Discrete fracture analysis using locally refined T-splines

Locally refined T‐splines are used to model discrete crack propagation without a predefined interface. The crack is introduced by meshline insertions in the locally refined T‐mesh, which yields discontinuous basis functions. To implement the method in existing finite element programs, Bézier extraction is used. A detailed description is given as to how the crack path is inserted and how the domain is reparameterized after insertion. The versatility and accuracy of the approach to model discrete crack propagation without the crack path being predefined is demonstrated by two examples, namely, an L‐shaped beam and a single‐edge notched beam. When the crack approaches the physical boundaries, limitations to reparameterization arise, as will be discussed at the hand of a double‐edge notched specimen

Mixed-mode fracture of concrete: An experimental approach

Civil Engineering and Geoscience

Analysis of temperature stresses in concrete breakwater elements: Hollow cubes and Tetrapods

In this report, the results of a numerical parameter study on temperature stresses caused by hydration of cement in concrete breakwater elements are shown. Two different geometries were analysed namely hollow cubes and tetrapods. The problem encountered in solid cube breakwaters is the undesirable temperature build up between the core and the outside surface. The main reason for the temperature build up, is the thermal heat, which is generated due to the heat of hydration of cement from the time of casting. This thermal gradient induces eigen-stresses and causes the early age cracking. The choice of a hollow cube is a way to reduce the temperature gradient and thus the eigenstresses. A parameter study is undertaken in order to arrive at an optimum dimension based on the thermal gradient and the eigen-stresses. The variables are the cube dimension (i.e., height H = 2, 3 and 4 m with the inner diameter to the height ratio d,/H = 0.4), the size of the hole (d= 0.9, 1.2 and 1.5 m for the 3 m hollow cube only), the cement content (225 and 325 kg/m3), the initial concrete mix temperature (5, 15 and 25 °C) and the degree of isolation (with and without isolation). For the analyses of the tetrapods, two geometries were chosen. The total height H of the tetrapod was 3.11 and 4.15 m with corresponding diameters D = 1.5 and 2 m. The favourable conditions for the reduction in the temperature gradient and the tensile stress peak for the hollow cubes were: the low mix temperature, the larger hole diameter, the low cement content and the smaller hollow cube. From the range of hollow cube specimens analysed, it appears the 2 m hollow cube is the best choice based on the temperature gradient as well as the tensile stress peak generated.Design and ConstructionCivil Engineering and Geoscience

An Experimental Study of Shear Fracture and Aggregate Interlock in Cementbased Composites

In the present paper the results of an exploratory study with the recently developed biaxial tension/shear apparatus of the Stevin Laboratory of Delft University of Technology are presented. The apparatus is unique in the sense that square double-edgenotched concrete plates up to a size of 200 x 200 mm can be loaded in any combination of tension and shear in displacement control. The two loading axes are completely independent of one another. In the paper, both results of experiments on plain concrete and on slurry infiltrated fibre concrete (SIFCON) are presented.Stevin LaboratoryCivil Engineering and Geoscience