Experimental study on the performance of ENTA damper systems in a two-story RC moment frame under cyclic loading

Abstract

This study experimentally evaluates the seismic performance of a two-story RC moment frame retrofitted with an external steel frame and an ENTA damper system, developed as a strengthening solution for seismically deficient RC structures. Cyclic lateral loading tests were conducted on two geometrically identical specimens: an as-built frame and a frame retrofitted with the ENTA damper system. In the retrofitted specimen, the ENTA damper yielded before the primary RC members, effectively delaying damage to critical components while enhancing lateral strength and stiffness. The retrofitted frame reached a maximum lateral strength of 531.70 kN, 1.62 times that of the as-built specimen, and exhibited an initial stiffness increase of 1.88 times. Furthermore, the cumulative energy dissipation at a 2% drift ratio increased by 3.07 times, indicating that the ENTA damper system effectively absorbed and dissipated energy throughout the loading history. Strain measurements and observed failure modes confirmed that the retrofitted frame maintained flexure-dominated behavior while suppressing significant damage in the beam-column joints and columns. The simplified plastic-mechanism-based strength predictions showed good agreement with the experiment results, with test-to-prediction ratios ranging from 1.02 to 1.33, demonstrating that the analytical model conservatively captures the strengthening effects. Overall, the results validate the ENTA damper system as an effective seismic retrofit strategy for RC moment frames.