Yuta NISHIO

Modeling the Time-Dependent Behavior of Steel-Concrete Joints

Takumi Shimomura

This study investigates the effects of concrete drying shrinkage and sustained loading on the mechanical properties of steel-concrete hybrid joints connected by headed studs. Discrepancies between calculated and measured behaviors in steel-concrete hybrid structures are often attributed to time-dependent factors like concrete creep and drying shrinkage. To evaluate these effects, push-out tests were conducted using specimens with a large surface-area-to-volume ratio. Variables included drying history before loading and drying during sustained loading. A novel "series loading method" was developed, connecting two specimens in series to ensure uniform loading environments and histories across different conditions while eliminating eccentricity. Furthermore, a one-dimensional analysis using a mechanical model examined the stress transfer behaviors. Results indicated that drying shrinkage before loading negligibly affects the joint's ultimate strength and initial stiffness. Additionally, embedded studs alone cannot fully restrain early-age concrete shrinkage. While the linear creep law holds under non-drying conditions, it fails under drying conditions, where drying creep significantly increases slip displacement. Joints with histories of sustained loading and drying shrinkage showed reduced static strength, particularly when influenced by drying creep. Finally, a one-dimensional trilinear model analysis confirmed that reproducing post-sustained loading behavior requires considering both the reduction in concrete's effective elastic modulus and changes in the interface "bond-slip relationship."