Rocking Pier Research Articles

Seismic performance of a rocking bridge pier substructure with frictional hinge dampers

The rocking pier system (RPS) allows the columns to rock on beam or foundation surfaces during the attacks of a strong earthquake. Literatures have proved that seismic energy dissipated by the RPS through the column impact is limited. To enhance the energy dissipation capacity of a RPS bridge substructure, frictional hinge dampers (FHDs) were installed and evaluated by shaking table tests. The supplemental FHDs consist of two brass plates sandwiched by three steel plates. The strategy of self-centering design is to isolate the seismic energy by RPS at the columns and then dissipate the energy by FHDs at the bridge deck. Component tests of FHD were first conducted to verify the friction coefficient and dynamic characteristic of the FHDs. In total, 32 shaking table tests were conducted to investigate parameters such as wave forms of the earthquake (El Centro 1940 and Kobe 1995) and normal forces applied on the friction dampers. An analytical model was also proposed to compare with the tested damping of the bridge sub-structure with or without FHDs.

Seismic performance of a rocking bridge pier substructure with frictional hinge dampers

The rocking pier system (RPS) allows the columns to rock on beam or foundation surfaces during the attacks of a strong earthquake. Literatures have proved that seismic energy dissipated by the RPS through the column impact is limited. To enhance the energy dissipation capacity of a RPS bridge substructure, frictional hinge dampers (FHDs) were installed and evaluated by shaking table tests. The supplemental FHDs consist of two brass plates sandwiched by three steel plates. The strategy of self-centering design is to isolate the seismic energy by RPS at the columns and then dissipate the energy by FHDs at the bridge deck. Component tests of FHD were first conducted to verify the friction coefficient and dynamic characteristic of the FHDs. In total, 32 shaking table tests were conducted to investigate parameters such as wave forms of the earthquake (El Centro 1940 and Kobe 1995) and normal forces applied on the friction dampers. An analytical model was also proposed to compare with the tested damping of the bridge sub-structure with or without FHDs.

Centrifuge modeling of rocking-isolated inelastic RC bridge piers.

Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil-footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking-isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self-centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism, exhibiting significant resistance to cumulative damage. Thanks to such mechanisms, the rocking pier survived, with no signs of structural distress, a deleterious sequence of seismic motions that caused collapse of the conventionally designed pier. © 2014 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.

Bidirectional Seismic Behavior of Controlled Rocking Four-Legged Bridge Steel Truss Piers

The behavior and design of four-legged controlled rocking bridge steel truss piers to three components of seismic excitation are presented in this paper. The controlled rocking approach for seismic protection allows a pier to uplift from its base, limiting the force demands placed on the bridge pier and deck, and can allow the structure to remain elastic during an earthquake, preventing damage toward the goal of keeping the bridge operational immediately following the earthquake. Passive energy dissipation devices [steel yielding devices (SYDs) or fluid viscous dampers (VDs)] are used at the uplifting location to control pier response. The bidirectional kinematic and hysteretic cyclic behavior of controlled rocking piers with SYDs is presented and verified with nonlinear static pushover analysis. This fundamental behavior is used to develop design equations to predict peak pier displacements, uplifting displacements, and forces (frame shear and leg axial force). Dynamic response history analyses are performed, compared with the design equations, and shown to provide reasonably accurate results for design. The use of fluid VDs in the controlled rocking system is then discussed.

Seismic Strengthening of Rocking-Critical Masonry Piers

Systems of discrete wall piers and spandrels created by large openings are particularly weak in resisting in-plane lateral loads. The rocking piers thus stabilized by hold-down vertical forces have excellent strength, stiffness, and ductility in a very stable manner for a safer and better performance under lateral loads. However, the undesirable compressive mode of failure of stabilized rocking piers at larger drifts can be eliminated by the use of yielding energy dissipation device to limit the forces in verticals and thereby the compression force in rocking piers. A displacement-based design procedure can be used to design the energy dissipation devices and other stabilizing elements. A simple mechanics model is developed for the nonlinear load–deformation relationship of the stabilized piers which is accurate enough for design purposes. This performance-based design scheme rationally accounts for the superior ductility and energy dissipation characteristics of strengthened rocking piers.

Seismic isolation of viaduct piers by means of a rocking mechanism

Rocking mechanism can be an effective means of seismic isolation, despite the fact that it is rarely conceived a possible alternative. In this study, the feasibility of utilizing a rocking mechanism for earthquake protection of slender viaduct pier structures is explored both analytically and experimentally. With a discontinuous interface between the pier footings and the underlying pile caps, a rocking system is designed to rock intermittently as the seismic overturning moment exceeds the restoring moment provided by gravity. During the rock mode, the resisting flexural moment in the pier is released while the earthquake load is counteracted by the rotational inertia with respect to the supporting foot, thus preventing the columns from yielding. Analytical modelling of this non-linear dynamic system is derived with a numerical procedure developed based on the fourth-order Runge–Kutta–Nystrom method. A series of tests including the free rocking and seismic performance test, has been conducted using a 1:50 scaled-down model structure of a typical viaduct pier system. Both analytical and experimental results show that the rocking pier system (RPS) for seismic protection of viaduct pier structures is effective and stable, and the stronger the earthquake intensity the more pronounced the control efficiency. The concept of using rocking mechanism for seismic isolation of viaduct pier structures has been demonstrated feasible and promising. Nevertheless, practical issues such as prevention of overturning, foot damage due to impact, or possible sliding of the pier following impact need to be carefully dealt with in the design aspect. Copyright © 2006 John Wiley & Sons, Ltd.

Seismic Strengthening of Unreinforced Masonry Piers with Steel Elements

The system of wall piers and spandrels, created by openings, largely controls the inplane lateral resistance of the wall. For the “rocking-critical” masonry wall piers, the overall hysteretic behavior can be significantly improved by installing a steel framing system consisting of vertical and horizontal elements around the wall — without any braces. Vertical elements provide the necessary hold-down forces to stabilize the rocking piers. The stabilized piers “rocked” through a number of cycles of large displacements (up to 2.5%) without crumbling or shattering, displaying a ductile response. The strengthened system has excellent strength, stiffness and ductility, despite the brittleness of the masonry because of considerable load sharing between the existing masonry and the added steel elements. FE analyses predicted the envelope response of the rocking piers accurately. A simple mechanics based model was developed to predict the load-deflection behavior of a stabilized rocking pier which can be used to design the strengthening system more rationally.