Seismic response control of low-rise unreinforced masonry building test model using low-cost and sustainable un-bonded scrap tyre isolator (U-STI)

https://doi.org/10.1016/j.soildyn.2020.106561Get rights and content

Highlights

  • Utilization of scrap radial car tyres for development of low cost isolation system.

  • Simplified design of un-bonded scrap tyre isolator (U-STI).

  • Evaluation of mechanical properties of U-STI.

  • Shake table testing of unreinforced masonry building model isolated by U-STI.

  • Simplified analysis of U-STI isolated building system.

Abstract

Large stock of scrap tyres in waste disposal ground is a huge threat to the environment. In many civil engineering applications, potential of using scrap tyres have been explored in the last two decades. In this paper, effectiveness of Un-bonded Scrap Tyre Isolator (U-STI), as a seismic isolation system, has been evaluated by both experimental and numerical studies. Simple design approach of low-cost U-STI for seismic response control of the test model is outlined first. The mechanical properties of U-STI, under simultaneous action of horizontal cyclic displacement and vertical load, have been determined. Shake table testing of 1/5th scale two-storey masonry building supported on U-STIs has been carried out. Shake table testing confirmed that transmissibility of peak ground acceleration to the test model is reduced to a large extent and the peak floor accelerations are of the order of 12%–15% of the peak table accelerations, which establishes the effectiveness of the U-STI in controlling the seismic response of the test model. Results of the numerical analysis of the test model, using SAP 2000 v.19, have been validated by the experimental results. The U-STIs have been modelled using multi-linear pivot hysteretic plasticity model. Comparison of acceleration and displacement responses at various floor levels obtained from numerical analysis is done with that obtained from shake table tests. Results from the numerical tests are found to be in reasonably good agreement with those obtained from the experimental tests under the action of considered ground motions. It is concluded from the study that low-cost U-STIs are effective in reducing the seismic response of low-rise masonry building test models.

Introduction

Earthquakes in the recent past have demonstrated a high level of vulnerability of unreinforced masonry buildings in the South Asian region, Iran and Italy. Lack of ductility and poor out-of-plane behaviour of the load-bearing walls of this type of buildings leads to extensive damage or total collapse in the event of moderate to high intensity earthquakes resulting in huge loss of lives and properties. However, this class of buildings with thick walls are very common in different parts of the world because of their higher durability and better thermal insulation. Therefore, there is a need for the development of innovative low-cost sustainable technologies for the enhancement of their earthquake resistance and resilience.

Earthquake resistant design protects the structure from global damage by allowing damage to occur in a controlled manner in the pre-defined elements of the structure. An alternative way of earthquake protection of structures is based on structural control approaches. Seismic base isolation technique is a passive structural control approach. In general, base isolation systems lengthen the natural period and enhance damping of the isolated systems for reducing transmissibility of ground motion to the superstructure. In this paper, a study on the development of low-cost isolation system for mitigation of seismic vulnerability of common masonry buildings is presented.

Kelly [1] reviewed various base isolation systems and discussed its range of applicability. A comparative study on the performance and effectiveness of different isolation systems under a variety of conditions was made by Su et al. [2]. Steel Reinforced Elastomeric Isolators (SREI), which are heavy and its installation needs skilled manpower, are most commonly used isolation system. SREIs are mostly used for seismic isolation of important heritage buildings or life-line buildings or structures. It is not cost-effective for common residential buildings. To reduce the cost and weight of the isolator, Kelly and Takhirov [3] carried out pioneering research for development of Fiber Reinforced Elastomeric Isolator (FREI) replacing steel reinforcement with fiber reinforcement. Both experimental and analytical studies were presented in this report for perfecting design and manufacturing of FREI. Moon et al. [4] in their study made use of carbon, glass, nylon, and polyester fibers to replace the steel shims and concluded that carbon reinforcement had over two times higher damping capacity as compared to steel reinforced elastomers. The FREIs were also tested considering un-bonded and bonded boundary conditions by Toopochi et al. [5] and it was concluded that the un-bonded FREIs are more effective in comparison to bonded FREIs and stress demand in the former is substantially lower as compared to that in the later. Thuyet et al. [6] implemented the FREI for seismic isolation for a two-storeyed masonry building in Tawang, which has resulted in substantial reduction of the seismic vulnerability of the building. However, both SREI and FREI are unlikely to be economically viable for seismic isolation of large stocks of low-cost unreinforced masonry buildings commonly constructed in the South Asian region.

Xiao et al. [7] proposed the introduction of a low-cost friction sliding isolation layer between the superstructure and the ground. Various materials such as sand, lighting ridge pebble, polypropylene PVC sheet and polythene membrane were tested to evaluate suitability of the materials when serving as the sliding layer. However, it was concluded that manufacturing large sheets of sliding layers is not feasible, and replacing them at a later stage would also incur substantial costs. In another study, Tsang [8,9] proposed a method known as Geotechnical Seismic Isolation (GSI). It involved replacing the soil below the foundation by rubber-soil mixture. It is observed that these methods are not suitable for low-rise buildings in view of the necessity of large excavation at the foundation level. Due to the low vertical stiffness of the soil mix, there may be certain rocking motion when subjected to a strong earthquake. In another study, Tsang et al. [10] proposed analytical modelling of GSI system considering dynamic soil-foundation-structure interaction. In this study it has been observed that GSI system was effective in reducing the seismic responses of the structure by 50%–60%.

Scrap tyres are waste material which are abundantly available at disposal sites. Moreover, these are non-biodegradable and present a distinct challenge in recycling and disposal. Rubber pads in radial car tyres have wire mesh reinforcement similar to steel or fibre reinforced elastomer/natural rubber laminates used in SREIs and FREIs. However, limited studies have been reported to evaluate their performance in seismic response control as an alternative to SREI and FREIs. Turer and Özden [11] conducted experiments on scrap tires pads to use them as an alternative to the conventional SREI. Rubber tyre pads were simply stacked one upon another and were glued using epoxy resin. These pads were tested under vertical compression and horizontal shear. However, it was concluded that the scrap tyre rubber pad isolators were ineffective for practical implementation for seismic isolation. Mishra and Igarashi [12] used only the tread part of the truck tyre for development of scrape tyre isolator. Both experimental study and finite element analysis have been carried out in the study, which showed that scrap tyres had higher damping capacity than natural rubber bearings. It was concluded that it is feasible to use scrap tyre pad isolators as low-cost base isolation devices for common low-cost residential buildings. Sow et al. [13] carried out study to observe the effectiveness of scrap tyre isolators for seismic protection of low-rise buildings in Malaysia. Five tyre layers were stacked and glued together using Dunlop adhesive. It was found that it could withstand high vertical loads and also had a high damping capacity. Numerical modelling of the low-rise structure subjected to earthquake showed that it could even withstand medium intensity earthquakes. There were few investigations [[14], [15], [16], [17], [18]] on shaking table test of scaled low-rise masonry building models which are isolated at the base level for reduction of their vulnerability.

From the review of the literature on low-cost materials for base isolation systems, it is observed that scrap tyres have better potential for design and development of low-cost base isolators. However, there were diverse findings on the effectiveness of scrap tyre isolators in the limited available papers. Further, no literature is available on specific design procedure for scrap tyre isolators to arrive at the target natural time period for effective seismic isolation of any building or test model. There is no work reported on shake table testing of scrap tyre isolators to evaluate extent of their effectiveness in reducing transmissibility of ground motion to the superstructure. Practical approach of numerical analysis, using experimentally determined Scrap Tyre Isolator parameters, for computation of response of the isolated test model is also not available.

This paper explores the viability of using Un-bonded Scrap Tyre Isolator (U-STI) as a seismic isolation device by both experimental and numerical studies. Design procedure for U-STI for seismic isolation of the test model has been presented. Experimental results of vertical load test and horizontal cyclic shear test, for evaluation of mechanical properties of the model U-STIs designed for seismic isolation of a 1/5th scaled masonry model, have been presented. Shake-table testing of a two-storeyed scaled masonry model isolated using four model U-STIs has also been carried out to record seismic response at various levels of the test model under the action of time scaled seismic excitations. The validation of the simplified numerical model of the scaled test model, developed using SAP 2000 (v-19), has been carried out by comparing the results of the seismic response of the test model obtained from numerical simulation with that recorded during shake table tests.

Section snippets

Design of the model U-STI

Performance of any seismic isolation system would be dependent on the appropriate characterization of mechanical properties of its constituent material. In this study, appropriate care has been taken for proper characterization of tread of the scrap radial car tyres and effort has been made to achieve target natural period of the isolated system to ensure efficient behaviour of the isolated test model. The tread part of radial car tyres has been used for assembling the model U-STI. Radial tyre

Testing of the U-STI

Experimental evaluation of vertical stiffness and horizontal stiffness of model U-STIs are very important components of this study to ensure stability of the isolated test model under seismic excitations and to check whether target natural period of the isolated system can be achieved during shake table testing. In this section, details of vertical compression test and horizontal cyclic shear test have been presented.

Estimation of mechanical properties of U-STI

In order to estimate the force-displacement characteristics of the U-STI, the two key parameters namely equivalent viscous damping and effective horizontal stiffness have been computed. These key parameters have been evaluated with the help of hysteresis loops obtained experimentally. For any horizontal displacement, the effective horizontal stiffness of isolator is mathematically defined by Kelly and Takhirov [3].Keffh=(FmaxFmin)(umaxumin)where, Keffh is the effective horizontal stiffness of

Experimental investigation of isolated test model on shake table

Brick masonry structure typology, which is highly vulnerable under seismic excitation, is prevalent in both urban and rural South Asian region. Effectiveness of low-cost model U-STIs, designed in this study, for seismic response control of low-rise brick masonry building model has been evaluated by shake table testing. Keeping the size and capacity of the shake table available in the laboratory in mind, a 1/5th scaled two storeyed brick masonry building model has been considered in this study.

Simplified numerical analysis

In the previous section, shake table testing of the 1/5th scaled model, supported on U-STIs at its four corners, has been presented. But it is not always feasible to perform shake-table testing of the model. Also, the material properties of scrap tyres are not consistent, hence performing finite element analysis may not yield accurate results. Therefore, a simplified numerical simulation of responses of the test model, subjected to same time scaled prescribed ground motions, has been carried

Conclusion

This paper examines the feasibility of using low-cost U-STI as a seismic isolation device by carrying out both experimental and numerical studies. Design procedure for U-STI for seismic isolation of the test model have been outlined. Mechanical properties of U-STI have been determined by subjecting it to horizontal cyclic displacement and vertical load simultaneously. Shake table tests of the 1/5th scaled base isolated un-reinforced masonry model have been carried out. Time-scaled earthquake

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (21)

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