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This paper investigated bond behaviour of concrete-filled steel tube (CFST) columns at the Arctic low temperatures. A testing program with ten square and ten circular CFSTs were tested under different low temperatures ranging from 30 °C to −80 °C. The influences of different low temperature levels, diameter to thickness ratio (D/t), grades of concrete, length to diameter ratio (L/D), and cross-section type were checked through these 20 tests. The test results showed that the Arctic low temperatures significantly improved the bond behaviour of CFST columns; lower grade concrete exhibited larger ultimate bond strength (τu); increasing D/t ratio reduces the ultimate bond strength; L/D ratio has marginal influences on τu values; and circular CFST columns exhibited higher ultimate bond strength than those of square ones. Different from the CFST column at ambient temperature, the frozen-ice bond for the CFST columns at low temperature improves its ultimate bond strength. A prediction equation was proposed for ultimate bond strength of CFST columns at low temperatures. The validations against the reported 20 tests show that the proposed equation offered conservative predictions but more accurate predictions than the design codes, e.g., Eurocode 4 and ANSI/AISC.

Firstly, this paper proposed a type of steel-concrete-steel (SCS) sandwich composite shear wall with J-hook connectors (SCSSWJ) and boundary concrete-filled-steel-tube (CFST) columns. Five full-scale cyclic tests were performed to study seismic performances of SCSSWJs. The studied parameters were connectors’ spacing and axial force ratio. Test results showed that flexure failure occurred to these five SCSSWJs with boundary CFST columns, which is characterized by tensile fracture of boundary steel tube, local buckling in the edge tube and faceplates, and concrete crushing. The test results revealed that increasing the spacing of J-hook connectors from 100 mm to 160 mm and 200 mm firstly slightly improves but then compromised the seismic behaviour of SCSSWJ due to early buckling of steel faceplate; increasing the axial force ratio significantly compromised the seismic behaviours of SCSSWJ. This paper also developed theoretical models to evaluate lateral peak shear resistance of SCSSWJ. The validations proved that the developed models predicted well lateral peak shear resistance of SCSSWJ with boundary CFST columns.

This paper evaluates the low-temperature compressive behaviours of square CFST stub columns (SCFST-SCs) in steel-concrete composite structures. 21 compressive tests were firstly performed on 14 SCFST-SCs and seven rectangular CFST stub columns (RCFST-SCs) at low temperatures of 20, -30, −60, and −80 °C. The key parameters in this testing program are low temperatures, wall-thickness of steel tube, and shape of the cross section. Concrete crushing, outward local buckling of steel tube, and tensile fracture at the corner of steel tube were three observed failure modes in the compressive tests. The SCFST-SCs and RCFST-SCs exhibited linear, elasto-plastic, and recession working stages. The test results showed that the ultimate compressive resistance and initial stiffness were increased, but the ductility was decreased for the square CFST stub columns as the temperature decreases from 20 to −80 °C. The wall-thickness of steel tube showed equivalent contributions on the improvements of ultimate compressive resistance due to different low temperature, but its influences on ductility tends to be weakened as temperature decreases. Modified Eurocode 4 code equations have been proposed for the predictions on ultimate compressive resistances of SCFST-SCs at low temperatures, and their accuracies were checked by 21 reported test results.

This paper firstly proposed steel-concretes-steel sandwich walls with J-hook connectors (SCSWJs) as protective structures in the Arctic offshore platforms. Followed, six large scale SCSWJs were tested under lateral cyclic loading to investigate their lateral seismic behaviours. The investigated parameters in the testing program included spacing of J-hook, concrete core strength, thickness of steel faceplate, and aspect ratio. Seismic behaviours of SCSWJs were reported in details, and the effects of these parameters on their seismic behaviours were reported and discussed. The test results showed that the SCSWJ failed in flexure mode with characteristics of tensile yielding of side plate and steel faceplate, concrete crushing at the bottom toe, and outward local buckling of steel faceplates. Pinching effect was observed in the load versus lateral drift curves after the peak load due to premature local buckling of side plates and faceplates locating between the first and second row of J-hook from the bottom. This paper developed analytical models to predict the peak lateral resistance of SCSWJ. The validations against 12 results from six cyclic tests confirmed that the developed models offered reasonable but conservative predictions on the peak lateral resistance of SCSWJ. This study promotes the applications of the SCSWJ in the earthquake-prone Arctic regions.