Seite - 1293 - in Book of Full Papers - Symposium Hydro Engineering

to 4 ℃ higher than the air temperature. In Xiluodu project, according to the stress analysis, the difference should be under 16℃ in the most unfavorable condition. （a） Schematic diagram of concrete cooling process control （b） Difference temperature control zone of different dam section Fig. 1 The time-space control method of the concrete temperature[9] 2.1.3. warn for over transfinite temperature value Local environment is an important factor affecting the concrete temperature, besides the grouting temperature. Both cold wave in summer and hot wave in winter will cause transfinite temperature. Therefore, the control system has to connect to the system of weather forecasting and timely adjust the limits, considering the principle of coordinating temperature and the problem of cracking in early aged concrete. Like in Xiluodu project, the temperature drop ratio is limited no more than 0.5℃ per day in the whole period of cooling down. Particularly, in the middle term of cooling down, the ratio is limited in 0.2℃ per day. In practice, continuously and gently reducing the temperature is an important measure for reducing temperature stress. The system must automatically adjust the temperature gradient to the feedback. 2.2. ANALOG PID CONTROL THEORY In current engineering, the temperature of concrete is affected by many factors. The process is very complex as following: (1) too many unknown factors affect the process. (2) a concrete section is a system of great inertia and delay. (3) the temperature gradient must be limited to as small as 0.2 to 0.5℃ per day and the temperature curve must be smooth and steady, neither suddenly going up nor down. (4) temperature in concrete is non-linear distributed. Since these characteristics, classic theory of control cannot meet the requirements. We should combine the modern and classic theory and work out an analogous PID system with property of fuzzy. 1293