International Concrete Abstracts Portal

Progressive microcracking and crack closure effects are the most important phenomena which need to be described in finite element calculations of reinforced concrete structures subjected to cyclic or seismic loads. Microcracking produces a loss of stiffness which is usually modeled with continuous damage mechanics. Crack closure effects such as inelastic deformations and stiffness recovery remain features that must be incorporated in the constitutive relations describing the response of concrete under cyclic loadings. These effects are introduced into a novel damage model in a rigorous, consistent fashion. An attempt to derive the constitutive relations for fiber reinforced concrete using this model is also described. The implementation of these constitutive relations into a layered beam finite element code is discussed, and computations on medium-size bending beams and a beam-column joint subjected to cyclic loading are compared with experiments. Although the computational method remains simple and sufficiently fast for engineering applications, the good agreement obtained with test data shows that the constitutive relations capture very well the main characteristics of the behavior of concrete.

The fracturing phenomenon in reinforced concrete structures has a profound effect on their flexural stiffness. Consequently, the effect of cracking in reinforced concrete has been the subject of intensive investigation for many years. Because of the complexities associated with the development of feasible methodologies, analytical procedures continue in many respects to investigate and verify with experimental results. Historically, a series of rational analytical procedures have evolved to incorporate various methodologies such as material nonlinear models, failure criteria, and layered finite elements to account for the effect of cracking. However, it is to complex and expensive to apply such approached in design practice. For practical purposes, the Direct Design Method and the Equivalent Frame Method are often adopted in accordance with ACI 318 to design two-way reinforced concrete slabs. But the effect of cracking in concrete is not included in those two methods. Hence, an incremental-iterative procedure is implemented as a tool to design reinforced concrete slabs. The proposed incremental-iterative proceduce follows Section 9.5.2.3 as defined in ACI 318 to treat the effect of cracking in reinforced concrete slabs. Although the use of ACI 318 Eq. (9-7) is primarily provided for flexural members, it is permitted for application for two-way slabs as well. In essence, cracks are smeared and assumed to propagate in in-plane directions determined by the maximum principal moment in a finite element. The effective slab stiffnesses are modified accordingly as progressive cracking is detected under increasing loads. Analytical results from design cases are presented to demonstrate its applicability. In addition, a modified procedure is presented to include the ACI 446.1R, based on fracture mechanics of concrete. Further investigations are also recommended for the future developments in the analysis and design of reinforced concrete slabs.

Proposes a fracture mechanics approach to crack control design of reinforced concrete beams in flexure (Mode I). The model yields the minimum area of tension steel required of a concrete beam of rectangular cross section to safely sustain a design moment within the prescribed limit of permissible crack height. An iterative procedure is developed by satisfying simultaneously the fracture criterion of crack growth and the equilibrium condition at incipient fracture.

Summarizes and presents preliminary results of a round-robin analysis of anchor bolts organized by RILEM TC 90-FMA, Fracture Mechanics of Concrete-Applications. The analyses employed finite element models using fracture mechanics approaches for the most part. The assumptions used in establishing the material/cracking models varied with investigator and included linear elastic fracture mechanics (LEFM), the fictitious crack model (FCM) with linear softening or non-linear softening, a fixed crack line, a variable crack line with non-rotating cracks or rotating cracks. Crack propagation was determined using Mode I parameters, in some cases, with consideration of mixed mode behavior.

Computer analyses of the pullout tests of anchors embedded in concrete were performed for the Round Robin Analysis of the RILEM Committee on Fracture Mechanics of Concrete. The test specimens were concrete plates with steel anchors in the plane stress state. The geometry of the specimen was varied in order to study the size effect and the shape effect. The investigation was performed by means of the computer simulation of the tests. Only limited comparison with the real laboratory experiments was used to verify the results. The computer simulation was made by means of the program SBETA, which was developed by the authors and is based on the smeared crack approach and the nonlinear elasticity. Two crack models were used to analyze each specimen: the rotated crack model and the fixed crack model. In total, 36 computer simulations were made. Each simulation provided the load-displacement diagram of the anchor and a sequence of crack patterns, deformed states, and stress states. A size effect law in the exponential form was derived from the computer experiments.