Re-using tennis balls as low-cost seismic isolation devices: Experimental Investigation

Seismic isolation is not applied in residential structures in the developing world due to the associated high cost. The present study shows the preliminary experimental results of a novel, low-cost spherical isolator, aiming to be used in low-rise masonry structures in developing countries. The examined system is based on mortar-filled, used tennis balls, rolling on concave or flat concrete surfaces. Distributing such isolators underneath the masonry walls would not require a heavily-reinforced isolation slab above the isolation level, further reducing construction costs. The experimental investigation comprised compressive and lateral cyclic tests of these systems. Parameters of investigation were the geometry of the rolling surface (i.e., flat or concave) and the applied vertical load (i.e., weight of the supported structure). First, the compressive behavior of the isolators was investigated showing that, if they are closely spaced, the isolators could support a low-rise building. Subsequently, lateral cyclic tests were performed, showing that the lateral cyclic response is bilinear when concave plates are used. The rolling friction coefficient (defined as the ratio of lateral to vertical force at zero displacement) was in the range of 4.7–7.2%, hence, suitable for seismic isolation applications. Special care should be given to the casting procedure since imperfections may affect the cyclic response of the system.