International Concrete Abstracts Portal

This work describes a modification to the two-parameter fracture method’s experimental procedure aimed at removing this operator/equipment dependence. With this method, three compliances are used to determine the focal point at which these compliances intersect. This focal point is then used to determine the slope of the unloading compliance that corresponds to the peak of the load vs. CMOD curve. The unloading compliance that corresponds to unloading at the peak load and initial compliance are then used to determine Ktc and CTODc as normally done with the Two Parameter Fracture Model. Use of this method makes it possible to remove operator and machine dependence, especially if the materials are extremely brittle, such as in pastes or high strength concrete, thereby permitting the loading and unloading to be programmed using testing software removing the need for manual operator loading changes. Tests on 15 mortar beams with 4 different notch lengths and initial unloading points ranging from 97% to 75% of maximum load are used to validate this approach. The experimental results are typically more consistent and better correlate to results from the peak load test method. These results indicate that utilizing the focal point correction typically reduces Ktc and CTODc by 12% and 38% respectively for the mortar tested thereby causing the TPFM and peak load method results to coincide even more closely.

Fracture mechanics concepts are increasingly being used in designing concrete structures and in understanding the fundamental behavior of concrete-like materials. Fracture mechanics concepts also have the potential for use in designing concrete FRP composites and in repairing concrete structures. Several of the 15 papers deal with these topics. Determining the fracture properties of concrete materials for various applications requires selecting the proper testing method, and many papers in the volume cover this issue. Practitioners, researchers, and potential users of fracture mechanics concepts will learn the recent technological advances, engineering applications, and research results presented. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP201

In the present paper the results of a three-dimensional finite element analysis of punching failure in reinforced concrete slabs are presented and discussed. The analysis is carried out using the three-dimensional special purpose finite-element code MASA. To demonstrate that the finite element code is able to realistically predict the punching failure, a punching test on an interior slab-column connection is analyzed. The results of the analysis are compared with the test results. Subsequently, a parametric study is performed where the concrete properties and the reinforcement ratio are varied. To investigate the size effect, for a fixed set of material parameters the slab geometry is scaled in a size range of practical interest.

Much research has been performed on measuring the fracture toughness of concrete, but inconsistent toughness values tn the literature leave some questions yet unanswered. This paper provides results ol a broad-based experimental program designed to determine (/certain tests produce an accurmte measure of h-actute toughness for concrete. The results of this study can he used to help make rational dccistons when selecting a combination of specimen size. geometry and data reduction method to measure the fracture toughness of concrete. To be accurate, the fracture toughness value must he the same as would he obtained from an infinitely large test specimen. To show that a value of fracture toughness is accumte requires consistent values from tests using different size and geometry specimens and different data reduction methods. Therefore. this investigation uses three sizes of single edge, SE. and round double heam. RDB, specimens. More than one data reduction method was appltcd to the results of each sire and geometry combination. Four different data reduction methods wet-e used: Itnear elastic fractut-e mechanics. the two-parameter method. the size-effect method, and the Barker method. Results are presented from three hatches of concrete, which represent two dtstinctively different mixes. The fracture toughness values ohtatned were not consistent withtn each batch; therefore, the most aceurate value could not he shown conclustvely. Howevjer, several significant conclusions were formed. The most common laboratory specimen size. no more than 310 mm deep/tall, is UOI sufficiently large to ohtarn an accurate measure of fracture toughness for concrete using either specimen geometry. Even the lat-gest specimens. 1240 mm-tall RDB. experienced significant nonltnear fracture mechanics conditions for all of the concrete mixes. Combtntng the experimental results wtth numerical simulations could provide sufficient informatton to judge uhich of the fracture toughness values, if any, are close to the value that would be obtained from an tnftnitely large spectmcn.

The initiation and propagation of interfacial cracks along the FRP-concrete interface may affect the concrete cracking behavior, load-carrying capacities, and stiffness characteristics.. Moreover, fracture in the shear stress transfer region may also lead to brittle premature failures of FRP-strengthened structures. All these factors must be taken into account in structure strengthening design. In order to estimate and simulate the fracture behavior of FRP-strengthened concrete structures, some basic material and physical parameters such as interfacial fracture energy, local interfacial shear strength and effective bond length are determined by some fundamental experiments. In this paper, experimental program using single-lap shear test and double-lap shear test specimens are presented. The variables include different types and layers of FRP sheets, and different types of the concrete surface preparation prior to bonding. Also, nonlinear equations, derived for two typical local shear-deformation curves with and without softening behavior, are used to discuss the shear stress transfer and fracture propagation behavior by comparing with experimental results, Through these experimental/analytical results, the interfacial fracture energies and the local shear stress-relative displacement relationships are determined.