Structural Performance of Full-Scale Cast-in-Place UHPC Moment Frames Under Pseudo-Static Cyclic Loading

Ultra-High-Performance Concrete (UHPC) reinforced with steel fibers has emerged as a promising alternative to conventional concrete, which exhibits limited tensile capacity and a low modulus of rupture and is prone to brittle damage under cyclic loading—a critical drawback in seismic applications. The increasing demand for resilient, damage-tolerant construction materials in seismically active regions worldwide has intensified the need to evaluate the seismic performance of UHPC structural systems at the structural scale. However, the seismic behavior of full structural frames built entirely with cast-in-place UHPC remains largely unexplored. This study presents a full-scale experimental evaluation of single-story UHPC frames with two steel fiber volume fractions (1.0% and 1.5%) subjected to pseudostatic in-plane cyclic loading. A conventional reinforced concrete frame was tested for comparison. Key performance parameters—including hysteretic response, stiffness degradation, and energy dissipation—were assessed. The results suggest that the UHPC frames exhibited enhanced performance in comparison to the conventional frame across the measured parameters. The UHPC frame with 1.5% steel fiber content consistently outperformed both the 1.0% UHPC frame and the conventional reinforced concrete frame in terms of lateral strength, initial stiffness, and energy dissipation capacity, highlighting the critical role of fiber dosage in optimizing seismic performance. The 1.5% fiber UHPC frame reached approximately 59 kN in maximum lateral strength and 6.3 kN/mm in initial stiffness, representing increases of around 59% and 58%, respectively, relative to the conventional frame (~37 kN and 4.0 kN/mm). While stiffness degradation was observed in all specimens, the UHPC frames retained higher stiffness values throughout the test. At 5.5% drift, the 1.5% UHPC frame dissipated approximately 146,000 J, compared to 80,000 J for the conventional frame. These findings indicate that steel fiber-reinforced UHPC may improve the cyclic performance of frame structures and could serve as a viable alternative for earthquake-resistant construction. The results reported here should be interpreted as indicative trends rather than statistically generalizable conclusions. A key limitation of this study is that the experimental program focused solely on single-story frames under quasi-static loading; dynamic effects and multi-story behavior were not addressed.