Development of a real-time hybrid testing method in a centrifuge

Abstract

This paper presents a pioneering real-time hybrid testing method for geotechnical centrifuges. The method was used to investigate the behaviour of a jack-up leg reinstalled near an existing footprint, a problem that is highly nonlinear, stress dependent and involves complex soil-structure interactions. By physically modelling only the footprintleg interaction and numerically modelling the rest of the jack-up structure, the method enables a realistic account of all the parameters involved in the interaction, including the footprint geometry, soil heterogeneity and structural properties of the jack-up unit. The paper also details the three-degree-of-freedom actuators developed to model the interaction, which features controlled loads and motions along the vertical, horizontal and moment directions, and the real-time algorithm that bridges the physical and numerical models. The algorithm allows the stiffness on each axis to be varied. Testing performed at 1g and in the centrifuge, modelling jack-ups with different stiffness on the horizontal and moment axes, is presented to validate the apparatus and methodology. The hybrid apparatus and real-time testing method were found to produce much more realistic boundary constraints than previous fixedsystem apparatuses, and this allowed the test results to be considerably more informative, accurate and useful.

Global jack-up rig behaviour next to a footprint

“…Preloading A, leg-by-leg preloading: The spudcans installed on the flat ground were assumed to be pre-embedded to a depth of 0.25D [8]. The spudcans were replaced by attached foundation springs (see Fig.…”

“…To alleviate this issue, the first step was to investigate the performance of a spudcan installation next to a footprint. Due to both physical testing and numerical simulation challenges, the problem was simplified by considering a single cylindrical leg attached to a flat plate or generic spudcan and either a fixed head condition at the top of the leg [4][5][6][7][8][9][10] or a free head condition that allows sliding of the leg [11][12][13]. The soil failure mechanisms were exposed, the underlying behaviour was elucidated, and the critical offset ratio  (defined as  = D, where  is the distance between the footprint centre and the spudcan centre, and D is the spudcan diameter) was identified as 0.5~1.…”

Centrifuge and Real-Time Hybrid Testing of Tunneling beneath Piles and Piled Buildings

“…Hybrid modeling of tunnel-building interaction using a reduced-scale centrifuge model is described in this paper and is referred to as coupled centrifugenumerical modeling (CCNM). The feasibility of hybrid modeling using a geotechnical centrifuge has been demonstrated by recent pioneering works (Franza et al 2016;Kong et al 2015;Idinyang et al 2018).…”

A simple strategy for dynamic substructuring: I. Concept and development

“…Moreover, since the virtual subsystem can be easily varied, parametric studies may readily be performed. Recently, DS has also been used to circumvent similitude limitations, [2][3][4] in soil-structure-interaction applications, [5][6][7] and for interconnected systems. 8 Dynamic substructuring has received considerable attention in the earthquake engineering field in recent years.…”

“…Moreover, since the virtual subsystem can be easily varied, parametric studies may readily be performed. Recently, DS has also been used to circumvent similitude limitations, in soil‐structure‐interaction applications, and for interconnected systems …”