## 4 Thermal Stress Analysis and Optimization of Contraction Joint Distance
### Optimization of Contraction Joint Distance  
When mentioning thermal tensile stresses (TTS) in CGD, as a rule they are always related to the normal stresses acting in the direction parallel to the dam's axis. Regarding the adopted coordinate system in the model, these are \(\sigma_{z}\) stresses which are designated as SZ in the software. By convention, tension stresses are positive. The length of the monolith is a distance in the direction of the longitudinal axis between two adjacent contraction joints. The length of the monolith is also equal to the length of the block. Parameters of impact on the position and number of joints are SF in the dam's body resulting from the thermal processes, the topography of the terrain, the adopted construction method, as well as the concrete pouring technology. Having in mind that CGD is an exceptionally massive structure, the greatest number of joints is constructed to limit TTS [1]. The methodology for optimization of the monolith length presented in this paper is based on successive reduction of its length, by monitoring for the exceedance of the concrete tensile resistance in the mid-plane of the monolith. The adopted monolith length  
Figure 7: Filling and water level in the reservoir in the exploitation phase. Figure 9 shows the concrete temperature in node 2787, which is located in the midplane of the monolith in the middle of the upstream face of block 25 (Figure 8), as a function of the duration of construction and exploitation. The node is exposed to the air with temperature periodically varying annually from \(-\)2.0 to 33.0 \({}^{\circ}\)C, from the moment of casting of the block (121 st day from the commencement of construction) up until the moment when it came in contact with the water from the reservoir (1020 th day from the commencement of construction) with a constant temperature of 9.0 \({}^{\circ}\)C. In Figure 9, the annual changes (long periods) and the daily changes (short oscillations) can be noticed. These changes are a consequence of variations in the air temperature during annual and daily oscillations. As opposed to the concrete temperature in node 2787, the concrete temperature in node 2853 (Figure 10), which is located in the mid-plane of the monolith in the middle of the downstream face of block 34, is, from the moment of the casting of the block (162 nd day from the commencement of construction) up until the end of the analysis period considered (1804 th day since the construction started), under the influence of air temperature on the substrate. The concrete temperature is \(\sim\)1  
whose temperature varies periodically annually from \(-2.0\) to \(33.0\)\({}^{\circ}\)C. In this case, the annual and daily temperature changes reflected through long and short oscillations shown in the figure can be noticed, as well. As the monolith is not in contact with the downstream side's tailwater, the impact of the water temperature in the nodes on the downstream face is non-existent. The concrete temperature in node 3016, which is located inside the mass of the concrete, in the mid-plane, and in the middle of the top face of block 61, is shown in Figure 11. After placing the block (418 th day from the commencement of construction) the node is exposed to December's air temperatures (which ranged from 0 \({}^{\circ}\)C to 4.5 \({}^{\circ}\)C). After 4.5 days, block 63 is poured on top of block 61, and afterward the subsequent blocks. The temperature in this node starts to rise as a consequence of the released hydration heat from cement and reaches the extreme value of 35.0 \({}^{\circ}\)C after 70 days.