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.
Rocking Timber Structure with Slip-Friction Connectors Conceptualized As a Plastically Deformable Hinge within a Multistory Shear Wall
AbstractRecent experiments on a 2.44×2.44  m rigid timber wall panel with slip-friction connectors have demonstrated the feasibility of enabling elastoplastic behavior in structures that would otherwise be essentially rigid. The slip-friction connectors are adopted as the hold-downs that anchor the ends of the wall to the foundation. These replace the traditionally used steel bracket hold-downs, which relied on inelastic damage to the screw or nail connections for energy dissipation. Overturning resistance of the wall directly relates to the slip-force in the slip-friction connectors. On the slip-force being reached, the intention is that the wall rocks in a controlled manner. A numerical study demonstrates the energy dissipation advantages of this approach. A direct-displacement-based design procedure is proposed for a multistory wall with slip-friction connectors. The wall is numerically modeled, and its response to earthquake time-history loadings compared with that of an idealized structure with a sin...
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.