Progressive collapse simulation of the steel-concrete composite floor system considering ductile fracture of steel

The prediction of the structural behavior under the progressive collapse scenario has received growing attentions in recent years. The failure of the bolted shear tab connection is usually dominated by the shear fracture. However, few researchers have considered the effect of the shear fracture in the progressive collapse simulation. This research develops a practical modeling routine to upscale the material shear fracture model in the collapse simulation of a large-scale floor system. The calibration and validation of the material shear fracture model employ five types of plate coupon specimens with significantly different stress triaxiality and Lode angle parameters. Via optimizing the coupon test data, this study determines the 3-D fracture locus of three fracture models, which are subsequently used to predict the fracture of a coupon specimen in the tension and shear conditions. Among the three fracture models, the Bai model has demonstrated good accuracy for a wide range of stress triaxiality and Lode angle parameters, while the applicability of the other two fracture models are confined to the stress triaxiality and Lode angle parameters, from which they are calibrated. These fracture models are also used to simulate the fracture of a girder-to-column connection under a center column removal scenario, which indicates the fracture in both the girder flange and girder web depends highly on the Lode angle. Prior to analyzing the full-scale composite floor system, the numerical study calibrates the fracture strain in the macro shell elements used to build the girder-to-column connection model, based on the fracture locus determined from the coupon tests. The fracture strain based shell element model is then used in the steel-concrete composite floor simulation, and demonstrates a good prediction of the structural resistance curve and the failure mode compared to the experimental results.