Fracture Mechanism and Ductility Construction of Joints of H-Style Beam-Square Tubular Column

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.

Fracture Test and Analysis of Notched Bars Fabricated from Q235 Steel at Room Temperature

Tensile tests at room temperature were performed on 20 notched bars fabricated from constructional steel Q235 specified in Chinese National Standards. The effect of the notch radius, r, and that of the notch depth ratio, d/D, on the fracture model of the constructional steel is examined. The experimental results demonstrate that cracks initiate at the notched section. Specimens with a sharper notch radius (a smaller r) and a larger notch depth (a smaller d/D ratio) show poor ductility, but high fracture strength. The experimental data are further analyzed using an elliptical yield model together with an elliptical fracture model originally proposed by the first author. The stress field computed from the numerical procedure indicates that the crack initiation occurs at the center of the notched section which experiences the highest stress triaxiality ratio (óm/óseq). As the stresses at the notched section reach the limiting values determined from the elliptical fracture model, macroscopic fracture failure in the notched bar occurs.

Fracture Analysis of Plates with Elliptical Hole Fabricated from Q235 Steel

Fracture tests of 10 plates with elliptical hole fabricated from Q235 steel with the thickness of 4mm were conducted. The effecting of sharpness of elliptical hole (a/b) on fracture mode and fracture ductility of structure steel was studied. The experiment results show that the first crack initiates at the edge of the major axis of elliptical hole and expands towards the thickness of the plates. And then the crack expands quickly vertical to loading direction until the specimen ruptures. The fracture ductility is low for the specimen with the sharp elliptical hole. Numerical simulation and analysis of Q235 steel plates with elliptical hole were implemented based on an elliptical yield model and an elliptical fracture model. The simulated stress field shows that the stress concentration severely at the edge of the major axis of elliptical hole. The accuracy of the proposed elliptical fracture model is proved for predicting the fracture of Q235 thin steel plates with elliptical hole.