Highway bridges are considered to be one of the most susceptible constituents of transportation networks when they are subjected to severe natural hazards such as earthquakes and environmental exposures like subfreezing temperatures. To facilitate and enhance pre-hazard event mitigation and post-hazard emergency response strategies, probabilistic risk assessment methodologies have attracted increased attention, recently. Seismic fragility assessment is one of the probabilistic techniques which predicts the damage risk of the structure for a given hazard level. While fragility curves can be developed using different methods, such as expert-based, empirical, experimental, analytical, and hybrid, analytical fragility curves are perceived to be the most reliable and least biased technique. Seismic isolation systems are prevalently used in bridge structures to mitigate the damage risk of bridge components against natural hazards. However, the effectiveness of implementing recently emerged isolators such as Stable Unbonded Fiber Reinforced Elastomeric Isolators (SU-FREI) should be examined by developing analytical fragility curves of retrofitted bridges and quantifying the mitigation in the damage probability of different bridge components. In this regard, incorporating the Soil-Structure Interaction (SSI) is critical since the lateral response of bridges relies on the relative stiffness of bridge components, such as columns and isolators and the supporting soil. In addition, all bridge components are exposed to environmental stressors like subfreezing temperature that can alter the seismic response of bridges. In the first phase of this thesis, a seismic fragility assessment is carried out on an existing multi-span continuous reinforced concrete bridge. Two bridge representations are developed to simulate the as-built bridge along with its retrofitted counterpart utilizing SU-FREI. An Incremental Dynamic Analysis (IDA) is conducted using 45 synthetic ground motion records developed for eastern Canada and damage limit states are applied to generate fragility curves and determine the probability of damage to different bridge components. Bridges are analyzed in longitudinal and transverse directions, independently, and component- and system-level fragility curves are developed. In the second phase, the previously generated bridge models are expanded to incorporate the SSI effects by introducing the pile groups under piers and abutments. Several interactions including deck-abutment, abutment-embankment, pile-soil, and pile-soil-pile interactions are considered. A significant challenge in this phase is the accurate simulation of the lateral and vertical behavior of pile groups since all pile groups comprised of closely-spaced vertical and battered piles. A ground motion suite consisting of 45 ground motions has been selected, which reflects the seismicity of the bridge site. IDA is conducted to monitor the seismic performance of the bridge from the elastic linear region up to collapse. Fragility curves, which serve as an important decision-support tool have been developed to identify the potential seismic risk of the bridge. In the third phase, a multi-hazard assessment is carried out by conditioning the previously developed bridge models (i.e. monolithic fixed-base, isolated fixed-base, monolithic with SSI, and isolated with SSI) to a range of room and subfreezing temperatures and applying a seismic excitation, simultaneously. The cold temperature behavior of the constitutive materials of different bridge components, namely, concrete, reinforcing steel, rubber, and the supporting soil are studied and reflected in the bridge models. IDA is performed and damage potential of different bridge components are quantified. In summary, it is demonstrated that SU-FREI is a competing alternative for seismic isolation of bridges by offering potentially less manufacturing time and cost, lower weight, and easier installation which is an attractive feature for accelerated bridge construction applications. In all three phases, it is shown that the bridges which are isolated using SU-FREI have improved seismic performance in comparison with monolithic bridges by exhibiting lower probability of damage to the primary bridge components like columns and pile caps and transferring the damage to less important components such as abutments at which damage does not cause bridge closure. In addition, it is shown that seismic isolation using SU-FREI can effectively mitigate the seismic demand and damage potential of the constitutive components of a bridge supported by weak soil. While occurrence of seismic events along with an environmental stressor such as cold temperature can drastically jeopardize the functionality of a bridge supported by weak soil, it is demonstrated that seismic isolation using SU-FREI can significantly alleviate the probability of damage to bridge components. / Dissertation / Doctor of Philosophy (PhD)

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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)

In this thesis, a process is developed for designing elastomeric vibration isolators in order to provide vibration isolation for sensitive equipment being used in ROKETSAN A.S.&rsquo / s products. For this purpose, first of all, similar isolators are examined in the market. After that, appropriate elastomeric materials are selected and their temperature and frequency dependent dynamic properties are experimentally obtained. Parametric finite element model of the isolator is then constituted in ANSYS APDL using the properties of elastomeric materials and the conceptual design of the isolator. Then, according to design requirements, final design parameters of the vibration isolator are determined at the end of design iterations. In the next step, vibration isolator that was designed is manufactured using the elastomeric material chosen, by a local rubber company. Finally, design process is verified by comparing analysis and test results.

<p> Steel-reinforced elastomeric isolator (SREI) bearings are currently the most commonly used type of seismic isolators. However, high manufacturing and associated installation costs prohibit their application in ordinary residential and commercial buildings. Fiber-reinforced elastomeric isolator (FREI) bearings are comprised of alternating layers of elastomer bonded to fiber-reinforcement layers. Research studies have shown that FREI bearings can be used as an alternative to SREI-bearings with comparable performance.</p> <p> FREis are much lighter in weight than traditional SREIs. In addition, their manufacturing cost can be lower, if individual FREI bearings, with the required size, are cut from a large sheet or a long strip, fabricated through mass production manufacturing techniques. An appealing application which simplifies the installation of FREI bearings is when they are placed between the substructure and superstructure with no bonding at their contact surfaces. This specific application is denoted as "unhanded application".</p> <p> When an unbonded FREI bearing is deformed laterally, it shows "rollover deformation" due to lack of flexural rigidity in the fiber-reinforcement sheets. The rollover deformation, as a beneficial feature, reduces the lateral stiffness of the bearing and enhances its seismic isolation efficiency, compared to the same bearing employed with bonded contact surfaces. However, it is important that the bearing is properly sized to maintain its lateral stability and hence exhibit ''stable rollover" (SR) deformation. Such a bearing is termed in this thesis as "stable unbonded" (SU)-FREI bearing.</p> <p> The main objectives of this research were to investigate the influence of geometry on the lateral response behavior of unbonded FREI bearings, and to evaluate the feasibility of employing SU-FREI bearings for seismic mitigation of low-rise buildings. The first objective was accomplished by conducting an experimental study on full-scale square FREI bearings. To achieve the latter objective a shake table study was performed on a 1/4 scale 2-storey steel frame which was seismically isolated with 1/4 scale SU-FREI bearings. The mechanical properties, including vertical and lateral stiffnesses and effective damping, of prototype samples of the 1/4 scale SU-FREI bearings were evaluated by vertical compression testing and cyclic lateral shear (under constant compression) testing. In addition, the influence of parameters such as lateral displacement amplitude and rate, amplitude history, and variations in the vertical pressure on the lateral response of the 1/4 scale SU-FREI bearings, were investigated.</p> <p> It was found that for FREI bearings having identical material properties and shape factor (the plan area of the bearing divided by the perimeter area of a single elastomer layer) the aspect ratio (length to total height of the bearing, also called second shape factor) plays an important role in achieving stable lateral response. All tested prototype 1/4. scale SU-FREI bearings exhibited SR-deformation with sufficient lateral flexibility and damping. Lateral response was found to be nonlinear and dependent on the amplitude and history of lateral displacement. However, due to the application of a relatively low design vertical pressure of 1.6 MPa, the influence of ±50% variation in the design vertical pressure on the lateral response was found to be insignificant. Lateral displacement capacity of the SU-FREI bearings was attained when their originally vertical faces fully contacted the upper and lower horizontal supports. This was accompanied with a significant increase in the lateral stiffness of the bearings which maintains the overall stability of the bearing to unexpectedly large ground motions. Shake table tests clearly demonstrated that SU-FREI bearings were efficient in seismic mitigation of the test-structure.</p> <p> The final component of this thesis involves investigating the applicability of two simplified analytical models in seismic response prediction of a base isolated structure. The two models use different techniques to simulate the lateral load-displacement hysteresis loops of prototype SU-FREI bearings which are obtained from cyclic shear tests (under constant compression). Model 1 includes the rate and the amplitude of bearings' lateral displacements to simulate the hysteresis loops through a multi-parameter curve fitting function. Model 2 uses bilinear idealization to simulate the hysteresis loops. Due to the highly nonlinear lateral response of SU-FREI bearings, these models utilize an iterative time history analysis approach to improve their accuracy. Comparisons with shake table results of a 1A scale structure show that both models can be used in response prediction of ordinary structures which are seismically isolated with SU-FREI bearings.</p>. / Thesis / Doctor of Philosophy (PhD)

<p>Seismic isolation is a seismic design philosophy that aims to reduce the demand on structures as opposed to increasing their capacity to endure forces. Seismic isolation can be achieved by placing isolating bearings with relatively low stiffness compared to the structure itself beneath the superstructure. This low stiffness layer increases the structural period, shifting the structure into a period range of low seismic energy content.</p> <p>The objectives of this research were to investigate the dynamic properties, durability and limitations of stable unbonded fibre reinforced elastomeric isolator (SU-FREI) bearings. Vertical compression testing indicated the bearings possessed adequate vertical stiffness. Due to lack of bonding at the bearing interface surfaces rollover deformation was observed to occur during lateral cyclic testing. This response behaviour was found to result in advantageous effective lateral stiffness and damping properties. The bearings maintained stability during rollout testing while serviceability and fatigue testing both conformed to code specified test specimen adequacy limitations. Experimental shake table testing showed that the isolated structure behaved essentially as a rigid body during testing. Test results showed that a SU‐FREI isolation system significantly reduced the seismic demand on the structure.</p> <p>Modelling of the bearings dynamic properties was completed using a bilinear model and a backbone curve model. Both models showed adequate results in predicting experimental peak responses. A simplified design spectrum analysis was presented and used to model the structure in four Canadian cities. This design spectrum analysis approach showed adequate capabilities in predicting peak response values, such that the method could be used in preliminary analysis and design of isolated structures.</p> / Master of Applied Science (MASc)