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...
Analytical predictions of the seismic response of friction damped timber shear walls
A new concept for the earthquake resistant design of timber shear wall structures is proposed. By providing friction devices in the corners of the framing system of the shear wall, its earthquake resistance and damage control potential can be enhanced considerably. During severe earthquake excitations, the friction devices slip and a large portion of the seismic energy input is dissipated by friction rather than by inelastic deformation of the sheathing-to-framing connectors. A simple numerical model is developed and results of inelastic time-history dynamic analyses show the superior performance of the friction damped timber shear walls compared to conventional shear wall systems. The proposed friction devices act both as safety valves by limiting the inertia forces transmitted to the structure, and as structural dampers by dissipating a significant portion of the seismic energy input. The devices can be used in any configuration of the framing system to accommodate architectural or construction requirements. The damping system may also be conveniently incorporated in existing timber shear wall buildings to upgrade significantly their earthquake resistance.