The analysis of failure in concrete and reinforced concrete beams with different reinforcement ratio

Abstract

In this paper the analysis of failure and crack development in beams made of concrete is presented. The analysis was carried out on the basis of the performed experimental investigation and numerical simulations. A fictitious crack model based on nonlinear fracture mechanics was applied to investigate the development of strain softening of tensile concrete in plain concrete and slightly reinforced concrete beams. The role of strain softening was also discussed according to the inclined crack propagation in highly reinforced concrete beams. The analysis has brought the evidence that the mode of failure in flexural beams varies according to a longitudinal reinforcement ratio. A brittle failure due to the formation of a flexural crack takes place in plain and slightly reinforced concrete beams, and strain softening of tensile concrete is of paramount importance at failure crack initiation and propagation. A stable growth of numerous flexural cracks is possible in moderately reinforced concrete beams, and then the load carrying capacity is connected with reaching the yield stress of reinforcing steel or concrete crushing in the compression zone. In higher reinforced concrete beams without transverse reinforcement, brittle failure can take place due to shear forces and the development of diagonal cracks. However, strain softening of tensile concrete is not the only mechanism influencing the propagation of an inclined crack. Such mechanisms as aggregate interlock and dowel action of steel bars contribute more importantly to the development of failure crack. Keywords Strain softening • Fictitious crack model • Failure process The paper entitled "The analysis of failure in concrete and reinforced concrete beams with different reinforcement ratio", presented at the ICSID 2017 Conference has been considered for publication in the Special Issue of the Archive of Applied Mechanics Journal (AAM SI ICSID 2017).

Crack mechanisms in concrete – from micro to macro scale

“…The use of the softening model in the analysis by Finite Element Method (FEM) rendered possible to describe more thoroughly fracture processes underlying the development of failure in concrete members. Also high crack resistance observed during the experiments as compared to cracking forces calculated on the basis of linear elastic theory could be properly explained [19].…”

“…Numerical simulations also helped to find a reason why the cracking moment in a lightly reinforced concrete beam is higher than in a plain concrete member ( [19], [23]). Significant differences in tensile stress distribution between non-reinforced and lightly reinforced concrete beam were obtained (see Fig.…”

“…The fracture process zone was modelled in the region of the highest bending moment by truss elements with nonlinear characteristics of the concrete; the bulk material was modelled by brick elements as elastic material. Source: [19], [23].…”

Analysis of fracture processes in reinforced concrete beams without stirrups

“…Therefore, the problem of shear capacity of members without transverse reinforcement is still attracted the interest of many researchers. Several works have been published recently, for instance [13][14][15][16][17]. The growing knowledge of shear behaviour in beams without stirrups brought the grounds for developing mechanical models of shear transfer mechanisms.…”

“…The important parameter which influences the failure process in the beams is the ratio of longitudinal reinforcement. The influence of the longitudinal reinforcement ratio on the character of failure in flexural members has been analyzed in depth in [17]. Slightly reinforced concrete beams fail soon after appearing of a few flexural cracks and the failure process has a brittle character.…”