Hybrid Bar linkage structure
The design of a Research Center for Advanced Mobility Technologies refers to an international research platform of fundamental and applied research with regard to environmental issues and alternative mobility ways, Fig. 3. The building has a total area of approximately 2000 m2 and envisages to provide adaptable, flexible spaces, where different researchers may work at different time periods, Fig. 4. The building reflects its interrelated functional areas with the construction and energy efficiency and provides a focal point of research and technological advancements.
The spatial structure is articulated as of interconnected planar modular systems. The planar systems comprise 9-bar linkages that are supported by a secondary system of struts and continuous cables of variable length, Fig. 5. The struts of rectangular hollow sections are divided at mid-length and interconnected through steel plates that pass through the joints of the rigid bars of double UPN sections joined together back-to-back. Diagonal spring elements connected between the bars and the struts are responsible for the self-centering of the struts following each joints angle change. The cables are responsible for the actuation of the planar systems. Thus, the operability of the structure primarily relates to its integrative composition and the dual function of the secondary system with regard to the system’s stability and kinematics. The planar systems are interconnected in the longitudinal direction through secondary telescopic members and continuous cable diagonals of variable length in accommodating any relative configuration differences between the primary planar linkages. Following the reconfiguration process, the horizontal members are locked in length, in order to ensure the diaphragm on the periphery of the spatial structure. In principle, expandability of the spatial structure is straightforward along all three directions. Given the modularity of the structure, each linkage can be augmented with additional members, but also the spatial structure can be expanded in the longitudinal direction with additional linkages.
Reconfigurations of the pin supported planar systems are possible through two linear actuators associated to the cables. The kinematics approach is based on the ‘effective 4–bar’ (E4B) mechanism, in order to stepwise adjust the system joints to the desired values . All internal joints of the planar linkages are equipped with brakes (e.g., electromagnetic, hydraulic or pneumatic brakes). Accordingly, four joint variables of each actuated linkage are determined in each reconfiguration step for the reduction of the system to a 1-DOF mechanism, based on an off-line planning procedure. In each step, one different angle is adjusted to the desired value and then remains locked until the overall reconfiguration is completed, i.e., the system obtains its target configuration. Based on the particular hybrid configuration of the structure, motion planning requires in each step, two consecutively unlocked joints, or an even number of locked joints between the two unlocked ones, in such a way that the cables actions do not compete with each other. In addition, an upper limit of 175° of any unlocked joint angle should avoid infeasible sequences. Throughout the reconfiguration, only slow motions are involved and inertial effects are negligible. Different feasible motion sequences are possible and a favorable one may be selected, based on specific kinematics and static response criteria. Once a motion sequence is selected, a control system manages in each reconfiguration step the operation of the individual brakes on the joints, which receive input from the position sensors (e.g., optical encoders or potentiometer-type sensors) installed on the joints. Application of the specific reconfiguration approach to the spatial structure involves coordinated shape adjustments performed on each individual actuated planar linkage. In the case of nonsymmetric reconfigurations among the planar linkages, the control system may also coordinate the reconfiguration of the overall structure by considering the relative motion of the horizontal members of the spatial system. The kinematics approach requires a minimum number of actuators, positioned on the ground and detached from the body of the main structure. In this way, minimum self-weight is preserved, since no actuators need to be moved about during the reconfigurations of the system, yielding also better energy performance.
The building envelope should enable lightweight of the material, structural efficiency, and have exclusive elastic deformations during transformation, without stress interactions with the primary structure. In addition, the envelope structure is required to be flexible in order to accommodate for cases of dissimilar configurations assumed by any adjacent actuated multi-bar linkages. In the specific example, a double layer of THV-membranes, Terpolymer of Tetrafluoroethylene-Hexafluoro-propylene-vinylidene fluorid, is to be supported on a dedicated secondary adaptive structure rather than being directly affixed to the members of the primary structure, Fig. 6.
Spatial Bar linkage structure
The design of an adaptive pavilion for a temporary aerospace and robotics exhibition aims at exploring the potential of a kinetic system in adjusting its shape in response to variable functional needs and external weather conditions. Specifically, the problem task refers to a temporary building suitable for easy and fast assembly, also capable to expand its floor area from 60 up to 120 m2. The ‘Medusa’ pavilion was inspired in its lightweight structure by the jellyfish and crystallize concepts of adaptability and transformability, Figs. 7, 8. The principal design concept refers to a structural system capable to perform multiple configurations and enhance the spatial experience of the visitors. In particular, three scenarios are addressed in this design project. Accordingly, a wider space for social interactions, seasonal transformability and accommodation to different climate zones is provided.
The primary arch-shape structure consists of radial planar bar linkages of sixteen rhomboid aluminium elements with dimensions of 600/200/100 mm. Figure 9 illustrates the structural system and the envelope of the proposed pavilion in two configurations. To enable transformation of the individual linkages, the effective crank–slider kinematics mechanism is applied as a multistep procedure through a linear motion actuator, which is associated with a sliding block connected to one of the supports . In each step, the system is reduced to a 1-DOF mechanism through selective release of an intermediate joint, while the pin joints at the supports on either side always remain unlocked. A specific joint is adjusted through respective displacement of the sliding block in each step; from then on, it remains locked. Once the target configuration has been obtained, i.e., all joints of the system are correspondingly adjusted, the actuator locks in place by applying all the brakes. Following a preliminary motion planning, the geometric path planning of discrete motions provides a motion sequence of valid reconfiguration steps. With a span of 3.2 m in the initial position and 4.9 m in the target position, the structural system succeeds to accomplish its initial aim to contract and expand its floor area. In the specific design, the stepwise shape adjustments of the system are controlled by a continuous cable of variable length, interconnecting the supports. A secondary X-bracing system of bending-active members connects the bar linkages in the periphery and provides stability to the tensile envelope, while it is capable to follow the shape adjustments of the primary structure according to its low friction coefficient.
Hybrid Scissor-like elements
The pavilion presented in Fig. 10 serves as a place of convergence of a closed and open exhibition. The pavilion is capable to meet the functional needs of the exhibition, as well as to accommodate to different weather conditions by changing its configuration. Moreover, the pavilion is conceived as an autonomous building making use of solar power and generating its own energy. Inspired by the aerospace industry, the origami solar panels are foldable and adjust their opening factor, predominantly based on visual comfort and solar radiation criteria. A focal point of the design project was the creation of an interactive building enhancing communication with its environment and visitors.
The primary structure imitating centipedes recalls the design of a building with a multi-legged envelope. Accordingly, eighteen pairs of arch-like scissor-like elements interconnected through continuous cables of variable length comprise each side of the building. At midspan, the elements are connected to a longitudinal beam supported on diagonal columns, Fig. 11. Sliding of the diagonal members supports in opposite direction and releasing of the continuous cables of the scissor-like elements induces an increase of the width of the pavilion at the base from 7.5 to 9 m. Further nonsymmetrical cases refer to the transformation of the pavilion space from a closed to an open one. The kinetic structure investigated in a small-scale model is shown in Fig. 12.
Hybrid bending-active plates
The Spiral Pavilion is inspired by the Fibonacci spiral, as well as the elastic behavior of flexible elements that generate new dynamic spaces and forms. The spiral typology provides a pavilion that transforms its shape through hybrid bending-active plates, while enhancing various expressions of the exhibition and the interaction with the visitors. Three scenarios implemented in this design project refer to a closed, semi-closed and open exhibition, hosting a digital, physical and interactive exhibition respectively. Shape adjustments of the building predominantly refer to the interaction with the visitors and the sun position. As indicated in Fig. 13, the higher the number of visitors, the wider is the span of the pavilion. In addition, a playful light performance takes place inside the pavilion, while creating an interplay of light and shadow during the exhibition based on the cut-out patterns on the envelope.
The spiral structure consists of arch-shaped bamboo members covered by bamboo thatch, Fig. 14. The transformable shell travels on a double-wheel track, in order to generate the shape adjustments and enable different spatial experiences. Along the arch, five V-shaped openings are evenly distributed and responsible for control of the light transmission to the indoor spaces. An increased light transmission factor is enabled when the bending-active elements are contracted. Thus, different variations of the openings are created based on the transformation of the bending-active plates. A folding membrane is installed on the openings, in order to accommodate the different reconfigurations of the primary structure. Moreover, the pavilion projects aspects of adaptive and energy-autonomous buildings to exploit capabilities and technological advancements of human-powered floor tiles.
Coupled Scissor-like elements and hybrid bending-active members
The design of a smart city unit prototype involves temporary activities that may be hosted within and renewable energy provision within the urban fabric, Fig. 15. The unit consists of two floors with autonomous kinematics. A shell unit on top of a deployable central mast follows through its own rotations, the position of the sun in collecting the solar radiation. Expandable steel diagonals in pairs that constitute scissor-like elements are supported on the mast and interconnected through vertical cables of variable length and bending-active members. The diagonals are additionally, horizontally interconnected through peripheral circular members. The bending-active members are activated by the vertical cables for their respective elastic deformations during the transformation process of the unit that in turn induces respective modification of the relative angle of the scissor-like elements. Shortage of the cables’ length induces bending deformations to the elastic members and corresponding height reduction of the associated structure, while release of the cables enables the elastic members to decrease their curvature and correspondingly increase the height of the structure. The linear motion actuators associated to the vertical cables in both floors of the unit are placed on the first floor. Textile membranes connected to the bending-active members, define the shell of the unit’s functional spaces. An expandable floor system follows the motion through respective transformations. Thus, the building units act as a living organism that responds continuously to the sun movement. In doing so, all individual components interact: the units’ shape, space, boundaries and the users’ activities.
The bending-active members of GFRP (glass fiber reinforced polymere) possess appropriate geometrical slenderness in the deformation direction and material properties of low elastic modulus and high strength, and are able to undergo reversible elastic deformations. In achieving active shape and deformation control, hybridization of the members with cables of variable length has been applied as presented in . Preliminary investigations on the deformability of the bending-active members have been contacted based on physical small-scale models, followed by parametric-associative digital modelling, Fig. 16. While the hybrid modular systems investigated possess enhanced deformability, further applications may extend from single to multi-segment configurations . Thus, a design and nonlinear numerical analysis process would be further required, which needs to consider all stages of development, and the residual stresses developed in the elastic members. The design of the structural members based on the modularization of the structure and its components, aimed at providing clarity and readability of the load-deformation behavior and corresponding detailing of the connections, Fig. 17.