Experimental Testing of a Small-Scale Truss Beam That Adapts to Loads Through Large Shape Changes

Abstract

Adaptive structures have the ability to modify their shape and internal forces through sensing and actuation in order to maintain optimal performance under changing actions. Previous studies have shown that substantial whole-life energy savings with respect to traditional passive designs can be achieved through well-conceived adaptive design strategies. The whole-life energy comprises an embodied part in the material and an operational part for structural adaptation. Structural adaptation through controlled large shape changes allows a significant stress redistribution so that the design is not governed by extreme loads with long return periods. This way, material utilization is maximized and embodied energy is reduced. A design process based on shape optimization has been formulated to obtain shapes that are optimal for each load case. A geometrically non-linear force method is employed to control the structure into required shapes. This paper presents the experimental testing of a small-scale prototype adaptive structure produced by this design process. The structure is a simply supported planar truss. Shape adaptation is achieved through controlled length changes of turnbuckles that strategically replace some of the structural elements. The stress is monitored by strain sensors fitted on some of the truss elements. The nodal coordinates are monitored by an optical tracking system. Numerical predictions and measurements have a minimum Pearson correlation of 0.86 which indicates good accordance. Although scaling effects have to be further investigated, experimental testing on a small-scale prototype has been useful to assess the feasibility of the design and control methods outlined in this work. Results show that stress homogenization through controlled large shape changes is feasible.

A proof of equivalence of two force methods for active structural control

“…The formulation stated in Equations (39) and (40) has been extended to geometrically non-linear problems in [29]. Other formulations exist that include buckling constraints [17].…”

“…Numerical and experimental studies have shown that well-designed adaptive structures save up to 70% of the energy with respect to weight-optimized passive structures [14,15]. Recent studies [16,17] have investigated structural adaptation through large shape changes. In this case the structure is designed to be controlled into a shape that is optimal to counteract the effect of the external load.…”

Force and Shape Control Strategies for Minimum Energy Adaptive Structures

“…Highrise structures, long-span bridges and self-supporting roof systems are generally stiffness governed and therefore they are could greatly benefit from adaptive design strategies. Structural adaptation through geometric non-linear control has been further investigated in Reksowardojo et al (2019Reksowardojo et al ( , 2020a. Numerical and experimental studies have shown that when the structure is designed to be controlled into shape configurations that are optimal to counteract the effect of the external load, the stress can be effectively homogenized and minimized under different loading conditions.…”

Using Influence Matrices as a Design and Analysis Tool for Adaptive Truss and Beam Structures

“…The integration of such active elements allows an adaptive structure to monitor its stress state and to react accordingly. In case of rarely occurring, high external loads, the structure may induce forces counteracting those from the external load, respectively change its stiffness distribution to homogenize stresses and strains (Sobek and Teuffel, 2001;Senatore et al, 2018a), induce counter deformations (Sobek et al, 2002;Senatore et al, 2018b;Kelleter et al, 2020), or generate shape changes to establish a more efficient load transfer (Neuhaeuser et al, 2013;Reksowardojo et al, 2019), thus increasing structural performance. Due to this increase in performance, the passive elements of the adaptive structure can be dimensioned for lower, more frequently occurring loads, which reduces the structures' resource consumption and embodied energy while using comparatively little operational energy (Senatore et al, 2018c;Schlegl et al, 2019).…”