A numerical investigation into the behaviour of flexible uplifting structures with slip-friction connectors under earthquake loading
While there has been significant research into the behavior of uplifting (or rocking) rigid structures under seismic loading, far less attention has been paid to the behavior of flex- ible structures allowed to uplift. Recently, however, Acikgoz and DeJong (1) have shown that these types of structures have unique dynamic characteristics that arise from the interaction of rocking motion with elastic vibration. An understanding of the behavior of uplifting flexible structures is required in order to fully benefit from the damage avoidance potential of allow- ing uplift. This is because building structures are invariably flexible with a finite fundamental frequency, and it is the desire of the structural designer that the structures themselves remain elastic, even while displaying non-linear behavior in a global sense. This paper is concerned with the behavior of flexible uplifting structures adapted with slip-friction devices. These de- vices act as hold-down connectors resisting overturning moment. They have a definite force threshold at which sliding will occur, and exhibit close to perfect elasto-plastic behavior. The ability of shear walls to avoid damage through the use of slip-friction connectors has been previously demonstrated by Loo et al. (2). The modeling of the slip-friction connectors, using a combination of elements commonly available in finite element software packages, and their verification is discussed. Both single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) flexible structures were modeled with a single plastic deformable hinge at their ba- ses, and their behavior under various earthquake simulations investigated. These flexible structures (both SDOF and MDOF) were then affixed at their bases to a rigid platform, with slip-friction connectors implemented at the ends of the platform, and then subjected to the same earthquake simulations. It was found that the maximum drifts of structures with slip- friction connectors compared favorably with their equivalent structures with a single plastic deformable hinge. With a small amount of vertical load, residual drifts were also found to be small. The performance of MDOF structures with slip-friction connectors was somewhat su- perior to that of the SDOF structures, with maximum drifts and residual drifts smaller than that of comparable SDOF structures.
A numerical study of the seismic behaviour of timber shear walls with slip-friction connectors
In the event of seismic overloading, timber shear walls have normally been designed to yield by allowing inelastic distortion of the sheathing-to-framing nail connections, thereby reducing the likelihood of brittle failure of timber chords or plywood sheathing. A new concept in shear wall design is presented. It involves the use of slip-friction connectors in lieu of traditional hold-down connectors. Slip-friction connectors, originally developed for the steel framing industry, rely on the mobilisation of friction across steel plates to resist loading up to a predetermined threshold. Upon this threshold being exceeded, relative sliding between the steel plates allows the shear wall to displace in an inelastic manner. This paper discusses the results of numerical analyses of timber shear walls which utilise slip-friction connectors. The results suggest that slip-friction connectors hold the promise of being able to effectively protect sheathing, framing, and nail connections from excessive stresses and deformations during earthquake events of design level intensity or higher. Walls with appropriately adjusted slip-friction connectors are highly ductile, are efficient dissipaters of seismic energy, and have a tendency to self-centre after an earthquake.
Numerical analysis and experimental observation of guidewire motion in a blood vessel model.
We have developed a computer-based system to simulate a guidewire in blood vessels for surgical planning, intra-operative assistance, and to facilitate the design of new guidewires. In this study, we compared simulation results with experimental results for validation of the simulation system. First, we inserted a commercial guidewire into a poly (vinyl alcohol) hydrogel blood vessel model using a two-axis automatic stage and measured the position of the guidewire tip and the contact force between the guidewire and the vessel. The experimental apparatus can be used not only for the validation of numerical analyses, but also as a simulation system. Second, similarly to the experiment, the motion of the guidewire in the blood vessel model was calculated when the proximal part of the guidewire model was pushed and twisted. The model of the guidewire is constructed with viscoelastic springs and segments, and the proximal part of the guidewire model is constrained by the fixed catheter model. Collisions between the guidewire and the vessel are calculated, and the contact forces are determined according to the stiffness of the vessel wall. The same tendency was seen in the trajectories and the contact force of both the experimental and simulated guidewire tips.