Numerical simulation and fracture analysis were performed on conventional joint of H-style beam-square steel tubular column based on suggested elliptical yield model. The modified coefficient of elliptical fracture model was obtained by equivalently calculating the effects of residual stress and flaws. Using the elliptical fracture model with equivalently calculating the effects of residual stress and disfigurement for evaluation, the parameters of slot holes and horizontal haunch at beam flanges on failure mode of joints of H-style steel beam-square steel tubular column were studied by finite element method. The results indicate that the plastic rotation of joints of H-style beam-square steel tubular column with slot holes and horizontal haunch at beam flanges reach 0.03rad and meet with the requirement of the interim guidelines FEMA, and the loading capacity decrease within 15% compared with that of the conventional joint.

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Fracture tests were performed on 20 notched bars fabricated from E50 solder at low temperature (-47°C~-43°C). The effect of notch radius, r, and notch depth, d, on fracture mode of E50 solder was studied. The experimental results demonstrate that cracks initiate at the center of notch section and the notched bars fracture at the notch section at low temperature. The fracture mode is cleavage fracture and the fracture sections are coarse. Specimens with a sharper notch radius (a smaller r) and a larger notch depth (a smaller d) show poor ductility, but high fracture strength. The stress-strain curve of E50 solder tested on standard specimen at low temperature (-47°C~-43°C) exhibits the character of yielding, hardening and necking. The ratio of ultimate strength to yield strength, σu/σy, and the ductility, δ5, at low temperature meet with the requirement in plastic design for structural steel.

In order to study fracture mechanics of high strength steel with the moderate thickness, fracture tests were performed on 10 plates with elliptical hole fabricated from high strength steel Q345 with the thickness of 16mm. The effect of the notch sharpness (the ratio of the length of short axis to that of long axis of elliptic hole, b/a) and the notch depth (the ratio of the length of long axis of the elliptic hole to the width of plate, 2a/w) on fracture model of high strength steel was examined. Test results show that the first crack initiates at the notch edge. The fracture ductility is lower for the specimens with the sharper notch (a smaller ratio b/a) and the deeper notch (a larger ratio 2a/w), and the point of crack load lies in hardening phase of load-displacement curve. The fracture ductility is higher for the specimens with the obtuse notch (a larger ratio b/a), and the point of fracture load lies in necking phase of load-displacement curve. The ultimate strength of notched plates is independent of the notch sharpness (b/a) and the notch depth (2a/w).