مدل سازی تحلیلی جداسازهای تقویت شده با فیبر novel در پیکربندی بدون مرز
Abstract
1- Introduction
2- Analytical models for U-FREIs
3- Description of the isolator prototypes
4- Experimental setups
5- Experimental results
6- Proposed analytical model
7- Conclusions
References
Abstract
Base isolation system is one of the most commonly used technologies implemented around the world for seismic protection of infrastructure. Its objectives are the protection of human life and the reduction of damage to buildings as a result of earthquakes. However, the system is rarely used in developing countries such as Colombia, due to its relatively high costs, including the cost of importing the devices. The development of an isolation system using local technology therefore eliminates the latter expense. This paper focuses on the experimental assessment and analytical modeling of low-cost seismic isolators for low-rise buildings, which represent most construction projects worldwide. Two types of unbonded isolator with a high damping rubber matrix and different reinforcement fibers were employed: carbon and polyester. Scaled prototypes were manufactured and tested under compression and shear loads. Despite the lower mechanical properties of polyester, the results revealed an adequate comparison between the vertical and horizontal properties of the two isolators, with both satisfying minimum required design values. Nevertheless, when taking into account the fact that the price of polyester fiber is one order of magnitude less than of carbon, this seems to be the option with greater potential to be implemented as a low-cost seismic isolation system. Based on the experimental results, an analytical model was proposed to estimate the horizontal stiffness of unbounded isolators, taking into account the reinforcement characteristics, the effective area and the shear modulus of the rubber. In comparison with other formulations, the proposed model was found to be sufficiently accurate to be used in the preliminary design of unbonded fiber-reinforced elastomeric isolators.
Introduction
Base isolation is one of the most effective technologies in seismic protection of structures. Its objectives are the protection of human life and a reduction of the damage caused to buildings during earthquakes. Nowadays, the isolation system has been widely implemented in more than 12000 projects [1], and its effectiveness has been proved during different seismic events worldwide [2]–[4]. In view of this, the system is rarely used in emerging countries such as Colombia due to its relatively high cost. The conventional devices used in the system are steel-reinforced isolators (SREIs), which are heavy and expensive [5]. However, over the last few decades, new kinds of bearings for seismic isolation have been developed and investigated [6]–[11] in order to be lower cost. These new devices contain fiber sheets rather than steel reinforcement within the bearing and are known as fiber-reinforced elastomeric isolators (FREIs). The main difference between SREIs and FREIs is that the latter can be used without a connection to the structure, thereby reducing costs, weight, and the installation and manufacturing process times. These characteristics may lead to the implementation of the isolation system in all types of project, including residential buildings. Reducing the cost of FREIs can be achieved by replacing the natural rubber with recycled elastomers derived from tires and industrial leftovers, scrap tire rubber pads, and nanocomposite rubber [12]–[15]. Alternatively, non-conventional materials can be used such as carbon-fiber-reinforced plastic meshes, polyamide and engineering plastic sheets [16]–[18], or low-cost fiber mesh like glass or nylon instead of carbon (bi-directional or quadri-directional fabrics) or Kevlar [5], [7], [12], [19]–[28]. In terms of behavior, the corners of unbonded FREIs (U-FREIs) roll off the supports during horizontal displacements due to the unbonded condition and the lack of flexural rigidity of the fiber reinforcement. This eliminates the high-tensile stress regions developed in a bonded isolator when it is displaced horizontally [29], [30].