A structure with rocking mechanism is able to prolong the period of vibration and reduce seismic internal force. Recent research demonstrated the effectiveness of a tendon made of superelastic ...material wire connected in series with steel wire in controlling the amount of rotation and providing a source of hysteretic energy dissipation, thereby lowering the risk of overturning to a rigid structure undergoing whole‐body rotation. This article proposed to extend the use of superelastic tendon restraint on a (flexible) shear frame to strike a balance between the need to reduce the seismic force demand and the need to exercise control of the overturning risk. Initially, an analytical model for the rocking response of shear frame with the superelastic tendon restraint was developed. In addition, a physical model of the shear frame with tendon restraint was fabricated and tested under base excitations. Analysis results showed to match with experiment on both strain gauge and rotation sensor readings in the dynamic testing. Simulations and tests were also applied to an unrestrained shear frame for comparison. It was also found that the total deflection of the shear frame during the rocking phase could be described as horizontal vibration about a non‐constant balancing deflection. The analytical models developed for flexible rocking systems were extended in the current study to deal with superelastic tendon restrained rocking shear frames. The validity and versatility were confirmed by shaker table test results.
Geotechnical Seismic Isolation (GSI) can be defined as a new category of seismic isolation techniques that involve the dynamic interaction between the structural system and geo-materials. Whilst the ...mechanism of various GSI systems and their performance have already been demonstrated through different research methods, there is a missing link between fundamental research and engineering practice. This paper aims to initiate the development in this direction. A new suite of equivalent-linear foundation stiffness and damping models under the same framework is proposed for four GSI configurations, one of which is a novel combination of two existing ones. The exact solutions for the equivalent dynamic properties of flexible-base systems have also been derived that explicitly include the foundation inertia and the strain-dependent equivalent damping of foundation materials, which are both significant for GSI systems. The application of the proposed analytical design models has been illustrated through response history analyses and a detailed hand-calculation design procedure has also been outlined and demonstrated.
ABSTRACT
Geotechnical seismic isolation (GSI) system involves the dynamic interaction between structure and low‐modulus foundation material, such as rubber‐soil mixtures (RSM). Whilst numerical ...studies have been carried out to demonstrate the potential benefits of GSI‐RSM system, experimental research is indispensable for confirming its isolation mechanism and effectiveness in reducing structural demand. In this regard, centrifuge modelling with an earthquake shaker under an acceleration field of 50 g adopted in this study can mimic the actual nonlinear dynamic response characteristics of RSM and subsoil in a coupled soil‐foundation‐structure system. This is the first time the performance of GSI‐RSM system was examined in a geotechnical centrifuge. It was found that an average of 40‐50% reduction of structural demand can be achieved. The increase in both the horizontal and rotation responses of the foundation was also evidenced. The unique augmented rocking mechanism with reversible foundation rotation was highlighted.
The innovative concept of geotechnical seismic isolation (GSI) system with the use of a continuous layer of low-modulus materials, such as rubber-soil mixtures (RSM), surrounding the foundation of ...structure has attracted considerable research interest on its performance at both system and material levels, since it was first proposed over a decade ago. The performance of the GSI system has been studied through a number of numerical, physical and hybrid modeling techniques; but due to the complexity of the problem, the isolation mechanism has not been thoroughly investigated. Hence, this article aims at initiating this aspect of development. A simple and efficient lumped-parameter analytical model is developed for analyzing the dynamic soil-foundation-structure interaction (SFSI) of the GSI system. Considering the importance of various nonlinearities involved, a theoretical approach for estimating effective shear strain is derived for capturing the nonlinearity of subsurface materials by the equivalent-linear method. The effectiveness of the analytical model is then demonstrated through a representative case study, based on which the main features of the isolation mechanism are investigated. The seismic isolation capability of the GSI system is founded on the reduced lateral stiffness of the RSM layer and the lower modulus of RSM that reduces the rocking stiffness. The proposed system could take advantage of the rocking isolation mechanism with reversible foundation deformations due to the higher elasticity of the RSM material.
•First lumped-parameter analytical model for geotechnical seismic isolation system.•Nonlinearity of subsurface material incorporated in soil-foundation-structure model.•New theoretical approach for estimating effective shear strain in equivalent-linear method.•Demonstrated and explained the mechanism of GSI system through case study.
AbstractDesigning a fully modular building, which is without the support of any separate lateral resisting elements, has the advantage of rapid site assembly, but runs the risk of a brittle style of ...connection failures in a rare earthquake event. Thus, this form of construction is currently limited to low-rise buildings. Isolating the building from its base and allowing the rocking motion to occur has been proven to be effective in dissipating energy and prolonging the natural periods by the lifting of the structure, thereby alleviating high strength demand on the building itself. To avert overturning, the amount of the rotation of the building needs to be controlled, and the use of superelastic tendons as a restraint is a promising solution. Previous studies into the seismic performance with this novel form of construction have been limited to experimenting with a rigid block or a single lumped mass system. In this study, this approach of seismic isolation is extended to a high-rise modular building with distributed mass and stiffness. A scaled-down model of a 19-story fully modular building, which was partially restrained by superelastic tendons, was tested on a shaking table. The key objective was to study the deflection profile and distribution of internal forces up the height of the superelastic tendon–restrained building and examine the contributions by the higher modes. The internal forces predicted by the analytical model developed in the study are shown to be in good agreement with experimental measurements.
Practical ApplicationsModular construction shortens construction time and reduces environmental impacts. Currently, fully modular buildings, which have a high degree of prefabrication, are limited to low-rise constructions because of concerns over the overturning risk in major earthquake events. A new seismic safe design employing a superelastic tendon is introduced in this article to extend fully modular construction to high-rise buildings. The building is designed to rotate about its base when subjected to high intensity ground shaking. The amount of rotation is controlled by the superelastic tendon in order to avoid overturning from occurring. Meanwhile, internal forces taken up by the structural elements within the building were kept much lower than a conventional fixed base building. The dynamic testing of the miniature model of a 19-story building on the shaking table was featured in the study, which laid down principles that are essential for the formulation of effective guidelines for the structural design of this type of building.
This article introduces an innovative system for enhancing the seismic performance of a structure through facilitating large rotational (rocking) motion to occur without risking overturning. The ...innovation of this study is in the use of tendons consisting of Nickel‐Titanium (superelastic) alloy connected in series with steel to impose partial restraints to the structure when experiencing rocking motion. Importantly, the large rotational motion is fully recoverable. Existing installations which can be made to rock may also be retrofitted with the device for improving its seismic resistance. The original contributions of the article are the derivation, and experimental validation, of an analytical model for simulating the seismic performance of a system that has been fitted with the restraining device. In a parametric study employing the newly developed modelling techniques, major trends in the seismic response behaviour of the structure have been identified.
In regions of low-to-moderate seismicity where representative strong motion data is lacking, the modelling of seismic hazard relies on the use of seismological models. This paper presents a set of ...expressions that can be used as ground motion prediction equations that have been transformed from seismological models which resolve the generation of seismic waves into several components. The feature of this presented set of expressions is that it can be adapted to represent earthquake ground motion behaviour that is defined by a diversity of seismological models. The motivation behind the development of the presented adaptive predictive relationship which is known as the Component Attenuation Model (CAM) was to fast track, and make transparent, the transformation from seismological models to predictions of response spectral values for engineering applications. Thus, CAM can be used to waive away the need of executing any software for undertaking stochastic simulations nor time-history analyses for calculation of the response spectral ordinates. An important and original, the feature of CAM is incorporating the shear wave velocity profile of the bedrock and the associated upper-crustal modification into the model. This article presenting CAM is essentially a contribution to engineering as opposed to seismology. The potential benefits derived from the fast-tracking can be considerable given that the transformation is seldom a one-off process and would need to be repeated for any given targeted area, in view of uncertainties surrounding seismological conditions of the earth crust around the globe.
Sustainability necessitates the protection of infrastructure from any kind of deterioration over the life cycle of the asset. Deterioration in the capacity of reinforced concrete (RC) infrastructure ...(e.g., bridges, buildings, etc.) may result from localised damage sustained during extreme loading scenarios, such as earthquakes, hurricanes or tsunamis. In addition, factors such as the corrosion of rebars or ageing may also deteriorate or degrade the capacity of an RC column, thereby necessitating immediate strengthening to either extend or ensure its design life is not limited. The aim of this paper is to provide a state-of-the-art review of various strengthening and repair methods for RC columns proposed by different researchers in the last two decades. The scope of this review paper is limited to jacketing techniques for strengthening and/or repairing both normal- and high-strength RC columns. The paper also identifies potential research gaps and outlines the future direction of research into the strengthening and repair of RC columns.
PDF