Abstract:
A method and apparatus for supporting heavy load is developed which consists of parallel spring sets in a M×N matrix, where M is the number of Modules and N is the number of spring sets in each module. Each spring set may be comprised of a single coil or multiple coils in series. Each module is pre-compressed to the design installation load employing hydraulic jacks working in parallel by a single pump.

Description:
BACKGROUND OF THE INVENTION 
     In the construction of various types of facilities, such as nuclear power plants, oil refineries, chemical plants, petrochemical plants, gas liquification plants and power generating plants, pipes and other equipments require some type of supports so that the thermal loads (expansion/contraction) of the system do not produce any extra stresses. One of the support system is a variable spring support wherein the deflection due to thermal loading of the system is accommodated by the compression/decompression of coil springs. For most cases variable spring supports are comprised of a single spring. As the load requirements increase, it becomes impractical to use a single spring to support these large loads. In such cases, several springs in parallel are configured to safely support large loads. This configuration of parallel springs we refer to as “large load variable spring” and hereafter we will denote these as “LLVS”. LLVS may find use in, for example, chemical reactors, turbine inlet/outlets, pressure vessels, compressors, etc. 
     Various types of parallel spring configuration and apparatus for supporting loads have been proposed. For example, parallel springs in a row ( FIG. 12 ), four parallel springs in a 2×2 matrix ( FIG. 13 ), or multiple parallel springs in a circular configuration ( FIG. 14 ). Up to a certain load capacity (approximately 100,000 lb), loading and unloading of such parallel spring configurations is possible via manually manipulating the heavy duty load bearing nuts. However, above this load range, the spring rate and the number of spring coils make it practically impossible to load/unload a LLVS manually. This led us to design and develop a multiple parallel spring system (LLVS) that is able to support heavy loads and permits loading and unloading via employment of hydraulic jacks activated by a single pump. 
     SUMMARY OF THE INVENTION 
     To attain the objective of supporting a large load, we designed, developed, and tested a parallel spring system (LLVS) that is comprised of:
         (a) M number of independent modules in a row, where each module contains N number of springs in a column i.e. total number of springs is M×N;   (b) An auxiliary hydraulic mechanism which aids in the pre-loading of each module to its fraction (1/M) of the total load;   (c) An integrated hydraulic jack system used to facilitate in transferring the total load from the LLVS to the supported load.       

     A common load bearing plate or load flange at the top of the system is supported by M×N numbers of springs. Evenly distributed hydraulic jacks, placed between fixed and movable plates at the front and the back of the LLVS aid in achieving the load/unload condition that is otherwise impractical by human power. Although design requirements vary depending upon specific application and load range, Variability factor, geometric restrains and maximum deflection criteria are a few of the common requirements. Variability Factor (VF) is defined as VF=(Spring Rate×Spring Deflection)/(Operating Load). As per MSS, VF&lt;0.25. Site conditions and space availability impose geometric constraints the design of the LLVS. Maximum Deflection Criteria require that, under full compression, the spring should not reach the solid height (bottom out). To avoid such condition, built-in travel stops are required. 
     In the current invention the concept of the modular design of a set of spring and the application of the hydraulic jacking systems are unique and have not been utilized previously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary perspective view of the invention. 
         FIG. 2  illustrates a perspective view of the invention with multiple components in phantom for illustrative clarity. 
         FIG. 3  illustrates an exploded view of the invention. 
         FIG. 4  illustrates a section view of the invention along line  4 - 4  in  FIG. 2  with the auxiliary hydraulic jacking system according to the present invention. 
         FIG. 5  illustrates another section view of the invention along  4 - 4  with the auxiliary hydraulic jacking system in an active state. 
         FIG. 6  illustrates another section view with travel stop lock nut repositioned against fixed top bar. 
         FIG. 7  illustrates another section view but with the invention in the locked position after repositioning of travel stop lock nuts 
         FIG. 8  illustrates another section view with the integrated hydraulic jacking system according to the present invention 
         FIG. 9  illustrates another section view with the integrated hydraulic jacking system according to the present invention in an active state creating displacement between fixed top bar and travel stop lock nut 
         FIG. 10  illustrates another section view with the integrated hydraulic jacking system according to the present invention with the travel stop lock nut repositioned against fixed top bar. 
         FIG. 11  illustrates another section view with the integrated hydraulic jacking system according to the present invention removed and the present invention supporting a variable load. 
         FIGS. 12-14  depict prior art devices. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows a three-dimensional exploded perspective view of the current invention of the Large Load Variable Spring  10 , which is comprised of a stationary structure frame including, spring base  50 , cross beams  60 , cantilever plates  62 , fixed top bars  90 , vertical columns  120 , channels  130 , I-beams  140  and base plate  150  while moving parts include load flange  20 , spring bars  30 , spring coils  40 , stop rods  71 , spring rods  170 , upper spring rod nuts  171 , lower spring rod nuts  172 , spring pressure plates  180  and floating bars  100 . The details of the stationary structure are best viewed in  FIGS. 2 and 3  while those of the moving parts are best viewed in any of  FIGS. 4-11 . 
     In the embodiment depicted in  FIGS. 1-11 , and with particular reference to  FIGS. 1-3 , five spring modules are arranged parallel to one another extending in a first direction on base plate  150  and comprise three spring coils  40  arranged in rows extending in a second direction. In this way a 5×3 spring matrix is formed consisting of 15 spring coils. Generally, the number of modules will be designated as M and the number of spring coils as N. Arranging these modules and springs in a matrix as shown yields M×N spring coils. While the embodiment of  FIGS. 1-11  depicts a 5×3 spring coil matrix, the present invention is not limited to these specific numbers. The values of M &amp; N will vary to match specific design requirements depending upon the load, spring rate, availability of space in all three directions, variability factor, geometric restraints and maximum deflection criteria as stated above. 
     In general, the base of any LLVS is established using structural steel components onto which the spring coils  40  will be positioned. The size, shape and quantity of these structural members should be adequate to support the design load and position the base of the spring coils  40  at the proper height. In this particular design, the base plate  150  supports I-beams  140  and channels  130  upon which the spring base  50  is supported. 
     The upper portion of the fixed frame provides support for travel stops. In the embodiment of  FIGS. 1-11 , this support is achieved by the four frame subassemblies best viewed in  FIGS. 1-3  which comprise fixed cross beams  60  welded to vertical columns  120 . The bottoms of vertical columns  120  are welded to base plate  150  and are strengthened by welded gussets. Cantilever plates  62  are affixed at the top of vertical columns  120  to establish the position of fixed top bar  90 . Two fixed top bars  90 , one at the front and one at the back end of fixed cross beams  60 , are welded to the bottom surface of the cantilever plates  62 . Each of the two fixed top bars  90  has 2×M (2×5 in the embodiment shown) number of through holes  72  to accept travel stop rods  71 . Through-holes  72  allow for translation of stop rods  71  freely relative to the fixed top bars  90  in a direction along the longitudinal axis of the stop rods  71  while offering constrained motion in horizontal directions. Travel stop rods  71  are threadably affixed at their superior ends to spring bars  30 . 
     As shown in  FIGS. 1 and 3 , the front plates  110  and side plates  160  cover the internal parts of the large load variable spring  10 . 
     Moving components are designed so that the overall height of LLVS  10  conforms to the design requirements, so that load flange  20  can move without interference in the vertical direction and so that the supported load can be adequately transferred from the load flange  20  through the spring coils  40  to the stationary frame. Spring coils  40  sit on the spring base  50  and are confined between spring bar  30  and floating bar  100  by threaded travel stop rods  71 . Load flange  20  rests on top of spring bar  30  while load flange guides  80  maintain stability and alignment of load flange  20 . Flange guides  80  are preferably securely attached to the underside surface of load flange  20 . With load flange  20  resting on spring bars  30 , flange guides  80  are received by through-holes formed in fixed top bar  90  near the distal ends. By engagement of flange guides  80  with these through-holes, flange guides  80 , and thereby load flange  20 , are permitted to move in a vertical direction but are constrained by the diameter of the through-holes in horizontal directions. In some embodiments it may be desirable to provide one or more bearing elements inside the distal through holes. 
     The spatial relationship between spring bar  30  and spring coil  40  is established because upper spring rod nut  171  is welded to spring bar  30  whereas lower spring rod nut  172 , which is not welded, can be positioned at any point along the threaded portion of spring rod  170 . The spring coil  40  is thus confined between spring base  50  and spring pressure plate  180  positioned by lower spring rod nut  172 . Fine adjustments to the height of spring coils within a given module may be made by threading of lower spring rod nut  172  along spring rod  170  in one direction or the other along. 
     Establishment of the Initial (Cold) Load 
       FIGS. 4-6  illustrate a section view along  4 - 4  of  FIG. 2 , showing one of the spring modules with an auxiliary hydraulic jack  184  prior to establishment of the installation/cold load. In this state, spring coils  40  are at their free length with no compression. Auxiliary hydraulic jack system  184  is then utilized to apply a load of “3 F” as shown in  FIGS. 4 and 5  to a top surface of spring bar  30  to compress coils  40 . The application of the force “3 F” causes a displacement of all spring coils within the module to a prescribed displacement “δ”. At this position, the fraction of the total installation load supported at the module is attained and travel stop lock nuts  188  are spaced from fixed top bar  90  in a downward vertical direction as depicted in  FIG. 5 . To maintain this established compression of spring coils  40 , travel stop lock nuts  188  are subsequently tightened against the lower surface of fixed top bar  90  to prevent relative vertical upward movement of lock rods  71  relative to fixed top bar  90  as in  FIG. 6 . Because of the fixed attachment of lock rods  71  to spring bars  30 , spring bars  30  are also prevented from vertical upward movement and thereby lock spring coils  40  in this compressed, installation load state. Once stop lock nuts  188  are tightened against fixed top bar  90 , auxiliary hydraulic jacking  184  is removed as shown in  FIG. 7 . This process is repeated to each spring module until all of the modules have been set to the prescribed height so that the total installation load can be established. 
     Transfer of the Installation Load to the Supported Component 
     To unlock LLVS  10  from its installation load and transfer the installation load to a large variable load  186 , an integrated hydraulic jacking system  182  is used as shown in  FIGS. 8-10 . When unlocking the LLVS, the hydraulic jacks of system  182  are positioned under the fixed top bar  90  and above the floating bar  100  as in  FIG. 8 . The size and quantity of the hydraulic jacks must be adequate to LLVS load range. Sufficient pressure is applied at the jacks to produce a load slightly higher than the installation load established earlier. This jack load will produce another displacement “δ” of the floating bar  100  as shown in  FIG. 9  to move stop rods  71  vertically downward. The vertical downward movement of stop rods  71 , in turn, causes a displacement of travel stop lock nuts  188  which are threadably fastened to stop rods  71 . The resulting displacement of stop lock nuts  188  from fixed plate  90  is visible in  FIG. 9 . With this displacement, the travel stop nut  188  can easily be relocated by loosening to a position away from the fixed top bar  90  as viewed in  FIG. 10 . The final position of the travel stop nut  188  is determined by the theoretical displacement of the load flange  20  under load  186 . After all of the travel stop nuts  188  have been relocated, integrated hydraulic jacking system  182  is disengaged to allow the installation load to be transferred from the LLVS to a supported load  186  such as piping, equipment, etc as shown in  FIG. 11 . 
     The above-described embodiments of the invention are presented for purposes of illustration and not of limitation. Let it be understood that the steps disclosed may be performed in a different order and remain within the scope of the present invention.