Seismic Isolation of a Shear Wall Structure Using Rectangular Fiber-Reinforced Elastomeric Isolators Peyman M. Osgooei 1 ; Michael J. Tait, M.ASCE 2 ; and Dimitrios Konstantinidis, M.ASCE 3 Abstract: The seismic response of a 2-story reinforced concrete shear wall structure seismically isolated using unbonded rectangular fiber-reinforced elastomeric isolators (FREIs) is investigated. Using rectangular isolators, rather than square or circular, for buildings with masonry or reinforced concrete structural walls allows a more uniform distribution of the gravity loads and eliminates the requirement of additional wall beam elements. Time history analyses are conducted for both fixed-base (FB) and base-isolated (BI) configurations using 10 earthquake ground motions, selected to match the design response spectrum. The properties of the isolators are taken from lateral cyclic test results carried out on scale model FREIs. A pivot-elastic model, previously introduced by the authors, is used to model the lateral response of the isolators in the time history analyses. The peak response values of the BI structure are significantly reduced compared with the results for the FB structure. It is concluded that unbonded rectangular FREIs can be effectively designed and used to seismically isolate masonry or reinforced concrete shear wall structures. DOI: 10.1061/(ASCE)ST.1943-541X.0001376. © 2015 American Society of Civil Engineers. Author keywords: Base isolation; Fiber-reinforced elastomeric isolators; Time history analyses; Pivot-elastic model; Structural control. Introduction Seismic isolation aims to mitigate the seismic demand on a struc- ture by shifting the natural period of vibration of the isolated struc- ture beyond the high-energy period range of earthquake ground motions. The isolator device needs to be flexible in the lateral di- rection while being able to carry a large vertical load. The near incompressibility and low elastic modulus inherent in elastomers have made elastomeric isolators the most common type of seismic isolator in use. Fiber-reinforced elastomeric isolators (FREIs) have been shown to be viable and potentially inexpensive seismic isolator devices (Toopchi-Nezhad et al. 2008b, 2009a). They use fiber material for the reinforcing layers, which reduces the manufacturing cost compared with steel-reinforced elastomeric isolators (SREIs). In addition, the removal of the thick steel end plates and the use of fiber reinforcement, instead of steel, result in a much lighter iso- lator. This can reduce installation costs compared with conventional SREIs, which because of their large weight require specialized lift- ing equipment (Kelly and Konstantinidis 2011). A number of fac- tors, which include high manufacturing and installation costs associated with heavy conventional SREIs, have limited their application in North America to high importance or historical buildings. It is expected that reducing the cost and weight of elas- tomeric isolators will extend their usage to smaller structures and typical residential buildings (Kelly 2002). Furthermore, the rollover behavior of an unbonded FREI, which leads to a lower effective lateral stiffness (resulting in a higher isolated building period), allows this type of bearing to achieve higher seismic isolation ef- ficiency compared with a SREI with the same dimensions and elastomer material properties. Fiber-reinforced elastomeric isolators can be installed in an unbonded application, in which isolators are placed between the superstructure and the foundation with no bonding or fastening. Unbonded FREIs undergo a unique rollover deformation when sub- jected to lateral loading. Osgooei (2014) showed that compared with the bonded application, unbonded FREIs are more efficient in mitigating the seismic demand on the structure. Toopchi-Nezhad et al. (2011) showed that the stress demand on both rubber and fiber reinforcement layers are reduced when an unbonded application is used. In seismic isolation projects, it is common practice to use rigid diaphragms immediately above and below the isolation interface and to install one isolator underneath each column between the two rigid diaphragms. For superstructures with reinforced concrete or masonry structural walls, additional wall beams are needed to span between isolators to support the superstructure. These addi- tional wall beams increase construction costs. It has been proposed that using long rectangular isolators for isolating buildings with structural walls could result in a more cost-effective isolation sys- tem, as they provide a more uniform support condition along the walls (Kelly 1999, 2002). Thus, the size and the reinforcement of the wall beams could be reduced or even eliminated altogether. Currently, nearly all isolators are manufactured in a circular or square shape. One of the benefits of FREIs is the ability to manu- facture large rectangular pads from which individual isolators can be cut to the required shape and size. In this paper, the seismic response of a 2-story reinforced con- crete shear wall structure is investigated. Numerical analyses are carried out on both the fixed-base (FB) and base-isolated (BI) struc- ture to determine the efficiency of the isolation system. The seismic 1 Ph.D. Candidate, Dept. of Civil Engineering, McMaster Univ., 1280 Main St. West, Hamilton, ON, Canada L8S 4L7. E-mail: m.osgooei@ gmail.com 2 Joe Ng/JNE Consulting Chair in Design, Construction and Manage- ment in Infrastructure Renewal, Dept. of Civil Engineering, McMaster Univ., 1280 Main St. West, Hamilton, ON, Canada L8S 4L7 (corresponding author). E-mail: taitm@mcmaster.ca 3 Assistant Professor, Dept. of Civil Engineering, McMaster Univ., 1280 Main St. West, Hamilton, ON, Canada L8S 4L7. E-mail: konstant@ mcmaster.ca Note. This manuscript was submitted on October 21, 2014; approved on June 10, 2015; published online on August 12, 2015. Discussion period open until January 12, 2016; separate discussions must be submitted for individual papers. This paper is part of the Journal of Structural Engineer- ing, © ASCE, ISSN 0733-9445/04015116(10)/$25.00. © ASCE 04015116-1 J. Struct. Eng. J. Struct. Eng., 2016, 142(2): 04015116 Downloaded from ascelibrary.org by MCMASTER UNIVERSITY on 04/25/16. Copyright ASCE. For personal use only; all rights reserved.