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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/067,785, filed Oct. 23, 2014, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to prefabricated modules for assembly into partially or fully enclosed hollow structures such as passageways, culverts or other roadway components as well as other uses such as parking garages and water holding tanks. More particularly, the invention relates to prefabricated modules which are assembled from separate segments. 
       BACKGROUND 
       [0003]    Prefabricated structural modules, which may be fabricated from concrete or other moldable material, can be configured to provide a wide variety of assembled structures. For example, prefabricated modules can be assembled into culverts, pipes or passageways for diverting water or other applications, as well as water retention systems for homes, businesses communities and other applications. As well, prefabricated modules can be used to assemble structures that serve other functions, such as storage or other utility structures, parking facilities, bridges or over/underpasses and a wide variety of other uses. Structural modules or components thereof may be prefabricated from concrete and transported to a remote location for assembly. Modules or their components should be of a size and weight that permits them to be transported and assembled using generally conventional equipment and facilities. Modules should be capable of being assembled into a wide variety of modules and structures that preferably have a high degree of durability and strength, ease of installation and if required, water tightness. 
         [0004]    Conventional modules and modular systems typically are designed for specific end uses, such as storm water retention, subsurface culverts and the like. However, it can be desirable to provide structural modules that may be assembled into a relatively wide variety of structures with little or no modification to the basic module design. Furthermore, it is desirable to provide modules that are relatively compact and lightweight that can be easily transported and assembled using conventional equipment, while still being capable of assembly into relatively large structures that have a relatively high weight-bearing capacity. Furthermore, it is desirable to provide modules that when assembled can be sealed against water leakage, in particular at the joints between modules. This is particularly desirable for modules used for water retention or derivation, such as water retention tanks, culverts and the like. 
         [0005]    Modular assemblies must often be capable of a high degree of load bearing, for example when used as underpasses, bridges or culverts for roadways or other applications in which significant weight-bearing is required. 
         [0006]    A modular assembly is disclosed, for example, in U.S. Pat. No. 8,770,890 to May et al. 
       SUMMARY 
       [0007]    The present invention relates to improved segments, modules and modular assemblies that may be fabricated from precast concrete, which have at least the potential to address the requirements and needs discussed herein. 
         [0008]    According to one broad aspect, the invention relates to a modular system for assembling a hollow structure. Modules are assembled from first and second segments each being defined by opposing ends with an elongate axis between said ends. The assembled module has opposing upper and lower decks, each of which has opposing sides and opposing ends. The respective surfaces of deck consist of opposing upper and lower surfaces, opposing side edges and opposing end edges. The first and second segments are configured for assembly in inverted, vertically aligned relation to each other to form a hollow module comprising the opposed upper and lower decks. The first and second segments are configured to engage each other when assembled in vertically and/or axially aligned relationship with mutually engaging three-dimensional structures that restrict lateral and/or vertical slippage between the segments. 
         [0009]    According to a further general aspect, the system comprises multiple segments that may be assembled into vertical aligned modules, which in turn can be axially aligned with similar modules to form elongate structures such as culverts and water-retention systems. 
         [0010]    The segments may, in one aspect, each comprise opposing sidewalls at their sides with the deck spanning the sidewalls. The first and second segments are configured for assembly in axially and vertically aligned relation to each other to form a hollow module wherein the respective sidewalls when assembled form essentially continuous outer walls of said structure and the respective decks oppose each other. The first and second segments are configured to engage each other when assembled in vertically aligned and/or end to end relationship with mutually engaging structures. The mutual engagement is provided by interlocking or mutually engaging three dimensional structural elements that restrict lateral slippage between segments and/or lateral/vertical slippage between adjacent modules. The vertical alignment between the segments comprises vertical alignment of the sidewalls. The ends of the respective segments may also be vertically aligned or may be out of alignment to form a staggered vertical joint structure. 
         [0011]    In one aspect, the deck may have a cantilever member protruding from a lateral edge of a deck for interlocking with a corresponding cantilever member in an abutting, axially aligned deck of a second segment. The cantilever joint member comprises a shelf protruding from an edge surface of the deck which is configured to bear upon or be borne upon a similar shelf protruding from a corresponding edge of the deck of a corresponding one of the segments when assembled in axial alignment. The deck may comprise opposing end edge surfaces and respective ones of the shelves of said deck are configured to engage and bear upon or be borne upon shelves of corresponding ones of said segments when assembled in axial alignment. A deck may have two exposed end edge surfaces, one exposed end edge surface or no exposed end edge surface depending on whether the segment includes no end walls, one end wall or two opposing end walls; it will be seen that the number of walls in the module relates to the number of exposed edge surfaces that are present at the wall-free edges of the decks. 
         [0012]    In one aspect, the cantilever joint members consist of four different cross sectional profiles that may be repeated in a multi-module structure. The four profiles consist of a first configuration for a first end surface of an upper deck, a second configuration for an opposed second surface of a second upper deck, a third configuration for a third end surface of a lower deck and a fourth configuration of an opposed lower deck. The opposing decks interlock in a load-bearing cantilever joint configuration when brought into end to and abutting relationship. 
         [0013]    In another aspect, vertical edge surfaces of the respective sidewalls may comprise vertically oriented protrusions which are continuous with the shelf structures of the decks. The protrusion interlocks with a similar protrusion in an adjacent segment when the respective modules are assembled in end-to-end axially aligned relationship. 
         [0014]    The segments and modules may be open at both ends for assembly into an open-ended four-sided hollow structure. Others of the segments may have a single end wall for assembly into a five-sided hollow structure having one closed end or two end walls at opposing ends for assembly into a fully enclosed, six-sided structure. 
         [0015]    According to another aspect, the segments may, (depending on span and loading) further comprise at least one half-column protruding from a surface of said deck towards an opposing one of said segments whereby when said first and second segments are assembled in vertically aligned relationship, the half-columns abut each other to form load-bearing continuous columns extending between opposing ones of said decks. A “half-column” is a vertically-oriented member having a length which is half the length of a full-height column, and which is configured to be vertically aligned with and abut a similar half column to form a full-height column that for structural purposes is equivalent to a monolithic weight-bearing column. The exposed ends of the half-columns may comprise interlocking projections and recesses, such as a mortice and tenon configuration. The columns may be configured such that a pair of the half columns is aligned along an axis transverse to the elongate axis of each module. 
         [0016]    According to another aspect, the sidewalls of the first segment may have axially-aligned lower edges comprising a tongue and groove structure configured to interlock with similar structures in the upper edges of sidewalls of the second segment when assembled in vertical alignment. 
       Definitions 
       [0017]    In this patent specification, the terms defined below shall have the meanings set forth herein, unless otherwise stated or the context clearly requires otherwise. 
         [0018]    “Module” refers to a structural member that can be assembled with other like modules in an interchangeable fashion into a structure. A given assembled structure may be composed of multiple identical modules or a plurality of module types. A module may be composed of multiple segments, or it may be a monolithic member. 
         [0019]    “Segment” refers to a structural member that forms part of a module. Multiple segments having the same or different configurations may be assembled into a module. 
         [0020]    The terms “slab” and “deck” are generally used interchangeably and refer to an essentially continuous plate-like member. 
         [0021]    “Cantilever” refers to a structure having a member projecting horizontally outwardly from a surface, supported only at one end of the member other than when bearing on another member. A cantilever member is normally capable of load bearing in either of a downwards or upwards direction when opposing ones of the cantilever members engage each other. 
         [0022]    “Column” is a vertically-oriented structure that is normally load-bearing when located in an assembled structure. A column may have any suitable cross-sectional configuration. A “half column” is an upper or lower half of a column that may be mated with a similar opposing half column to form a column. 
         [0023]    Directional references herein are used purely for convenience and are not intended to limit the scope of the invention in any respect. For example, directional references such as vertical, upwardly, horizontal and like, are intended purely for ease of description. Furthermore, it will be understood that embodiments of the invention may be produced on essentially any scale. Accordingly, references to specific dimensions are, unless otherwise expressly stated, not intended to limit the scope of the invention in any respect. The embodiments described herein are intended purely for illustration purposes, to provide teachings that describe certain aspects of the invention. The specific embodiments described herein are purely by way of example and illustration and are not intended to limit the scope of the invention in any respect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is an isometric view of an assembly according to an embodiment of the invention, shown with the segments and modules separated from each other for illustration. 
           [0025]      FIG. 2  is an isometric view of the encircled portion of  FIG. 1 . 
           [0026]      FIGS. 3A and 3B  are sectional views of portions of the assembly, showing the overlapping portions of the respective horizontal slabs thereof. 
           [0027]      FIG. 4  is a side view of an embodiment of an assembled structure wherein the segments are assembled in an overlapping, staged configuration. 
           [0028]      FIG. 5  is a side view of the encircled portion of  FIG. 4 . 
           [0029]      FIG. 6  is a further side view of the embodiment of  FIGS. 4 and 5 . 
           [0030]      FIG. 7  is a front elevational view of a module having an end wall which may form a closed end of an assembled structure. 
           [0031]      FIG. 8  is a cross-sectional view along line  8 - 8  of  FIG. 7 . 
           [0032]      FIG. 9  is a cross-sectional view of a module having a configuration which is a mirror image of the module shown in  FIGS. 7 and 8 , which may form a closed end of an assembled structure, opposed to the closed end of  FIGS. 7 and 8 . 
           [0033]      FIG. 10  is a cross-sectional view of a module having open opposing ends. 
           [0034]      FIG. 11  is an isometric view of an assembly showing opposing end segments having closed ends and an open-ended segment sandwiched between the end segments to form an enclosed six-sided structure. 
           [0035]      FIG. 12  is an isometric view showing of a four-sided structure composed of multiple open-ended segments positioned in end-to-end abutting relationship, in exploded view. 
           [0036]      FIG. 13  is a further isometric view of the structure of  FIG. 12 , assembled together. 
           [0037]      FIG. 14  is an isometric view of a further embodiment of the invention, partially exploded. 
           [0038]      FIG. 15  is an isometric view of an alternative structure according to the invention. 
           [0039]      FIG. 16  is a further isometric view of the structure of  FIG. 15 . 
           [0040]      FIG. 17  is an isometric view of an alternative structure according to the invention. 
           [0041]      FIG. 18  is a further isometric view of the structure of  FIG. 17 . 
           [0042]      FIG. 19  is an isometric view of a further embodiment of the invention, showing a structure free of end and side walls. 
           [0043]      FIG. 20  is a further isometric view of the embodiment of  FIG. 19 . 
           [0044]      FIG. 21  is an isometric view of a module similar to the embodiment of  FIG. 19 , wherein overlapping cantilever members project from side edge surfaces of upper and lower decks of the module. 
           [0045]      FIG. 22  is a further isometric view of a partially assembled structure according to the embodiment of  FIG. 21 . 
           [0046]      FIG. 23  is an isometric view of a module wherein cantilever members project from each of the side and end edge surfaces of the upper and lower decks. 
           [0047]      FIG. 24  is a further isometric view of a partially assembled structure according to the embodiment of  FIG. 23 . 
           [0048]      FIG. 25  is an isometric view of an assembled structure according to a further embodiment of the invention. 
           [0049]      FIG. 26  is an isometric view of an assembled structure according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
     Segments and Modules 
       [0050]      FIGS. 1-8  depict upper and lower segments  10  and  12  respectively, which are configured for assembly into a partially enclosed, hollow module  1  having an open first end and an opposed second end which is closed. Module  1  may comprise a modular component of a larger structure or it may instead form the entire finished structure. Segments  10  and  12  have opposed ends with an elongate axis “A” between the respective ends. A first end  28  (see  FIG. 8 ) is open and the opposed second end is closed with end wall  30 . 
         [0051]    Upper and lower segments  10  and  12  are similar (but not identical nor mirror image) in configuration to each other and are configured to be assembled in vertical alignment with each other to form module  1 . 
         [0052]    Segments  10  and  12  (and the similar segments described herein) are fabricated from a moldable material such as concrete and are typically pre-cast at a concrete plant and transported to a remote assembly. Preferably, the concrete is reinforced and may be pre-stressed. The materials used for reinforcing and pre-stressing comprise any suitable reinforcing materials known to art and may be ferrous and/or non ferrous. 
         [0053]    As seen in more detail in  FIGS. 7 and 8 , upper segment  10  comprises opposing side walls  20  and  22  and an upper slab  24  which spans side walls  20  and  22  and is supported thereon. Slab  24  has opposing ends which correspond with the ends of segment  10  and opposing lateral sides, with a longitudinal axis extending between the ends, which is parallel or coaxial with axis A. Slab  24  forms a load-bearing upper deck which comprises an uppermost surface of upper segment  10 . A similar slab  64  forms a lowermost surface of lower segment  12  and forms a lower deck of the assembled module  1 . Upper and lower decks  24  and  64  oppose each other and are normally vertically aligned in the assembled module  1 . Decks  24  and  64  comprise continuous upper and lower surfaces of module  1 . Each of side walls  20  and  22  meet slab  24  at a corner gusset  26  extending parallel to the longitudinal axis of the entire assembly between ends  28  and  30 . Gusset  26  has a triangular cross section, which provides additional structural support for slab  24  to transmit the weight of slab  24  to side walls  20  and  22 . Walls  20  and  22  and slab  24  form an inverted U-shaped structure or segment, which defines an interior space. 
         [0054]    Upper segment  10  further comprises half-columns  32   a  and  32   b  which extend downwardly from the underside of slab  24  towards the interior space of segment  10 . Lower segment  12  has similar half-columns  66   a  and  b,  described below, that extend upwardly to join with half-columns  32  to form structurally continuous weight-bearing columns extending between slabs  24  and  64 . The number and dimensions of half columns  32  may vary depending on the structural requirements of the assembled structure. Furthermore, in some cases interior columns  32  and  66  may not be required in the structure, for example if the structure is expected to experience reduced load-bearing requirements and/or reduced unsupported span distances relative to structures that normally require interior columns. Half-columns  32  may have a square or rectangular cross-sectional configuration, as illustrated, or any other suitable cross-sectional configuration. In the present example, two half-columns  32  are provided in side by side relation along an axis which is transverse to the longitudinal axis A. Half-columns  32  may taper inwardly from slab  24  to their exposed end surfaces  34  (see  FIG. 7 ). In other embodiments, half-columns  32  may be non-tapering (not shown). A tenon  36  projects downwardly from each end of surface  34  of half columns  32   a  and  b.  Half-column  32  joins slab  24  at a neck  38 , which flares outwardly from half-column  32  to slab  24  to effectively transmit load to the shaft of half-column  32 . Optionally, the columns described herein may intersect with the slab without the neck, for example to conserve floor or ceiling space. 
         [0055]    Sidewalls and end walls  20 ,  22  and  30 , as well as half columns  32 , all extend downwardly to the same extent wherein the lower surfaces thereof are co-planar and comprise a plane of engagement with the corresponding upper surfaces of lower segment  12 . 
         [0056]    In one embodiment, half-columns  32  may range from 0.5 m to 2.0 m in height. Their width can range from 0.15 m to 0.5 m at the lower surface at the plane of engagement and from 0.15 to 0.6 m where column  32  meets neck  38 . Tenon  36  has an overall height of between 25 mm to 75 mm. 
         [0057]    Slab  24  comprises opposing end surfaces  40  and  41  at the respective ends thereof. A first end surface  40  is adjacent to open end  28  of segment  10  and normally faces an adjacent modular segment when module  1  is assembled end to end with similar modules to form an elongate segmented structure with a hollow interior. An opposing end  41  of slab  24  meets end wall  30 . End surface  40  has a stepped configuration which will be described in more detail below, which cooperates with a similar structure an adjoining segment to interlock in a cantilever-type joint. 
         [0058]    Side walls  20  and  22  have horizontally-disposed lower edges  48  that are aligned with axis A and vertically disposed end edges  50 . End edges  50  are exposed at the open end  28  of segment  10  (see  FIG. 1 ) and define the open end of segment  10 . The stepped configuration of end  40  of slab  24  is continuous with the end edges  50  of side walls  20  and  22 , which likewise comprise outwardly projecting projections  42 , inwardly stepped recesses  44  and intermediate slopping shoulders  46 . 
         [0059]    The lower edges  48  of sidewalls  20  and  22  are configured to rest upon and engage corresponding upper edges of lower segment  12  with an interlocking engagement, such that the respective sidewalls are vertically aligned to form an essentially continuous wall of the assembled structure. The exposed lower edges of walls  20  and  22  each comprise a central downwardly projecting tongue  51  flanked by recessed portions  52   a  and  52   b  (see  FIG. 2 ), which fits in a corresponding groove  54  recessed into the upper surface of the side walls of the lower segment  12 , as described below. Grout or other adhesive/filler  55  may be applied between the respective contacting surfaces of the segments to seal the joints between segments and improve structural rigidity. 
         [0060]    Turning now to the opposed lower segment  12 , as seen in  FIGS. 7 and 8 , this has a similar configuration to upper segment  10 . Segment  12  comprises side walls  60  and  62 , a floor slab  64  that spans side walls  60  and  62  and upwardly-projecting half columns  66   a  and  66   b . Lower gussets  61  buttress walls  60  and  62  to slab  64 . The vertical end surfaces of walls  60  and  62  and slab  64  have a stepped configuration matching that of upper segment  10 . Slab  64  has an end surface  65  which will be described below for interlocking with end surface  109  of segment  84  or end surface  86  of segment  156 . 
         [0061]    Half-columns  66   a  and b each have a flat upper surface  70 , having a mortice  72  recessed therein. Mortice  72  is configured to snuggly receive tenon  36  therein to interlock the respective exposed end surfaces of half-columns  32  and  66  when assembled. An adhesive such as grout may be applied between the contacting mortice and tenon members. After the grout or other adhesive hardens, the respective half-columns effectively form a continuous, monolithic structural member. Half-columns  32  and  66  are configured and located within segments  10  and  12  such that when assembled in vertical alignment, the respective half-columns are vertically aligned and their exposed surfaces meet whereby tenon  36  fits within mortice  72  and columns  32  and  66  form an essentially continuous load-bearing column spanning the full height of the assembled module. The dimensions of half-columns  66  match those of half-columns  32  whereby when module  1  is assembled and columns  32  and  66  meet at their plane of engagement, the respective half-columns define mirror images with the respective mortice and tenons thereof interlocking. 
         [0062]    The respective half-columns  32  and  66  thus transfer load from upper slab  24  to lower slab  64  when the respective segments  10  and  12  are assembled. In a similar fashion, side walls  20  and  22  of upper segment  10  bear upon the sidewalls  60  and  62  of lower segment  12  using grout if necessary to form essentially continuous, load-bearing sidewalls of the assembled module  1 . Side walls  60  and  62  have recessed grooves  54  within their upper surfaces extending lengthwise the full length of the respective walls, configured to snuggly receive projecting tongues  51  from the sidewalls  20  and  22  of corresponding upper segment  10 . In this fashion, a tongue and groove (or other suitable structural connection) interlocking structure is provided between respective side walls and a mortice and tenon (or other suitable structural connection) interlocking structure is provided between upper and lower columns so as to rigidly interlock upper and lower segments  10  and  12 . 
         [0063]    The vertical walls of the modules (e.g. sidewalls  20 ,  22 ,  60  and  62 ; end walls  30 , and similar walls described herein) may be in the range of 100 mm to 800 mm thick, but commonly between 200 mm to 300 mm in thickness. These walls range in both width and height from 500 mm to 4 m. Slabs  24  and  64  may range in thickness between 150 mm and 600 mm thick, but commonly 200 mm to 400 mm in thickness. Slabs  24  and  64  may range in length along axis A from 500 mm to 4 m, and in width between the sidewalls from 4 m to 15 m or more. 
         [0064]      FIG. 9  depicts an opposing end module  80 , comprising upper and lower second end segments  82  and  84  having upper and lower slabs  77  and  79  respectively. Upper slab  77  has an exposed end surface  107  and lower slab  79  has an exposed end surface  109 . Segments  82  and  84  have configurations substantially identical to first end segments  10  and  12 , being substantially mirror images thereof. However, module  80  differs from being a precise mirror image of module  1  in that it is configured to interlock therewith if brought into end to end abutting relation. As a result, if first and second opposing modules  1  and  80  are brought into end-to-end contact with each other, the respective exposed end surfaces  40  and  107  on the one hand and  71  and  109  on the other hand interlock, as described below. 
         [0065]      FIGS. 1 and 10  depict open-ended (middle) modules  120 , having both opposing ends open. Module  120  thus comprises in essentially tubular structure having opposed open ends to form a four-sided structure comprised of upper and lower segments  122  and  124 . Upper segment  122  comprises opposing side walls  126  and  128 , spanned by an upper slab  130 . Half columns  140  decend downwardly from the lower (interior) surface of slab  130 . As seen in  FIG. 10 , slab  130  comprises exposed opposed end surfaces  132  and  133 , which partially define the open ends of segment  120 . Surfaces  132  and  133  are configured to provide a cantilevered joint similar in configuration to edge surfaces  40  and  86  of the respective end segments. 
         [0066]    Turning to the opposing lower segment  124 , this has a complimentary structure to upper segment  122 , including upwardly-projecting columns  150  and opposing side walls  152  and  154  (seen in  FIG. 1 ), and a lower slab  156 . The exposed opposing end surfaces  86  and  87  of lower segment  124  have a configuration continuous with and identical to the end edge surfaces of upper segment  122 . Furthermore, as with end segments  10  and  12 , horizontal surfaces of the end walls and columns have an interlocking configuration. 
         [0067]    The upper and lower segments described herein may have equal top to bottom heights, or unequal heights. 
       Cantilever Joint Configuration 
       [0068]    The segments described herein have four different configurations or profiles, identified as A-D, of their respective end surfaces of the horizontal slabs which interlock to form cantilever joints when assembled in end to end axially aligned relationships. Repeating patterns of configures A-D may be provided. The term “cantilever joint” as used herein refers to an overlapping configuration wherein a cantilever member projecting from a first module rests upon and transfers load to a similar cantilever member projecting from an abutting second module. The respective cantilever members are thus configured to rest one upon the other when the respective modules are horizontally aligned.  FIGS. 3A and 3B  show the interlocking function between the four slab end surface configurations, identified as configurations A through D. The four different configurations are as follows: 
         [0069]    A) First end surface: end surface  40  of slab  24  (segment  10 ) defines a first end surface configuration A. Surface  40  comprises an outwardly protruding shelf  42  adjacent the lower surface  43  of slab  24  and an inwardly stepped recess  44  adjacent to the upper surface of slab  24 . A sloping shoulder  46  forms the transition between portions  42  and  44 . As will be described below, the configuration of end  40  provides a cantilever joint between adjacent segments of the adjacent modular structure wherein shelf  42  and shoulder  46  support a corresponding shelf and shoulder of an adjacent segment. 
         [0070]    B: Second end surface: end surface  132  of slab  130  of segment  122  defines a second end surface configuration B, which mates with first end surface  40 . Surface  132  comprises an outwardly projecting cantilever (shelf) region  136 , an inwardly stepped region  138  and a sloping transition zone  141 . Shelf  136  is adjacent the upper surface  137  of slab  130 , while recessed portion  138  is adjacent the lower surface  139  thereof. 
         [0071]    C: Third end surface: end surface  65  of lower slab  64  (segment  12 ) defines a third end surface C. Surface  65  comprises a protruding shelf  67  continuous with the bottom surface of slab  64 , a recess  69  adjacent to the upper surface  73  of slab  64  and a sloping shoulder  71  which forms a transition zone between shelf  67  and recess  69 . 
         [0072]    D: Fourth end surface: end surface  86  of lower slab  156  of segment  124  defines a fourth end surface D, which mates with third end surface  65 . Surface  86  comprises an outwardly projecting shelf  100  which is continuous with upper surface  105  and above inwardly stepped region  102 . A sloping shoulder  104  forms the transition zone between the respective regions  100  and  102 . 
         [0073]    The four configurations described above are repeated within the various segments described herein to form an interlocking structure when the segments are assembled in various configurations. Accordingly, module  120  comprises upper and lower end surfaces  133  and  87  which are opposed to end surfaces  132  and  86 . These in turn are identical in configuration to the first and third end surfaces (A and C). Similarly, end module  80  comprises upper and lower end surfaces  107  and  109  which are identical in configuration to the second and fourth end surfaces (B and D). In this fashion, when assembled together, the shelves of the four end surface configurations all fit within corresponding inwardly stepped regions of abutting segments whereby the respective shelves and shoulders rest one upon other. Any number of segments and modules may be combined with these four combinations of deck end surface profiles. This interlocking structure provides a cantilever joint configuration which restricts vertical slippage between the respective segments and allows vertical forces to be transmitted from one module to another via the cantilever joint configuration. It will be seen that an end module  1  or  80  that includes an end wall, wherein the upper and lower decks comprise only a single exposed end surface, comprise two distinct end surface profiles. A middle module  120  wherein the decks have both end surfaces exposed comprises all four profiles on the respective end surfaces of the upper and lower decks. The middle modules can thus join with either one of the end modules or another middle module  120 . 
         [0074]    In one aspect, the respective shelves of upper and lower decks may differ in top to bottom depth. 
       Structures 
       [0075]    Turning to  FIG. 11 , a fully enclosed six-sided structure  157  may be formed by sandwiching an open-ended module  120  between opposing end modules  1  and  80 . The abutting vertical surfaces of the respective segments interlock to form a unitary rigid structure having a hollow interior spanned by supporting columns. Such a structure may be used, for example, for water retention. For this purpose, it can be desirable to provide inlet and outlet openings, not shown. Furthermore, to improve the water tight seals between the respective segments, the joints may be grouted or otherwise sealed to minimize water leakage and provide full bearing transfer from upper to lower segments. Furthermore, it will be seen that multiple four-sided modules  120  may be provided to vary the overall length of the resulting enclosed structure. As well, one of end modules  1  or  80  may be dispensed with, to provide a five-sided structure which combines modules  1  and  120  having a closed first end and an open second end (see  FIG. 1 ). Such a structure may be used, for example, as a storage structure, a vehicle parking structure, or any other use that benefits from an open end. 
         [0076]      FIGS. 12-15  illustrate a structure  160 , comprised of multiple open-ended modules  120 , positioned in end-to-end (axially aligned) abutting relationship to form an elongated 4-sided structure  160 . The opposing ends of the resulting structure are both open. As a result, the structure may be used, for example, as a culvert or as an over or underpass for a roadway, rail bed or the like. 
         [0077]      FIG. 14  shows a structure  162  having two opposed closed ends, both closed by end walls  30 . Any one or more of the walls and slabs (e.g. end walls  30 , side walls and/or slabs) may be provided with cutouts, which may comprise circular or oval cutouts  164  or rectangular cutouts  166 , or any other suitable configuration. The cutouts can provide passageways for water, or serve other functions. 
         [0078]      FIGS. 15 and 16  illustrate an embodiment of a structure  200  having a single, central column  220  therein. This structure may comprise one or more of a first or second end wall segment or open ended segment. 
         [0079]      FIGS. 17 and 18  show a further embodiment wherein structure  240  is free of internal columns. Such a structure may be used for applications that require reduced load-bearing capacity and/or a smaller cross-sectional configuration. 
         [0080]    In one embodiment, shown in  FIGS. 4-6 and 14-18 , segments  122  and  124  may be assembled to be staggered in an axial direction wherein an upper segment overlaps bears on two lower segments. The vertical alignment of the respective sidewalls is maintained. According to this embodiment, an overlapping region  290  is generated. In order to generate the staggered effect, one of the segments has a reduced depth (e.g. axial length) and a second segment has an increased depth, by the same extent. The first and second segments are installed at respective ends of the assembled structured. When thus assembled, this permits the interior modules to have staggered walls, while the respective ends of the structure are fully aligned vertically. 
         [0081]      FIGS. 19 through 24  show further embodiments wherein structure  260  is free of both end and side walls. The embodiment shown in  FIGS. 19 and 20  show a structure  260  is formed from upper and lower segments as described herein, which of which comprise paired two-part columns  270  as described herein. Columns  270  are located immediately adjacent to the side edges of upper and lower slabs  280  and  282 , thereby providing similar structural support as continuous sidewalls. In other embodiments, columns  270  may be inboard of the sides of slabs  280  and  282 , depending on structural requirements. The total number and configuration of columns will depend on structural requirements; by way of a non-limiting example, structure  260  (and the similar structures described herein) may comprise up to 5 pairs of columns for each module. The end surfaces of slabs  280  and  282  comprise the stepped, cantilever joint profiles described above. In this fashion, structure  260  may comprise a tiled arrangement of modules which are interlocked with cantilever joints in the axial dimensions. 
         [0082]      FIGS. 21 and 22  show a structure similar to  FIGS. 19 and 20  but wherein cantilever joint profiles are provided on side surfaces of the upper and lower decks, rather than the end surfaces as shown in  FIGS. 19 and 20 .  FIG. 21  shows a module  300  wherein the upper deck  302  comprises first and second opposing side (lateral) surfaces  304  and  306 . Lower deck  308  likewise comprises first and second opposing side surfaces  310  and  312 . Side surfaces  304  and  306  comprise cantilever joint profiles A and C. Side surfaces  310  and  312  comprise joint profiles B and D. The respective end surfaces  314  of the upper and lower decks are planar. In this fashion, a structure  320  may be assembled from these modules as shown in  FIG. 22  wherein the cantilever joints interlock between adjacent modules  300  that are side by side laterally. 
         [0083]      FIGS. 22  shows a structure  320  with two upper segments removed to show internal structure of the modules. It will be seen that modules  300  may be either aligned in both of these dimensions to form a checkerboard pattern as shown or staggered in one of these dimensions to form a tiled array (not shown). 
         [0084]      FIGS. 23 and 24  show a further structure similar to  FIGS. 19 and 20  but wherein cantilever joint profiles are provided on both of the end and side surfaces of the upper and lower decks.  FIG. 23  shows a module  400  wherein the upper deck  402  comprises first and second opposing side (lateral) surfaces  404  and  406  and opposing end surfaces  405  and  407 . Lower deck  408  likewise comprises first and second opposing side surfaces  410  and  412  and end surfaces  411  and  413 . Side surfaces  404  and  406  comprise cantilever joint profiles A and C. Side surfaces  410  and  412  comprise joint profiles B and D. End surfaces  405 ,  407 ,  411  and  413  may likewise comprise joint profiles A through D. In this fashion, a structure  420  may be assembled from these modules as shown in  FIG. 24  wherein the cantilever joints interlock between adjacent modules  300  in both of the axial and lateral (transverse) dimensions. 
         [0085]      FIG. 24  shows an assembled structure  430  wherein the modules  432  comprise upper and lower decks  434  and  436  having cantilever joint profiles on the respective end and side surfaces thereof. In this fashion, interlocking cantilever joints are formed between axially and transversly aligned modules within structure  330 .  FIG. 24  shows structure  330  with two upper segments removed to show internal structure of the modules. It will be seen that modules  430  may be either aligned in both of these dimensions to form a checkerboard pattern as shown, or staggered in one of these dimensions to form a tiled array (not shown). 
         [0086]      FIG. 25  provides a further embodiment, showing an assembled structure  400  formed from modules  402 . Modules  402  are provided with upper and lower decks  404  and  406  respectively and sidewalls  408 . Modules  400  are comprised of upper and lower segments  410  and  412  respectively are in inverted relationship to each other as described above. Segments  401  and  412  are free of internal columns whereby the assembled structure  400  has a fully open interior space. Segments  410  and  412  are fabricated from prestressed concrete to improve structural strength, which can be beneficial in certain applications such as relatively large unsupported spans. The pre-stressing may comprise either pre-tension and pos-tension. As is known in the art, pre-tension is applied before pouring of the concrete in the forming process and post-tension is applied after the pouring of the concrete. Tension is applied to reinforcing steel bars (not shown) that extend through openings  414  extending horizontally within the upper and lower decks  404  and  406  between the lateral edges of the structure. The tensioned bars apply an internal force that opposes external loads that the structure will bear in its lifetime to increase its strength. The tensioned bars are stressed to induce internal actions of a magnitude and distribution that the actions resulting from given external loading are counteracted to a desired degree. 
         [0087]      FIG. 26  provides a further embodiment similar to  FIG. 25  but wherein the segments comprise upper and lower half-columns  420  and  422  respectively. This provides the assembled structure with columnar support between the upper and lower decks  404  and  406 , in place of one or both of sidewalls  408 . 
         [0088]    It will be seen that one may provide a structure wherein the above embodiments of modules and segments are combined, such that certain of the modules include multiple columns, while others include different numbers of columns or are free of columns. For example, the end segments may require a reduced number of columns, due to the additional structural support provided by the end walls. 
         [0089]    The segments according to the present invention may be fabricated by conventional concrete casting techniques, wherein concrete is poured into a mould and allowed to harden. As discussed above, the concrete may be reinforced and/or pre-stressed. The resulting segments may be transported to a remote location for assembly into finished structures. 
         [0090]    Assembly of the segments into a finished structure may be performed by routine construction techniques. For example, a suitable trench or other excavation may be provided, which optionally is provided with footings or the like for additional support. The lower segments are then placed into position in axial (horizontal) alignment abutting each other whereby adjacent segments interlock, using a crane or other heavy lifting equipment to place the bottom segments. Following this step, the upper segments are then positioned on top of the lower segments whereby respective pairs of upper and lower segments are vertically aligned, thereby forming modules which are incrementally installed to form the finished assembly. Alternatively, each module may be assembled and installed individually, whereby installation occurs incrementally with each module being fully assembled before installation of a subsequent module. When assembled, the segments are all interlocked vertically and horizontally (axially), by the interlocking structures described herein including the tongue and groove features of the sidewalls, mortice and tenon features of the columns and cantilever joints of the decks. Furthermore, the cantilever joints serve to transmit loads between axially aligned segments, thereby minimizing the risk of the segments being urged out of alignment by vertical forces acting unequally on the segments. 
         [0091]    The segments may be fabricated on the basis of a design that is based on specific requirements for a given installation. The design process may begins with identifying a set of potential constraints such as the size of the required structure, which may dictate the overall number of modules and segments. This can range from a small number of segments to the many hundreds. Soil bearing capacities of the sites in question are reviewed and segment sizes and weights may be adjusted accordingly. Trucking regulations govern the weight of each load, which in turn, may affect the configuration and size of the segments. Segment sizes and weights are designed to try and minimize trucking costs. Similarly, availability of heavy and expensive lifting equipment is taken into account in the design. 
         [0092]    The scope of the invention should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole. The claims are not to be limited to the preferred or exemplified embodiments of the invention.

Summary:
The invention relates to a modular system for assembling a hollow structure. The system comprises segments for assembly into modules to assemble hollow structures such as culverts and water-retention systems. The segments comprise opposing sidewalls and a deck spanning said sidewalls having opposing sides and opposing ends which are assembled in inverted, vertically aligned relation to each other to form a hollow module. The segments engage each other with mutually engaging three dimensional structures that prevent lateral and vertical slippage between the segments. The segments may include half-columns that meet along the plane of engagement to form full-height load bearing columns in the assembled structure.