Tailoring stiffness of deployable origami structures

Origami has gained popularity in science and engineering because a compactly stowed system can be folded into a transformable 3D structure with increased functionality. Origami can also be reconfigured and programmed to change shape, function, and mechanical properties. In this thesis, we explore origami from structural and stiffness perspectives, and in particular we study how geometry affects origami behavior and characteristics. Understanding origami from a structural standpoint can allow for conceptualizing and designing feasible applications in all scales and disciplines of engineering. We improve, verify, and test a bar and hinge model that can analyze the elastic stiffness, and estimate deformed shapes of origami. The model simulates three distinct behaviors: stretching and shearing of thin sheet panels; bending of the flat panels; and bending along prescribed fold lines. We explore the influence of panel geometry on origami stiffness, and provide a study on fold line stiffness characteristics. The model formulation incorporates material characteristics and provides scalable, and isotopic behavior. It is useful for practical problems such as optimization and parametrization of geometric origami variations. We explore the stiffness of tubular origami structures based on the Miura-ori folding pattern. A unique orientation for zipper coupling of rigidly foldable origami tubes substantially increases stiffness in higher order modes and permits only one flexible motion through which the structure can deploy. Deployment is permitted by localized bending along folds lines, however other deformations are over-constrained and engage the origami sheets in tension and compression. Furthermore, we couple compatible origami tubes into a variety of cellular assemblages that can enhance mechanical characteristics and geometric versatility. Practical applications such as deployable slabs, roofs, and arches are also explored. Finally, we introduce origami tubes with polygonal cross-sections that can reconfigure into numerous geometries. The tubular structures satisfy the mathematical definitions for flat and rigid foldability, meaning that they can fully unfold from a flattened state with deformations occurring only at the fold lines. From a global viewpoint, the tubes do not need to be straight, and can be constructed to follow a non-linear curved line when deployed. From a local viewpoint, their cross-sections and kinematics can be reprogrammed by changing the direction of folding at some folds

Elastically and Plastically Foldable Electrothermal Micro‐Origami for Controllable and Rapid Shape Morphing

Integrating origami principles within traditional microfabrication methods can produce shape morphing microscale metamaterials and 3D systems with complex geometries and programmable mechanical properties. However, available micro‐origami systems usually have slow folding speeds, provide few active degrees of freedom, rely on environmental stimuli for actuation, and allow for either elastic or plastic folding but not both. This work introduces an integrated fabrication–design–actuation methodology of an electrothermal micro‐origami system that addresses the above‐mentioned challenges. Controllable and localized Joule heating from electrothermal actuator arrays enables rapid, large‐angle, and reversible elastic folding, while overheating can achieve plastic folding to reprogram the static 3D geometry. Because the proposed micro‐origami do not rely on an environmental stimulus for actuation, they can function in different atmospheric environments and perform controllable multi‐degrees‐of‐freedom shape morphing, allowing them to achieve complex motions and advanced functions. Combining the elastic and plastic folding enables these micro‐origami to first fold plastically into a desired geometry and then fold elastically to perform a function or for enhanced shape morphing. The proposed origami systems are suitable for creating medical devices, metamaterials, and microrobots, where rapid folding and enhanced control are desired.An elastically and plastically foldable micro‐origami is developed and tested to create controllable and functional 3D shape morphing systems with multiple active degrees of freedom. The work demonstrates a versatile design–fabrication–actuation method to achieve rapid folding, enhanced control, and function in different atmospheric environments, enabling applications in microrobots, medical devices, and metamaterials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/2/adfm202003741.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/1/adfm202003741-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/3/adfm202003741_am.pd

Nonlinear seismic analysis of quasi-isolation systems for earthquake protection of bridges

Quasi-isolation is a modern bridge seismic design philosophy where nonlinearity is permitted to occur in specific bearing components such that forces transferred into the substructure are reduced and isolation is achieved by sliding of the bearings. The system is a pragmatic approach for providing earthquake resilient bridges in locations such as the eastern and central United States, as well as in many locations around the world where there is significant earthquake risk at long recurrence periods. Such a seismic risk does not typically justify the design of a rigorous classical isolation system, but instead, a low-complexity, low-cost quasi-isolation approach could provide significant mitigation of earthquake effects. The proposed system employs a set of fixed bearings at one intermediate substructure, and all other substructures are instrumented with isolation bearings that permit thermal expansion such as elastomeric bearings with an elastomer-concrete sliding interface or elastomeric bearings with a PTFE (Teflon) to stainless steel sliding interface. L-shaped steel side retainers are placed in the transverse direction of the elastomeric bearings, and along with the low-profile fixed bearings, these components prevent bridge movement during service loading, but break-off and permit sliding at high earthquake loads. This thesis outlines a base bridge prototype, with the anticipated nonlinear behaviors in the structural components defined in a finite element model of the global structure. New nonlinear elements have been formulated to capture the bi-directional stick-slip behaviors in the bridge bearings and the bilinear (and eventual fracture) behavior of steel retainers and fixed bearings. Longitudinal and transverse static pushover analyses are performed to demonstrate local limit states and progression of damage in the bridge structure. A large scale parametric study carried out to investigate the quasi isolated system performance on different superstructure types, substructure types, substructure heights, foundations and isolation bearing types. Different suites of ground motions are scaled and incremental dynamic analyses (IDA) are carried out for each parametric variation such that the sequence of damage and global seismic performance can be evaluated. Results indicate that the bearing systems with the flat PTFE slider, would likely result in critical damage from the unseating of bearings at moderate and high seismic events in the New Madrid Seismic Zone (NMSZ). The sequence of damage for many bridge cases indicates yielding of piers at low-earthquake hazards which justifies further calibration of the quasi-isolation bearing systems. Finally the, type of ground motion, foundation stiffness, pier height and bearing type were noted to have significant influence on the global bridge response

Seismic Performance of Quasi-Isolated Highway Bridges in Illinois

The Illinois Department of Transportation (IDOT) commonly uses elastomeric bearings to accommodate thermal deformations in bridges, and these bearings have potential utility in seismic events. IDOT has developed an Earthquake Resisting System (ERS) using the displacement capacity of typical bearings to achieve a structural response similar to isolation. Project R27-70 was conducted to validate and calibrate the quasi-isolated ERS based on full-scale laboratory tests of bearings and computational models capturing full-bridge seismic response. The overall report is divided into two volumes. Volume 1 discussed the experimental program. This second volume focuses on the analytical program but also contains retainer design recommendations. Results from the experimental testing program were used to develop constitutive bearing models, which were incorporated into the finite element model of a three-span bridge with simply supported abutments and fixed bearings at one pier. A suite of 48 bridges was created to represent the most common highway bridge configurations in Illinois. Variables included superstructure type, pier type, pier height, elastomeric bearing type, and foundation flexibility. Two sets of ten synthetic ground motions from the New Madrid Seismic Zone were scaled to match the AASHTO seismic design spectra for Cairo, Illinois, and applied in the longitudinal and transverse directions. A total of 12,000 nonlinear dynamic analyses were conducted in OpenSees at six scale factors from 0.5 to 1.75 and used to create coarse incremental dynamic analyses. On the basis of the findings of the parametric study, most bridges in Illinois would not experience severe damage during a 75-year design life, and bearing unseating or span loss are not likely to occur in regions with moderate seismic hazard. Piers with fixed bearings commonly yielded for small earthquakes, but future calibration of fuse capacities may improve this behavior.Illinois Department of Transportation R27-70published or submitted for publicationnot peer reviewe

Experimental Investigation of the Seismic Response of Bridge Bearings

The Illinois Department of Transportation (IDOT) commonly uses elastomeric bearings to accommodate thermal deformations in bridges. These bearings also present an opportunity to achieve a structural response similar to isolation during seismic events. IDOT has been developing an earthquake resisting system (ERS) to leverage the displacement capacity available at typical bearings in order to provide seismic protection to substructures of typical bridges. The research program described in this report was conducted to validate and calibrate IDOT’s current implementation of design practice for the ERS, based on experiments conducted on typical full-size bearing specimens, as well as computational models capturing full bridge response. The overall final report is divided into two volumes. This first volume describes the experimental program and presents results and conclusions obtained from the bearing and retainer tests. The experiments described in this volume provide data to characterize force-displacement relationships for common bearing types used in Illinois. The testing program comprised approximately 60 individual tests on some 26 bearing assemblies and components (i.e., retainers). The testing program included (1) Type I elastomeric bearings, consisting of a steel-reinforced elastomeric block vulcanized to a thick top plate; (2) Type II elastomeric bearings, distinct from Type I bearings with a steel bottom plate vulcanized to the bottom of the elastomeric block, and a flat sliding layer with polytetrafluoroethylene (PTFE) and stainless steel mating surfaces between the elastomer and the superstructure; and (3) low-profile fixed bearings. Tests conducted to simulate transverse bridge motion also included stiffened L-shaped retainers, consistent with standard IDOT practice. Tests were conducted using monotonic and cyclic displacement protocols, at compression loads corresponding to a range of elastomer compression stresses from 200 to 800 psi. Peak displacements from initial position ranged from 7-1/2 in. to 12-1/2 in., depending on bearing size. Test rates were generally quasi-static, but increased velocities up to 4 in./sec were used for bearings with PTFE and for a subset of other elastomeric bearings. On the basis of all of the experimental findings, bearing fuse force capacities have been determined, and appropriate shear stiffness and friction coefficient values for seismic response have been characterized and bracketed.Illinois Department of Transportation R27-70published or submitted for publicationnot peer reviewe