Design and Control of Minimum Energy Adaptive Structures

The construction industry is the largest consumer of raw materials and most of the environmental impacts of structures are embodied into load-bearing systems [1]. Civil structures are usually designed to meet strength and deformation requirements to withstand rare events such as earthquakes and strong winds which in practice occur very rarely. Most structures are thus overdesigned during their service life. Instead, structures could be adaptive to counteract the effects of external loads through sensing and actuation. A new optimum design methodology for adaptive structures has been formulated by Senatore et al. [2]. The main objective is the minimization of the whole-life energy which encapsulates material and operational energy minimization. Instead of relying only on passive resistance through material mass, an actuation system is optimally integrated to alter the flow of internal forces and to change the shape of the structure. The internal forces are controlled to achieve stress homogenization and the shape is changed to control deflections or to morph the structure into optimal shapes as the load changes [3]. To ensure the embodied energy saved this way is not used up to by actuation, the adaptive solution is designed to cope with ordinary loading events using only passive load bearing capacity whilst relying on active control to counteract larger events with a smaller probability of occurrence. Extensive numerical simulations show that the whole-life total energy could be reduced by up to 70% when the design is stiffness governed (e.g. slender structures, strict deflection limits) [4]. A large scale prototype was successfully tested demonstrating the feasibility [5]. Structural adaptation allows a much more efficient utilization of material resources, thus lowering environmental impact. Adaptive structures can be extremely slender while still being capable of reducing deflections at the expense of a small amount of operational energy. This allows for taller and more slender buildings resulting in increased floor area via reduction of structural cores as well as longer span bridges and self-supporting roof systems. Combining these aspects is unique in structural engineering. References