Ribbed slab foundation for cylindrical refrigerated tanks for liquified gas storage

Abstract

A foundation for cylindrical refrigerated tanks for liquified gas storage, at locations where the minimum ambient temperature is always greater than 0° C., characterized by a reinforced concrete ribbed slab structure at grade level, where the clear spaces in between the parallel webs of the ribbed slab are configured as air circulation channels to provide ambient air circulation suitable to prevent the ground underneath the foundation itself from reaching freezing temperatures, i.e. ≤0° C., while providing the necessary bearing and structural capacity.

1 . Foundation for cylindrical refrigerated tanks for liquified gas storage, at locations where the minimum ambient temperature is always greater than 0° C., comprising a reinforced concrete ribbed slab structure at grade level, where the clear spaces in between the parallel webs of said ribbed slab are configured as air circulation channels to provide ambient air circulation suitable to prevent the ground underneath the foundation itself from reaching freezing temperatures, while providing the necessary bearing and structural capacity;
 wherein said air circulation channels are placed within the thickness of said reinforced concrete ribbed slab structure of the foundation, and wherein the cross section of said air circulation channels is calculated by a method for designing the cross section of air circulation channels provided within a foundation for cylindrical refrigerated tanks for liquified gas storage, at locations where the minimum ambient temperature is always greater than 0° C., in order to ensure enough natural ventilation to prevent the ground underneath the foundation itself from reaching freezing temperatures, while providing the necessary bearing and structural capacity, said method including performing a thermal analysis of the real behavior of the tank/foundation/soil system by means of a finite elements 3D Model, in order to simulate the heat transfer from ambient air in the channels to the liquified gas inside the tank; wherein said thermal analysis is performed during the design stage of the foundation both to select the size and spacing of air circulation channels, and to allow performing the structural design of the ribbed slab foundation that creates these channels, taking into account the reduction of structural cross section due to the presence of said channels, as well as of any piles required to support the foundation itself, 
 said method being performed to ensure enough natural ventilation notwithstanding the prevailing wind direction at the site where the foundation is placed. 
 
     
     
         2 . The foundation of  claim 1 , wherein said air circulation channels are open to the outside ambient to allow the continuous heat transfer from ambient air—which temperature is always greater than 0° C.—to the inside of the foundation supporting the tank containing the liquified gas, thus preventing the freezing of soil underneath the foundation itself. 
     
     
         3 . The foundation of  claim 2 , wherein said air circulation channels are evenly distributed in plan and are substantially parallel to each other and to the upper face of the foundation supporting the tank bottom; where said air circulation channels are crossing the foundation from one side to the opposite one. 
     
     
         4 . The foundation of  claim 2 , wherein said air circulation channels have a 600 mm minimum dimension of their cross section to facilitate inspection and cleaning. 
     
     
         5 . The foundation of  claim 2 , wherein said air circulation channels are prismatic in section with a nominal longitudinal slope in order to enhance the stack effect. 
     
     
         6 . The foundation of  claim 2 , wherein said air circulation channels are oriented perpendicular to the prevailing wind direction at the site where the foundation is placed, in order minimize the possibility of sand or dirt being dragged inside said air circulation channels. 
     
     
         7 . (canceled) 
     
     
         8 . The foundation of  claim 2 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         9 . The foundation of  claim 3 , wherein said air circulation channels have a 600 mm minimum dimension of their cross section to facilitate inspection and cleaning. 
     
     
         10 . The foundation of  claim 3 , wherein said air circulation channels are prismatic in section with a nominal longitudinal slope in order to enhance the stack effect. 
     
     
         11 . The foundation of  claim 4 , wherein said air circulation channels are prismatic in section with a nominal longitudinal slope in order to enhance the stack effect. 
     
     
         12 . The foundation of  claim 3 , wherein said air circulation channels are oriented perpendicular to the prevailing wind direction at the site where the foundation is placed, in order minimize the possibility of sand or dirt being dragged inside said air circulation channels. 
     
     
         13 . The foundation of  claim 4 , wherein said air circulation channels are oriented perpendicular to the prevailing wind direction at the site where the foundation is placed, in order minimize the possibility of sand or dirt being dragged inside said air circulation channels. 
     
     
         14 . The foundation of  claim 5 , wherein said air circulation channels are oriented perpendicular to the prevailing wind direction at the site where the foundation is placed, in order minimize the possibility of sand or dirt being dragged inside said air circulation channels. 
     
     
         15 . The foundation of  claim 3 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         16 . The foundation of  claim 4 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         17 . The foundation of  claim 5 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         18 . The foundation of  claim 6 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         19 . The foundation of  claim 7 , wherein, in case foundation with piles is necessary, the foundation is configured to be built in a bottom-up construction sequence: piles followed by ribbed slab; instead of the top-down construction sequence adopted in the usual industrial practice for these cases, namely in construction sequence order: embankment above grade, piles, slab, digging-out of embankment material. 
     
     
         20 . The foundation of  claim 9 , wherein said air circulation channels are prismatic in section with a nominal longitudinal slope in order to enhance the stack effect. 
     
     
         21 . A method for designing the cross section of air circulation channels provided within a foundation for cylindrical refrigerated tanks for liquified gas storage, at locations where the minimum ambient temperature is always greater than 0° C., in order to ensure enough natural ventilation to prevent the ground underneath the foundation itself from reaching freezing temperatures, while providing the necessary bearing and structural capacity, said method including a thermal analysis of the real behavior of the tank/foundation/soil system by means of a finite elements 3D Model, in order to simulate the heat transfer from ambient air in the channels to the liquified gas inside the tank; wherein said thermal analysis is performed during the design stage of the foundation both to select the size and spacing of air circulation channels, and to allow performing the structural design of the ribbed slab foundation that creates these channels, taking into account the reduction of structural cross section due to the presence of said channels, as well as of any piles required to support the foundation itself.