International Concrete Abstracts Portal

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.

At the Fall meeting of the American Concrete Institute in Philadelphia in 1990, ACI Committee 446 sponsored a technical paper session entitled "Design Based on Fracture Mechanics." The purpose of the session was to present recent advances in our understanding or fracture in concrete in such a way that practitioners could understand and use it, and also to identify ways in which practitioners can make use of fracture mechanics in design of concrete structures. Currently, designers in the United States use the ACI 318 Building Code, which currently makes absolutely no use of fracture mechanics concepts. To enable designers to use fracture mechanics, a logical next step would be to incorporate these concepts into a revised building code. 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. SP134

Discusses the shear design problem in concrete in the context of mixed mode crack propagation in concrete structures. Shear behavior and fracture of precast concrete segmental bridges are presented as a design case study. Joints between the precast segments of these bridges are critical locations through which large shear stresses, combined with normal stresses, must be transmitted. Crack initiation and propagation at these locations represent a mixed mode concrete fracture problem. General concepts for the representation of mixed mode fracture in concrete are briefly discussed, and a combined analytical and experimental methodology is presented for predicting this cracking behavior. Finally, using the developed fracture mechanics approach, a preliminary design concept is proposed for the shear design of prestressed concrete elements.

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.