Abstract:
A tilt-up door for a building having an opening including a door frame with vertical track members, cam surfaces extending laterally from the vertical tracks at the upper portion of the tracks and a door sized to span the opening. The door can be pivotally coupled with rollers disposed within the vertical tracks and cam followers extending laterally from the upper portion of the door to contact the cam surfaces. The cams can include a first steep inclined segment, a second inclined segment and a third segment. When an upwardly directed motive force acts on the door the cam followers come into engagement with the cam surface to lift the door generally vertically and then rotate the door inwardly as the door is raised into an open raised position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation in part of U.S. patent application Ser. No. 14/482,277, filed on Sep. 10, 2014 which is continuation in part of U.S. patent application Ser. No. 14/284,511 filed on May 22, 2014, now U.S. Pat. No. 9,015,996, which is a continuation of U.S. patent application Ser. No. 14/011,041 filed on Aug. 27, 2013, now U.S. Pat. No. 8,769,871, which is a continuation of U.S. patent application Ser. No. 13/547,172 filed on Jul. 12, 2012, now U.S. Pat. No. 8,539,716, which is a continuation of U.S. patent application Ser. No. 12/652,241 filed on Jan. 5, 2010, now U.S. Pat. No. 8,245,446. U.S. patent application Ser. No. 12/652,241 claims the benefit of U.S. Provisional Application No. 61/219,435 filed on Jun. 23, 2009. This application is also related to U.S. patent application Ser. No. 14/663,780 filed on Mar. 20, 2015 which is a continuation of U.S. patent application Ser. No. 14/284,511 filed on May 22, 2014, now U.S. Pat. No. 9,015,996 mentioned above. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to doors for large buildings such as airplane hangers, farm equipment storage buildings, marine storage buildings and heavy equipment storage buildings. Such buildings can have doors that pivot up to an open position to allow the stored equipment to be moved into or out of the building. For door openings wider than approximately 15′ to 25′ conventional sectional overhead doors are typically not used because of the span and the problem of preventing door panel sections from sagging in the middle as the door is opened. A single panel door can be provided with a truss to support the door to preclude sagging of the door in the open position. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    The invention relates to a tilt-up door system for a building having an opening including a pair of vertically juxtaposed members that can define a vertical track. The vertical members can each have a first cam extending generally laterally from the vertical track at an upper portion. The first cams can have a first steep inclined segment, a second inclined segment and a third segment. A door sized to span the opening can be pivotally coupled to the vertical members with at least one roller disposed within each of the vertical tracks, and a cam follower extending laterally from an upper portion of the door in register with each of the first cams. When the door is placed in alignment with the opening in a closed, lowered position with the rollers disposed within the vertical tracks and the cam followers located adjacent to the first cams and an upwardly-directed motive force acts upon the door, the cam followers come into abutment with the first steep inclined segments of the first cams which moves the door generally vertically, then into abutment with the second inclined segments of the first cams which rotates the upper portion of the door inwardly, and then into abutment with the third segments of the first cams to bring the door into an opened, raised position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a perspective view of a tilt-up door installed on an aircraft hanger building. 
           [0005]      FIG. 2  is a perspective view of the tilt-up door shown in  FIG. 1  partially opened. 
           [0006]      FIG. 3  is a perspective view of the tilt-up door shown in  FIG. 1  fully opened. 
           [0007]      FIG. 3A  is a perspective view of the tilt-up door shown in  FIG. 3  showing an alternate door stop arrangement. 
           [0008]      FIG. 4  is a view of the tilt-up door shown in  FIG. 1  with the door fully open showing the door support and a hydraulic actuator operating mechanism. 
           [0009]      FIG. 4A  is a view of the tilt-up door shown in  FIG. 1  with the door fully open showing the door support and an alternate hydraulic actuator operating mechanism. 
           [0010]      FIG. 4B  is a partial schematic cutaway drawing of a hydraulic pump assembly that can be used with the alternate hydraulic actuator of  FIG. 4A . 
           [0011]      FIG. 4C  is a partial schematic drawing of the lower portion of the alternate hydraulic actuator of  FIG. 4A . 
           [0012]      FIG. 4D  is a partial view looking at one side the lower portion of the alternate hydraulic actuator of  FIG. 4A . 
           [0013]      FIG. 4E  is a partial view looking at the opposite side of the lower portion of the alternate hydraulic actuator of  FIG. 4A . 
           [0014]      FIG. 5  is a partial view looking up showing a carriage in the U-shaped channel pivotally connected to the door frame. 
           [0015]      FIG. 6  is a partial view looking down showing the carriage in the U-shaped channel pivotally connected to the door frame. 
           [0016]      FIG. 7  is a partial view looking down showing the top of the carriage in the U-shaped channel pivotally connected to the door frame. 
           [0017]      FIG. 8  is a top view of a carriage. 
           [0018]      FIG. 8A  is a side view of a carriage. 
           [0019]      FIG. 8B  is a top view of an alternate carriage. 
           [0020]      FIG. 8C  is a side view of the alternate carriage of  FIG. 8B . 
           [0021]      FIG. 8D  is a partial top view of an alternate carriage. 
           [0022]      FIG. 8E  is a partial top view of an alternate carriage. 
           [0023]      FIG. 9  is a partial view looking up showing a cam follower pivotally mounted to the tilt-up door with the cam follower engaging the cam surface. 
           [0024]      FIG. 10  is a partial view showing the track and cam surface with the cam follower engaging the cam surface with the tilt-up door in the closed position. 
           [0025]      FIG. 10A  is a partial view showing an alternate track and cam surface with the cam follower engaging the cam surface with the tilt-up door in the closed position. 
           [0026]      FIG. 10B  is a partial view showing an alternate track and cam with the cam follower engaging the cam with the tilt-up door in the closed position. 
           [0027]      FIG. 11  is a partial view showing the cam follower engaging the cam surface with the tilt-up door in the open position. 
           [0028]      FIG. 12  is a schematic view illustrating an alternate U-shaped channel and track arrangement. 
           [0029]      FIG. 12A  is a schematic view illustrating a track and cam arrangement including the alternate cam illustrated in  FIG. 10B . 
           [0030]      FIG. 13  is an exploded view of  FIG. 5  illustrating the U-shaped channel, carriage, pivot shaft and door frame pivot shaft tube. 
           [0031]      FIG. 14  is a schematic drawing of a hydraulic circuit that can be used with a tilt-up door. 
           [0032]      FIG. 14A  is a schematic drawing of an alternate hydraulic circuit that can be used with a tilt-up door. 
           [0033]      FIG. 14B  is a schematic drawing of the alternate hydraulic circuit of  FIG. 14A  with the hydraulic cylinders activated to raise a tilt-up door. 
           [0034]      FIG. 14C  is a schematic drawing of the alternate hydraulic circuit of  FIG. 14A  with the check valves activated to allow a tilt-up door to close. 
           [0035]      FIG. 15  is a partial schematic front view looking into the door opening of a building having a tilt-up door with the door removed showing an alternate U-shaped channel arrangement that can be used with the alternate carriage illustrated in  FIGS. 8B-8E . 
           [0036]      FIG. 16  is a partial schematic top view showing an alternate actuator that can be used with the U-shaped channel arrangement of  FIG. 15 . 
           [0037]      FIG. 16A  is a partial schematic top view illustrating the alternate actuator that can be used with U-shaped channel arrangement illustrated in  FIG. 15 . 
           [0038]      FIG. 17A  is a partial schematic front view looking into the door opening of a building having a tilt-up door with the door removed showing an alternate U-shaped channel arrangement that can be used with an alternate carriage as illustrated in  FIGS. 8B-8E . 
           [0039]      FIG. 17B  is a partial schematic top view showing the alternate U-shaped channel arrangement of  FIG. 17A . 
           [0040]      FIG. 18  is a partial schematic side view looking at the edge of a door opening of a building having a tilt-up door with the door removed showing an alternate U-shaped channel arrangement that can be used with an alternate carriage as illustrated in  FIGS. 8B-8E . 
           [0041]      FIG. 19A  is a partial schematic front view of an alternate U-shaped channel looking into the door opening of a building having a tilt-up door with the door removed showing an alternate linear actuating mechanism that can be used with an alternate carriage as illustrated in  FIGS. 8B-8E . 
           [0042]      FIG. 19B  is a partial schematic side view of the alternate U-shaped channel of  FIG. 19A  showing the alternate carriage. 
           [0043]      FIG. 19C  is a partial schematic side view of the alternate U-shaped channel and alternate linear actuating mechanism of  FIG. 19A  showing the alternate linear actuating mechanism. 
           [0044]      FIG. 19D  is a partial schematic view of the pulley block for use with the alternate linear actuating mechanism of  FIG. 19A  removed from the U-shaped channel. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0045]    Tilt-up doors can be used on storage buildings that can include, but are not limited to, aircraft hangers, farm equipment storage buildings, marine storage buildings and heavy equipment storage buildings requiring doors that are too wide for sectional overhead doors used on residential and commercial buildings. Typically sectional overhead doors can used for door openings up to 15′ to 25′ wide without requiring extra support for the door sections to prevent the door sections from sagging when the door is in the open position. Tilt-up doors are well known for storage buildings requiring door openings wider than 20′ to 25′ wide. The tilt-up door can include an improved door lift arrangement. 
         [0046]    Turning to  FIGS. 1 to 3 , a tilt-up door  10  can be seen pivotally mounted on a building  20  having a door opening  19  and a roof  21 . The tilt-up door  10  can have a passage door  15  to permit individuals to enter the building  20  without opening tilt-up door  10 . Tilt-up door  10  can include a truss  12  that can be mounted on the outside  11  of tilt-up door  10  above passage door  15 . Tilt-up door  10  can have a frame  16  that can include horizontal members  17  and vertical members  18  that can be square or rectangular box members that can be fastened together into a frame  16  as is well known in the art. Truss  12  can be sized to provide the desired support for tilt-up door  10  to prevent sagging in the open position shown in  FIG. 3  and to support the door for loads such as can be presented by rain, snow and wind conditions. Truss  12  can be attached to tilt-up door  10  with suitable mounting brackets  14  that can be attached to vertical members  18  of door frame  16  and can receive mounting bolts, not shown, to connect truss  12  to tilt-up door  10 . Truss  12  can be mounted on tilt-up door  10  in a position where truss  12  will not interfere with building  20  when the tilt-up door  10  is in the open position as shown in  FIG. 3 . An advantage of mounting truss  12  generally in the vertical center portion of the door is that truss  12  is spaced above the floor and surface in front of building  20  and above a passage door  15  when a passage door is desired. In addition, truss  12  can be located near the pivot point for tilt-up door  10  as described below. Tilt-up door  10  can have door panels  13  attached to horizontal members  17  and additional vertical members  18  for frame  16 . As desired door panels  13  can be selected to match panels used to enclose building  20 . Door panels  13  can be typical door panels and can be insulated panels if desired as are well known. Truss  12  can be mounted to tilt-up door  10  after door panels  13  are attached to frame  16  to avoid inserting door panels  13  between truss  12  and frame  16 . 
         [0047]    Tilt-up door  10  will be illustrated in combination with a steel frame aircraft hanger building although, as mentioned above, a tilt-up door  10  can be installed on other types of storage buildings including, but not limited to, wood frame pole barns, masonry buildings and open web truss buildings as desired. Building  20  can have a plurality of I-beams or columns  22  that can collectively form the framework  28  for building  20  and support roof  21 . In the event the building framework  28  does not include I-beams a U-shaped channel that can be similar to U-shaped channel  32  can be employed adjacent the door opening. Building  20  can have walls  25  as desired to enclose building  20 . Roof trusses  23 , see  FIG. 10 , can be provided to support roof  21  as are well known. While I-beam trusses are shown in the drawings other roof support systems can be used as desired. 
         [0048]    As mentioned above, a tilt-up door  10  can be pivotally mounted to building  20 . 
         [0049]    Turning to  FIG. 4 , an I-beam  22  forming part of the building framework  28  at one side of door opening  19  can be seen. While the tilt-up door  10  will be described employing an I-beam  22  those skilled in the will appreciate that other support columns can be used and can be provided with a U-shaped channel in lieu of an I-beam  22 . A similar I-beam  22  or U-shaped channel can be provided on the other side of door opening  19  and the following description applies to an I-beam  22  and the pivotal mounting structure for tilt-up door  10  on both sides of door opening  19 . I-beam  22  can be attached to floor  24  with a plurality of mounting bolts  26 , or other suitable well known fasteners, and can be connected to the building framework  28  at the top of I-beam  22 , not visible, as is well know. I-beam  22  can include a web  30  and a pair of flanges  31  that can form generally U-shaped channel  32 . When a tilt-up door  10  is used with building structures that do not include I-beams, as discussed above, a U-shaped channel, not shown, can be mounted to the building support structure on each side of door opening  19  to provide a channel that can be similar to channel  32  shown in  FIG. 4 . 
         [0050]    In one embodiment the actuator  39  for the tilt-up door  10  can be single acting hydraulic cylinders  40  that can be mounted in channel  32  on each side of door opening  19  to a support plate  42  that can be supported by web  30  and flanges  31 . A double acting hydraulic cylinder can be used instead of a single acting hydraulic cylinder. When I-beam  22  is a steel beam, support plate  42  can be welded to web  30  and flanges  31 . The hydraulic cylinders  40  can be secured in channels  32  with a bracket or clamp  44  that can be attached to I-beam  22  spaced from support plate  42  to secure hydraulic cylinder  40  in place. In  FIG. 4  tilt-up door  10  is in the open position and piston  41  of hydraulic cylinder  40  is extended. The distal end  45  of piston  41  can be connected to a carriage or push block  60  that can be pivotally connected to door frame  16  as will be described below. 
         [0051]    Turning to  FIGS. 5 ,  8  and  13 , one embodiment of a pivotal mounting arrangement for pivotally mounting tilt-up door  10  to the building  20  will be described. As noted above, the mounting structure of tilt-up door  10  can be the same on both sides of the tilt-up door  10  and door opening  19 . Accordingly, while the tilt-up door  10  pivotal mounting arrangement on one side of tilt-up door  10  will be described in detail those skilled in the art should understand the following description applies to both sides of tilt-up door  10  and door opening  19  in building  20 . In  FIG. 5  carriage  60  can be seen in channel  32  with tilt-up door  10  in the partially open position. Referring to  FIGS. 5 ,  8 , and  13 , carriage  60  can be formed by connecting plates  62  and  64  in spaced relationship with end plates  66  and  68 . A horizontally extending pivot shaft journal  70  can be attached to carriage  60  by plates  62  and  64 . Plates  62  and  64  can have an opening to receive pivot shaft journal  70  and pivot shaft journal  70  can be welded to plates  62  and  64  and end plates  66  and  68  can be welded to plates  62  and  64  to form carriage  60 . Reinforcing plates  72  can be welded to pivot shaft journal  70  and end plates  66  and  68  to further support pivot shaft journal  70  relative to plates  62  and  64 . Pivot shaft journal  70  can be a hollow cylinder to receive pivot shaft  71 , see  FIG. 13 , to pivotally connect tilt-up door  10  to carriage  60 . For example, pivot shaft  71  can be a 1″ diameter solid rod. Those skilled in the art will understand that the diameter of pivot shaft  71  and the pivot shaft journal  70  can be smaller or larger depending on the size and weight of the tilt-up door  10  Likewise those skilled in the art will understand that carriage  60  can be formed in other ways to support a pivot shaft journal if desired. In addition, pivot shaft  71  can have a threaded hole  85  adjacent one end to facilitate removal of pivot shaft  71  if desired following installation. The end of pivot shaft journal  70  at plate  62  can have a plug, not shown, welded in pivot shaft journal  70  to close the end of pivot shaft journal  70  at the outer surface  63  of plate  62 . 
         [0052]    Vertical members  18  on both sides of door frame  16  can have a horizontally extending pivot shaft tube  78  that can be connected to vertical member  18  to rotatably support pivot shaft  71 , see  FIG. 13 , to pivotally connect door  10  to carriage  60 . Pivot shaft tube  78  can be welded in an opening in vertical member  18  at a desired location that can be generally in the vertical center portion of tilt-up door  10 . The vertical position of pivot shaft tube  78  can be determined by the vertical height of door  10  and whether tilt-up door  10  includes a passage door  15  as illustrated in  FIG. 1 . When a passage door  15  is included in tilt-up door  10  pivot shaft tube  78  can be located above the top of passage door  15  in order to allow truss  12  to be located generally adjacent the pivot point of tilt-up door  10 . Typically pivot shaft tube  78  can be located at least one quarter of the vertical height above the bottom edge  37  of the tilt-up door  10  and less than three quarters of the vertical height above the bottom edge of the tilt-up door  10 . The location of pivot shaft tube  78 , and accordingly the pivot point of tilt-up door  10  can be determined by the overall height of tilt-up door  10 , whether a passage door  15  will be included and how much of tilt-up door  10  should extend from the face of the building  20  when the tilt-up door is in the open position which can determine the location of truss  12 . It can be advantageous to locate the pivot point of tilt-up door  10  generally in the vertical center portion of the door, but, as noted above, the pivot point can be located as desired in the vertical center portion of the tilt-up door  10  to accommodate a passage door  15  and to allow vertical location of truss  12  generally adjacent to the pivot shaft tube  78 . In the embodiment illustrated in  FIGS. 1-3  the pivot shaft tube  78  can be located approximately  2 / 3  of the distance up from the bottom  37  of tilt-up door  10  to the top of tilt-up door  10 . 
         [0053]    Pivot shaft tube  78  can have a shaft tube closure  80  that can be mounted to a mounting ring  79  attached to the end of pivot shaft tube  78 . Shaft tube closure  80  can be mounted to mounting ring  79  using suitable fasteners  83 . Shaft tube closure  80  can have an adjusting bolt nut  81  attached to the external surface of shaft tube closure  80 . An adjusting bolt  82  can be threaded into adjusting bolt nut  81  to bear against the end of pivot shaft  71  in shaft tube  78  to position door frame  16  relative to carriage  60  and accordingly I-beams  22  and building  20 . By adjusting the adjusting bolts  82  on the opposite sides of tilt-up door  10  the tilt-up door  10  can be positioned side to side as desired in door opening  19  by adjusting the adjusting bolts  82 . Adjusting bolts  82  can have a square or hex head  82 ′ or can have a recessed socket to receive a tool to facilitate rotation of the respective adjusting bolts  82  on the opposite sides of tilt-up door  10  to position the tilt-up door  10  as desired. A lock nut  84  can be secured to each adjusting bolt  82  after the tilt-up door  10  is satisfactorily positioned in door opening  19  to lock adjusting bolts  82  in position. In order to adjust, or re-adjust, the side to side position of tilt-up door  10  in door opening  19  lock nuts  84  can be loosened and adjusting bolts  82  rotated to position the tilt-up door  10  in door opening  19  as desired and then lock nuts  84  can be retightened to secure the adjusting bolts  82  in the desired position. To remove pivot shaft  71 , tilt-up door  10  can be partially opened to provide access to shaft tube cover  80  and tilt-up door  10  can be supported at the bottom edge  37  to remove weight from pivot shaft  71 . Shaft tube cover  80  can be removed and a shaft puller can be threaded into threaded hole  85  to pull pivot shaft  71  from the pivot shaft tube  78 . Pivot shaft  71  can be replaced and adjusted and the shaft tube cover can be replaced to complete any service of the pivot shaft and/or tilt-up door. Pivot shaft  71  can allow pivot shaft tube  78  to rotate relative to pivot shaft journal  70  as tilt-up door  10  is moved from the closed to the open position or from an open position to the closed position. Grease fittings  73  can be provided for pivot shaft journal  70  and pivot shaft tube  78  as shown on  FIGS. 5 ,  8  and  13 . Applicant has found that sleeve or other bearings are not required for pivot shaft  71  in pivot shaft journal  70  or pivot shaft tube  78  since the amount of relative rotation of pivot shaft  71  in pivot shaft journal  70  and pivot shaft tube  78  is relatively small in a door opening or closing cycle. If desired, suitable sleeve bearings could be used in addition to or instead of grease fittings to facilitate rotation of pivot shaft tube  78  relative to pivot shaft journal  70  on pivot shaft  71  as the tilt-up door  10  is opened and closed. 
         [0054]    Carriage  60  end plate  68  can have a piston connector  74  attached to the outer surface  69  of end plate  68 . Piston connector  74  can be arranged to receive the distal end  45  of piston  41  and a connector bolt  77 , see  FIGS. 8 and 8A . Distal end  45  can have a connector hole  46  bored transversely through the distal end  45 . Connector  74  can have a connector bolt hole  75  on one side of connector  74  and tapped threads  76  on the opposite side of connector  74  to receive connector bolt  77  to secure carriage  60  to distal end  45  of piston  41 . In the embodiment disclosed in  FIGS. 4-8A  a threaded connector bolt  77  is shown to secure carriage  60  to piston  41 . Those skilled in the art will understand that other known fasteners such as a pin or a set screw or other fastener can be used to secure carriage  60  to the distal end  45  of piston  41  as desired. 
         [0055]    Referring to  FIGS. 5 ,  6  and  7 , carriage  60  can have a plurality of wheels that can facilitate movement of carriage  60  in channel  32  as tilt-up door  10  is opened and closed. Carriage  60  can have an exterior side  60 ′, namely the side of carriage  60  that faces the outside of building  20  when carriage  60  is positioned in channel  32 , and an interior side  60 ″ that faces the interior of building  20 . As tilt-up door  10  is opened by operating an actuator  39  such as hydraulic cylinder  40 , carriage  60  is pushed upward in channel  32  by piston  41  pushing door frame  16  and, accordingly, tilt-up door  10  upward. Carriage  60  can have a pair of bearing wheels  86  rotatably mounted between plates  62  and  64  on bearing wheel shafts  87 . As carriage  60  is pushed upward by hydraulic cylinder  40 , carriage  60  is forced toward the exterior of building  20  due to the load of tilt-up door  10 . Bearing wheels  86  can be steel bearings that can withstand the load of tilt-up door  10  thereby facilitating the movement of carriage  60  in channel  32 . While steel bearing wheels can be used as illustrated in the embodiment of  FIGS. 4-8 , those skilled in the art will understand that other wheels designed to support the anticipated load of a tilt-up door  10  can be used. Carriage  60  can also have a pair of idler wheels  88  rotatably mounted between plates  62  and  64  on the interior side  60 ″ of carriage  60  on idler wheel shafts  89 . Bearing wheel shafts  87  and idler wheel shafts  89  can be attached to carriage  60  utilizing cotter keys  92  as shown in  FIGS. 5 and 6  or other well know shaft retainers as desired. Idler wheels  88  can be urethane wheels since, normally, idler wheels  88  are not in contact with flange  31  on the inside of building  20 . Idler wheels  88  can help assure that carriage  60  remains generally centered in channel  32  during opening or closing of tilt-up door  10 . Carriage  60  can also have a low friction pad  90  positioned on the outer surface  63  of plate  62  to facilitate movement of carriage  60  along web  30  in channel  32  as tilt-up door  10  is opened and closed. Low friction pad  90  can be a well known plastic resin material such as nylon or Delrin®. Those skilled in the art will understand that other low friction materials can be used for low friction pad  90 . A low friction pad such as low friction pad  90  can be attached to plate  62  with a plurality of countersunk flat head machine screws  91  that can be threaded into tapped holes in plate  62 . Those skilled in the art will understand that the number of screws required to secure low friction pad  90  to plate  62  depends on the size of low friction pad  90 . Typically 4 to 6 screws  91  can be used to secure low friction pad  90  to plate  62 . 
         [0056]    In addition to the pivotal mounting of tilt-up door  10  to building  20  described above, the tilt-up door mounting arrangement can include a track  50  that can be attached to I-beam  22  adjacent the top end of I-beam  22  on each side of door opening  19 . Referring to FIGS.  1  and  9 - 11 , the first end  48  of track  50  can be connected to I-beam  22  and roof truss  23  adjacent the top of I-beam  22 . Track  50  can be a C-section steel beam having a bottom flange  51  and a top flange  52  in addition to a mounting flange  53  to facilitate attachment of track  50  to I-beam  22 . Top flange  52  can be attached to roof truss  23  to connect track  50  to the building structure. While the building  20  illustrated in the drawings includes roof trusses  23 , those skilled in the art will understand that other building trusses can be used to secure track  50  in place at the top of I-beam  22 . In addition, as described below in connection with  FIG. 12 , a tilt-up door  10  can be used in combination with buildings that to not have trusses or other supports positioned above track  50 . The length of track  50  can be determined based on the overall height of tilt-up door  10  and the pivot point that determine how far tilt-up door  10  will extend into building  20  when tilt-up door  10  is in the open position as shown in  FIG. 3 . Those with ordinary skill in the art will understand that track  50  can be a beam having a configuration other than a C-section as desired. 
         [0057]    Track  50  can include a cam surface  55 . Door frame  16  can have a horizontally extending cam follower  95  positioned adjacent to top edge  36  of tilt-up door  10 . Cam follower  95  can include a mounting bracket  96  that can be connected to vertical member  18  of door frame  16  adjacent to the top horizontal member  17 . Mounting bracket  96  can be welded to vertical member  18  and can be arranged to support flange bearings  98  on opposite faces  97  of mounting bracket  96 . Flange bearings  98  can be secured to mounting bracket  96  with fasteners  99  and can include grease fittings  73 . Cam follower  95  can further include a cam follower shaft  102  that can be rotatably supported by flange bearings  98  on opposite sides of mounting bracket  96  and shaft  102  can extend outwardly from door frame  16  to rotatably support cam follower wheel  104 . Cam follower wheel  104  can be an enlarged end of shaft  102  and can have a relatively hard urethane surface formed on the enlarged end of shaft  102 . As can be seen best in  FIG. 11  cam follower wheel  104  can engage cam surface  55  as tilt-up door  10  moves from the closed position, shown in  FIG. 10 , to the open position shown in  FIG. 11 . When the pivot point of tilt-up door  10  is above the vertical center of tilt-up door  10 , cam follower wheel  104  can be biased into contact with cam surface  55  by the unbalanced weight of tilt-up door  10  with respect to the pivot point about pivot shaft  71 . Accordingly, as an actuator  39  such as hydraulic cylinders  40  are operated, carriages  60  are forced upward by pistons  41  thus pushing tilt-up door  10  upward as pivot shaft tubes  78  attached to door frame  16  are forced upward. As door frame  16  moves upward the top edge  36  of tilt-up door  10  rotates inward as cam follower wheels  104  roll along cam surfaces  55 . As tilt-up door  10  moves upward, tilt-up door  10  rotates approximately 90° as shown in  FIGS. 2 and 3 . Thus, tilt-up door  10  has a moving pivot point, pivot shaft  71  in pivot shaft tubes  78 , moving along a substantially straight line (carriages  60  and pivot shaft journals  70  move in substantially vertical channels  32 ), about which tilt-up door  10  rotates as it is moved upward. Cams  55  can be arranged to rotate tilt-up door  10  from the vertical position in  FIG. 1  to a generally horizontal position as shown in  FIG. 3  as hydraulic cylinders  40  lift tilt-up door  10  from the closed position in  FIG. 1  to the open position in  FIG. 3 . 
         [0058]    Referring to  FIG. 10 , as tilt-up door  10  approaches the closed position cam surface  55  becomes substantially vertical adjacent the first end  48  of track  50  so that tilt-up door  10  initially moves generally vertically for the first few inches from closed position as tilt-up door  10  opens and moves generally vertically over the last few inches to the closed position as tilt-up door  10  closes. An advantage of generally vertical movement from and to the closed position is that material lying against the outside surface of tilt-up door  10  such as snow or ice does not need to be moved by the door opening mechanism as tilt-up door  10  initially rises vertically. An additional advantage of vertical movement at the beginning of an opening cycle and the end of a closing cycle is that a mechanical latch arrangement can be employed to secure the bottom edge  37  of tilt-up door  10  in the closed position. One mechanical latch arrangement can be seen in  FIGS. 2 and 3  and can include hooks  34  that can be attached to vertical members  18  on the outside edges of door frame  16  spaced above the bottom edge  37  extending inward from door frame  16 . Tabs  35  can be attached to I-beams  22  on opposite sides of door opening  19  extending into door opening  19  and positioned to be engaged by hooks  34  as tilt-up door  10  moves to the closed position shown in  FIG. 1 . Hooks  34  and tabs  35  can be dimensioned and positioned so that hooks  34  engage/disengage tabs  35  as tilt-up door  10  moves generally vertically to the closed position/from the closed positioned as described above. In addition, tabs  35  can prevent over swing of tilt-up door  10  past the closed position during closing and provide a secure stop for tilt-up door  10  in the event of wind pressure and the like. Referring to  FIG. 3A , extended tabs  35 ′ can be provided to extend along I-beam  22  from adjacent the floor  24  to a position adjacent the top of hydraulic cylinder  40  to provide an extended door stop and to provide an improved door seal. An improved door seal arrangement can be desirable for applications in climates where climate control of the interior of building  20  may be desired. Extended tabs  35 ′ can have a slot  38  to allow hook  34  to engage tab  35 ′ as described above. 
         [0059]    Referring again to  FIGS. 10 and 11 , track  50  can include additional cam surfaces that can restrain cam follower wheel  104  as tilt-up door  10  approaches the open position adjacent the second end  49  of track  50 ,  FIG. 11 , and the closed position adjacent the first end  48  of track  50 ,  FIG. 10 . A closed cam follower surface  56  can be provided on track  50  beneath cam surface  55  that can prevent cam follower wheel from moving out of contact with cam surface  55  allowing tilt-up door  10  to lift and rotate cam follower wheel  104  out of contact with cam surface  55  such as might occur in a high wind condition before tilt-up door  10  is open enough to provide sufficient cantilever load to hold cam follower wheel  104  in contact with cam surface  55 . An open cam follower surface  57  can be provided to engage cam follower wheel  104  as tilt-up door  10  approaches the open position adjacent the second end  49  of track  50 ,  FIGS. 3 and 11 . By engaging cam follower wheel  104 , open cam surface  57  can help prevent tilt-up door  10  from bouncing up and down when substantially open as might otherwise occur in high wind conditions. Alternately as illustrated in  FIG. 10A , track  50  can have secondary cam surface  58  positioned below and generally parallel to cam surface  55  to assure that cam follower wheel  104  remains generally in contact with cam surface  55  or secondary cam surface  58  as cam follower wheel  104  moves from the first end  48  to the second end  49  of track  50 . A secondary cam surface  58  can be used when the pivot point of tilt-up door  10  is near or below the vertical mid-point of tilt-up door to preclude the cam follower wheel  104  from dropping out of contact with cam surface  57  due to a nearly balanced tilt-up door  10  about the pivot point or unbalanced weight of tilt-up door  10  above the pivot point. Secondary cam surface  58  can be vertically spaced from cam surface  55  sufficiently to allow cam follower wheel  104  roll freely along cam surface  55  and or secondary cam surface  58 . Thus, in the embodiment illustrated in  FIG. 10A , cam surface  55  and secondary cam surface  58  can form a track or channel for cam follower wheel  104  that can prevent the cam follower wheel  104  from losing contact with the cam surface  55  and/or secondary cam surface  58  regardless of the vertical location of the pivot point of tilt-up door  10  or adverse weather conditions. 
         [0060]    Turning to  FIGS. 10B and 12A  an alternate track  450  is illustrated that can be attached to a juxtaposed vertical member  22 , that can be an I-beam, adjacent the top end of vertical member  22  on each side of door opening  19 . The first end  448  of track  450  can be connected to vertical member  22  generally adjacent the top of tilt-up door  10  when tilt-up door  10  is in the closed lowered position. Track  450  can be a fabricated steel beam including a back member  447 , a first end member  448  that can be welded to one end of back member  447  and a second end member  449  that can be welded to an opposite end of back member  447 . Top member  452  can be welded to the top edge of back member  447  and a bottom flange  452  can be welded to the bottom edge of back member  447 . Top member  452  can be a square or rectangular box member. A suitable mounting bracket  464  can be attached to vertical member  22  and can have openings  466 , not visible, for mounting bolts  465  to secure track  450  to a vertical member  22 . In addition, as described below in connection with  FIG. 12A , tilt-up door  10  can be used in combination with buildings that do not have trusses or other supports positioned above track  450 . The length of track  450  can be determined based on the overall height of tilt-up door  10  and the pivot point that determine how far tilt-up door  10  will extend into building  20  when tilt-up door  10  is in the open position. 
         [0061]    Track  450  can include a cam  455  that can have plural segments. A first segment  454  can be formed by the inside surface  453  of first end member  448 . A second segment  456  and third segment  457  can be formed by a plate member. Segment  456  can be welded to back member  447  and segment  457  can be welded to back member  447  and top member  452 . Segments  456  and  457  can be a formed continuous plate member or can be separate plate members as desired. Cam  455  can also have a curved segment  462  positioned between second segment  456  and first segment  454  that can be a continuation of second segment  456  and welded to back member  447  and first end member  448 . Door frame  16  can have a horizontally extending cam follower  95  that can be connected to vertical member  18  of door frame  16  generally adjacent the top horizontal member  17  as described in detail above. Similar to the embodiment illustrated in  FIGS. 10 and 11 , cam follower wheel  104  can engage cam  455  as tilt-up door moves from the closed position shown in  FIG. 10B  to the open position. When the pivot point of the tilt-up door  10  is above the vertical center of tilt-up door  10 , cam follower wheel  104  can be biased into contact with cam  455  by the unbalanced weight of tilt-up door  10  with respect to the pivot point about pivot shaft  71 . As described above, when an upwardly directed motive force acts upon the tilt-up door  10  pushing tilt-up door  10  upward, door frame  16  moves upward and tilt-up door  10  rotates inward as cam follower wheels  104  roll along cams  455  that can be positioned on opposite sides of door opening  19 . As tilt-up door  10  moves upward, tilt-up door  10  rotates approximately 90° as shown in  FIGS. 2 and 3 . 
         [0062]    A second cam  458  can be positioned below and generally parallel to cam  455  to assure that cam follower wheel remains generally in contact with cam  455  or second cam  458  as cam follower wheel  104  moves from the first end  448  to the second end  449  of track  450 . Second cam  458  can prevent cam follower wheel  104  from moving out of contact with cam  455  allowing tilt-up door  10  to lift and rotate cam flower wheel  104  out of contact with cam  455  as might occur in a high or gusty wind condition and to help prevent tilt-up door  10  from bouncing up and down when substantially open as might occur in high or gusty wind conditions. A second cam  458  can be used when the pivot point of the tilt-up door is near or below the vertical mid-point of tilt-up door  10  to preclude the cam follower wheel  104  from dropping out of contact with cam  455  due to a nearly balanced tilt-up door  10  about the pivot point or unbalanced weight of tilt-up door  10  above the pivot point. Second cam  458  can be vertically spaced from cam  455  sufficiently to allow cam follower wheel  104  to roll freely along cam  455  and or second cam  458 . Thus, in the embodiment illustrated in  FIG. 10B , cam  455  and second cam  458  can form a track or channel for cam follower wheel  104  that can prevent the cam follower wheel  104  from losing contact with the cam  455  and/or second cam  458  regardless of the vertical location of the pivot point of tilt-up door  110  or adverse weather conditions. 
         [0063]    Referring again to  FIGS. 10B and 12A , cam  455  can have a first steep inclined segment  454 , a second inclined segment  456  and a third segment  457 . First steep inclined segment  454  can extend generally vertically so that tilt-up door  10  can initially move generally vertically for the first few inches from the closed position as tilt-up door  10  opens and can move generally vertically over the last few inches to the closed position as tilt-up door  10  closes. An advantage of generally vertical movement from and to the closed position is that material lying against the outside surface of tilt-up door  10  such as snow or ice does not need to be moved by the door opening mechanism as tilt-up door  10  initially rises vertically. An additional advantage of vertical movement at the beginning of an opening cycle and the end of a closing cycle is that a mechanical latch arrangement can be employed to secure the bottom edge  37  of tilt-up door in the closed position as described in detail above. Second inclined segment  456  can be generally linear, and third segment  457  can be generally horizontal. Cam  455  can have a curved segment  462  positioned between the first steep inclined segment  454  and second inclined segment  456  that can allow cam follower wheel  104  to roll from first steep inclined segment  454  to inclined segment  456 , and vice versa, as tilt-up door  10  is moved from the closed lowered position to the open position and back. 
         [0064]    Second cam  458  can have a first steep inclined portion  459 , a second inclined portion  460  and a third portion  461 . Second portion  460  and third portion  461  can be square or rectangular box members and can be welded to back member  447 . Similar to second inclined segment  456 , second inclined portion  460  can be generally linear. Similar to third segment  457 , third portion  461  can be generally horizontal. First steep inclined portion  459  can be a surface of bracket  463  positioned between the second portion  460  and bottom flange  451  as shown in  FIG. 10B  or can be integrally formed as part of cam  458 . As can be seen in  FIG. 10B , mounting bolts  465  can be used to secure bracket  463  to back member  447  and bottom flange  451  to mounting bracket  464 . Mounting holes  466  can be provided in the bottom flange  451  adjacent mounting bracket  464  and in back member  447 , not visible, to accommodate mounting bolts  465 . Those with ordinary skill in the art will understand that track  450  can be a beam having a configuration other than configuration illustrated in  FIG. 10B  as desired to provide first and second cams as described above. 
         [0065]    As noted above, a tilt-up door  10  can be used in combination with storage buildings that do not have a building truss spanning the building adjacent to top of the door opening. Turning to  FIG. 12 , an alternate I-beam and track arrangement can be seen in schematic form. Building  120  can have a roof  121  supported by roof trusses  123  that do not extend horizontally at the top of door opening  119 . I-beam  122  can be similar to I-beam  22  in the embodiment of  FIGS. 1-11  and  13  and can include a hydraulic cylinder and carriage mechanism as described above but not shown in  FIG. 12 . I-beam  122  can have a support plate  152  that can be similar to support plate  42  as illustrated in  FIG. 4  and can support an actuator  39  or a hydraulic cylinder, not shown in  FIG. 12  that can be similar to hydraulic cylinder  40  as illustrated in  FIG. 4 . Track  150  can be attached to I-beam  122  as described above in the embodiment of  FIGS. 1-11  and  13 . In absence of a building truss or beam to secure track  150  to, as in the embodiment described above, a support tube  125  can be provided to support the end  151  of track  150  opposite I-beam  122 . Support tube  125  can be a square or rectangular tube, or could be an I-beam as desired, and can be attached to the floor  124  with mounting bolts  126  or other fasteners in a manner similar to I-beam  22 . As above, an I-beam  122 , track  150  and support tube  125  can be provided on each side of door opening  119 . In addition, a spreader  127  can be provided to connect support tubes  125  on opposite sides of door opening  119  to prevent tracks  150  from moving horizontally apart in operation since tracks  150  are not attached to the building structure adjacent to the inner end  151  as in the embodiment of  FIGS. 1-11  and  13  described above. The alternate I-beam and track arrangement described above can also be used with the alternate pivotal mounting arrangements and operating mechanisms described below. 
         [0066]    Turning to  FIG. 12A , a track  450  can be used in combination with a building  120  that can have a roof  121  supported by roof trusses  123  that do not extend horizontally at the top of door opening  119 . Vertical member  122  can be an I-beam and can be similar to vertical member  22  in the embodiment of  FIG. 10B  and can include a hydraulic cylinder and carriage mechanism as described above but not shown in  FIG. 12A . Vertical member  122  can have a support plate  152  that can be similar to support plate  42  as illustrated in  FIG. 4  and can support an actuator  39  or a hydraulic cylinder, not shown in  FIG. 12A  that can be similar to hydraulic cylinder  40  as illustrated in  FIG. 4 . Track  450  can be attached to vertical member  122  as described above in connection with  FIG. 10B . As above, vertical member  122  and a track  450  can be provided on each side of door opening  119 . If desired, a spreader  127  can be provided to connect tracks  450  on opposite sides of door opening  119  to prevent tracks  450  from moving horizontally apart in operation. The alternate vertical member and track arrangement described above can also be used with the alternate pivotal mounting arrangements and operating mechanisms described below. 
         [0067]    Turning to  FIGS. 4 and 14  a hydraulic circuit  132  for supplying hydraulic cylinders  40  when the tilt-up door actuator  39  consists of one or more hydraulic cylinders will be described. A control panel  130  can be provided to support controls and hydraulic circuit components. While control panel  130  is shown adjacent door opening  19  in  FIG. 4  those skilled in the art will understand control panel can be located at other positions in building  20  or mounted to columns or I-beams as desired. A pump and motor  135  can be mounted on control panel  130  adjacent a spool valve  137  and a hydraulic fluid tank  139 . Hydraulic fluid tank  139  can be sized to hold sufficient hydraulic fluid for the hydraulic circuit  132  and to allow for expansion of the hydraulic fluid under warm weather temperature conditions without overflowing. As illustrated in  FIG. 4 , tank  139  can include a vent  148  to the atmosphere. While pump and motor  135 , spool valve  137  and relief valve  141  are illustrated as a single or combined component those skilled in the art will understand that a separate pump and motor, spool valve and relief valve can be employed if desired. Supply lines  142  can connect the “A” side of spool valve  137  to the supply port  143  of a holding valve  140  adjacent to each hydraulic cylinder  40 . In the  FIGS. 16 and 17A  embodiments a single linear actuator  39  can be a hydraulic cylinder that can be connected in a hydraulic circuit that can be similar to the hydraulic circuit illustrated in  FIG. 14  but having a single hydraulic cylinder. In the  FIGS. 16 and 17A  embodiments a suitable control panel, not shown, can be similar to control panel  130  and can be located in a suitable location in building  20 . In the case of the  FIG. 17A  embodiment a control panel that can be similar to control panel  130  but not shown in  FIG. 17A , can be located adjacent I-beam  206  if desired to minimize the length of the hydraulic lines required to connect the hydraulic cylinder to the control panel. In the embodiments described in connection with  FIGS. 1-11 ,  14 ,  16  and  17 A, holding valves  140  can be a well known holding valve such as a Gresen Holding Valve model MHB-015-LEAE-51E-00. While holding valves  140  and hydraulic cylinders  40  are illustrated as separate components, those skilled in the art will understand that a suitable holding valve can be incorporated in the hydraulic cylinder. Supply lines  142  can be arranged to supply the hydraulic cylinders  40  from a center point, when more than one hydraulic cylinder is employed, so that length of the supply lines  142  from spool valve  137  to supply ports  143  of holding valves  140  to hydraulic cylinder  40  for each of the hydraulic cylinders  40  can be equal. Supply lines  142  can be ½″ steel lines. Release lines  144  can connect the “B” side of spool valve  137  through “B” port relief valve  141  to the release port  145  of holding valves  140 . Release lines  144  can be ⅜″ steel lines. Whenever hydraulic cylinders  40  are partially or fully extended by operation of pump and motor  135  and actuation of spool valve  137 , holding valves  140  prevent reverse flow from hydraulic cylinders  40  and thereby prevent pistons  141  from retracting regardless of whether pump and motor  135  are operating, or even if one or more of supply lines  142  is opened or damaged leading to loss of hydraulic fluid from the supply lines  142 . 
         [0068]    In order to retract pistons  141  and lower tilt-up door  10 , pump and motor  135  can be restarted and spool valve  137  can be moved to the “B” position to pressurize release ports  145  on holding valves  140  to allow reverse flow of hydraulic fluid from hydraulic cylinders  40  back to tank  139  and thereby allow pistons  141  to retract into hydraulic cylinders  40 . “B” port relief valve  141  can be provided to reduce the fluid pressure in the release lines  144  from the supply lines  142  pressure since the pressure applied to release ports  145  can determine the reverse flow rate through holding valves  140 , and thus can determine the closure rate for tilt-up door  10 . For example, the pressure in supply lines  142  applied to the hydraulic cylinders  40  can be in the range of 1,200 to 1,500 psi, the pressure applied to release ports  145  can be on the order of 500-800 psi. Those skilled in the art will understand that the supply lines pressure and release lines pressure can be higher or lower than the pressures mentioned above as an example depending on the application and components used in the hydraulic circuit. “B” port relief valve  141  can be adjustable to allow the user to select and set the pressure in the release lines that can be applied to release ports  145 . “B” port relief valve  141  can have an adjustment screw  147  that can have a jam nut to secure adjustment screw  147  when the release line pressure has been adjusted to provide the desired descent rate for tilt-up door  10 . Since release lines  144  supply pressure to release ports  145  without flow of hydraulic fluid through release lines  144  the length of release lines  144  to release ports  145  of holding valves  140  do not need to be equal as can be the case of supply lines  142 . While a manually controlled spool valve is illustrated in  FIGS. 4 and 14 , those skilled in the art will understand that electrically or electronically controlled spool valves can be used to control operation of hydraulic cylinders  40  if desired. An electrical circuit breaker box  146  can be mounted on control panel  130  if desired to provide power to pump motor  135  and any other electrical components mounted on or powered through control panel  130 . The embodiments illustrated in  FIGS. 16  when the linear actuator  39  is a hydraulic cylinder and  FIG. 17A  can similarly be provided with controls for the hydraulic circuit. When the linear actuator is other than a hydraulic cylinder a control panel similar to control panel  130  can be provided for the control devices for the linear actuator. 
         [0069]    Turning to  FIGS. 4A-4E  and  14 A- 14 C an alternate hydraulic circuit  332  for supplying hydraulic cylinders  40 ′ when the tilt-up door actuator  39  consists of one or more hydraulic cylinders  40 ′ will be described.  FIGS. 4A and 14A  illustrate an embodiment including two hydraulic cylinders  40 ′, however, an alternate hydraulic circuit  332  and hydraulic cylinders  40 ′ can be employed as a tilt-up door actuator employing one or more that two hydraulic cylinders  40 ′ if desired.  FIG. 4B  illustrates a submersible hydraulic pump  334  and motor  335  that can be mounted in a hydraulic fluid tank  339  to form a hydraulic pump assembly  330 . A pilot operated check valve  354  can be provided adjacent an upper wall  339 ′ of tank  339  that can be connected to hydraulic line  336  from pump  334  and to hydraulic line  336 ′ leading to hydraulic line connector  339 ′ at the top of hydraulic pump assembly  330 . Pilot operated check valve  354  can be a DECVC- 30  valve. A return hydraulic line  336 ″ can lead from check valve  354  to the interior of tank  339 . Pilot operated check valve  354  can close when pump  334  starts sending hydraulic fluid from hydraulic pump  334  to hydraulic line  342  when the pump  334  is operated by motor  335 . When pump  334  shuts down pilot operated check valve  354  opens and hydraulic fluid in hydraulic line  342  can flow through check valve  354  to hydraulic line  336 ″ into tank  339 . Accordingly, after operation of pump  334  to operate hydraulic cylinders  40 ′, pilot check valve  354  can open allowing hydraulic fluid in hydraulic lines  342  to drain back to tank  339  with tilt-up door being held open by hydraulic cylinders  40 ′ as will be described in detail below. Hydraulic fluid tank  339  can be sized to hold sufficient hydraulic fluid for the hydraulic circuit  332  and to allow for expansion of the hydraulic fluid under warm weather temperature conditions without overflowing. Submersible pump  334  and motor  335  can be a conventional submersible hydraulic pump and motor as are well known in the art. For example, hydraulic pump  334  can be a DFP-A2PL-8 pump and motor  335  can be a WEG 5 hp motor. If desired, hydraulic pump assembly  330  can include a suitable pressure relief valve, not shown, that can be similar to pressure relief valve  341  illustrated in  FIG. 4C  to bypass hydraulic fluid from hydraulic lines  336  or  336 ′ back into tank  339  in the event pressure in the hydraulic circuit rises above a predetermined limit such as if tilt-up door  10  is blocked during an opening cycle or if the hydraulic pump assembly  330  continues to operate after tilt-up door is fully opened. While submersible pump  334  and motor  335  and hydraulic fluid tank  339  are illustrated in  FIGS. 4 and 14  as an assembly those skilled in the art will understand that a separate, submersible or non-submersible, pump and motor can be employed if desired. 
         [0070]    Hydraulic lines  342  can connect the hydraulic pump assembly  330  at hydraulic line connector  339 ′ to a supply port  343  that can be provided in a hydraulic cylinder housing extension  340  adjacent the bottom of each hydraulic cylinder  40 ′. Hydraulic cylinders  40 ′ can be similar to hydraulic cylinders  40  described above and, in addition, can have a housing extension  340  adjacent the bottom of the hydraulic cylinder  40 ′. As can be seen in schematic  FIG. 4C , hydraulic cylinder  40 ′ can include a flow control valve  337  connected between the supply port  343  and a check valve  345 . Check valve  345  can be connected to flow control valve  337  and to the bottom of hydraulic cylinder  40 ′ at  349 . Flow control valve  337  can permit free flow of hydraulic fluid (illustrated with a solid arrow) from supply port  343  to check valve  345  and can permit a controlled flow of hydraulic fluid (illustrated with a dashed arrow) from check valve  345  to supply port  343 . The flow rate from check valve  345  to supply port  343  can be adjusted by an adjusting mechanism that can include a screw  338  so that adjusting screw  338  can function as a closing speed adjustment for tilt-up door  10 . Check valve  345  can permit free flow of hydraulic fluid (illustrated with a solid arrow) from flow control valve  337  to the check valve connection  349  into hydraulic cylinder  40 ′ and can have a solenoid  347  that, when actuated, can allow reverse flow of hydraulic fluid (illustrated with a dashed arrow) from hydraulic cylinder  40 ′ to flow control valve  337 . Unless solenoid  347  is actuated hydraulic fluid cannot flow through check valve  345  from hydraulic cylinder  40 ′ to supply port  343  through flow control valve  337 . In addition, a pressure relief valve  341  can be connected to hydraulic cylinder at  351  and to a hydraulic line at  353  to allow bypass flow of hydraulic fluid from cylinder  40 ′ to supply port  343  in the event the pressure inside hydraulic cylinder  40 ′ exceeds a predetermined limit. For example, pressure in hydraulic cylinder  40 ′ could increase in the event the ambient temperature to which hydraulic cylinders  40 ′ are exposed increases causing the hydraulic fluid to expand in the confined volume of the hydraulic cylinder  40 ′. For example, flow control valve  337  can be a Vonburg 226-08 valve, check valve  345  can be a Delta DES 2 A- 00  valve and pressure relief valve can be a Delta DERCA-2800 valve. 
         [0071]    As illustrated in  FIGS. 4C ,  4 D and  4 E, flow control valve  337 , pressure relief valve  341  and check valve  345  can be mounted in hydraulic cylinder housing extension  340  and check valve solenoid  347  can be mounted below housing extension  340  on the lower side of support plate  42  on which hydraulic cylinder  40 ′ is supported. Adjustment screw  338  can extend outwardly from the hydraulic cylinder extension  340  to facilitate adjustment of the closing speed of tilt-up door  10  when closing is selected and check valve solenoids  347  operate check valves  345 . While flow control valve  337 , pressure relief valve  341  and check valve  345  can be mounted in a hydraulic cylinder housing extension  340  as illustrated in  FIGS. 4A-4E , one or more of the valves  337 ,  341  and  345  and supply port  343  and associated connections can be positioned separately adjacent hydraulic cylinder  40 ′ if desired. 
         [0072]    Turning to  FIG. 14A , hydraulic line first portion  342 ′ can be arranged to supply the hydraulic cylinders  40 ′ from a center point  344  through hydraulic line second portions  342 ″ when more than one hydraulic cylinder is employed, so that length of the hydraulic lines  342 ″ from the center point  344  to supply ports  343  for each of the hydraulic cylinders  40 ′ can be substantially equal. Hydraulic lines  342  can be ½″ steel lines. A low voltage DC supply  331  can be provided to power a low voltage circuit  329  connecting solenoids  347  at connector  348  with a control switch  333  to operate check valve solenoids  347  to operate check valves  345  with control switch  333 . Control switch  333  can be mounted on control panel  130 , or can be incorporated in a controller for the tilt-up door  10  as desired. Control switch  333  can include switch operators  333 ′ that can be “open”, close” and “stop” buttons for operating the hydraulic pump assembly  330  to open the tilt-up door  10 , operating the check valve solenoids  347  to lower the tilt-up door  10 , or de-energizing the hydraulic pump assembly  330  and check valve solenoids  347  to stop movement of the tilt-up door  10  by stopping flow of hydraulic fluid in hydraulic circuit  332 . Control switch  333  can also activate a low voltage beeper  327  connected to low voltage circuit  329  when check valve solenoids  347  are energized to warn any persons in the vicinity of tilt-up door  10  that tilt-up door  10  is closing. Similarly, control switch  333  can be arranged to activate low voltage beeper  327  when pump and motor  335  are activated to warn any persons in the vicinity of tilt-up door  10  that tilt-up door  10  is opening if desired. 
         [0073]    In order to open tilt-up door  10  with alternate hydraulic circuit  332 , an operator can operate the “open” control switch operator  333 ′ to energize submersible pump  334  and motor  335  to pump hydraulic fluid to close pilot operated check valve  354  for hydraulic fluid to flow through hydraulic lines  342  to hydraulic cylinder supply ports  343 . Hydraulic fluid can flow freely through flow control valve  337  and check valve  345  (illustrated by the solid arrows) into the hydraulic cylinders  40 ′ causing pistons  41  to rise lifting door  10  from the closed to the open position as described above. When tilt-up door  10  is fully opened the “open” control switch operator  333 ′ can be released or the “stop” control switch operator  333 ′ can be manually or automatically operated to stop motor  335  and submersible pump  334 . As noted above, when pump  334  stops pilot operated check valve  354  can open allowing hydraulic fluid in the hydraulic lines to flow back into tank  339 . Since hydraulic fluid cannot flow from hydraulic cylinders  40 ′ unless solenoids  347  are energized operating check valves  345 , hydraulic fluid cannot flow out of hydraulic cylinders  41 ′ and tilt-up door  10  is held in the open position without pump  334  and motor  335  operating. 
         [0074]    In order to retract pistons  41  and lower tilt-up door  10 , the “close” control switch operator  333 ′ can be operated to energize check valve solenoids  347  to operate check valves  345  to allow reverse flow of hydraulic fluid (illustrated by the dashed arrows) from hydraulic cylinders  40 ′ to tank  339 . With check valves  345  operated hydraulic fluid can flow out of hydraulic cylinders  40 ′ through flow control valves  337  and through hydraulic lines  342  to pilot operated check valve  354 . With check valve  354  “open” due the pump  334  no longer running, hydraulic fluid can flow from hydraulic lines  342  into tank  339  through hydraulic line  336 ″ rather than back to hydraulic pump  334  through hydraulic line  336 . The force of gravity on tilt-up door  10  can cause reverse flow of hydraulic fluid and thereby allow pistons  41  to retract into hydraulic cylinders  40 ′. As noted above, the reverse flow rate through flow control valves  337  can be adjusted with flow control adjustment screws  338  to control the flow rate of hydraulic fluid from the hydraulic cylinders  40 ′ back to the tank  339  and thereby the closing rate of the tilt-up door  10 . An electrical circuit breaker box  146  can be mounted on control panel  130  if desired to provide power to pump motor  135 , low voltage supply  331  for low voltage circuit  329  and any other electrical components mounted on or powered through control panel  130 . 
         [0075]    In  FIGS. 8B-8E  and  16 - 18  other embodiments of pivotal mounting arrangements and operating mechanisms for a tilt-up door  10  for a building  20  are illustrated. Turning to  FIGS. 8B-8E  and  16 - 18 , tilt-up door  10  can be pivotally mounted to a building  20  as described above with  FIGS. 1-3  and  9 - 11 . However, in the alternate embodiments of  FIGS. 8B-8E  and  16 - 18 , carriages  160  can be operated by a single actuator  39  via cables  168  instead of hydraulic cylinders  40  as illustrated in  FIG. 3 . Carriage  160  can be similar to carriage or push block  60  shown in  FIGS. 8 and 8A  except that piston connector  74  on end plate  68  ( FIGS. 8 and 8A ) can be replaced by cable bracket. In the embodiment of  FIGS. 8B and 8C  carriage  160  can have a cable bracket  162  on opposite end plate  66 . Cable bracket  162  can have an opening, not visible, to receive clevis pin  166  to attach clevis  164  to cable bracket  162 . The remaining elements of carriage  160  can be the same as the corresponding elements of carriage or push block  60  and are identified with the same reference numeral as in  FIGS. 8 and 8A  and will not be described again. A steel cable  168  can be connected to carriage  160  with a clevis  164  connecting loop  170  in cable  168  to cable bracket  162  with a clevis pin  166 . While loop  170  is shown without a thimble clip those skilled in the art will understand that a thimble clip can be used in forming loop  170  if desired to strengthen and extend the working life of loop  170 . Loop  170  as shown in  FIGS. 8B and 8C  can be formed with a loop crimp  172 . Those skilled in the art will understand that instead of a loop crimp  172  a loop sleeve or rope clip can be used to form loop  170  if desired. Referring to  FIGS. 8D and 8E  alternate arrangements to connect cable  168  to a carriage  160  can be seen.  FIGS. 8D and 8E  are partial views of a carriage  160  that can be similar to carriage  60  as shown in  FIG. 8B  except for an alternate cable bracket and cable connecting mechanism. Other than the differing cable connection arrangements the embodiments illustrated in  FIGS. 8D and 8E  carriage  160  can be similar to carriage  160  illustrated in  FIGS. 8B and 8C . In the embodiment of  FIG. 8D , a generally U-shaped cable bracket  163  can be connected to end plate  66  and can include an hole  161  to allow cable  168  to pass through cable bracket  163  so that cable termination  167  can secure cable  168  to carriage  160 . Cable termination  167  can be any well known wire rope termination and can be crimped or otherwise affixed to cable  168 . Cable bracket  163  can be welded to end plate  66  as illustrated, or alternately can be provided with flanges and attached to end plate  66  with suitable fasteners as is well known in the art. In the embodiment of  FIG. 8E , a pair of spaced cable brackets  165  can be connected to end plate  66  of carriage  160  that can be similar to cable bracket  162  and can have a hole  159  arranged to receive pin  169 . Cable  168  can have a connector  173  affixed to the end of cable  168 . Connector  173 , like cable brackets  165  can have a hole  178  to receive pin  169  to attach cable  168  to carriage  160 . Wire rope cable connectors  173  are well known in the art, as are methods of attaching such connectors to wire rope cables. Thus, carriages  160  in the embodiments illustrated in  FIGS. 8B-8E  can be lifted by cable as illustrated in the embodiments of  FIGS. 15-18 . 
         [0076]    Turning to  FIGS. 15 and 16 , a portion of an I-beam  156  that can be similar to I-beam  22  in the embodiment of  FIGS. 1-11  and  13  can be seen looking in through door opening  19  in building  20  having a tilt-up door  10  as described above, but not shown in  FIGS. 15 ,  16  and  16 A. As in the embodiment illustrated in  FIGS. 1-11  and  13 , an I-beam  156  can be provided on both sides of door opening  19  and can have flanges  31  forming a channel  32  as described above. Portions of flange  31  in  FIG. 15  are cut away to show carriage  160  in channel  32  and pulley  174 . I-beam  156  can be part of a building framework  28  and can be an I-beam or other structure forming a U-shaped channel  32  all as described above in connection with  FIGS. 1-11  and  13 . In the embodiment of  FIGS. 15 ,  16  and  16 A, I-beams  156  can extend above track  50  and can support a pulley  174  on shaft  175 . Pulley shaft  175  can be supported by I-beam  156  or can be supported by a bracket mounted to I-beam  156  as will be obvious to one having ordinary skill in the art. Pulley  174  can be positioned above track  50  so that cable  168  will not interfere with the top edge  36  of tilt-up door  10 , not shown in  FIGS. 15 ,  16  and  16 A, as tilt-up door  10  is opened and closed as described above. A building truss  180  is illustrated spanning I-beams  156  in  FIGS. 16 and 16A  although the building structure or roof trusses, not shown, may include different elements to support the upper ends of I-beams  156 , or the alternate arrangement described above in conjunction with  FIG. 12  can be used. 
         [0077]    Turning to  FIGS. 16 and 16A  embodiments of an actuator  39  for the alternate embodiment operating mechanisms will be described. As illustrated in  FIG. 16 , cables  168  can pass over pulleys  174  associated with I-beams  156  toward the center of door opening  19 . A building truss  182  can be provided extending into the building from door opening  19  adjacent and above door opening  19  and can provide support for an actuator  39 . In the embodiment of  FIG. 16  the actuator  39  can be a linear actuator  190  that can have a fixed portion  192  that can be connected to building truss  182  and can have a movable portion  194 . Movable portion  194  can have a cable connector  196 . In the embodiment illustrated in  FIG. 16  linear actuator  190  can be a hydraulic cylinder  192  having a piston  194 . Cables  168  can pass over pulleys  176  and can be connected to cable connector  196  in a manner similar to the cable connection to carriage  160  as shown in  FIGS. 8B-8E , or other well known cable connections. Cables  168  can include a turnbuckle, not shown, to permit ready adjustment of the length of cables  168  for the tilt-up door  10  so that the carriages  160  supporting opposite sides of tilt-up door  10  move together when linear actuator  190  is activated. Linear actuator  190  can be a hydraulic cylinder as shown or can be a rack and pinion, a power screw, ball screw linear actuator or other well known linear actuator that can have a suitable electric motor to operate the linear actuator, as is well known in the art, to draw cables  168  upward to lift or lower carriages  160  to move tilt-up door  10 . While linear actuator  190  is illustrated in  FIG. 16  having fixed end  192  positioned away from the door opening  19  so that the movable portion  194  is extended when tilt-up door  10  is closed, those skilled in the art will understand that, if desired, linear actuator  190  can be repositioned in the opposite direction so that movable portion is extended to open tilt-up door  10  rather than be retracted. In the event linear actuator is repositioned in the opposite direction the connection for cables  168  can be arranged to space cables  168  from linear actuator  190  so the cables  168  can pass along side linear actuator  190 . A suitable control circuit, not shown, can be provided to operate the linear actuator can be provided on a control panel that can be similar to control panel  130  as described in conjunction with the embodiment of  FIGS. 1-11  and  13 . A hydraulic cylinder linear actuator can have a hydraulic circuit  132  and control similar to that illustrated in  FIG. 14 , again as is well known in the art. An electrically operated linear actuator can be provided with an electric release brake to prevent tilt-up door  10  from closing in the event of interruption of electric power to the control circuit similar to the operation of the holding valves  140  in the hydraulically operated embodiments. 
         [0078]    In the actuator  39  embodiment illustrated in  FIG. 16A  a winch  200  can be mounted on a building truss  184  that can be connected to the framework of building  20 . Building truss  184  can be positioned above and adjacent door opening  19  in a position where it will not interfere with tilt-up door  10 , not shown in  FIG. 16A , as tilt-up door  10  is opened and closed as described above. Winch  200  can have a cable drum  202  and an electric motor  204 . Cables  168  can be attached to opposite ends of cable drum  202  so that as cable drum  202  is rotated by electric motor  204  cables  168  are wound on cable drum  202  thus lifting carriages  160 , and accordingly tilt-up door  10 , or unwound from cable drum  202  thus lowering carriages  160 , and accordingly tilt-up door  10 . Winch motor  204  can have a control circuit, not shown, that can allow an operator to activate winch motor  204  to open or close tilt-up door  10 . Winch  200  can be provided with a suitable electric release brake to prevent the tilt-up door  10  from inadvertently closing in the event of loss of electric power to the control circuit, not shown, or to the winch  200 . Alternately, winch  200  can be a hydraulic winch as are well known in the art and can be powered by a hydraulic circuit and control that can be similar to hydraulic circuit  132  illustrated in  FIG. 14 . 
         [0079]    Turning to  FIGS. 17A and 17B  another cable operated embodiment can be seen. A portion of an I-beam  206  that can be similar to I-beam  22  in the embodiment of  FIGS. 1-11  and  13  can be seen looking in through door opening  19  in building  20  having a tilt-up door  10  as described above, but not shown in  FIGS. 17A and 17B . As with I-beam  22  in the embodiment illustrated in  FIGS. 1-11  and  13 , an I-beam  206  can be provided on opposite sides of door opening  19  and can have a web  30  and flanges  31  forming a channel  32  as described above. Portions of flange  31  in  FIG. 17A  are cut away to show carriage  160  in channel  32 . I-beam  206  can be part of a building framework  28  and can be an I-beam or other structure forming a U-shaped channel  32  all as described above in connection with  FIGS. 1-11  and  13 . In the embodiment of  FIGS. 17A and 17B , I-beams  206  can extend above track  50  and can support pulleys  174  on shafts  175 . Pulley shafts  175  can be supported by I-beam  206  or can be supported by a bracket mounted to I-beam  206  as will be obvious to one having ordinary skill in the art. Pulleys  174  can be positioned above track  50  to avoid cables  168  interfering with the top edge  36  of tilt-up door  10 , not shown in  FIGS. 17A and 17B , as tilt-up door  10  is opened and closed as described above. The right hand I-beam  206  in FIG.  17 A can include a first cable  168  connected to carriage  160  movably carried in I-beam  206  that passes over two pulleys  174  mounted at the top of column  206  and down to linear actuator  190 . The left hand I-beam  206 ′ can have a single pulley  174  carried on shaft  175  at the top of I-beam  206  to carry a cable  168  from the carriage  160 , not shown in  FIG. 17B , but similar to that shown in  FIG. 17A , movably carried in I-beam  206 ′ across door opening  19  to I-beam  206 . A building truss  180  is illustrated spanning I-beams  206  in  FIGS. 17B  although the building structure or roof trusses, not shown, may include different elements to support the upper ends of I-beams  206 , or the alternate arrangement described above in conjunction with  FIG. 12  can be used. The I-beam  206  (on the right hand side of  FIG. 17B ) can include an actuator  190  that can be seen in the cut-out portion of I-beam  206 . Linear actuator  190  can be a hydraulic cylinder or other linear actuator as described above in connection with  FIG. 16  and can be provided with a suitable control, again as described above in connection with  FIG. 16 . Fixed portion  192  of linear actuator  190  can be attached to I-beam  206  similar to the mounting arrangement described above in connection with  FIG. 4 . The distal end of movable portion  194  of linear actuator  190  can have a suitable cable bracket  196  to connect cables  168  from I-beams  206  and  206 ′ to linear actuator  190 . 
         [0080]    Turning to  FIG. 18  an alternate I-beam or U-shaped column can be seen in partial schematic form. A portion of an I-beam  208  that can be similar to I-beam  22  in the embodiment of  FIGS. 1-11  and  13  can be seen looking at door opening  19  in building  20  having a tilt-up door  10  as described above, but not shown in  FIGS. 17A and 17B . As with I-beam  22  in the embodiment illustrated in  FIGS. 1-11  and  13 , an I-beam  208  can be provided on opposite sides of door opening  19  and can have a web  30  and flanges  31  forming a generally U-shaped channel  32  as described above. The embodiment of  FIG. 18  can employ a cable system and a block or pulley carried by movable carriage  160  that can be used to reduce the force required to open a tilt-up door  10 . Such an arrangement can be advantageous in the case of large tilt-up doors by providing a two-time mechanical advantage to facilitate lifting the tilt-up door although the opening time can be increased depending on the speed of the actuator  39 . While a two to one mechanical advantage arrangement is illustrated in  FIG. 18 , those skilled in the art will understand that a three to one or greater mechanical advantage arrangement can be employed as desired. 
         [0081]    As in the case of the embodiments described above, an I-beam  208  can be located on both sides of door opening  19 , not shown. Carriage  160  can have a block bracket  214  connected to end plate  66  that can support block or pulley  212 . I-beam  208  can have a cable anchor  210  adjacent the top end of I-beam  208  and can be located so that anchor  210  is above block  212  when tilt-up door  10 , not shown in  FIG. 18 , is fully opened. The first end  211  of cable  168  can be secured to anchor  210  and can pass over block  212  and then to pulley  174  mounted on shaft  175  adjacent to top of I-beam  208 . Cables  168  from the opposite sides of the door opening  19  can be connected at their second end  213 as illustrated in of the embodiment illustrated in  FIG. 16A  to an electric or hydraulic winch  200  as desired. 
         [0082]    To open tilt-up door  10  from the closed position to the open position an actuator  39  such as illustrated in  FIGS. 16 ,  16 A,  17 A and  18  can be activated by a control circuit as described above to draw cables  168  away from door opening  19  thus causing cables  168  to lift carriages  160  pivotally attached to opposite sides of tilt-up door  10  similar to the operation of hydraulic cylinders  40  as described above in detail. To close the tilt-up door  10  actuator  39  can be activated to allow the cables  168  to extend toward the door opening  19  thus allowing cables  168  to lower carriages  160  pivotally connected to opposite sides of tilt-up door  10 . Thus, in the embodiment of  FIGS. 8B-8E ,  15 ,  16 ,  16 A,  17 A,  17 B and  18  a single actuator  39  can lift and lower carriages  160  by cables  168  while in the embodiment of  FIGS. 3 ,  4 ,  5 - 7 ,  8  and  8 A carriages or push blocks  60  are pushed upward and lowered by an actuator  39  comprising two hydraulic cylinders  40 . Carriages  60  and  160  can operate in the channel formed by the respective I-beams or columns in conjunction with the cam surface(s) in tracks  50  in a similar manner to lift and tilt door  10  to the open position and return tilt-up door  10  to the closed position. 
         [0083]    Turning to  FIGS. 19A-19D  an alternate I-beam or U-shaped channel and alternate actuating mechanism can be seen. In the embodiment of  FIGS. 19A-19D  a linear actuator  220  can be mounted in I-beam or U-shaped channel  222  that can be similar to I-beam  22  described above. As in the embodiment illustrated in  FIGS. 1-11  and  13 , an I-beam or U-shaped channel member  222  can be provided on both sides of a door opening  19 , not shown, and can have a web  230  and flanges  231  forming a generally U-shaped channel  232 . Portions of flanges  231  are cut away to show carriage  160  and pulley block  242  in channels  232  and  232 ′. In the embodiment of  FIGS. 19A-19D  instead of a two to one or greater mechanical advantage as illustrated in the embodiment of  FIG. 18 , the alternate actuating mechanism can be a one to two mechanical advantage that, while requiring generally two times the force to lift the door  10 , provides carriage travel that is two times the travel of the linear actuator. A one to two mechanical advantage arrangement as illustrated in  FIGS. 19A-19D  can be desirable for use with tilt-up doors to reduce the required travel of the linear actuator. Turning to  FIGS. 19A and 19C , a linear actuator  220  can be positioned in channel  232 ′ on one side of I-beam  222  adjacent the web  230  opposite the vertical channel  232  facing door opening  19  and mounted on an actuator mounting bracket  234  at one end and can include an actuator securing bracket  236  adjacent the upper end of linear actuator  220  similar to the hydraulic cylinder mounting arrangement described above in connection with  FIG. 4 . An anchor bracket  228  can be attached to I-beam  222  adjacent the top of linear actuator  220  and can be arranged for connection of a first end  252  of flexible link  240 , that can be a flat chain or cable, to I-beam  222  as is well known in the art. Mounting bracket  234  and actuator securing bracket  236  can be connected to I-beam  222  as described above in connection with  FIG. 4 . I-beam  222  can have a web  230  that can include a slot  224  extending from adjacent the top of linear actuator  220  to adjacent track  50  that can be secured to I-beam  222  adjacent the top of I-beam  222 . 
         [0084]    Turning to  FIGS. 19A and 19B , U-shaped channel  232  of I-beam  222  facing the door opening  19  can be seen with carriage  160  that can be similar to carriage  160  illustrated in  FIG. 8D  and can include a cable bracket  163  that can be arranged for connection of a second end  253  of flexible link  240  to carriage  160  as is well known in the art. Carriage  160  can be similar to carriage  160  described above and to carriage  60  described above except for flexible link connection apparatus and will not be described in further detail. Turning to  FIGS. 19A and 19D , a pulley block  242  can be slidably carried in slot  224  and can have a connector  247  that can be connected to the distal end  245  of linear actuator  220  similar to the arrangement illustrated in  FIGS. 8A and 8B . Pulley block  242  can be a generally rectangular hollow box having sides  243  and ends  244  dimensioned to be slidably carried in slot  242  and can have an axle  246  mounted to sides  243  to rotatably carry a pulley  248  that can be arranged for use with a flexible link  240  as desired. Connector  247  can be carried by the bottom end  244  as illustrated in  FIG. 19D . Pulley blocks  242  can also have a guide bar or flange  250  that can be attached to pulley block  242  to the top end wall  244  or other desired part of pulley block  242  and can be positioned to slide on one surface of web  230 . Guide bar  250  can have a low friction surface that can be similar to low friction surface or pad  90  on carriage  60 . If desired a guide bar or flange  250  can be provided for pulley block  242  to engage both sides of web  230  as illustrated in  FIG. 19A  or on one side of web  230 . If guide bars or flanges  250  are provided to engage both sides of web  230 , one or both of the guide bars or flanges  250  can be removably mounted to pulley block  242  to facilitate assembly and removal of pulley block  242  to beam  222 . Guide bar(s)  250  can help maintain pulley block  242  aligned in slot  244  as linear actuator  220  moves pulley block  242  up and down to lift and lower carriage  160  and accordingly door  10 , not shown in  FIGS. 19A-19D . Thus, in operation linear actuators  220  carried by the I-beams  222  on opposite sides of door  10 , not shown, can be actuated to cause the linear actuators  220  to lift pulley blocks  242  in slots  224  in I-beams  222 . As pulley blocks  242  are lifted in slots  224 , carriages  160  are lifted twice as far in channels  232  as the movement of linear actuator  220  by flexible links  240 . Linear actuators  220  can be hydraulic cylinders as illustrated in  FIGS. 19A-19C  connected to a hydraulic circuit similar to the hydraulic circuit illustrated in  FIG. 14 , or can be other linear actuators as described above in connection with  FIG. 16 . Thus, in the embodiment of  FIGS. 19A-19D  the linear actuators  220  can be connected to carriages  160  by a flexible link  240  arranged to provide a one to two mechanical advantage that provides a carriage travel that is two times the linear actuator travel. 
         [0085]    The tilt-up door  10  should not be understood to be limited to the use of hydraulic cylinders as illustrated in the embodiments of  FIGS. 3 ,  4 ,  5 - 7 ,  8 ,  8 A and  19 A- 19 D the linear actuators of the embodiments of  FIG. 16 ,  17 A and  18  or the winch embodiment of  FIG. 16A , but can be used in connection with any desired actuator  39  to move carriage or push blocks  60  and  160  vertically in channels  32 ,  232  to move a tilt-up door  10  from the closed position of  FIG. 1  to the open position of  FIG. 3 . Further, a linear actuator can be positioned at other locations adjacent door opening including, but not limited to, a wall of building  20  if desired. 
         [0086]    While the tilt-up door has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation.