Abstract
To study fatigue of defective welds, beam-column joints were cyclically loaded at MWD Central Laboratories. However, local buckling occurred in the beam flanges during the first few cycles at displacement ductilities 2.25-2.6. Despite the buckling, the peak resisted load had a maximum of 15% reduction after 10 cycles at these ductilities, and the hysteresis loops showed little change in shape. Nevertheless, because steel frame structures can be expected to sustain a ductility demand of about 4/SM or 6, there is clearly some doubt as to whether the strength of a system already buckling at a DF < 3 would be maintained under the design earthquake. The 310 UB 40 beam tested complied with the current NZ Steel Code, which required no stiffeners in this case.
Highlights
STATEMENT OF PROBLEM To study fatigue of defective welds, beam-column joints were cyclically loaded at MWD Central Laboratories
Local buckling can be studied from the theory of "torsional buckling of a restrained plate" which provides an upper limit of the ratio of flange width to thickness for no buckling of[3]:
Equation 1 is well verified by experimental results*^ for monotonic loading
Summary
STATEMENT OF PROBLEM To study fatigue of defective welds, beam-column joints were cyclically loaded at MWD Central Laboratories. Local buckling is generally only of concern in plastic design^ and is often coupled with lateral torsional buckling^. Because local buckling causes the crosssection to become unsymmetrical, the rate of lateral deformation increases. There may be little strength degradation with buckling, it may effect local stability.
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