CYCLIC TESTING OF 1:40 SCALE CANTILEVER RC ELEMENTS WITH DIGITALLY MANUFACTURED REINFORCEMENT

Abstract

Time history analysis is considered as the state-of-the-art in modeling of the seismic response of RC structures. Its validation involves predicting the response of an RC structure tested on a shaking table. However, blind prediction contests show that most contestants fail to predict the seismic response of the tested specimens. Given that numerical models are able to accurately capture the behavior of RC members at a component level, we can conclude that a large part of the error sources from the assumptions made to pass from component level to system level, i.e. assumptions related to damping formulation, component interaction, boundary conditions etc. In parallel, the prediction of the response of a structure subjected to a single ground motion has been proven to be too strict of a validation procedure. Oftentimes, a statistical approach involving many specimens and ground motions is necessary. Such an approach is clearly only feasible at a very small scale. At such scales, the reinforcement fabrication and positioning become major issues. We propose to use additive manufacturing technology to digitally fabricate the reinforcement cage necessary for the micro RC element. This paper presents the results from cyclic tests on 1:40 scale RC cantilever columns. The reinforcing cages were manufactured using a Selective Laser Melting 3D printer that was able to print rebars with submillimeter diameter and yield strength 378MPa. Two different microconcrete mixtures were used based on cement and gypsum. Each sample was reinforced with 18 longitudinal rebars of 0.6mm diameter, and 0.35mm stirrups with 2.5mm of spacing. The cyclic behavior of the columns closely resembles the behavior of full-scale columns indicating that such small-scale specimens can be used of the statistical validation of global level assumptions that numerical models make.