1. The formation process of temperature stress
Regarding the formation process of temperature stress, it is mainly divided into the following three stages:
1. Early temperature stress
This stage is from the beginning of pouring concrete to the end of cement heat release. The main characteristics of this stage are: first, the cement releases a large amount of heat of hydration; second, the sharp change of the elastic modulus of the concrete. This period develops residual stresses in the concrete due to the change in modulus of elasticity.
2. Medium-term temperature stress
This stage is from when the exothermic effect of cement basically ends to when the concrete cools to a stable temperature. During this period, the temperature stress is mainly caused by the cooling of the concrete and the change of the outside air temperature, and these stresses are superimposed with the residual stress formed in the early stage. The modulus of elasticity of the concrete did not change much during this period.
3. Late temperature stress
This stage is the operation period after the concrete has completely cooled. Temperature stress is mainly caused by changes in external air temperature, and these stresses are superimposed with the first two residual stresses.
二、 Causes of temperature stress
1. Self-generated stress
There are no constraints on the boundary or a completely static structure. If the internal temperature is distributed nonlinearly, the temperature stress that occurs due to the mutual constraints of the structure itself. For example, if the structure size is relatively large, the surface temperature of the concrete is low when it is cooled, and the internal temperature is high, so tensile stress appears on the surface and compressive stress appears in the middle.
2. Constraint stress
The stress caused by all or part of the boundary of the structure being constrained by the outside world and unable to deform freely.
