【正文】 fter the operation. Thermal stress is mainly caused by external temperature changes, the stress and the first twophase superposition of residual stress. Under the thermal stress caused by the reasons can be divided into two categories: (1) selfstress: there is no constraint on the border or pletely static structure, if the internal temperature distribution is nonlinear, due to structural constraints arising from their cotemperature stress. For example, the conversion layer of its relatively larger size, concrete cooling surface temperature low, the internal temperatures are high, the surface tensile stress, pressive stress appears in the middle. (2) bound by stress: the structure of all or part of the boundary bound by the outside world can not be freeform deformation caused by stress. Roof box, such as concrete and concrete barrier. Both the temperature and the concrete stress is often caused by shrinkage of the bined effect of stress. Known to be in accordance with an accurate analysis of the temperature of the thermal stress distribution, size is a more plex task. In most cases, the need to rely on model test or numerical calculation. Creep of concrete so that the temperature there is considerable stress relaxation, thermal stress calculation, we must consider the effects of creep, is no longer calculated in detail here. 第 108 頁 3. temperature control and measures to prevent the cracks In order to prevent cracking, reduce the thermal stress can control the conditions of temperature and to improve the binding of two aspects. Temperature control measures are as follows: (1) used to improve the aggregate gradation, dry hard concrete, mixed mixture, add airentraining agent or plasticizer, etc. measures to reduce the amount of cement concrete。 (2) mixing concrete by adding water or cooling water will be gravel and pouring concrete to reduce the temperature。 (3) pouring hot days to reduce the pouring of concrete thickness, the use of pouring heat levels。 (4) laid in concrete water pipes, access to cold water to cool。 (5) the provisions of reasonable time, the temperature drop when the surface insulation, concrete surface in order to avoid a sharp temperature gradient。 (6) Construction of longterm exposure to block the surface of the concrete pouring, or thinwalled structures, thermal insulation in the cold season to take measures。 Measures to improve the constraints are: (1) a reasonable subblock joints。 (2) basis to avoid too much ups and downs。 (3) reasonable arrangements for the construction process, to avoid excessive side elevation and longterm exposure。 In addition, to improve the performance of concrete to improve the anticracking ability, to strengthen the conservation, to prevent surface drying, in particular, is to ensure the quality of concrete is very important to prevent cracks, should pay special attention to avoid crosscracks appears to restore the integrity of its structure it is very difficult, so the construction should be to prevent the occurrence of crosscutting the main crack. In concrete construction, in order to increase the turnover rate of the template, often require new pouring concrete as soon as possible. When the concrete temperature is higher than the temperature should be appropriate to consider time, so as to avoid the early cracks in the concrete surface. New pouring early, a lot of the surface tensile stress, a temperature shock phenomenon. Concrete pouring in the early heat of hydration as a result of the dissemination of the surface caused by a large tensile stress, when the surface temperature is higher than the temperature at this time to remove the template, a sharp fall in surface temperature is bound to lead to 第