abstract
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Welded built-up structural steel members are widely used as columns, beams, and beam-columns in various buildings, bridges, industrial complexes, etc. Modern cutting techniques are used in the fabrication of such members. Besides traditional saw cutting and oxy-flame cutting, the modern cutting techniques include plasma cutting, laser cutting, water- jet cutting, etc. The different cutting techniques induce different degrees of Heat Affected Zones (HAZ), which subsequently creates different degrees of geometrical and mechanical imperfections (residual stresses). Therefore, it could be expected that the true behavior of structural steel columns manufactured by such cutting techniques be different.
The main objective of this investigation was to study the characteristics and behavior of plasma cut-welded H-shaped steel columns at different slenderness ratios. However, this investigation also considered similar flame cut-welded H-shaped steel columns for comparison purposes. The H-shaped column sections were fabricated from plates having specified yield strength of 350MPa. First, the initial plate was cut into plate strips and then the plate strips (flanges and web) were welded together to form the H-shaped section in this investigation. The strength of these columns were established under uni-axial compressive loading with pinned end condition, allowing for minor axis rotation. Moreover, the structural imperfections such as residual stresses and geometrical imperfections were established. The residual stresses distributions were established at various stages of fabrication processes using the "method of section" technique. That is, the residual stresses in initial plate, plate strips (cutting effects), and column sections (cutting and welding effects) were established. Similarly, the geometrical imperfections were established at various stages of fabrication processes in this investigation.The temperature profiles were measured during the cutting and welding processes. As part of the scientific documentation, the mechanical characteristic of virgin steel plates were obtained by standard coupon tensile test.
Based on the experimental results on column strength, the general behavior of plasma cut columns and flame cut columns were similar. However, it was found that the plasma cut-welded steel columns seemed to carry higher loads than that of flame cut-welded columns for higher slenderness ratios( λ≥1). For lower slenderness ratios (0.5<λ<1), it was found that the flame cut-welded columns had higher strength than plasma cut-welded columns in this investigation. The residual stress distribution of both plasma cut column section and flame cut column section had the same general distribution. However, in general, the flame cut columns had high intensity of tensile residual stresses at their flange tips than the plasma cut columns. Moreover, the out-of-plane imperfections of column sections were within the code limitations. However, it was found that the flame cut-welded H-shaped steel columns seemed to have higher out-of-plane imperfections than the similar plasma cut-welded H-shaped steel columns in this investigation.