MAT-761: THE EFFECT OF TEMPERATURE ON THE LATERAL RESPONSE OF UNBONDED FIBER-REINFORCED ELASTOMERIC ISOLATORS

Base isolation is a method that can be employed to significantly reduce the demands on a structure during a seismic event. This method has shown considerable success in reducing the adverse effects of earthquakes, including damage and loss of life. The main concept of base isolation is to reduce the seismic demand on a structure by placing isolators beneath the superstructure at points where load is transferred to the foundation. One of the most commonly used types of isolator is the elastomeric isolator. These isolators are traditionally comprised of layers of elastomer and steel. More recently, research has been completed on the use of fibers as a replacement to the steel reinforcement layers, in order to reduce weight and potentially reduce costs. Fiber reinforced elastomeric isolators (FREI) can be placed (unbonded) between the superstructure and its foundation. This research investigates the behaviour of unbonded fiber-reinforced elastomeric isolators (U-FREI) under lateral deformations expected during seismic events. The objective of this study is to investigate the lateral behaviour of FREI under a range of temperatures, representative of those expected in various regions throughout Canada. Results from preliminary experimental tests show that the influence of temperature on the lateral response of U-FREI is negligible under the range of temperatures considered

NDM-563: THE VERTICAL, ROTATIONAL AND LATERAL RESPONSE OF UNBONDED FIBER REINFORCED ELASTOMERIC ISOLATORS

Bridge structures often experience damage during an earthquake, which is one of the most devastating types of natural disasters. Base isolation can be employed to mitigate earthquake-induced damage. The main concept of base isolation is to reduce the seismic demand on the structure by shifting its fundamental time period away from the predominant periods associate with earthquakes. Base isolation involves placing horizontally flexible isolators between the bridge superstructure (i.e. deck/girder) and the substructure (i.e. pier/column). There are two main types of seismic isolators: (1) elastomeric, and (2) sliding. A fiber reinforced elastomeric isolator (FREI) is a particular type of reinforced elastomeric isolator. In an FREI the steel reinforcement used in a traditional elastomeric isolator is replaced with fiber fabric, which results in a reduction in the weight and potentially the manufacturing cost. FREI can be either bonded (B-FREI) or unbonded (U-FREI) to the substructure and superstructure. This paper investigates the behaviour of U-FREI under combined vertical, rotational, and lateral loading, as bridge bearings are expected to experience this combination of loads. Accordingly, the test program includes different vertical loads, angles of rotation, as well as a number of lateral sinusoidal input motions varying in both frequency and amplitude. The objective of this study is to investigate the response of U-FREI under serviceability and extreme loading conditions. The findings of this paper also address the feasibility of using U-FREI as bridge bearings/isolators

Vertical and Lateral Behavior of Unbonded Fiber-Reinforced Elastomeric Isolators

Fiber-reinforced elastomeric isolators (FREIs) are relatively lightweight, can be cut to the required size from larger pads, and can be placed unbonded (i.e., unfastened) between the supports. The two major geometric parameters that influence the vertical and lateral response of unbonded fiber-reinforced elastomeric isolators (U-FREIs) are the shape factor and the aspect ratio. The vertical response is strongly influenced by the shape factor, while the aspect ratio is the controlling parameter for the stable response of U-FREIs under lateral displacement. This paper describes an experimental study on the vertical and lateral response of U-FREIs under different loading conditions in both the lateral and vertical directions. Three U-FREIs, with different aspect ratios and shape factors, were tested using a multiload test apparatus. Results from vertical tests indicate that, in addition to the shape factor, the vertical stiffness is influenced by the vertical rate of loading. Furthermore, it was found that the static lateral offset did not significantly affect the vertical stiffness of the isolators considered. These observations are in part attributed to the composite action of the fiber reinforcement and the elastomer