A previous paper (Marshall et al 2009) describes the Singaporean concept for an Arctic caisson, consisting of a pre-fabricated hollow steel shell, transported to site on a submersible heavy-lift vessel, and filled with concrete after being set on a prepared foundation. The resulting curved sandwich shell, steel-concrete-steel (30-500-30 mm), was shown to be capable of resisting the full range of broad-area and higher localized patch loads specified in the draft ISO 19906. Tests of a large-scale shell reinforced with J-hook radial ties inside the sandwich showed excellent performance. However, this would be more expensive to fabricate than a plain double shell. Finite element analysis and large-scale testing of the latter showed it to be vulnerable to early disbanding and loss of serviceability, even though its ultimate strength exceeded the ISO guidelines. Various methods of bond improvement have been proposed, with the goal of approaching the shear and tensile strength of the fiber-reinforced bulk concrete. Recent small scale testing (ASTM shear push-out) will be reported, exploring two methods of surface treatment which improve strength and ductility at the concrete-steel interface. They are called “hairy epoxy” and “steel Velcro.”

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