H σεισμική μόνωση στις γέφυρες συνδυάζει δύο φαινόμενα: (α) αύξηση της θε-μελιώδους ιδιοπεριόδου του συστήματος, και (β) προσθήκη αυξημένης απόσβεσης στο σύστημα. Το πρώτο επιτυγχάνεται με την εισαγωγή εύκαμπτων εφεδράνων ή εφεδράνων ολίσθησης στην επιφάνεια μόνωσης. Το δεύτερο επιτυγχάνεται είτε με την εισαγωγή α-ποσβεστήρων με ιξώδη συμπεριφορά, είτε με τη χρήση ελαστοπλαστικών μονωτήρων, είτε με τη χρήση εφεδράνων αυξημένης ικανότητας απόσβεσης (π.χ. εφέδρανα με πυρή-να μόλυβδου LRB, εφέδρανα τριβής με επίπεδη ή σφαιρική επιφάνεια - FPS, εφέδρανα με ελαστομερή υψηλής απόσβεσης - HDRB). Σε πολλές χώρες υψηλής σεισμικότητας και υψηλής στάθμης αντισεισμικής τε-χνολογίας (π.χ. στην Ιταλία) δεν συνηθίζεται, ούτε επιτρέπεται, η χρήση κοινών ελαστομερών εφεδράνων για την επίτευξη του πρώτου από τα δύο ανωτέρω φαινόμε-να/αποτελέσματα. Μάλιστα, η σεισμική μόνωση θεωρείται ότι πρέπει να συνδυάζει και τα δύο φαινόμενα/ αποτελέσματα με χρήση ειδικών προς τούτο συσκευών. Αντίθετα, στις ΗΠΑ και στην Ελλάδα συνηθίζεται, και επιτρέπεται, η χρήση κοινών ελαστομεταλλικών εφεδράνων για την επίτευξη του πρώτου αποτελέσματος, με ή χωρίς πρόσθετη απόσβεση μέσω ειδικών αποσβεστήρων. Γενικότερα, η σχέση μεταξύ των δύο φαινόμενων δεν προσδιορίζεται στους κα-νονισμούς, παρόλο που επηρεάζει τόσο την ασφάλεια της κατασκευής όσο και την απο-τελεσματικότητα του συστήματος μόνωσης. Για τον λόγο αυτό διενεργήθηκε μια σειρά δοκιμών, με την ψευδοδυναμική μέθοδο, γεφυρών μονωμένων με διάφορα εύκαμπτα ε-φέδρανα (ειδικά ή κοινά). Τα κοινά εφέδρανα δοκιμάσθηκαν με ή χωρίς πρόσθετη από-σβεση μέσω ειδικών αποσβεστήρων. / -

Seismic base isolation has become an increasingly common approach to reduce earthquake induced losses. Base isolation aims to decouple structures, such as buildings or bridges, from strong ground motions through the introduction of a flexible layer, typically located at the foundation. Base isolation is a well-established concept and accepted as an effective method of protecting both the structure and its contents from damage due to earthquakes. Elastomers are ideal for base isolation due to their soft material properties and ability to undergo large recoverable strains. Steel-reinforced elastomeric isolators (SREIs) have been widely applied as base isolators; however, the weight and cost of SREIs have been perceived as barriers to the widespread application of base isolation. In order to alleviate these concerns, it has been proposed that the steel reinforcement could be replaced with lighter fiber reinforcement with similar tensile properties as steel. Recent investigations have demonstrated that fiber-reinforced elastomeric isolators (FREIs) are viable and have desirable characteristics. An additional proposed cost saving measure was to place the FREI unbonded between the upper and lower supports. The combination of the flexible fiber reinforcement and the unbonded application resulted in a unique rollover deformation under horizontal displacement. Rollover causes a nonlinear force-displacement relationship characterized by a softening and stiffening phase. This nonlinear relationship is believed to be advantageous and to allow the performance of the device to be tailored to the earthquake hazard level. This work investigates the adaptive characteristics of unbonded FREIs. It is demonstrated that the softening and stiffening characteristics of the isolator can be altered through modifications to the isolator or to the surrounding support geometry. Equations are developed to predict the horizontal force-displacement relationship. Furthermore, simple expressions appropriate for use in building and bridge design codes are proposed for critical isolator properties. Potential limitations introduced due to the unbonded application are identified and addressed through the development of a new partially bonded hybrid isolator. It is demonstrated that unbonded FREIs are highly versatile and a potentially competitive device appropriate for widespread application in developed and developing countries. / Thesis / Doctor of Philosophy (PhD) / Earthquakes remain a significant and potentially devastating threat to both developed and developing countries. Structural elements within a building, such as beams and columns, must deform considerably to accommodate the relative floor displacements that develop due to ground motion. Conventional construction materials are not capable of undergoing these large deformations without irreversible and potentially catastrophic damage. The introduction of a flexible layer at the foundation level of a structure, using elements known as isolators, can dramatically reduce damage. The deformation is concentrated at the flexible layer, which can undergo large displacements without any damage. This concept, known as base isolation, protects both the structure and its contents. Traditional isolators are expensive, thus far hindering the application of base isolation systems. A novel isolator design has been proposed that has the potential for widespread economical application. To increase the application, building codes need to be developed, requiring substantial research on the isolator properties. A key component of the novel isolator is the ability to alter the isolator geometry to further enhance the response. This is validated through experimental testing and complex computer models.

A new seismic isolation system for steel building structures based on the principle of mass isolation is introduced. In this system, isolating interfaces are placed between the lateral-load-resisting sub-system and the gravity-load-resisting sub-system. Because of the virtual decoupling existing between the two structural sub-systems, the gravity-load resisting one is susceptible to instability. Due to the fact that the provided level of isolation from the ground is constrained by the stability requirements of the gravity-load resisting structure, the system is named stability-dependent mass isolation (SDMI). Lyapunov stability and its association with energy principles are used to assess the stable limits of the SDMI system, its equilibrium positions, the stability of the equi-librium positions, and to propose a series of design guidelines and equations that allow the optimal seismic performance of the system while guaranteeing the restoration of its undistorted position. It is mathematically shown that the use of soft elastic interfaces, between the lateral- and gravity-load-resisting sub-systems, can serve the dual role of stability braces and isolators well. The second part of the document is concerned with the analytical evaluation of the seismic performance of the SDMI method. First, a genetic algorithm is used to find optimized SDMI building prototypes and, later, these prototypes are subjected to a series of earthquake records having different hazard levels. This analytical testing program shows that, with the use of SDMI, not only can structural failure be avoided, but a dam-age-free structural performance can also be achieved, accompanied by average reductions in the floor accelerations of ca. 70% when compared to those developed by typical braced-frame structures. Since the SDMI system is to be used in conjunction with viscous energy dissi-paters, the analytical testing program is also used to determine the best places to place the dampers so that they are most effective in minimizing the floor accelerations and controlling the floors’ drift-ratios. Finally, recommendations on continuing research are made.

In this research, the dynamic behavior of a seismic isolation system composed of high strength geotextile placed over an ultra-high molecular weight polyethylene (UHMWPE) geomembrane (together called as composite liner) beneath the structure is investigated experimentally. The results of the shaking table experiments which were performed on model structures both under harmonic and modified earthquake motions with and without the seismic isolation (composite liner system), are presented in the thesis. The main focus is given on the potential improvement obtained by use of the composite liner system as compared to the unisolated cases. Based on the performed experiments, it is observed that the utilization of composite liner system provides significant reduction in the accelerations and interstorey drift ratios of structures under harmonic motions while signifant drop is obtained in the spectral accelerations under earthquake motions which provide noticeable improvement in the durability of structures under dynamic effects at the expense of increased translational displacements.

The damaging effects of strong ground motions on highway bridges have revealed the limitations of conventional design methods and emphasized the need for innovative design concepts. Although seismic isolation systems have been proven to be an effective method of improving the response of bridges during earthquakes, the performance of base-isolated structures during near-field earthquakes has been questioned in recent years. Near-field earthquakes are characterized by long period and large- velocity pulses. They amplify seismic response of the isolation system since the period of these pulses usually coincides with the period of the isolated structures. This study explores the feasibility and effectiveness of shape memory alloy (SMA)-based isolation systems in order to mitigate the response of bridge structures against near-field ground motions. SMAs have several unique properties that can be exploited in seismic control applications. In this work, uniaxial tensile tests are conducted first to evaluate the degree to which the behavior of SMAs is affected by variations in loading rate and temperature. Then, a neuro-fuzzy model is developed to simulate the superelastic behavior of SMAs. The model is capable of capturing rate- and temperature-dependent material response while it remains simple enough to carry out numerical simulations. Next, parametric studies are conducted to investigate the effectiveness of two SMA-based isolation systems, namely superelastic-friction base isolator (S-FBI) system and SMA/rubber-based (SRB) isolation system. The S-FBI system combines superelastic SMAs with a flat steel-Teflon bearing, whereas the SRB isolation system combines SMAs with a laminated rubber bearing rather than a sliding bearing. Upon evaluating the optimum design parameters for both SMA-based isolation systems, nonlinear time history analyzes with energy balance assessment are conducted to compare their performances. The results show that the S-FBI system has more favorable properties than the SRB isolation system. Next, the performance of the S-FBI systems is compared with that of traditional isolation systems used in practice. In addition, the effect of outside temperature on the seismic response of the S-FBI system is assessed. It is revealed that the S-FBI system can successfully reduce the response of bridges against near-field earthquakes and has excellent re-centering ability.

In this study, seismic roof isolation solutions were investigated with a case study of Halkapinar Gymnasium, izmir. In the first part, seismic isolation was explanied and philosophy behind it was given. In the second part, existing seismic roof isolators, elastomeric bearing and viscous damper, were investigated with different support isolation combinations. In the third part, two more types of seismic isolators, lead rubber bearing and friction pendulum isolators, were also analyzed by using the same model and all results were compared with each other and that of non-isolated roof system. Furthermore, bilinear effect of the non-linear isolators were also studied. Finally, all results were compared with each other considering structure responses and effectiveness of the seismic isolators. It has been tried to find the most efficient seismic isolation solution for Halkapinar Gymnasium.

<p>The rolling isolation system (RIS) studied in this dissertation functions on the principle of a rolling pendulum; an isolated object rests on a steel frame that is supported at its corners by ball-bearings that roll between shallow steel bowls, dynamically decoupling the floor motion from the response of the object. The primary focus of this dissertation is to develop predictive models that can capture experimentally-observed phenomena and to advance the state-of-the-art by proposing new isolation technologies to surmount current performance limitations. To wit, a double RIS increases the system's displacement capacity, and semi-active and passive damped RISs suppress the system's displacement response.</p><p>This dissertation illustrates the performance of various high-performance isolation strategies using experimentally-validated predictive models. Effective modeling of RISs is complicated by the nonholonomic and chaotic nature of these systems which to date has not received much attention. Motivated by this observation, the first part of this dissertation addresses the high-fidelity modeling of a single, undamped RIS, and later this theory is augmented to account for the double (or stacked) configuration and the supplemental damping via rubber-coated bowl surfaces. The system's potential energy function (i.e. conical bowl shape) and energy dissipation model are calibrated to free-response experiments. Forced-response experiments successfully validate the models by comparing measured and predicted peak displacement and acceleration responses over a range of operating conditions.</p><p>Following the experimental analyses, numerical simulations demonstrate the potential benefits of the proposed technologies. This dissertation presents a method to optimize damping force trajectories subject to constraints imposed by the physical implementation of a particular controllable damper. Potential improvements in terms of acceleration response are shown to be achievable with the semi-active RIS. Finally, extensive time-history analyses establish how the undamped and damped RISs perform when located inside biaxial, hysteretic, multi-story structures under recorded earthquake ground motions. General design recommendations, supported by critical-disturbance spectra and peak-response distributions, are prescribed so as to ensure the uninterrupted operation of vital equipment.</p> / Dissertation

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16821号 / 工博第3542号 / 新制||工||1535(附属図書館) / 29496 / 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 竹脇 出, 准教授 五十嵐 晃 / 学位規則第4条第1項該当

<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)

During strong ground motions, structures equipped with base isolation systems have been shown to have their seismic demand significantly reduced, mitigating adverse effects such as damage and loss of life. More recently, the fiber-reinforced elastomeric isolator (FREI) has been investigated as a relatively new type of isolator for the base isolation of structures. Constructed from alternating layers of elastomer and carbon-fiber cloth, FREI can be produced in large pads that can be cut to any desired size and shape when required. In bridges, FREI can to be used in an unbonded application (U-FREI) by placing them between the bridge deck and the piers. Experimental and numerical investigations have shown U-FREI as a viable option for the isolation of bridges. However, experimental studies have been limited to room temperature testing. In North America, climates vary drastically across the continent. Northern climates, such as those existent in Canada, are capable of reaching extremely low temperatures. Thus, base isolated bridges in these regions require isolation systems that perform adequately at cold temperatures. The studies presented in this dissertation have been completed in order to investigate the effects that low temperatures have on U-FREI used in bridge structures. An experimental program was conducted that evaluated the behaviour of U-FREI. It was found that U-FREI performed adequately under lateral displacements expected during a seismic event, and provided acceptable response under vertical and rotational testing that is typical of normal bridge operation. Using these results, a numerical model for U-FREI was then updated to account for the effects of low temperature. The model was combined with a bridge model to evaluate the seismic response of a bridge structure isolated with U-FREI subjected to low temperatures. A substantial reduction in seismic demand was achieved, even under the most severe conditions tested. / Thesis / Master of Applied Science (MASc)