Long-term Behavior of Reinforced Composite Cross Laminated Timber Floor Structures

90mm x 90mm square timbers produced from thinned small logs were glued laterally to form 1,200mm x 4,800mm core panels for CLT manufacturing. Three ply composite CLT panels were manufactured by using two 18mm thick plywood panels as surface and back panels, respectively, with small square timber core panels. Because this three ply composite CLT has low stiffness for long span and show too much deflection, it cannot be used as floor panels with long span such as 4.8m. In this study, five methods were applied to reinforce the three ply composite CLT floor panel including 2x4 joist and floor sheathing(18mm thick plywood), 2x6 joist and floor sheathing (18mm thick plywood), hybrid CLT floor with 2x4 joist and concrete, hybrid CLT floor with 2x6 joist and concrete and hybrid CLT floor with 2x6 joist, 13mm reinforcing steel bar and concrete. And these reinforced CLT floor structures were tested under long-term loads corresponding to floor live load for residential building(2kPa). The results of long-term tests for reinforced composite CLT floor panels for about one year can be summarized as follows: 1) Initial deflection was higher for joist and floor sheathing reinforcements than hybrid floor structure of joist and concrete, but this trend was reversed right after the initial deflection 2) Hybrid floor structures of joist and concrete showed much higher deflection than joist and floor sheathing reinforcements and their deflection was over the deflection limit(L/240) at around 40-50 days of loading 3) Joist and floor sheathing reinforcements showed less deflection than the deflection limit(L/240) for about one year of loading, and 2x6 joist reinforcement showed less deflection than 2x4 joist reinforcement