terms of mass and energy savings as well as monetary costs for both strength- and stiffness-governed design problems; and (2) design scalability to complex spatial configurations. The case studies confirmed that even for large complex structures, significant energy savings can be achieved, the more so as the structure becomes more stiffness-governed. In this case, the adaptive solution becomes competitive also in terms of monetary costs

Shape control and whole-life energy assessment of an ‘infinitely stiff’ prototype adaptive structure

A previously developed design methodology produces optimum adaptive structures that minimise the whole-life energy which is made of an embodied part in the material and an operational part for structural adaptation. Planar and complex spatial reticular structures designed with this method and simulations showed that the adaptive solution achieves savings as high as 70% in the whole-life energy compared to optimised passive solutions. This paper describes a large-scale prototype adaptive structure built to validate the numerical findings and investigate the practicality of the design method. Experimental results show that (1) shape control can be used to achieve 'infinite stiffness' (i.e. to reduce displacements completely) in real-time without predetermined knowledge regarding position, direction and magnitude (within limits) of the external load; (2) the whole-life energy of the structure is in good agreement with that predicted by numerical simulations. This result confirms the proposed design method is reliable and that adaptive structures can achieve substantive total energy savings compared to passive structures

Adaptive Structures for Whole Life Energy Savings

The design methodology described in this paper takes a substantial shift from conventional methods. Traditionally sizing is based on the worst expected load scenario. By contrast to this conventional passive approach the method presented here replaces passive member strategically with active elements (actuators) which are only activated when the loads reach a certain threshold. The structure can withstand low level of loads passively. Above the threshold, actuation comes in to allow the structure to cope with high but rare loading scenarios. Active control introduces operational energy consumption in addition to the energy embodied in a passive design. In this paper we use this dual design to minimize the overall energy required by the structures. This methodology has been used on a simple truss structure and it was showed that it allows significant weight saving compared to conventional passive design. We extend the application of the methodology to a more complex 3D structure. It is confirmed that an optimum activation threshold exists that leads to design that minimises the total energy of the structure. Compared to an optimised passive design we show that the total energy saving is 10-fol

Computation and geometry in structural design and analysis

Through three examples from practice spanning decades, this paper demonstrates the evolution of the geometric definition and structural analysis of complex geometry buildings. Gaps in current knowledge relating to computation and geometry are then discussed, and of the case is then made for the birth of the new Computation and Geometry study group as part of the IASS SMG. The study group aims to support research in computational geometry in structural engineering by bringing expert researchers and practitioners together in order to increase and share knowledge. Research themes relate to digital design and the description of structural geometry based on computational methods and techniques. The use of computational methods and software tools in the creation of structural geometry will also be explored