Vibrational behaviour of thin concrete-timber-composite floors reinforced with basalt textile

Abstract

In the context of loft extensions, retrofitting Dowel Beam Ceilings (DBCs) is often necessary to meet Serviceability Limit State requirements, even if the existing structure meets Ultimate Limit State requirements. Adding a reinforced concrete layer on top of timber floors is a well-established method for retrofitting such ceilings. The concrete layer thickness of 5-7 cm, primarily determined by durability considerations rather than strength requirements, adds additional weight and thus requires additional supporting and strengthening measures on the existing structure. In this study, we examine the application of thin basalt Textile-Reinforced Concrete (TRC) layers on top of a DBC to minimise concrete mass and overall system height. Of particular interest is the dynamic behaviour of retrofitted DBC ceilings, which could be negatively affected by the lower TRC layer thickness. The investigation includes experimental modal tests on two large-scale timber-concrete composite floors with 4.7 m in length: (a) a standard DBC–Steel-Reinforced Concrete (RC) composite floor with a conventional concrete layer thickness of 7 cm, and (b) a DBC–TRC composite floor featuring a slender 3 cm basalt textile-reinforced concrete layer. Modal tests indicate that the slender and lighter DBC-TRC composite floor maintains a natural frequency above the 8 Hz threshold (14.52 Hz for RC, 14.61 Hz for TRC) specified in current Austrian standards. However, the TRC specimen exhibited a lower damping ratio (1.40%) than the RC specimen (2.68%), which was still higher than the assumed damping ratios for non-retrofitted ceilings. The results underscore the great potential of such thin TRC overlays for retrofitting existing DBCs.