Incorporating Fracture Mechanics in the Design of Reinforced Concrete Structures

Abstract

Concrete is usually described as the quasi-brittle material; its internal structure is entirely different from that of other engineering materials, which observes that the fracture processes in concrete are much different from that of classical theories. Concrete shows micro-cracking even at initial stages of construction. Under the action of applied loading stress concentration is developed around the tip of initially introduce micro-cracks and as the concentration of stresses reaches an ultimate capacity the micro cracks tend to overlap and propagate. The contemporary codes tend to ignore fracture mechanics parameters on the basis of enhanced level of safety, thus providing more the required conservative designs. These above mentioned reasons have grasped the interest of our research team. For most of the structural engineering applications concrete needs to be reinforced because its tensile strength is only one tenth of its compressive strength. The presence of conventional reinforcement makes it difficult for cracks to initiate and propagate. Once they go across reinforcement layers, the rebars provide considerable resistance to the opening of the crack. Therefore the percentage of reinforcements, location and orientation should be ideal enough since failure mode is highly dependent on the said attributes. Recently another important material is used in contrast to steel bars, known as fibers. Most significant applications of fibers are generally to prevent or control the tensile cracking occurring in concrete structures. Structural steel fibers are the fibers exhibiting structurally-effective properties such as increase of toughness and/or load-carrying capacity after cracking. The introduction of steel fibers ensures the ductile failure of Concrete members. In this research our objective is to generate a methodology for designing Reinforced Concrete Structures by incorporating the theories of Fracture Mechanics. Moreover we shall discuss the size effect behavior of Reinforced Concrete structures based on the principles of Fracture Mechanics which states that, the shear strength of reinforced concrete beams which decreases with increase in depth. The evidence of the size effect has been emphasized through several research efforts made on normal beams. Some predictive equations have been proposed for evaluating the size-dependent shear strength of such beams. Reviewing these early researches we’ll model the RC structural elements in computer aided software. On the basis of above described problems we’ll provide suitable justifications on why fracture mechanics should be included in building codes of ACI for designing and analysis.