Multi-Functional Performance of Upcycled High-Density Polyurethane Floor Fillers in Multi-Story RC Buildings: A Combined Seismic Mitigation, Thermal Insulation, and Sustainability Approach, with Field Validation on an Existing Building.

This study investigates upcycled high-density polyurethane (HD-PUR) as a substitute for conventional cement-based screed in multi-story reinforced concrete (RC) buildings. Conventional screed (≈2400 kg/m3) adds substantial seismic dead mass without contributing to lateral stiffness, amplifying base shear, inter-story drift, and overturning moments. HD-PUR, produced from industrial waste via mechanical re-pressing, has a density of ≈150 kg/m3 and thermal conductivity of 0.025 W/m·K. It is crucial to clarify that this yields a 16-fold mass reduction specifically at the floor-screed layer level (dropping from 120 kg/m2 to 7.5 kg/m2). Consequently, this localized weight saving translates to an approximately 16.6% reduction in the total seismic weight (W) of the entire building. This substitution also provides near-negligible inter-story heat transfer. Three-dimensional finite element models of 5-, 10-, and 15-story moment-resisting RC frames were developed in SAP2000, with modal and response spectrum analyses performed per the Turkish Building Earthquake Code (TBEC, 2018). HD-PUR substitution reduced base shear by 10.5-20.0% and inter-story drift by 10.4-20.2% across all models. These trends were validated against an existing five-story RC building in Beyoğlu, Istanbul (site class ZC; PGA = 0.359 g; in situ concrete class C14), modeled in SAP2000 and STA. The fundamental period shortened from 0.888 s to 0.793 s, global base shear (FX) decreased by 10.5%, vertical base reaction (FZ) decreased by 16.6%, and the nonlinear pushover-based performance level improved from Collapse Prevention to Life Safety without any intervention on load-bearing members. Thermal calculations per TS 825 indicate an 18% reduction in the heating degree-day load associated with the floor-slab envelope interfaces (basement ceilings and roof slabs), while life-cycle assessment data reported in the literature point to appreciably lower embodied carbon, supporting circular economy objectives. In short, HD-PUR floor fillers offer a low-cost strategy that jointly improves seismic resilience, energy efficiency, and environmental performance in multi-story RC buildings.