Behavior Of Circular Steel Tubes Research Articles

The Stability of Corroded Circular Steel Tubes Under Axial Compression Investigated Through Testing, Finite Element Analysis and Theoretical Approaches

Circular steel-tube members are extensively used in various large-scale steel structures. The detrimental effects of corrosion on the ultimate bearing capacities of these structures require urgent attention. This study designed six circular steel tube specimens to explore the degradation pattern of the ultimate bearing capacity of corroded circular steel tubes under axial compression; three were subjected to accelerated corrosion by electrification, and the other three were used as the control group. Following the accelerated corrosion test, both groups of specimens were subjected to material-property and axial-compression tests. These tests provided data on the bearing capacity and midspan displacement of the corroded circular steel tubes, allowing for the construction of load–displacement relationship curves. The test results demonstrate that corrosion significantly affects the bearing capacity of circular steel tubes. As the severity of the corrosion increased, the bearing capacity and stiffness of the corroded circular steel tubes progressively weakened. To simulate the behavior of circular steel tubes, a numerical model was established that provided the ultimate bearing capacity under axial compression and generated load–displacement curves. The simulation results closely aligned with the test results. This study introduced a novel approach for accurately computing the stability-bearing capacity of circular steel tubes subjected to corrosion and axial compression. Comparative analyzes with test results validated the superior performance of the proposed method in accurately predicting the ultimate bearing capacity.

Effect of local corrosion on the axial compression behavior of circular steel tubes

The sustainability of spatial structures, where the main bearing members are steel tubes, is becoming more and more prominent. In order to investigate the effect of local corrosion on the mechanical properties and ultimate compressive strength of circular steel tubes, outdoor accelerated corrosion tests on 11 steel tubes were conducted considering the effects of different corrosion locations and corrosion degrees. The experimental results showed that the ultimate bearing capacity of the specimens was significantly affected by local corrosion, and the corrosion in the middle of the tube was more unfavorable than that in the end. Moreover, local corrosion can change the failure phenomenon of circular steel tubes. Finite element analysis on the bearing capacity of circular steel tubes after local corrosion was carried out, and the reliability of the simulation method was verified by comparison with experimental findings. The stress evolution on different sections during axial compression was also analyzed. Finally, the effect of different corrosion conditions on the bearing capacity was studied using parametric analysis. The analysis results demonstrated that the circumferential corrosion ratio and corrosion depth are important indices to evaluate the corrosion effect. Meanwhile, it was found that the corrosion location has a significant impact on the residual bearing capacity of tubes; however, the impact decreases with the increase in circumferential corrosion ratio and corrosion depth. The research results of the present work can provide a technical reference for the study of the mechanical properties of building components, such as round steel tubes, after corrosion.

Buckling behavior of circular steel tubes infilled with C170/185 ultra-high-strength concrete under fire

Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in design of composite columns. This paper investigates the structural fire performance of UHSC filled steel tubular (CFST) columns. Experimental studies were carried out on 9 CFST columns with C170/185 concrete under standard ISO fire. The columns were subjected to concentrated or eccentric compressions and then heated to failure to record the fire resistance time. The simple calculation model in EC 4 was examined by predicting the fire resistance time and comparing them with the test results; the axial force–moment (N-M) interaction strength model for room temperature design was extended to predict the fire resistance. The test results showed that the CFST columns with UHSC exhibited similar fire performance to those with normal/high strength concrete with respect to thermal expansion, axial contraction and failure modes. Adding 0.1% polypropylene fibers in UHSC was found to be effective in preventing explosive spalling especially when it was heated rapidly under the standard fire. The N-M interaction strength model gave better predictions than the EC 4 model as it gave less scattered results when compared to the test data. EC 4 buckling curve “c” was found to be conservative in predicting the fire resistance time of CFST columns with UHSC subjected to pure compression. Parametric study showed that the fire resistance of CFST columns with UHSC reduced faster than those with normal strength concrete (NSC) and high strength concrete (HSC) in early stage of heating but slower at the later heating stage. Within the practical range of load level (i.e.,≤0.7), the CFST columns with UHSC employed by this study had better fire resistance than those columns infilled with NSC and HSC.

Research on Behavior of Circular Steel Tubes with Different Coating Subjected to Fire Load

The fire experiment was conducted for three of circular steel tubes protected with two different gypsum fireproof panel and the steel tube without any protective material. The fire response temperature of surface of steel tubes was measured and the axial compressive bearing capacity of the specimens after fire were tested and analyzed. The test results show that gypsum fireproof panel has better fire protection characteristics. It is noted that the variation of temperatures of inner surface of gypsum fireproof panel under fire is consistent with the temperature of outer surface of the steel tube. The maximum difference of temperature between the outer surface of the tube and the furnace space is 150°C as the fire keeps stable for the steel tube without any protection. It is concluded that two of the specimens protected with gypsum fireproof panel have larger post-fire capacity, which means that the gypsum fireproof panel has better effect on fireproof of the steel tube under fire.