An Experimental Study on the Seismic Response of Base-Isolated Secondary Systems

Seismic response of submerged secondary systems in base-isolated structures

Seismic responses of secondary systems in base-isolated structures

The concept of base isolation for equipment is well known. Its application in buildings and structures is rather challenging. Introduction of horizontal flexibility at the base helps in proper energy dissipation at the base level thus reducing the seismic demand of the super structure to be considered during design. The present study shows the results of a series of numerical simulation studies on seismic responses of secondary system (SS) housed in non-isolated and base-isolated primary structures (PS) including equipment-structure interactions. For this study the primary structure consists of two similar single bay three-store reinforced cement concrete (RCC) Frame building, one non-isolated with conventional foundation and another base isolated with Lead plug bearings (LPB) constructed at IIT Guwahati, while the secondary system is modeled as a steel frame. Time period of the base isolated building is higher than the fixed building. Due to the presence of isolator, Acceleration response is significantly reduced in both (X and Y) direction of Building. It have been found that when compared to fixed base building, the base isolated building gives better performance in high seismic prone areas.

In this paper, the effects of shape factors on the buckling loads in the laminated rubber bearing (LRB) are investigated to guide the design of LRB in determination of the rubber plate thickness and the total rubber height. To substantiate the application of LRB to the seismic isolation of nuclear power plants, the seismic analyses and shaking table tests are carried out for a seismically isolated structure using four LRBs. The parameter equations of seismic isolation frequency are obtained from the shaking table tests and the quasi-static tests of LRB itself to investigate the effects of the LRB characteristics in prediction of maximum peak acceleration responses by analysis. From the comparison of the maximum peak acceleration responses obtained from numerical analyses and experiments, it is verified that the horizontal stiffness variations of LRB should be considered in seismic analysis to get more accurate results.

Horizontal Denture: A Prosthodontic Alternative for Severe Maxillary Atrophy

Secondary systems are nonstructural components that serve important functions within a structure, but are not considered as an integral part of the main structural system. There are many categories of secondary systems addressing architectural aspects, mechanical, electrical, communication, water supply and plumbing functions, as well as being part of the structure's content. The main issue regarding the installation of secondary systems in structures placed in seismically prone regions is preservation of their integrity and functionality during earthquake motions, since failure can have dramatic consequences in terms of property losses and safety concerns. This study introduces a new methodology for approximating the seismic response of acceleration‐sensitive secondary systems with a mass lower than 1% of the total mass of the primary structure, and whose seismic excitation derives exclusively from the motion of that structure, that is, interaction phenomena are ignored. The methodology applies to secondary systems installed on regular and flexible primary structures exhibiting floor diaphragm action and quantifies the seismic demand from information based solely on the deflected shape of the structure at the instant it reaches peak seismic response. The methodology can be applied in alternative ways, depending on the required accuracy of the results and on acceptable computational cost, yielding good quality results when compared to those derived from detailed time‐history analyses. Thus, the present methodology signifies a departure from the current state‐of‐design of acceleration‐sensitive secondary building components, which does not fully account for the vibrations of the primary structure. Finally, the accuracy of the methodology is gauged through a number of application examples involving different combinations of primary‐secondary systems.

Recently, there are a lot of technological developments in the earthquake engineering field to reduce structural damage and one of them is a base isolation system. The base isolation system is one of the best technologies for the safety of human beings and properties under earthquake excitations. The aim of this paper is to review previous research works on simulation of base isolation systems for RC buildings and their efficiency in the safety of these buildings. Base isolation decouples superstructure from substructure to avoid transmission of seismic energy to the superstructure of RC buildings. The most effective way to assess the base isolation system for RC building under different earthquake excitations is by conducting experiment work that consumes more time and money. Many researchers had studied the behavior of base isolation system for structure through modeling the behavior of the base isolation in which base isolator is modeled through numerical models and validated through experimental works. Previous researches on the modeling of base isolation systems of structures had shown similar outcomes as the experimental work. These studies indicate that base isolation is an effective technology in immunization of structures against earthquakes.

During the past decade the need to perform nonlinear static and dynamic analyses on bridge structures has increased significantly. Nonlinear dynamic analysis has become the approach that is used when protective systems such as base isolators and isolation systems are present in the bridge structure. The commercial computer programs available that are used for these types of analyses and that can be understood and used by structural bridge engineers have been far from adequate. Recently, the research community has produced a number of useful computer programs. Among these are the IDARC-Bridge and 3D-BASIS family of programs from the State University of New York at Buffalo. Bridge engineers are not usually familiar with the available computer codes primarily used by researchers, and it is generally known that these programs are not user friendly. Prediction of the nonlinear dynamic responses of bridge structures has presented other challenges. These range from the volume of input and output to the computational effort needed to obtain solutions. The increase in computer speed and the use of faster-solution algorithms have drastically reduced the time needed to perform iterative nonlinear dynamic analysis. Use of the Microsoft Windows-based standardized graphical user interface with the ability for the seamless exchange of data between programs makes the volume of input and output manageable. The implementation of 3D-BASIS-ME—type nonlinear base isolators and isolation systems and the analysis methods used in the family of Microsoft Windows-based software LARSA, with which bridge engineers have become familiar over the years using a wide range of applications for bridges and buildings, are presented.

Nonlinear dynamic analysis for multi-storey RC structures with hybrid base isolation systems in presence of bi-directional ground motions

One of the main shortcomings in current base isolation design/practice is lack of adaptability. As a result, a base isolation system that is effective for one type earthquake may become ineffective or may have adverse effect for other earthquakes. The vulnerability of traditional base isolation systems can be exaggerated by two types of earthquakes, i.e. near-field earthquakes and far-field earthquakes. This paper addresses the challenge facing current base isolation design/practice by proposing a new type of seismic isolator for the base isolation system, namely an adaptive seismic isolator. The novel adaptive seismic isolator utilizes magnetorheological elastomer (MRE) for its field-sensitive material property. Traditional seismic isolator design with a unique laminated structure of steel and MRE layers has been adopted in the novel MRE seismic isolator. To evaluate and characterize the behavior of the MRE seismic isolator, experimental testing was conducted on a shake table facility under harmonic cycling loading. Experimental results show that the proposed adaptive seismic isolator can successfully alter the lateral stiffness and damping force in real time up to 37% and 45% respectively. Based on the successful development of the novel adaptive seismic isolator, a discussion is also extended to the impact and potential applications of such a device in structural control applications in civil engineering.

This paper presents a numerical investigation of a smart base isolation system employing magneto-rheological (MR) elastomers or an MR elastomer-based base isolation system. MR elastomers are a new class of smart materials whose elastic modulus or stiffness can be adjusted depending on the magnitude of the applied magnetic field. Hence, they can be used as controllable stiffness elements in engineering systems. The primary goal of this study is to investigate the dynamic performance of the smart base-isolation in mitigating excessive vibrations of a building structure under earthquake loadings. To this end, a five-story shear building model coupled with a smart base-isolation is developed. Using this model, a series of numerical simulations is performed to evaluate the effectiveness of the MR elastomer-based base isolation system under several historic seismic excitations. The results show that the proposed base isolation system outperform the conventional passive-type base isolation system in reducing the responses of the building structure for all seismic excitations considered in this study.

Stochastic prediction of maximum seismic response of light secondary systems

Base isolation is, in recent times, an accepted design philosophy as an earthquake resistant strategy for structural systems and sensitive instruments. Predicting the behavior of laminated rubber bearings, usually obtained from Haringx’s theory, has been developed by many researchers. They have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in past theoretical and experimental studies, the effects of rotation in the bottom and top ends of bearings have been neglected. In this study, an analytical method is presented and formulated by considering the rotation of the top and bottom ends of multilayer rubber bearings, as new boundary conditions. According to these rotations, the horizontal stiffness of laminated rubber bearings, which is the one of the most important characteristics of bearings, will change. Comparisons of theoretical and experimental results show that the present analysis model has a good accuracy for analyzing laminated rubber bearings. Examples are presented to demonstrate the validity of the development method in predicting the horizontal stiffness of laminated elastomeric bearings with specified geometric parameters. The results of this study have shown that the horizontal stiffness of laminated rubber bearings will increase or decrease according different boundary conditions. Key words: Seismic isolation, earthquake engineering, base isolation, elastomeric bearing, laminated rubber bearing, horizontal stiffness.

Sustainable development not only deals with the protection of environment but also with the development that can be sustained for generations. Large part of the world is subjected to earthquake forces, which demands that structural engineers have to design the buildings so that it can withstand the consequence of these earthquakes. In order to mitigate this problem, seismic base isolation technique is used in recent years. In seismic base isolation, laminated rubber bearing (LRB) is the most extensively used technology, because of its fruitfulness and reliability. The principal purpose of seismic isolation is to lessen the seismic demand on structure. Isolation works on the principle of increasing structural time period. Hence decreasing the vulnerability of earthquake demand on the structure. In urban environment, for the purpose to provide parking facility at the ground storey of building, the concept soft storey has taken its place. However, the buildings with soft storey are most vulnerable to earthquake. In Bhuj earthquake (2001), most of the buildings damaged were of soft storey type. This investigation is to find out the efficacy of laminated rubber bearing isolation system in managing the reciprocating action of the soft storey frame model for the installation of isolation system at the top and at the bottom of soft storey column when subjected to El Centro, 1940 ground motion by using state-space method and a comparison is made between structures with and without infill wall. The response behavior in terms of absolute acceleration, inter storey drift, and storey shear have been investigated, for example, building models. With the use of isolation system, storey shear for all storey level is reduced. When LRB is placed at bottom of soft storey column base shear is reduced by 31.91% and absolute top floor acceleration is reduced by 42.23% that of soft storey building with fixed base.KeywordsEarthquake-resistant buildingLaminated rubber bearingSoft storey buildingBase isolation

Shaking table test of space double-layer cylindrical reticulated shell with three-dimensional isolation bearing