The influence of stress states on the behaviour of concrete is a key consideration in the design of concrete structures. This paper examines the results from a variety of studies that have been conducted into the effect of stress states on concrete strength and behaviour.
The compressive strength of concrete is an important factor in determining the structural behaviour of a concrete element and as such, the current state of stress in the material has a direct effect on its behaviour and performance. When concrete is subjected to normal stress, its strength increases with increasing age and temperature, whereas when concrete is subject to uniaxial stress, its strength decreases with growing age. It is difficult to generalise the effects of stresses on concrete properties and behaviour, as the results will depend on the type of concrete, the size of the element and the environmental conditions associated with the application of the load.
Concrete exposed to high levels of sustained loading will tend to become brittle over time, due to the increased levels of stress in the material. The brittleness of concrete exposed to uniaxial loading has been extensively studied and the results have demonstrated that post peak stress reduction, ultimate strains and stiffness decrease rapidly with increasing applied stresses. This behaviour is referred to as concrete softening. The softening of concrete can be caused by a number of factors, including creep, shrinkage, plastic strain and material fatigue.
Concrete is also susceptible to thermal effects and changes in temperature can significantly affect its strength. An increase in temperature can result in an increase in effective stress, which can in turn cause a decrease in the strength of concrete. Heat and thermal cycling can cause cracking in both hardened and fresh concrete and also reduce the strength of concrete.
In terms of alloy steel reinforcement, the influence of stress states is slightly different. When uniaxial tensile stress is applied to steel reinforcement, its strength increases with increasing age. This is due to the fact that steel is a ductile material and its strength and ductility increase with increasing temperature. While the strength and stiffness of steel increase with age and temperature, it is important to remember that steel is susceptible to corrosion and rusting, so it is important to pay attention to the effects of stress on the corrosion of the steel bars.
The effects of stress states on the behaviour of reinforced concrete are complex, as each type of concrete and steel behaves differently under different conditions. It is important to remember that the order of magnitude of the stress applied also has an effect on the behaviour and performance of the reinforced concrete. In most cases, the behaviour of reinforced concrete under tensile loading is more pronounced than under compressive loading and has a greater influence on its strength and behaviour.
In conclusion, the influence of stress states on the behaviour of concrete and steel reinforcement is an important consideration in the design of reinforced concrete structures. The variations in concrete properties under different stresses can significantly influence the strength and behaviour of concrete and steel reinforcement. It is important to note that even under similar levels of stress, each material behaviour can vary, depending on the type of material and the associated environmental conditions.
