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This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions. • The compressive behaviour of circular RACFSST stub columns after exposure to fire is investigated. • Post-fire compression tests on twelve circular RACFSST stub column specimens are conducted. • The influences of heating durations and RCA replacement ratios are analysed. • Thermal and mechanical FE models are validated against test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. [ABSTRACT FROM AUTHOR]

• Flat-ended circular hollow sections were tested in tension. • Three bolt configurations were established in flattened ends. • Bearing failure and net-section fracture were observed. • The test load increased with increase in the number of bolts. • An adjusted bearing coefficient is suggested for bearing. Experiments were performed to investigate the behaviour of 28 circular hollow sections (CHSs) in tension, with flat ends and three bolt configurations (2, 3 and 4 bolts). The length of the members between the flat ends was kept constant at 1500 mm for all CHSs, and the sizes of the sections ranged from 60.3x2.0 to 101.6x4.5. Two modes of failure were observed, viz; bearing failure (BF) and net-section fracture (NSF). CHSs connected with 2 bolts failed in bearing, whilst net-section fracture was dominant in sections with 3 and 4 bolts. The notion that the change in the number of bolts can lead to different behaviours of the connections is a significant contribution to knowledge, particularly if flat-ended CHSs are used as structural truss elements. This paper demonstrates that the sections are capable of supporting large loads, however, the capacity of the tested specimen did not reach the full yield strength. It is apparent from the tensile strengths that a larger increase in strength was accomplished when the number of bolts was increased from 2 to 3 bolts than from 3 to 4 bolts. A comparison of the tensile strength with the strengths predicted by the North American standard (AISI S100-16w/S1-18), Australia/New Zealand standard (AS/NZS-4600:2018) and European standard (EN 1993–1-3) confirm that both standards provides a reasonable assessment of the strength of the 3 and 4 bolt configuration, which failed purely by net-section fracture. However, for the 2-bolted connections, which failed in bearing, it is proposed to use AS/NZS 4600:2018, with a bearing coefficient of C = 2.85, instead of C = 3.0, to increase the accuracy of the bearing strength expression for these specimens. [ABSTRACT FROM AUTHOR]