EXPERIMENTAL INVESTIGATION OF SEISMIC RESPONSE PARAMETERS OF RUBBERISED AGGREGATE CONCRETE FRAME STRUCTURE

This paper presents the results of experimental investigations on a reduced-scale, reinforced, rubberised, aggregate concrete frame structure for the evaluation of seismic response parameters. The considered frame has twenty percent scrap-tyre rubber (crumb) replacing fine aggregates. A one-third reduced scale model of a two-storey single-bay frame was fabricated using the mix ratio of 1:1.68:1.72 (cement: sand: aggregate) and water/cement of 0.48, replacing twenty percent of fine aggregates via waste rubber (crumb) by volume. The model frame was subjected first to a free vibration test for evaluation of dynamic characteristics (frequency/period, elastic viscous damping). It was subjected to simulated multiple base excitations using 1994 Northridge earthquake time history for the evaluation of seismic response parameters (ductility factor, overstrength factor, and response modification factor). Seismic response curve (lateral displacement versus peak base acceleration) was developed for the model to assess the viability of crumb in concrete in areas of active seismicity. The fundamental period of vibration and damping were calculated as 0.75 sec and 10.85 percent, respectively using records of free vibration tests. The ductility, overstrength and response modification factors, and maximum acceleration resisted were computed using multiple base excitations which came out to be 3.10, 2.16, 6.70 and 0.72g, respectively.