Long-term performance of timber-concrete composite (TCC) connections with self-tapping screws

Timber–concrete composite (TCC) systems effectively combine the compressive strength of concrete with the tensile capacity of timber, but their design is often governed by serviceability limit states due to long-term deformations. This study investigated the short- and long-term behaviour of TCC connections with self-tapping screws installed at various angles to the shear plane. Short-term shear tests were conducted to determine the required sustained load for each specimen and to evaluate strength, stiffness, and failure modes, followed by six-month sustained-load tests to determine creep coefficients and predict 50-year performance using rheological modelling. Results showed that inclined self-tapping screws significantly enhanced stiffness and strength compared to perpendicular screws while exhibiting smaller instantaneous slip and lower long-term creep coefficients. The 50-year creep coefficients ranged from 0.8 to 1.0 for inclined and perpendicular configurations, respectively, indicating that current design provisions for TCC systems may be conservative.