Inelastic lateral and seismic behaviour of concrete-filled steel tubular pile foundations

Undertaken with industry, this paper analyses concrete-filled steel tube (CFTs) pile members in deep foundation systems under cyclic and seismic loads considering inelasticity for both pile and soil. Real seismic events have pointed out that piles may fail by forming multiple plastic hinges at various location or global buckling instability. This study confirms that CFT piles efficiently reduce damage in pile-heads and over the pile length, in depths that is difficult to access and repair the damage. The paper performs a set of analyses that enables understanding of the nonlinear mechanical behaviour of CFT piles and soil-structure interaction effects. The capacity margins of the novel foundation system are firstly assessed through controlled loading analyses (i.e., monotonic and cyclic loading histories), and then investigated further by a two-level seismic-intensity analysis. CFT pile damage patterns, displacement profiles and residual displacement are discussed and compared with those of corresponding concrete piles. Moreover, comparisons with four test campaigns taken from the literature confirm the correctness of the adopted nonlinear models for soil-pile interaction and soil inelasticity. Although its simplicity, the developed p-y modeling can successfully account for soil degradation effects making possible the simulation of the rather demanding, but advanced “s” shape of soil's cyclic behaviour, allowing for a reasonable comparison between composite and concrete piles. While the damage areas of both CFT and RC piles are mainly developed in pile heads and stiffness-discontinuous soil layers, CFT piles exhibit a lower damage than that of the RC piles nearly by 40% on average.