- Superior protection of stored products, given its excellent thermal insulation, waterproofing properties and ultraviolet radiation, it optimizes floor area occupied and significantly improves the environmental impact from the beginning of construction.
- Monolithic double-curved surface has a better performance against puntual and distributed loads.
- Totally hermetic. Excellent protection against moisture.
- Excellent thermical insulation. It is possible to maintain low temperatures in the inside with less energy cost.
- Eliminates dust emission.
- Eliminates noise pollution.
- Very solid and resistant to earthquakes and hurricanes.
- Superior protection of stored items.
- Without joints: it is monolithic, which gives better structural behaviour.
- Optimization of the surface as it has a completely diaphanous interior area.
- Allows different geometries.
- Possibility of large spans without intermediate supports.
- Maximum durability and low maintenance costs.
- No need for staff in its interior for operation.
- Reduces considerably the area of occupation of the auxiliary elements during construction.
- Possibility of extracting 100% of volume stored.
- Greatly reduced execution time .Competitive cost against other solutions.
APPENDIX 1. SEISMIC ANALYSIS
The response of two silos for clinker with the same 50,000 t capacity is compared.
The first, the conventional silo, cylindrical with a radius of 19 m and 25 m in height. The second, a silo dome with spherical geometry and the center at a height of 6.75 m and an interior radius of 23 m.
Both structures are excited by a uniform movement on their base in the form of the elastic spectra responding to the horizontal acceleration defined in the Seismic Resistance Construction Standard NCSE-94, using a value of 0.12 g for basic seismic acceleration.
The clinker mass is distributed sinusoidally on the wall of the silo, as indicated in the Règles Professionnelles de Conception et de Calcul des Silos en Béton Armé ou Précontraint.
60 initial frequencies and the corresponding vibration modes are obtained and the square root SRSS method of the sum of the squares is used as a technique to combine the values of the sliding in order to estimate maximum response stress, which is the most common method, considering a value of 0.10 for the cluster factor.
The following figures show the stress values obtained in both cases, observing that the stress peak reaches a value that is 3 times higher in the case of a conventional silo and is limited to a very specific area in the case of the dome. Furthermore, in the case of the conventional silo, most of its surface area is subjected to stress between the factors of 1 and 4 and in comparison with the most significant value in the extended area of the dome.
The most favourable response of the dome is first due to the fact that it is a dome structure that is closed at the top, compared with the open cylinder, and with extraordinary behaviour compared with non-centered loads. This has been historically proven by the duration of these structures, often dating back to the ancient world.
In our case, the response is even more favourable because the dome is elastically supported on the foundations using a combined system of banded elastomeric material supporting appliances and angular guides to lessen the effect of an earthquake.
This leads to an increase in the natural frequencies of the structure, which decreases the values of spectral acceleration and, therefore, the overall response.
APPENDIX 2. THERMAL EFFECTS
The effect produced on the wall of the silo when clinker is stored inside at high temperatures is considered.
A reference temperature Tr when the clinker enters the silo of 150ºC is used.
The Règles Professionnelles de Conception et de Calcul des Silos en Béton Armé ou Précontraint are taken into account.
The effects produced by the temperature in the most unfavourable part of the silo will be studied, which is the part of the wall that is not in direct contact with the clinker but with the irradiated air, reaching a temperature of 0.72Tr.
On the part of the wall in direct contact with the clinker, the temperature is lower due to its insulating power in its surrounding area (0.51 m2 ºC/W). It has an insulating effect to the clinker further inside and reduces the temperature on the inside of the wall to a value below that of the case of a wall without clinker touching it.
The difference in behaviour between a conventional silo and a dome lies in the presence of a 2.5 cm insulating layer of rigid polyurethane foam in the latter.
The distribution of temperatures on the wall is studied, bearing in mind concrete conduction coefficient values Lb of 1.75W/m ºC, 0.11 m2 for internal wall surface resistance 1/hi and 0.06 for external 1/he and a conduction coefficient Lp of 0.03 for the polyurethane. (See (1)).
With a constant heat flow and an exterior air temperature of 0ºC for a concrete wall 30 cm. thick, the difference in temperatures between the interior and exterior sides of the concrete wall of the silo is around 54º in the case of the conventional silo, whereas it is reduced to 15º for the dome silo.
This is extremely significant for both the cost and durability of the structure, as the conventional silo is subject to the constant activity of bending movements proportional to this difference in temperature, which are 3 times higher in the case of conventional silos.
The unit flow is expressed as follows:
ti=interior temperature of concrete wall
te=exterior temperature of concrete wall
tp=exterior temperature of polyurethane wa