Strength Degradation Characteristics of the Steel-Concrete Interface Under Cyclic Shear

Abstract

The shear capacity of the steel-concrete interface (SCI) of concrete-filled steel tubular piles (CFSTs) degrades due to the cyclic shear action of external loading and unloading and can result in a reduction in the bearing capacity. To explore the shear strength degradation characteristics of the steel-concrete interface under cyclic shear, cyclic shear tests for three roughness types and under four different normal stresses were carried out by using a large-scale repeated direct shear test system. The characteristics of the shear load-displacement curve and failure mode of the SCI under external cyclic shear were analyzed, and the influence of the roughness and normal stress on the SCI shear strength degradation was explored. The results indicate that the CFSTs experienced shear failure in the first three shear cycles and then exhibited wear failure. The peak shear load of the SCI increases exponentially with increasing normal stress and decreases logarithmically with increasing cyclic shear time. A larger interfacial roughness and normal stress results in a faster interfacial shear strength ratio (τfn/τf1) weakening during the first three shear cycles, and with an increase of the cyclic shear times, the weakening rate is reduced.

Calculation Model of Vertical Bearing Capacity of Rock-Embedded Piles Based on the Softening of Pile Side Friction Resistance

“…Zhang et al proposed a bilinear shear model to describe the relationship between shear stress and concrete-rock's relative displacement for rock-socketed bored piles in soft rock, elucidating the critical shear displacement at the concrete-rock interface and establishing a load transfer method for soft rock-socketed piles [17]. Based on the indoor shear test, Liu et al showed that the peak SCI shear load increased exponentially with the increase of directional stress and decreased logarithmically with the increase of cyclic shear time [18]. Lei et al found that the shear expansion effect existed in the interface sliding of rock-socketed piles.…”