Abstract:
A mobile support apparatus that includes one or more extension and retraction devices and a unit that is releasably attachable to vertical members of the apparatus such that the apparatus can be extended in one or more stages to a vertical height that is substantially greater than the height of the fully retracted apparatus. The mobile support apparatus is useful for a multitude of new and existing construction-related applications.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 12/833,087, filed Jul. 9, 2012, which claims the benefit of U.S. Provisional Application No. 61/226,490, filed Jul. 17, 2009, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to temporary support apparatuses, particular apparatuses used to support high-weight structures during a construction process. 
     Typically, large-scale construction requires the use of expensive and bulky equipment to provide temporary support for structures as they are being constructed or renovated. Overhead cranes and gantry cranes require extensive setup time and are highly limited in that they cannot be used where there is insufficient overhead clearance for positioning of the lifting apparatus. Overhead cranes and gantry cranes have the additional disadvantages of requiring substantial ground clearance or other support bases on the sides of the structure that is to be supported. These cranes are also prohibitively expensive to purchase or rent, and due to their large size, are very difficult to transport and operate. 
     Vehicle-mounted cranes are limited in that they require substantial clearance for positioning of the vehicle chassis adjacent to the work zone, and additional clearance for proper extension of the outriggers. Vehicle-mounted cranes are also highly limited in their lifting capacity, and are very expensive to purchase, rent, and maintain. Further, these cranes require substantially level ground for setup of the vehicle chassis, and require extensive setup time before they can be used. They also suffer from the same drawback as do overhead cranes and gantry cranes with respect to the requirement of sufficient overhead clearance. 
     Existing multi-stage and telescoping support apparatuses do not have high weight capacity, and are not mobile. In addition to also having a high purchase cost, these apparatuses are bulky and difficult to transport. 
     Accordingly, there is a need for a low cost, mobile support apparatus that can be quickly set up in the desired location and raised into position to temporarily support a high-weight structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings certain embodiments of the present invention. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings, the same reference numerals are employed for designating the same elements throughout the several figures. In the drawings: 
         FIG. 1  is a front perspective view of one embodiment of the mobile support apparatus with the wheels in engagement with the ground; 
         FIG. 2  is a right side view of the apparatus with the first support portion in engagement with the ground via dunnage; 
         FIG. 3  is a front perspective view of the apparatus with the second support portion in a fully-extended position; 
         FIG. 4  is a right side view of the apparatus as shown in  FIG. 3 ; 
         FIG. 5  is a rear view of the apparatus with the second and third support portions in fully-extended positions; 
         FIG. 6  is a left side view of the apparatus as shown in  FIG. 5 ; 
         FIG. 7  is a view of the area contained approximately within line  7 - 7  of  FIG. 5 ; 
         FIG. 8  is a flowchart illustrating an exemplary method of operating the apparatus of  FIGS. 1-7 ; and 
         FIG. 9  is a right side view of an alternative embodiment of an apparatus according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention, as set forth in the appended claims. 
     To aid in describing the invention, directional terms are used in the specification and claims to describe portions of the present invention (e.g., upper, lower, left, right, etc.). These directional definitions are merely intended to assist in describing and claiming the invention and are not intended to limit the invention in any way. In addition, reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures without additional description in the specification in order to provide context for other features. 
     Referring generally to  FIGS. 1-7 , an exemplary embodiment of a mobile support tower  10  according to the present invention is shown. As can best be seen in  FIGS. 1 and 2 , the tower  10  comprises a transport chassis  12 . In this embodiment, the transport chassis  12  is comprised of a pair of horizontal chassis beams  14   a ,  14   b  that provide structural support for the chassis  12 . Wheels  16   a - 16   d  are rotatably coupled to the chassis  12  and permit the tower  10  to be moved as desired. As best seen in  FIG. 1 , a towing bar  18  is connected to the chassis  12 , and permits the tower  10  to be towed by a vehicle. 
     In this embodiment, the tower  10  is manually positioned into the desired location. Other means for moving the tower  10  are envisioned within the scope of this invention. For example, the tower  10  could be self-propelled (e.g., by a hydrostatic drive system for the wheels  16   a - 16   d ) or the chassis  12  could be mounted to a trailer (not shown). In self-propelled embodiments, movement of the tower  10  could be automated via a remote control device (wired or wireless) and processing means (not shown) or other known vehicle-control methods. Such a remote control device could also be used to actuate the hydraulic cylinders, the operation of which are discussed in greater detail herein. 
     In this embodiment, a ground-engaging portion  20  is connected to the chassis  12 . The ground-engaging portion  20  is comprised of ground supports or outriggers  22   a - 22   d . The extension length of the outriggers  22   a - 22   d  is adjusted, respectively, by outrigger cranks  28   a - 28   d , and the outriggers  22   a - 22   d  are held in position, respectively, by outrigger pins  24   a - 24   d  ( 24   c  and  24   d  not labeled). In this embodiment, the outriggers  22   a - 22   d  are each fitted with multiple outrigger pin holes, e.g. pin hole  26 , which allow for the respective outrigger  22   a - 22   d  to be set to the desired length via the insertion of the respective outrigger pin  24   a - 24   d.    
     While the tower  10  is being transported, the outriggers  22   a - 22   d  are refracted such that they do not make contact with the ground. After the tower  10  has been positioned in the desired location, the outriggers  22   a - 22   d  can then be extended. As best seen in  FIG. 2 , the outriggers  22   a - 22   d , when extended, function to lift the wheels  16   a - 16   d  off of the ground. In addition, the outriggers  22   a - 22   d  are used to lift the ground-engaging portions  56   a - 56   d  of the respective vertical members  54   a - 54   d  above the ground to a height sufficient such that a ground-engaging apparatus, for example dunnage  48 , can be placed between the ground and the ground-engaging portions  56   a - 56   d . The outriggers  22   a - 22   d  are also used to provide overall stability to the apparatus by increasing the “footprint” area of the ground-engaging portion  20  of the tower  10 . 
     In alternate embodiments (not shown), outriggers that are extendable outwardly from the chassis  12  (like those used to stabilize cranes, ladder trucks and aerial booms) may be included that provide increased stability to the tower  10  when it is positioned and operated. A secondary hydraulic unit, as described in greater detail below, may also be used to properly balance the tower  10  once it has been positioned in its desired location. 
     In the embodiment illustrated in the Figures, the dunnage  48  is wooden blocks with cross sections that are approximately 12 inches by 12 inches in size. It should be understood that many other types of dunnage could be used to stabilize the ground-engaging portions  56   a - 56   d  where the ground is unlevel or uneven, such as for example one or more sandbags, or blocks or shims made of wood, metal, rubber, or other suitable material. Regardless of what material is selected for the dunnage, it is desirable that the dunnage be arranged such that the tower  10  is as level as possible with the load to be engaged thereby, i.e. the top surface of the chassis beams  14   a ,  14   b  should be substantially parallel with the bottom surface of the load to be engaged by the tower  10 . This parallel arrangement not only minimizes the risk that the tower  10  will become accidentally disengaged from the load, but also maximizes the lifting capacity of the tower  10 , since the lifting force provided by the tower  10  is in a generally vertical direction. Preferably, the lifting force provided by the tower  10  is in a precise upward direction. The dunnage  48  also serves to distribute the weight of the tower  10  (and any load engaged thereby) over a larger surface area of the ground than would be engaged by the ground-engaging portions  56   a - 56   d  of the vertical members  54   a - 54   d  alone. 
     The tower  10  further comprises a power source  30 , which in this embodiment is a gas-powered engine that drives a hydraulic pump  33 . Other sources of power are envisioned within the scope of this invention, for example battery or plug-in electric power, or engines that consume other types of fossil fuels. A hydraulic fluid chamber  32  is operably connected to the hydraulic pump  33 , and is further operably connected to a hydraulic cylinder control means  31  (see  FIG. 2 ) via hydraulic fluid lines  34   a ,  34   b  (see  FIG. 1 ). The control means  31  is further operably connected to a pair of extension and retraction devices. In this embodiment, the extension and retraction devices are hydraulic cylinders  36   a ,  36   b.    
     In this embodiment, the tower  10  comprises a first support portion  50 . The first support portion  50  is comprised of vertical beams  54   a - 54   d , which terminate at their respective bottom ends at ground-engaging portions  56   a - 56   d . In this embodiment, the vertical beams  54   a - 54   d  are arranged such that when viewed in cross-section from above they form the corners of a rectangle. It should be understood that other cross-sectional shapes for the first support portion are suitable, for example square or triangular. In this embodiment, adjacent vertical beams are joined by one or more horizontal supports, such as for example horizontal beams  52   a - 52   b , which join together vertical beams  54   a  and  54   d  (see  FIG. 2 ) and horizontal beams  52   c - 52   d , which join together vertical beams  54   b  and  54   c  (see  FIG. 4 ). A greater or lesser number of horizontal and vertical beams could be used to provide the requisite structural integrity to the first support portion  50 , within the scope of this invention. At least three vertical beams are preferred. 
     In this embodiment, the vertical beams  54   a - 54   d  are joined to the transport chassis  12  via brackets  51   a - 51   d  (bracket  51   c  is shown in  FIG. 5 ). As can be seen in  FIGS. 1 and 5 , brackets  51   a  and  51   d  connect vertical beams  54   a  and  54   d , respectively, to the transport chassis  12  via chassis beam  14   a . Likewise, brackets  51   b  and  51   c  connect vertical beams  54   b  and  54   c , respectively, to the chassis  12  via chassis beam  14   b . In this embodiment, the brackets  51   a - 51   d  are welded to the respective vertical beam  54   a - 54   d , and are affixed to the respective chassis beam  14   a ,  14   b  via bolts or rivets. It should be understood that the brackets  51   a - 51   d , vertical beams  54   a - 54   d , and chassis beams  14   a ,  14   b  could be connected via known welding techniques or via nuts and bolts, rivets, or other suitable fasteners, within the scope of this invention. 
     Where reference is made in this application to the connectivity and functionality of hydraulic cylinder  36   a , it should be understood that hydraulic cylinder  36   b  functions identically thereto. Referring now to  FIGS. 1 and 3 , hydraulic cylinder  36   a  is connected at one end to a vertical beam  51  of the first support portion  50  at a first connection point  38   a , and at a second end (i.e. the end containing the piston rod  37   a ) to a beam  43   a  of a support portion-engaging unit  42  at a second connection point  40   a . In this embodiment, the first connection point  38   a  remains stationary at all times during the operation of the tower  10 . 
     In an alternate embodiment (not shown), the first connection point  38   a  of the hydraulic cylinder  36   a  could be free to shift upwards after an initial extension motion, thereby retracting the piston rod  37   a  while bringing the bottom of the hydraulic cylinder  36   a  to a raised position approximately level to the top of the first support portion  50 . The first connection point  38   a  could then be supported at this level, via a support pin or other suitable means, and the piston rod  37   a  could again be extended such that the third support portion  70  is raised out of its nested position within the first support portion  50 . In this embodiment, the support portion-engaging unit  42  could be eliminated, and the second connection point  40   a  could be located directly on the bottom surface of a load-engaging portion  80 . 
     Returning to the embodiment shown in the attached Figures, support portion-engaging unit  42  is comprised of two beams  43   a ,  43   b  (see  FIGS. 3  and ) that respectively include the second connection points  40   a ,  40   b , and two beams  44   a ,  44   b  (see  FIG. 4 ) that connect the beams  43   a ,  43   b  together such that the support portion-engaging unit  42  is a rigid, level structure of approximately rectangular shape when viewed in cross-section from above. The support portion-engaging unit  42  further comprises sleeves  74   a - 74   d  (see  FIGS. 4 and 6 ) located at its respective corners. The sleeves  74   a - 74   d  are fitted around vertical beams  62   a - 62   d , respectively, and have pin-receiving holes (not labeled) formed therein. The sleeves  74   a - 74   d  may be releasably connected to and are slidable along the respective vertical beams  54   a - 54   d.    
       FIG. 7  is a view of the area contained approximately within line  7 - 7  of  FIG. 5 , showing the support portion-engaging unit  42  in greater detail. In this embodiment, the support portion-engaging unit  42  has multiple pin-storage slots, e.g. slot  76 , which are sized to hold stored pins, such as pin  78 , when not in use. It should be understood that the support portion-engaging unit could be of any suitable structure and design within the scope of this invention. The support portion-engaging unit need only be designed such that it has means for engaging the one or more extension and retraction devices, and means for engaging the one or more support portions of the apparatus. In an alternate embodiment, as discussed above, the support portion-engaging unit may be eliminated completely. 
     In  FIGS. 1 and 2 , the tower  10  is shown in its fully retracted position. As best seen in  FIG. 1 , when the tower  10  is in the retracted position, no pins need be inserted into the pin-receiving holes, e.g. pin-receiving holes  66   a - 66   d , that are located, respectively, in plates  58   a - 58   d  (plates  58   c ,  58   d  are shown in  FIG. 5 ) at the top of the respective vertical beams  54   a - 54   d . In the retracted position, the tower  10  requires no bracing via support pins because the vertical beams  62   a - 62   d  that comprise the second  60  and third  70  support portions (see  FIGS. 5 and 6 ) are fully nested within the vertical beams  54   a - 54   d  that comprise the first support portion  50 , and the vertical beams  62   a - 62   d  rest at the bottom of the respective ground-engaging portions  56   a - 56   d . The second support portion  60  and the third support portion  70  are telescopically movable with respect to the first support portion  50 . 
     Referring now to  FIGS. 3 and 4 , the tower  10  is shown in a partially extended configuration, wherein second support portion  60  has been fully extended from out of its nested position within the first support portion  50 . In this embodiment, in order for the second support portion  60  to be moved into an extended position, the support portion-engaging unit  42  is first coupled via one or more support pins  64   a - 64   d  (see  FIG. 5 ) to pin-receiving holes, e.g. pin-receiving holes  63   c ,  63   d  (see  FIG. 5 ), which are located in the vertical beams  62   a - 62   d . The piston rod  37   a  of the hydraulic cylinder  36   a  is then extended the desired distance, such that the support portion-engaging unit  42  draws the attached vertical beams  62   a - d  upward an equivalent distance. 
     When the maximum, or desired, height of the second support portion  60  has been reached, the user inserts support pins  68   a - 68   d  into pin-receiving holes  66   a - 66   d  (see  FIGS. 1 ,  4 , and  6 ), respectively. In this embodiment, the support pins  68   a - 68   d  extend entirely through the respective vertical beam  62   a - 62   d , such that the weight of the second support portion  60 , the load-engaging portion  80  (discussed in greater detail below), and any load engaged thereby is supported by the support pins  68   a - 68   d . Once the support pins  68   a - 68   d  have been placed within the respective pin-receiving holes  66   a - 66   d , the support portion-engaging unit  42  may be disengaged from the vertical beams  62   a - 62   d  via removal of support pins  64   a - 64   d , respectively. If, at this stage, the desired height of the tower  10  has been reached, it is most preferable to maintain the hydraulic cylinder  36   a  in the extended position and the support portion-engaging unit  42  in engagement with the vertical beams  62   a - 62   d , respectively, for maximum structural rigidity of the tower  10 . In the alternative, if the desired height of the tower  10  has not been reached, the sleeves  74   a - 74   d  of the support portion-engaging unit  42  may be disengaged from the vertical beams  62   a - 62   d , the piston rod  37   a  of the hydraulic cylinder  36   a  retracted, and the support portion-engaging unit  42  lowered to its rest position. In this embodiment, where the desired height of the tower  10  has not yet been reached, these steps must be taken in order to put the support portion-engaging unit  42  and the hydraulic cylinder  36   a  in a position to further extend the height of the tower  10 . 
     Referring now to  FIGS. 5 and 6 , the tower  10  is shown in a fully extended configuration, wherein third support portion  70  has been extended from out of its nested position within the first support portion  50 . In order to extend the third support portion  70  from out of its nested position with the first support portion  50 , the support portion-engaging unit  42  must first be fully lowered into the position shown in  FIGS. 1 and 2  and as described above. The support portion-engaging unit  42  is then coupled via support pins  64   a - 64   d  to additional pin-receiving holes (not labeled), which are located in the lower portions  72   a - 72   d  of the respective vertical beams  62   a - 62   d . Once the support pins  64   a - 64   d  have been positioned within respective pin-receiving holes, they will provide the structural support necessary such that support pins  68   a - 68   d  may be removed from pin-receiving holes  66   a - d , respectively, without the second  60  and third  70  support portions falling back into a nested position within the first support portion  50  via the force of gravity. Removal of the support pins  68   a - 68   d  thus permits the piston rod  37   a  of the hydraulic cylinder  36   a  to then be extended the desired distance, such that the support portion-engaging unit  42  draws the lower portions  72   a - 72   d  (lower portion  72   a  not shown in the figures) of the respective vertical beams  62   a - d  upward an equivalent distance. 
     Because the vertical beams  62   a - 62   d  rest at the bottom of the respective ground-engaging portions  56   a - 56   d , the vertical beams  62   a - 62   d  are approximately the same length as the respective ground-engaging portions  56   a - 56   d , and full extension of the vertical beams  62   a - 62   d  almost doubles the height of the tower  10 , thereby allowing the tower  10  to support a load that is located significantly higher than the height of the tower  10  when the vertical beams  62   a - 62   d  are at the bottom of the respective ground-engaging portions  56   a - 56   d . Conversely, because the height of the tower  10 , when the vertical beams  62   a - 62   d  are at the bottom of the respective ground-engaging portions  56   a - 56   d , is only about half the height of the tower  10  when the vertical beams  62   a - 62   d  are fully extended from the respective ground-engaging portions  56   a - 56   d , the tower  10  can be transported under most road overpasses without difficulty. 
     When the maximum, or desired, height of the third support portion  70  has been reached, the user reinserts support pins  68   a - 68   d  into pin-receiving holes  66   a - 66   d , respectively. Support pins  68   a - 68   d  are again inserted entirely through the respective vertical beam  62   a - 62   d , such that the weight of the second support portion  60 , third support portion  70 , the load-engaging portion  80 , and any load engaged thereby can be supported by the support pins  68   a - 68   d . The support pins  64   a - 64   d  may then be removed such that the support portion-engaging unit  42  is disengaged from the vertical beams  62   a - 62   d , allowing the piston rod  37   a  of the hydraulic cylinder  36   a  to be fully retracted. More preferably, for added structural rigidity, the hydraulic cylinder  36   a  is maintained in a fully extended position and the support portion-engaging unit  42  is maintained in engagement with the vertical beams  62   a - 62   d  via support pins  68   a - 68   d , respectively. 
     As can be seen in  FIG. 6 , the load-engaging portion  80  is vertically aligned with the ground-engaging portion  56  of the first support portion  50 . This enables the load being supported by the tower  10  to be transmitted directly to the ground through the vertical beams  62   a - 62   d , the ground-engaging portion  56   a - d , and the dunnage  48  placed between the ground-engaging portion  56   a - d  and the ground. 
     It should be noted that when the tower  10  is in a fully-extended position, the box-like structure of the support portion-engaging unit  42  adds a significant amount of lateral stability to the beams  62   a - 62   d . This enables the tower  10  to support much larger loads than would be possible without the support portion-engaging unit  42 . 
     When the user desires to remove the tower  10  from the extended height, the second  60  and/or third  70  support portions may be lowered back into a nested position within the first support portion  50  by substantially reversing the lifting process as described above. The tower  10  can then be quickly moved to another location and re-extended for continued use. 
     Referring again to  FIG. 2 , located at the top of the tower  10  is the load-engaging portion  80 . In this embodiment, the load-engaging portion  80  is comprised of a pair of beams  82   a ,  82   b , which are mounted to the top of the vertical beams  62   a - 62   d . Beam  82   a  is mounted to the top of vertical beams  62   a  and  62   b , and beam  82   b  is mounted to the top of vertical beams  62   c  and  62   d . In this embodiment, beams  82   a ,  82   b  are mounted to the vertical beams  62   a - 62   d  via a plurality of rivets. Other affixation techniques, such as the use of nuts and bolts or known welding techniques, should be understood as being within the scope of this invention. The load  84  located on top of the beams  82   a ,  82   b  are representative of a load that would be engaged by the load-engaging portion  80  when the beams  82   a ,  82   b  are placed in a position adjacent thereto. Most preferably, as shown in  FIGS. 1-6 , the load-engaging portion  80  engages the load  84  such that the load  84  is perpendicular to and substantially centered on the beams  82   a ,  82   b . This ensures the most stable connection between the beams  82   a ,  82   b  and the load  84 . It should be understood that other engagement angles and alignments between the beams  82   a ,  82   b  and the load  84  are envisioned within the scope of this invention. 
     It should also be understood that the load-engaging portion may comprise any number of alternate structures, such as for example where the load-engaging portion comprises a structure with a wider load-contacting area or a structure that is specifically shaped, sized, or configured in order to more effectively engage the load. The load-engaging portion could also be changeable, such that a user could quickly replace the load-engaging portion with a structure having a desired shape, size, or configuration. Storage areas for alternate load-engaging portions could be provided on or in engagement with the body of the apparatus. 
     In the embodiment as substantially shown in  FIGS. 1-7 , the weight-bearing components of the tower  10  are constructed of construction-grade steel. In field tests, Applicant has determined that this embodiment of the tower  10  has a lifting capacity of at least 300 tons (about 272,000 kg). In an exemplary use, the tower  10  may be used to support bridge beams during construction and/or repair work on a bridge. 
     In the alternative, other suitable materials, for example metals or plastics, may be used to construct some or all of the weight-bearing components of the apparatus. 
     In an alternative embodiment (not shown), the tower  10  could include a secondary extension and retraction means, which may be a secondary hydraulic unit. The secondary hydraulic unit may, in one embodiment, be located between the load-engaging portion  80  and the top of the vertical beams  62   a - 62   d . In the alternative, the secondary hydraulic unit could be located below the first support portion  50 . Other locations for the secondary hydraulic unit are also envisioned within the scope of this invention. 
     Preferably, the secondary hydraulic unit is comprised of one or more hydraulic cylinders that are shorter in length and/or greater in diameter—and have a greater lifting capacity—than the hydraulic cylinders  36   a ,  36   b . In one embodiment, the hydraulic cylinders  36   a ,  36   b  would provide the means for adjusting the tower  10  to the proper height, i.e. would be used to move the load-engaging portion  80  into contact with the load  84 . Once the load  84  has been placed adjacent to the load-engaging portion  80 , the tower  10  would be secured by support pins  64   a - 64   d  and  68   a - 68   d  as substantially described above. The secondary hydraulic unit could then be used to perform the function of displacing the load  84 . 
     In addition, the secondary hydraulic unit could be used in addition to, or instead of, the outriggers  22   a - 22   d  to raise the wheels  16   a - 16   d  off of the ground so that the ground-engaging portion  20  is placed in contact with the ground and/or dunnage  48 . Where the secondary hydraulic unit is comprised of more than one hydraulic cylinder, the separate cylinders could be operated independently to assist in leveling the tower  10 . 
     In an alternate embodiment, the tower  10  could be operated entirely via hydraulic means. The wheels  16   a - 16   d , outriggers  22   a - 22   d , outrigger pins  24   a - 24   d , and support pins  64   a - 64   d , and  68   a - 68   d , for example, could be adjusted, positioned, engaged, and/or disengaged via hydraulic control means. 
     Referring to the flowchart  800  of  FIG. 8 , an exemplary method of operating tower  10  is described. In step  802 , wheels  16   a - d  are used to position tower  10  directly beneath a load to be supported, such as, for example, load  84  shown in  FIG. 5 . The tower  10  may be towed into the desired position. In step  804 , outriggers  22   a - d  are operated to lift wheels  16   a - d  off the ground. In step  806 , after the wheels  16   a - d  are lifted sufficiently from the ground, dunnage  48  is placed below the wheels  16   a - d  and, in step  808 , the outriggers  22   a - d  are operated to lower the ground-engaging portions  56   a - d  onto the dunnage  48 . 
     In step  810 , the vertical beams  62   a - d  are telescopically extended vertically to engage the load. In step  812 , the vertical beams  62   a - d  are securely locked into the vertical members  54   a - d , respectively. Optionally, in step  814 , if the load is too high, the sleeves  74   a - d  are released from the vertical beams  62   a - d  and in step  816 , the sleeves  74   a - d  are lowered. In step  818 , the sleeves are re-engaged with the vertical beams  62   a - d  and, repeating step  810 , the sleeves  74   a - d  are extended until they engage and support the load-engaging portion  80 . 
     An embodiment of a tower  110  according to an alternative exemplary embodiment of the present invention is illustrated in  FIG. 9 . In this example, elements shared with the first example are represented by reference numerals increased by factors of  100 . For example, the chassis  14  of the first example corresponds to the chassis  114  of the second example. In the interest of clarity, some features of this embodiment that are shared with the first embodiment are numbered in  FIG. 8 , but are not repeated in the specification. 
     Tower  110  includes an elongated chassis  112  comprised of a pair of horizontal chassis beams (only one chassis beam  114   a  shown in  FIG. 9 ) that support a plurality of first support portions  150   a ,  150   b ,  150   c . While three of the first support portions  150   a ,  150   b ,  150   c  are shown, those skilled in the art will recognize that more or less than three of the first support portions  150   a ,  150   b ,  150   c  may be incorporated onto chassis  112 . 
     Each of the first support portions  150   a ,  150   b ,  150   c  supports a respective second support portion  160   a ,  160   b ,  160   c  in the same manner that second support portion  60  is supported by first support portion  50  as described above. A load-engaging portion  180   a ,  180   b ,  180   c , respectively, is supported by a respective second support portion  160   a ,  160   b ,  160   c  in the same manner that load-engaging portion  80  is supported by second support portion  60  as described above. 
     A power source  130  is operably connected to a hydraulic cylinder control means  131 . Hydraulic cylinder control means  131  is used to independently operate each of the second support portions  160   a ,  160   b ,  160   c  to raise and lower the second support portions  160   a ,  160   b ,  160   c  from within the first support portions  150   a ,  150   b ,  150   c , respectively, in a manner similar to operation of the tower  10  described above. 
     While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.