Shaking table test of a cost-efficient isolation system for light frame timber buildings

Abstract

The construction of timber buildings is a sustainable alternative to reduce the carbon footprint generated by the construction industry. The structural typology called Light Frame Timber Building (LFTB) is very attractive due to its good seismic performance and lower cost compared to mass timber structures. However, mid-rise LFTBs in areas of high seismic hazard are more expensive than reinforce concrete buildings, mainly due to the high cost of hold-downs (or ATSs) and shear brackets. Various authors have estimated that this cost is roughly equal to 35% of the total cost of the structure. On the other hand, seismic isolation is a very effective technology to protect structures subjected to destructive earthquakes. However, its use in timber buildings is still incipient. This paper presents the results of shaking-table tests of a 1:2 scale, 3-story LFTB isolated with 4 Impact Resilient Double Concave Frictional Pendulum (IR-DCFP) devices. These seismic isolators have two types of sliding interfaces: (i) the spherical contact surfaces (SCS), typical of DCFP devices, and (ii) a high-friction flat interface (HFI), which is activated when the internal slider impacts the perimeter rings, allowing a large amount of energy to be dissipated. Results can be summarized as follows: (i) for contact pressures of 20 MPa, the PET-type polymeric material used in the SCSs reached a coefficient of friction at high velocity of approximately 0.13, thus allowing control of the lateral deformations of the isolators (no significant reductions due to thermal effects were observed); (ii) peak story drift ratios did not exceed 0.5% (i.e., essentially elastic behavior of the timber superstructure), even though in several tests the HFI of the isolators was activated (the friction coefficient was found to be roughly equal to 0.20). The IR-DCFP isolation system can then be expected to be cost-effective in LFTBs due to the significant savings in metallic elements and edge studs, and also due to the small size (i.e., low cost) of the IR-DCFP devices.