Flexural behaviours of concrete-filled circular steel tubes at cold-region low temperatures

Abstract

This study investigated the flexural behaviours of concrete-filled steel tubes (CFSTs) employed in cold-region engineering structures. Firstly, two-point loading tests were conducted on seven circular CFSTs and two square CFSTs to investigate their flexural bending behaviours. The studied parameters included low temperature levels (T = 20°C, −30°C, −60°C, −80°C) and cross section types. It indicated that all CFSTs at low temperatures exhibited flexural failure with characteristics of vertical smeared cracks in concrete core and flexure large deformations (defection/span ratio ≥ 6.5%). Low temperatures did not influence the flexural failure mode of CFSTs. The load-deflection curves of CFSTs exhibit a ductile manner with three working stages. Reducing T from 20 to −30, −60, and −80°C resulted in an average increase on the ultimate bending resistance (or initial stiffness) of CFSTs 8.5% (16.5%), 15.4% (23.4%), and 26.5% (32.7%), respectively. Moreover, with the same cross-section area and steel content, square CFSTs exhibited higher bending resistance and initial resistance than circular CFSTs. AISC 360 and Eurocode 4 were checked to estimate the flexural resistance (M_u) and initial stiffness (K₀) of circular CFSTs at low temperatures. Moreover, theoretical models were formulated to forecast M_u and K₀ values for circular CFSTs at low temperatures.