# The Effect of Subgrade Coefficient on Static Work of a Pontoon Made as a Monolithic Closed Tank
## 4 Discussion  
The prefabricated pontoon analysed in the study as a ready-made element makes a good alternative to currently available reinforced concrete platforms, consisting of a box and a separate cover. The article presents the results of calculations made for a monolithic rectangular tank intended to be used as a pontoon. There are still problems related to the analysis, design and execution of concrete floating structures [38]. The literature on the subject provides few works related to this subject. This article presents a pontoon that was made on a 1:1 scale. The authors of [7] presented the series of closed tanks for use as a pontoon with the following axial dimensions: \(\mathrm{l}_{x}\), \(\mathrm{l}_{y}\) and \(\mathrm{l}_{x}\) at a ratio of 1:1:0.5; \(\mathrm{l}_{x}\), \(\mathrm{l}_{y}\) and \(\mathrm{l}_{x}\) at a ratio of 2:1:0.5; \(\mathrm{l}_{x}\), \(\mathrm{l}_{y}\) and \(\mathrm{l}_{x}\) at a ratio of 3:1:0.5; and \(\mathrm{l}_{x}\), \(\mathrm{l}_{y}\) and \(\mathrm{l}_{x}\) at a ratio of 4:1:0.5. However, the effect of Poisson's ratio and the subgrade coefficient was not taken into account. When analysing the tanks of increasing length, it can be concluded that, for long tanks with size proportions \(\mathrm{l}_{x}\), \(\mathrm{l}_{y}\) and \(\mathrm{l}_{x}\) at \(\gamma\):1:0.5 for \(\gamma>3\); the effect of disturbances resulting from the gable walls' load disappear in their central part; and the central part works similar to a closed frame, i.e., a rod system. The paper [8] shows the effect of the increasing values of bottom thickness on the values of deflections and moments. By thickening the bottom at all points of the calculated tanks, the following regularity was noticed: deflections decreased when the bottom plates became thicker. It was observed that the hydrostatic load acting on the tank walls and the uniform load acting on the bottom combined with an increase in bottom thickness led to an increase in bending moments acting in the middle of the bottom plate span towards a shorter span, while reducing bending moments at other points of the tank. In contrast, the uniform load acting on the upper plate led to an increase in bending moments, but only in the bottom, both for fastening moments and for the moment working in the centre of the plate towards a shorter span. Bending moments at other points of the tank practically did not change. Reference [9] indicates that taking into account the effect of the thermal insulation layer made of spray-applied polyurethane foam in the plate calculations causes that with an increase in the modulus of subgrade reaction, deflections and bending moments to decrease. Pontoons are structures exposed to numerous loads, difficult to define; therefore, conducting research on real-scale objects helps to understand the specifics of their structure [7; 39]. The consideration of the Poisson's ratio or subgrade coefficient in calculations has practically no effect on buoyancy and stability calculations. The tilt angles for the calculated pontoon were 7.0\({}^{\circ}\) and 6.92\({}^{\circ}\) (Table 2). According to the standard [36], the freeboard should be at least 0.05 m at a tilt angle not exceeding 6\({}^{\circ}\). The standard [34] states that this angle should not exceed 10\({}^{\circ}\). Simplified calculations are allowed by the standard [35] and then the tilt angle should not exceed 15\({}^{\circ}\). The calculation procedure for the purpose of this article was carried out in accordance with [35]. Reference [40] relates to purposefulness of designing heavy floating systems. A pontoon should be of such height as to keep the deck above the water level and should be heavy enough to balance the upsetting moment in violent winds.  
This article includes calculations for a unique rectangular tank with a partition in its centre, made at a 1:1 scale, for which the effect of filling with Styrofoam as an elastic substrate was taken into account. Figure 9 shows the pontoon during execution and launching.