Element location and classification following a damage event of a near-full-scale deployable tensegrity structure

Current infrastructure is designed and built such that it must resistall possible loads. This leads to overdesigned structures that are inefficient in terms energy and cost. A structure that can self-identify damage, adapt, and learn for future events results from research intothe emerging field of intelligent infrastructure and structural health monitoring.Two halves of a “hollow-rope” tensegrity structure deploy from supports to join at midspan by controlling the length of active cables on each half of the structure. These active cables are continuous throughthe length of the half-structure, guided by intermediary jointswhere cables slide. Springs along the circumference of the structure facilitate deployment due to increasing the diameter of the structure when folding and subsequent decreasing during deployment. Although previous work has addressed damage locationand mitigationof ruptured cableswhen the cables are the load-critical elements of the structure, this work hasnot studiedthe classification of the type of element that is damaged, element locationand damage mitigation.This paper presents work on element classification, detection,and location of damaged elements in a deployable tensegrity footbridge. The footbridge isstudied through monitoring dynamic behavior. Displacement and strain values are measured before, during, and after cable breakage. Natural frequencies inhealthy and damaged states are compared. Free-vibration dynamic behavior of the tensegrity structure are characterized for two situations,deployment and in-service. Examination of ambient vibrations for the half structure and forced vibrations for the full structure successfully led to detection of ruptured cables. Correlation methods using strain measurements also successfullydetect and locate a ruptured cable. Detection of abuckled strut and aruptured cableis successful by observing differences of natural frequencies between healthy and damaged states. Location of a damaged element is successful using nodal-position measurements through excluding possible damage scenarios and using strain measurements to identify elements of significant changes in eigenvector coefficients using principal component analysis. Therefore, excluding scenarios from a population for damageidentification is effective for highly-coupled structures that are capable of large shape changes. These methods reveal the potential for damage identification of complex sensed structures.Classification and location of a damaged element on a complex near-full-scale structure is successful using nodal position measurements through excluding possible damage cases and using strain measurements to identify elements of significant changes in eigenvector coefficients using principal component analysis. Implementing error-domain model falsification to exclude possible scenarios for location of damaged elements successfully reduced the number of probable casesof damage location. Paterns of influence from damaged cables and struts are useful to classify the type of element that is damaged. Therefore, the methodology involving error-domain model falsification (EDMF) for damage location is useful for closely-coupled structures that are capable of large shape changes.

Damage mitigation of a near-full-scale deployable tensegrity structure through behavior biomimetics

Ian Smith, Ann Christine Sychterz

Current infrastructure is designed and built such that it must simultaneously comply with all possible loads. This leads to overdesigned structures that are inefficient in terms energy and cost. A structure that can self-identify damage, adapt, and learn for future events addresses the emerging field of intelligent infrastructure through inspiration from biology. The required material and embodied energy of structural elements is reduced while maintaining structural integrity with a small increase in operational energy for active control. Tensegrity structures are cable-strut systems held in equilibrium due to self-stress. There is potential for damage tolerance when they are kinematically redundant. This paper presents active control algorithms applied for damage mitigation and service loading of the tensegrity structure. Active control using a path-planning RRT*-connect algorithm and soft-constraint algorithm changes the shape of the tensegrity structure to reduce member stresses and to restrict vertical (downward) displacement caused by a damaged element. Though the effect improves the configuration of the structure, it cannot be fully restored to the design configuration. Effectiveness of the RRT*-connect and soft-constraint algorithms for the half structure depends on the relative change of nodal positions and feasibility to bring the structure back within serviceability limits. Since correction of end-node coordinates can be grouped according to the direction vector to mitigate the configuration of the structure and resulting cable-length changes, case-based reasoning (CBR) is useful to reduce time of execution and to avoid unnecessary cable-length changes. Mitigation techniques are successfully demonstrated for serviceability thresholds for a uniformly distributed load.

2019

Deployment of a tensegrity footbridge

Seif Dalil Safaei, Ian Smith, Nicolas Willy Veuve

Deployable structures are structures that transform their shape from a compact state to an extended in-service position. Structures composed of tension elements that surround compression elements in equilibrium are called tensegrity structures. Tensegrities are good candidates for deployable structures since shape transformations occur by changing lengths of elements at low energy costs. Although the tensegrity concept was first introduced in 1948, few full-scale tensegrity-based structures have been built. Previous work has demonstrated that a tensegrity ring topology is potentially a viable system for a deployable footbridge. This paper describes a study of a near-full-scale deployable tensegrity footbridge. The study has been carried out both numerically and experimentally. The deployment of two modules (one half of the footbridge) is achieved through changing the length of five active cables. Deployment is aided by energy stored in low stiffness spring elements. Self-weight significantly influences deployment, and deployment is not reproducible using the same sequence of cable- length changes. Active control is thus required for accurate positioning of front nodes in order to complete deployment through joining both sides at center span. Additionally, testing and numerical analyses have revealed that the deployment behavior of the structure is nonlinear with respect to cable-length changes. Finally, modeling the behavior of the structure cannot be done accurately using friction-free and dimension- less joints. Similar deployable tensegrity structures of class two and higher are expected to require simulation models that include joint dimensions for accurate prediction of nodal positions. DOI: 10.1061/(ASCE)ST.1943-541X.0001260 . © 2015 American Society of Civil Engineers.

Asce-Amer Soc Civil Engineers2015

A transformable tensegrity-ring footbridge

René Motro, Landolf-Giosef-Anastasios Rhode-Barbarigos, Ian Smith

Tensegrity structures are spatial reticulated structures composed of cables and struts. A tension-compression equilibrium leads to lightweight systems that change shape through length changes in their members. Active members thus control several degrees of freedom simultaneously. Tensegrity-ring modules are transformable circuit-pattern modules. The linear combination of tensegrity rings has been shown to be viable for a footbridge application. Shape transformations of a ¼ scale four-ring-module tensegrity-footbridge system are studied in this paper. Transformations are obtained employing active continuous cables and springs in the tensegrity system to reduce the number of active elements. Obtaining a desired shape may involve independent actuation in several active elements. Independent actuation steps are found with the combination of a dynamic relaxation algorithm and a stochastic search algorithm.

2012