Rubber material used in seismic isolation systems has a tendency to stiffen in cold climate conditions. Structural responses of rubber based seismic isolation bearings are known to be temperature dependent. The main focus of this research is to investigate the temperature related behavior shifts at a certain type of a rubber based seismic isolation system. This research is a complementary study to a recent experimental study on a newly developed seismic isolator called &ldquo / Ball Rubber Bearing&rdquo / (BRB). BRBs can be easily manufactured as in the case of a standard rubber based bridge bearing and can provide adequate energy dissipation during an earthquake. However, structural response of BRBs at low temperatures has not been examined yet. In this research, behavior of BRBs exposed to different temperatures is examined under combined axial and cyclic lateral load. The performance of the specimens used in this study, &ldquo / Elastomeric Bearing&rdquo / (EB) and &ldquo / Ball Rubber Bearing&rdquo / (BRB) are compared with each other and also with previous researches conducted in this topic. The results indicated that BRBs show better performance at low temperatures in terms of energy dissipation compared to room temperature performance. Big size bearings have higher energy dissipation per cycle compared to small size bearings by reason of size effect. The higher damping percentage is observed at the small size bearings compared to big size bearings due to better confinement of the inner core. As a result of temperature records heat exchange is not detected in the rubber during cyclic loading.

No description available.

2nd International Conference on Advances in Experimental Structural Engineering, Tongji Univ., Shanghai, China, December 4-6, 2007

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17137号 / 工博第3627号 / 新制||工||1551(附属図書館) / 29876 / 京都大学大学院工学研究科都市社会工学専攻 / (主査）教授 小池 武, 教授 杉浦 邦征, 准教授 五十嵐 晃 / 学位規則第4条第1項該当

Seismic isolation systems are widely used to protect reinforced concrete (RC) structures against the effects of strong ground motions. After a magnitude 6.6 earthquake, the outpatient building of Lushan People’s hospital in China remained in good condition due to the seismic isolation technology, while the non-isolated older outpatient building nearby experienced major damage. The building provides a good opportunity to study and assess the contribution of isolation systems to seismic performance of RC structures. In the current research project, the isolated outpatient building was modelled and analyzed using computer software SAP2000. The post-yield behaviour of the structure was modelled by assigning multi-linear plastic links to frame objects. The rubber isolators were represented by rubber isolator link elements, assigned as a single joint element between the ground and the superstructure. The isolated structure was subjected to four earthquake records with increasing intensity. The performances of the isolated structure were compared with those of the fixed-base structures in terms of lateral inter-storey drifts, peak absolute floor accelerations, and residual drifts. The laminated rubber bearings, the high damping isolation devices, composed of rubber bearings and viscous dampers, and the hybrid isolation system of rubber bearings and friction pendulum bearings were analysed. The effectiveness of the three base isolation systems considered in enhancing structural performance was investigated. The results show the level of improvement attained in seismic response by each system. They also illustrate that the rubber bearings coupled with friction pendulum bearings produce the best drift control without causing excessive horizontal displacements at the base level and without adversely affecting floor accelerations.

<p>Seismic isolation has been widely adopted for structural protection. This technique, which introduces a flexible layer between the structure and the support, isolates the structure from earthquake ground motions by lengthening the structural period. The lead rubber bearing (LRB) is one of the most commonly used seismic isolators. The sizes of the rubber bearing and the lead core determine its stiffness and damping characteristics. The parameters, which characterize the seismic performance of a LRB, are the elastic stiffness (k₁), post-elastic stiffness (k₂), yield strength (F_y) and the total weight (w) of the isolated structure. In this study, an assessment of the nonlinear performance of LRB isolators is carried out using a series of spectra, which are referred to as bilinear spectra, as they are based on the bilinear behaviour of LRBs. The LRB parameters are non-dimensionalized using post-to-pre elastic stiffness ratio (n=k₂/k₁) and yield strength to weight ratio (r=F_y/w) to construct the bilinear spectra. Feasible ranges of n and r have been considered according to design code recommendations. The spectra are constructed from statistical analyses of LRB responses due to sets of real earthquake ground motions. These spectra plot the displacement and the shear force response of isolated structures for various combinations of n and r, vs. the elastic period.</p> <p>The results of the study show that displacement decreases as the lead content increases, as expected. However, the corresponding shear forces fluctuate over different isolated periods. An increase in the rubber bearing size increases only the shear response, but has negligible influence on the displacement. It is also found that earthquakes with a lower ratio of PGA/PGV tend to result in higher displacement and shear force responses of the LRB compared to ground motions with higher PGA/PGV ratios.</p> <p>A new chart-based method (referred to as the Chart Method) is developed by using a regression-based bilinear spectrum for estimating the LRB isolator displacement and shear force responses. The design capability of the Chart Method is compared to a more conventional method for designing LRBs, by solving several examples. The study concludes that the Chart Method has improved accuracy and versatility and can be used to evaluate the design suitability of commonly available LRB sizes.</p> / Master of Applied Science (MASc)

In this study influences of vertical ground motion on seismically isolated bridges were investigated for seven different earthquake data. One assessment of bearing effect involves the calculation of vertical earthquake load on the seismically isolated bridges. This paper investigates the influence of vertical earthquake excitation on the response of briefly steel girder composite bridges (SCB) with and without seismic isolation through specifically selected earthquakes. In detail, the bridge is composed of 30m long three spans, concrete double piers at each axis supported by mat foundations with pile systems. At both end of the spans there exists concrete abutments to support superstructure of the bridge. SCBs which were seismically isolated with nine commonly preferred different lead&amp / #8208 / rubber bearings (LRB) under each steel girder were analyzed. Then, the comparisons were made with a SCB without seismic isolation. Initially, a preliminary design was made and reasonable sections for the bridge have been obtained. As a result of this, the steel girder bridge sections were checked with AASHTO provisions and analytical model was updated accordingly. Earthquake records were thought as the main loading sources. Hence both cases were exposed to tri&amp / #8208 / axial earthquake loads in order to understand the effects under such circumstances. Seven near fault earthquake data were selected by considering possession of directivity. Several runs using the chosen earthquakes were performed in order to be able to derive satisfactory comparisons between different types of isolators. Analytical calculations were conducted using well known structural analysis software (SAS) SAP2000. Nonlinear time history analysis was performed using the analytical model of the bridge with and without seismic isolation. Response data collected from SAS was used to determine the vertical load on the piers and middle span midspan moment on the steel girders due to the vertical and horizontal component of excitation. Comparisons dealing with the effects of horizontal only and horizontal plus vertical earthquake loads were introduced.

Simplified methods of analysis described in codes and specifications for seismically isolated structures are always used either directly in special cases or for checking the results of nonlinear response history analysis (RHA). Important predictions for seismically isolated structures by simplified methods are the maximum displacements and base shears of the isolation system. In this study, the maximum isolator displacements and base shears determined by nonlinear RHA are compared with those determined by the equivalent lateral force (ELF) procedure in order to assess the accuracy of the simplified method in the case of bi-directional excitations with near-field characteristics. However, although there are currently many methods for ground motion selection and scaling, little guidance is available to classify which method is more appropriate than the others in any applications. Features of this study are that the ground motions used in analysis are selected and scaled using contemporary concepts and that the ground excitation is considered biv directional. The variations in response of isolated structures due to application of ground motions uni-directionally and bi-directionally are also studied by employing a scaling procedure that is appropriate for the bi-directional analysis. The proposed new scaling methodology is an amplitude scaling method that is capable of preserving the horizontal orthogonal components and it is developed especially for dynamic analysis of isolated structures. Analyses are conducted for two different symmetric reinforced concrete isolated structure for two different soil conditions in structural analysis program SAP2000. Effect of asymmetry in superstructure on isolator displacement is also investigated with further analyses considering 5% mass eccentricity at each floor level. Furthermore, once the significance of the orthogonal horizontal component on the response of isolation system is shown, the biaxial interaction of hysteretic behavior of lead rubber bearings is implemented in OpenSees by developing a subroutine which was not readily available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24220号 / 工博第5048号 / 新制||工||1788(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 五十嵐 晃, 教授 杉浦 邦征, 教授 KIM Chul-Woo / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Isolator displacements, floor accelerations, roof displacements, base shear and torsional moments are basic parameters that are considered in the design of seismically isolated structures. The aim of this study is to evaluate the effects of bidirectional earthquake excitations of near fault records on the response of base isolated structures in terms of basic parameters mentioned above. These parameters computed from nonlinear response history analysis (RHA) and they are compared with the parameters computed from equivalent lateral force procedure (ELF). Effect of asymmetry in superstructure is also examined considering mass eccentricity at each floor level. Torsional amplifications in isolator displacements, floor accelerations, roof displacements and base shear are compared for different level of eccentricities. Two buildings with different story heights are used in the analyses.The building systems are modeled in structural analysis program SAP2000. The scaling of ground motion data are taken from the study of &ldquo / Response of Isolated Structures Under Bi-directional Excitations of Near-fault ground Motions&rdquo / (Ozdemir, 2010). Each ground motion set (fault normal and fault parallel) are applied simultaneously for different range of effective damping of lead rubber bearing (LRB) and for different isolation periods.