108年1月2日(三) 10:00 休士頓大學Prof. Roberto Ballarini演講
|訊息內容||演講者: Prof. Roberto Ballarini, 休士頓大學土木系
演講題目: Fracture Mechanics Design of Anchor Bolts: Progress and Future Needs
Fracture Mechanics Design of Anchor Bolts: Progress and Future Needs
In the 1980’s it became evident that the load-carrying capacity of steel anchors embedded in concrete, for cases where the failure is a result of the pullout of a concrete cone, is directly related to the concrete fracture toughness and not to its compressive/shear/tensile strengths. Experimental, theoretical and computational studies made it abundantly clear that pulling an anchor out of a concrete matrix amounts to performing a fracture toughness test, and that the load-carrying capacity is not proportional to the surface area of the pullout cone. This led to the replacement of strength theory-based design formulas for the load-carrying capacity of anchors with those derived using linear elastic fracture mechanics (LEFM); a precedent for the application of fracture mechanics to the design of concrete structures. However, while the formulas that are available in the ACI and CEB codes to determine the capacity of an individual anchor are consistent with LEFM, the same codes retain that for a group of anchors (and for other configurations) the load-carrying capacity is proportional to the surface area of the pullout cone(s); essentially the design formulas multiply the LEFM based formula for a single anchor by a dimensionless factor related to the surface area of the pullout cone and the anchor spacing. In this talk it is shown through incremental crack propagation simulations of the failure scenario of an idealized anchor group geometry that the formula provided by the design codes lead to inaccurate predictions, and it is suggested that the resistance to break out of a group of anchors and of other complex configurations such as anchors near free surfaces should be predicted using fracture mechanics-based simulations.