Marios C. Phocas

Kinetic Hybrid Structure Development and Simulation

Supported through technological advances, the concept of kinetic architecture is internationally increasingly acknowledged in the past years in the development of adaptable buildings as to differing functional requirements, or external loading conditions. Most decisive factor is the structure in terms of materials and geometrical configurations, and the control system integrated within. Based on general principles of tensegrity structures, a hybrid system has been developed that consists of continuous hinge connected compression members, strengthened by an internal system of struts and continuous cable diagonals with closed loop. The kinetic mechanism is achieved through alteration of the cables length and the respective relative inclination of any adjacent compression members. In this way the transformability of the system arises primarily from the inherent integrative composition and dual capabilities of its members. Following the construction design of the prototype structure, the interactive development, as regards geometric properties and structural configurations, is presented analytically, as based on a parametric-associative design approach applied. Along this line, the specific syntax of structural development and simulation through parametric design is suggested to support in real terms the control design of the innovative structure in an integrated interactive context.

Optimized retrofit of multi-storey buildings using seismic isolation at various elevations: assessment for several earthquake excitations

This work is concerned with the seismic retrofit of multi-storey buildings by installing isolation devices at various levels along their height. The design of an effective retrofit solution of this type requires the selection of the appropriate number of isolation levels to introduce in a building, the elevations at which to place these isolation levels and the properties of each of the isolators to install. The task of identifying configurations of isolators vertically distributed over the height of a building that yield favourable structural behaviour is handled in the present paper with a specially developed optimization procedure, which can automatically and effectively explore the huge set of potential retrofit solutions formed by all possible combinations of isolator numbers, locations and properties. Specifically, a genetic algorithm is implemented to detect the isolation configuration that minimizes the maximum floor acceleration of the building under retrofit, subject to constraints ensuring that maximum allowable values for interstorey drifts, base displacements and overall isolation cost are not exceeded. A 6-storey building is used to test the presented optimization procedure, while several recorded strong earthquake motions are considered, which are applied either individually or in sets to the building in the framework of time-history analyses. The numerical results obtained demonstrate the validity and effectiveness of the optimization procedure, which manages to identify feasible isolation configurations for all test cases examined. Of particular importance is the ability of the optimization procedure to provide valid retrofit solutions for buildings with narrow seismic gaps subjected to very strong earthquakes, in which configurations employing only base isolation usually prove to be ineffective.

Motion Planning for Shape–Controlled Adaptable Buildings Resembling Topologically Closed–Loop Robotic Systems

Shape–controlled adaptable building structures have a potential of superior performance and flexibility compared to traditional fixed–shape ones. A building concept is proposed consisting of a number of interconnected planar n–bar linkages performing coordinated motions thus resembling a system of cooperating closed–loop robotic manipulators. For shape control an “effective 4–bar” linkage concept is proposed. That is, each individual n–bar mechanism is equipped with one motion actuator, and at any time of motion its degrees–of–freedom are reduced to one through the selective locking of (n – 4) joints using brakes. Shape adjustments of the overall structure can be carried out through appropriate control sequences where in each step exactly four joints of each linkage are unlocked giving rise to an effective 4–bar system. Motion planning is considered together with the relevant limitations arising from singular configurations that need to be taken into account. The concept is demonstrated through simulation examples.Copyright

Dual earthquake resistant frames

Structural control through energy dissipation systems has been increasingly implemented internationally in recent years and has proven to be a most promising strategy for the earthquake safety of structures. In extending the “classical” approach of the capacity design for earthquake structural resistance, the integration of passive damping devices within the structure aims at energy dissipation within specific structural zones. The present paper examines an alternative control system for achieving dynamic structural adaptability, which consists of an energy dissipation device and a cable bracing mechanism with a kinetic closed circuit, working only in tension. The closed bracing mechanism does not practically affect the initial stiffness of the system, i.e. the concept relies on two completely “separate” systems: a primary for the verticaland wind loads and a secondary for the earthquake loads. An additional feature of the bracingdamper mechanism compared to conventionally passively controlled systems is the contribution of all bracing members to the energy dissipation during a loading cycle. Three “dual systems” with different configurations of the closed bracing mechanisms and damping devices are investigated in their dynamic behaviour, in the time-history range under actual earthquakes of the GreekMediterranean region. The study provides significant response comparisons of the dual systems, in respect to the stiffness of the hysteretic dampers, its effect on the base shear force and the maximum relative displacements of the systems and to the energy dissipation behaviour of the bracing-damper mechanism.

TOWARDS REALIZATION OF SHAPE-CONTROLLED ADAPTABLE BUILDINGS FOLLOWING A ROBOTICS APPROACH

Shape‐controlled adaptable buildings constitute a major excursion from traditional architectural approaches with a potential for superior performance and enhanced flexibility compared to traditional fixed‐shape building structures. A building concept is examined whose skeleton structure consists of a parallel arrangement of planar closed‐loop n‐bar linkages and it is covered with a flexible material. Shape adjustments involve coordinated reconfigurations of the constituent closed‐chain mechanisms. Each individual linkage is equipped with one motion actuator as well as brakes installed on every joint. For the reconfigurations an “effective 4‐bar” concept has been proposed that involves stepwise adjustments. Each step involves the selective locking of (n 4) joints of each linkage so that it is effectively reduced to a single‐DOF 4‐bar mechanism the configuration of which can be adjusted using the available motion actuator. Appropriately planned control sequences can be used for a complete reconfiguration of the linkage. Motion planning is concerned with the generation of optimal control sequences while taking into account imposed limitations arising from the moving structure as well as the flexible envelop. This paper is a continuation of a prior work paying special attention to the envelop design. Simulation examples as well as an experimental study are used to demonstrate the feasibility of the concept and investigate relevant issues.

Dual System Configuration for Earthquake Safety

Structural control through integration of passive damping devices within structures has proven to be a most promising strategy for earthquake safety. Within this research field, the concept of adaptable dual control systems has been initially proposed for application in frame structures supplemented with a cross cable bracing with closed circuit and a hysteretic damper of steel plates. The control mechanism enables the elastic response of the primary structure through energy dissipation only effected by the damper that is activated by all bracing members. In extending the applicability range of the control concept in both, in engineering and broader architectural context, and further improving the controlled system’s performance, an alternative configuration of the bracing-damper mechanism is investigated. Following the construction design of the control system members a numerical dynamic analysis of a SDOF system is performed for three representative international earthquake motions of differing frequency contents. The characteristic stiffness and yield force of the integrated damper are investigated in their optimum values for achieving high energy dissipation capacity of the system, while preventing possible increase of the maximum base shear and relative displacements.

Prototyping of an Adaptive Structure based on Physical Conditions

Latest advances in digital architectural design enable applications of computation and fabrication strategies for the development of adaptive mechanisms. Adaptive design processes, influenced by environmental and human related conditions, are only developed partially with regard to the design, fabrication, and multi-objective performance based context. The current paper proposes an adaptive design process that investigates the design of a kinetic structure emphasizing material behaviour, embedded technology and computation. In parallel, it allows design proposals to adapt or transform with regard to geometrical configuration and structural behaviour according to external and internal influences. An adaptive hybrid structure is developed at digital and physical prototype level, where its behaviour is examined in real time under the influence of physical conditions. The development is based on a holistic design approach driven by environmental and human activity related conditions, while focusing on the application of elastic materials and embedded technology.

Interdisciplinary Research-based Design: the Case of a kinetic form-active Tensile Membrane

In the last years it is increasingly acknowledged that advances in digital technology are paving the way to achieve integrated interdisciplinary design, a type of practice that covers a mindset of collaboration and cross-disciplinary communication and experimentation, visualization and research at all stages of the architectural design process. Along these lines interdisciplinary research is necessary to engage complex topics that bridge between design and engineering. An open loop design methodology of interdisciplinary physical and digital investigations from the conceptual development up to the detailed physical prototyping is proposed in the current paper. The approach is exemplified with the design of a kinetic form-active membrane system. Membrane surfaces comprise the basic component of the hybrid system developed, whereas any form modification is activated through the system’s cablenet and struts. The interactive platform of investigation, based on physical- and digital modelling serves for the definition of the system’s adaptability, its composition and the structural components design.

Adaptable dual control systems for earthquake resistance

The use of passive energy dissipation systems for seismic control has been proven internationally over the past years as most promising. The proposed concept of Adaptable Dual Control Systems (ADCS), presented in the present paper, relies on the seismic performance of braced frames with cables or tension only rods, following a closed circuit, and hysteretic dampers. ADCS are based on a dual function of the component members, resulting in two practically uncoupled systems: a primary and a secondary system. The primary frame is responsible for the normal vertical and horizontal forces, while the closed damper-bracing mechanism, for the earthquake forces and the necessary energy dissipation. The bracing members are fixed at the bottom of the columns and are free to move horizontally at the primary frame’s joints. Relative displacements are induced between the energy dissipation system’s component members and the main frame’s members. The potentials for maximum energy dissipation of the proposed systems are investigated in three configurations of the control system. In all cases the damper utilizes the relative displacement between its end joints to yield in the inelastic region, enabling the primary frame to resist elastically. ADCS may result to significant energy dissipation, when all design parameters involved are accordingly predefined. The predominant parameters that characterize ADCS seismic behavior are verified in respect to the mechanical properties of the control elements under the action of ten selected earthquake records of the Greek-Mediterranean region. A comparative parametric analysis of the three systems’ seismic behavior leads to significant recommendations for their application as alternative energy dissipation systems.

Multi-storey Structures with Seismic Isolation at Storey-Levels

Through increasing international research and application activities in the last years, seismic isolation has proven to be an innovative passive control technique in the area of performance-based design of buildings. Seismic isolation is principally based on the incorporation of flexible isolators at the base of low-rise buildings in order to shift the fundamental period outside of the dangerous for resonance, range of periods. In extending the concept of base isolation, the present contribution refers to the control of multi-storey structures under earthquake actions by means of introducing seismic isolation at different elevations of the structure. Thus, the structural response is influenced decisively by the vertically distributed seismic isolation, which at the respective storey-levels is alone capable of controlling the partial and overall stiffness, the force transmission and the energy dissipation process of the respective dynamic adaptable system. During strong earthquakes the effectiveness of the system in further enlarging the period of the building, compared to the classical method of seismic isolation at a unique level, is achieved, most often with decreased inter-storey deflections, and without introducing extensive displacements at the building base, which are often limited by practical constraints. The effectiveness of the proposed control system is investigated in parametric studies, in the time-history range, for a 6-storey building under ten selected earthquakes of the Greek-Mediterranean region, scaled to a maximum ground acceleration of 0.25 g. Most effective vertical distribution of seismic isolation at various storey-levels is proposed, based on the earthquake, structural and isolation characteristics used in the numerical study.