Composite concrete roof for an outer lng containment tank and method of making the same

Abstract

A method for constructing a composite concrete roof on an outer LNG containment tank is disclosed. The roof includes a roof assembly and a plurality of precast reinforced concrete roof elements. The roof assembly is mounted on a tank shell. At least some of the roof elements including a concrete body and embedded metal plates adapted to be welded to the roof assembly. The roof elements are welded to the roof assembly to provide additional strength and stiffness to the roof assembly. Preferably, no or minimal cast in place concrete structural joints are needed to join the roof elements to the roof assembly and or top of the shell. Ideally, the roof assembly includes a membrane and mounting beams connected to the membrane. The embedded plates of the roof assemblies are welded to the mounting beams on the roof assembly. The method may further include mounting or welding the roof elements to the roof assembly while workers access the interior of the shell to perform work therein. A tank having a composite concrete roof made according to the above method is also disclosed.

1 . A method for constructing a composite concrete roof on an outer LNG containment tank, the method comprising:
 mounting a roof assembly on a tank shell; providing a plurality of precast reinforced concrete roof elements, at least some of the roof elements including a concrete body and embedded metal plates adapted to be welded to the roof assembly;   and mounting the roof elements to the roof assembly by welding the metal plates of the roof elements to the roof assembly to form structural welds there between and to enhance the stiffness of the roof.   
   
   
       2 . The method of  claim 1  wherein:
 the roof assembly includes longitudinally extending mounting beams; and the metal plates of roof elements are welded to the mounting beams.   
   
   
       3 . The method of  claim 1  wherein:
 the roof assembly includes a membrane and overlying mounting beams;   and the metal plates of the roof elements are welded to the mounting beams.   
   
   
       4 . The method of  claim 1  wherein:
 the roof assembly includes a membrane and overlying mounting beams, the mounting beams extending circumferentially and radially over the membrane;   and the metal plates of the roof elements are welded to the mounting beams.   
   
   
       5 . The method of  claim 1  further comprising the steps of:
 pressurizing the tank shell to air lift the roof assembly to the top of the tank shell and mounting the roof assembly to the top of the tank shell;   opening an access opening in the tank shell to allow access within the shell; and   concurrently welding the roof elements to the roof assembly as work is being performed within the shell.   
   
   
       6 . The method of  claim 1  wherein:
 the pressure within the shell is at atmospheric pressure so that workers may work within the shell of the tank as roof elements are being welded to the roof assembly.   
   
   
       7 . The method of  claim 1  further comprising:
 welding the roof elements to the roof assembly to form concentric courses of ring elements.   
   
   
       8 . The method of  claim 7  wherein:
 the radial outer most course of roof elements is first welded to the roof assembly before any of the other courses of roof elements.   
   
   
       9 . The method of  claim 7  wherein:
 the radial outer most course of roof elements is welded to the roof assembly first;   and then the remaining courses of roof elements are successively added from the radial outermost course to the radial innermost course.   
   
   
       10 . An outer LNG containment tank comprising:
 a tank shell and a composite concrete roof mounted to the top of the tank shell, the roof including a roof assembly and a plurality of roof elements welded to the roof assembly by structural welds.   
   
   
       11 . The tank of  claim 10  wherein:
 at least some of the roof elements including a concrete body and embedded metal plates which are welded to the roof assembly.   
   
   
       12 . The tank of  claim 11  wherein:
 the roof assembly includes longitudinally extending mounting beams; and the metal plates of roof elements are welded to the mounting beams.   
   
   
       13 . The tank of  claim 11  wherein:
 the roof assembly includes a membrane and overlying mounting beams;   and the metal plates of the roof elements are welded to the mounting beams.   
   
   
       14 . The tank of  claim 11  wherein:
 the roof assembly includes a membrane and overlying mounting beams, the mounting beams extending circumferentially and radially over the membrane;   and the metal plates of the roof elements are welded to the mounting beams.   
   
   
       15 . The tank of  claim 10  wherein:
 the roof elements are welded to the roof assembly to form concentric courses of ring elements.   
   
   
       15 . The tank of  claim 15  wherein:
 the radial outermost course of ring elements is welded to the roof assembly and to the tank shell.