Patent Publication Number: US-2023135211-A1

Title: Additively manufactured structure with reinforced access opening

Description:
FIELD 
     The present disclosure relates in general to additively manufactured structures, and more particularly to an additively-manufactured wind turbine tower structure having a reinforced access opening and method of making same. 
     BACKGROUND 
     Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known foil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid. 
     The wind turbine tower is generally constructed of steel tubes, pre-fabricated concrete sections, or combinations thereof. Further, the tubes and/or concrete sections are typically formed off-site, shipped on-site, and then arranged together to erect the tower. For example, one manufacturing method includes forming pre-cast concrete rings, shipping the rings to the site, arranging the rings atop one another, and then securing the rings together. As wind turbines continue to grow in size, however, conventional manufacturing methods are limited by transportation regulations that prohibit shipping of tower sections having a diameter greater than about four to five meters. Thus, certain tower manufacturing methods include forming a plurality of arc segments and securing the segments together on site to form the diameter of the tower, e.g., via bolting and/or welding. Such methods, however, require extensive labor and can be time-consuming. 
     In view of the foregoing, the art is continually seeking improved methods for manufacturing wind turbine towers. For example, more recently, progress has been made in the construction of wind turbine towers, at least in part, using additive printing techniques. Such methods allow for the tower structures to be erected on site and also allow the structures to be built to taller heights. 
     However, during construction of existing towers, it may be desirable to include a tower portion having an access opening, such as a pre-fabricated door or a section of a foundation, in the structure. However, additional reinforcement must also be included around such access opening as the structure is being built. In addition, reinforcement placement can be difficult to automate since the reinforcements (e.g., rebar, tension cables, etc.) must be placed in various orientations around the access opening to properly reinforce the access opening. 
     Accordingly, the present disclosure is directed to an additively-manufactured structure having a reinforced access opening that addresses the aforementioned issues. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present disclosure is directed to a method of additively-manufacturing a structure having a reinforced access opening. The method includes printing, via an additive printing device having at least one printer head, a portion of the structure adjacent to a support surface. The portion of the structure is printed of a cementitious material, and the printed portion of the structure defines an access opening. Moreover, the method includes providing a void of the cementitious material at a top boundary of the access opening, placing one or more reinforcement members in the void such that the one or more reinforcement members extend across the void, and continuing to print the printed portion of the structure around the void to build up the structure. Thus, the method also includes backfilling the void with a backfill material to incorporate the one or more reinforcement members within the void into the printed portion of the structure. 
     In another aspect, the present disclosure is directed to structure including a support surface and a printed portion formed from a cementitious material. The printed portion of the structure is adjacent to the support surface and comprises a reinforced access opening, which is achieved via a backfilled void. In particular, the printed portion comprises a pre-fabricated door assembly to define, at least in part, the access opening. The reinforced access opening is achieved via a backfilled void at a top boundary of the access opening. The backfilled void includes backfilled cementitious material and one or more reinforcement members embedded within the backfilled cementitious material and extending across the backfilled void such that the one or more reinforcement members are incorporated into the printed portion of the structure. As such, the structure includes a reinforced access opening and a backfilled void. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG.  1    illustrates a perspective view of one embodiment of an additively-manufactured structure according to the present disclosure; 
         FIG.  2    illustrates a partial, cross-sectional view of one embodiment of a tower structure of a wind turbine according to the present disclosure; 
         FIG.  3    illustrates a schematic view of an embodiment of an additive printing device being used to print the structures according to the present disclosure; 
         FIG.  4    illustrates a close-up view of certain components of the additive printing device of  FIG.  3    according to the present disclosure; 
         FIG.  5    illustrates another close-up view of an embodiment of certain components of an additive printing device according to the present disclosure; 
         FIG.  6    illustrates a block diagram of one embodiment of a controller of an additive printing device according to the present disclosure; 
         FIG.  7    illustrates a perspective view of an additively-manufactured structure having a pre-fabricated door assembly integrated therewith according to conventional construction; 
         FIG.  8    illustrates a perspective view of a pre-fabricated foundation assembly according to conventional construction; 
         FIG.  9    illustrates a perspective view of one embodiment of an additively-manufactured structure having a reinforced access opening with a backfilled void and a pre-fabricated door assembly integrated therewith and formed using methods according to the present disclosure; 
         FIG.  10    illustrates a front view of the reinforcement member grid extending across and through the backfilled void of the additively-manufactured structure of  FIG.  9   ; 
         FIG.  11    illustrates a perspective view of the reinforcement member grid extending across and through the backfilled void of the additively-manufactured structure of  FIG.  9   ; 
         FIG.  12    illustrates a flow diagram of one embodiment of a method for manufacturing an additively-manufactured structure having a reinforced access opening according to the present disclosure; 
         FIG.  13    illustrates a schematic diagram of one embodiment of a sequence by which the tower structure of  FIGS.  9 - 11    is manufactured; 
         FIG.  14    illustrates a schematic diagram of another embodiment of a sequence by which the tower structure of  FIGS.  9 - 11    is manufactured; 
         FIG.  15    illustrates a schematic diagram of yet another embodiment of a sequence by which the tower structure of  FIGS.  9 - 11    is manufactured; 
         FIG.  16    illustrates a schematic diagram of still another embodiment of a sequence by which the tower structure of  FIGS.  9 - 11    is manufactured; 
         FIG.  17    illustrates a simplified front view of an embodiment of an additive printing device having a variable width printer head that may be used to print the tower structures described herein according to the present disclosure; and 
         FIG.  18    illustrates a simplified front view of another embodiment of an additive printing device having a variable width printer head that may be used to print the tower structures described herein according to the present disclosure. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Generally, the present disclosure is directed to an additively-manufactured structure, such as a tower structure or a tower segment (with emphasis on the section of a tower segment adjacent to an interface between two or more tower segments, for example), having a reinforced access opening(s) and methods for manufacturing same using automated deposition of cementitious materials and/or other construction materials via technologies such as additive manufacturing, 3-D printing, spray deposition, extrusion additive manufacturing, concrete printing, automated fiber deposition, as well as other techniques that utilize computer numerical control and multiple degrees of freedom to deposit material. More specifically, methods of the present disclosure include using an automated additive printing device to print a tower structure, while also incorporating a pre-fabricated component (such as a door frame), or while using formwork or a cast component, to yield the reinforced access opening for the printed tower structure. 
     For example, in an embodiment, the tower structures of the present disclosure may include a pre-fabricated door assembly or a pre-fabricated foundation assembly and a backfilled void. The pre-fabricated component is constructed of a composite material reinforced with a plurality of reinforcement members, with portions of the reinforcement members protruding from the composite material. In particular, the reinforcement members around the pre-fabricated component are purposely left extending beyond the component and into the surrounding printed or print-poured section of the broader tower structure being built. Similarly, the backfilled void is situated adjacent to the pre-fabricated component and includes backfill material reinforced with one or more reinforcement members embedded within the backfill material and extending across the backfilled void and protruding therefrom. The backfill material may include any suitable workable paste that is configured to bind together after curing to form a structure. Suitable cementitious materials include, for example, concrete, pitch resin, asphalt, geopolymers, polymers, cement, mortar, cementitious compositions, or similar materials or compositions. 
     Accordingly, in an embodiment, the additive printing device is configured to: (1) print cementitious material to build up the tower structure layer by layer around the pre-fabricated component or the formwork; (2) in doing so, leaving a void to be backfilled; and (3) then subsequently backfilling the void after the reinforcement member(s) are placed into/through the void. As such, the portions of the reinforcement members protruding from the composite material, and the portions of the reinforcement members extending across the backfilled void reinforce the cementitious material around the access opening. Alternatively, the pre-fabricated component, for example, a pre-fabricated door assembly, or formwork may be positioned and installed about the access opening after at least a portion of the void is backfilled. 
     In another embodiment, manufacturing the tower structure may include positioning formwork to define the access opening and/or the backfilled void before, during, or after printing the portion of the tower structure around the access opening and/or the void is constructed, built up, or printed. As described herein, the formwork may include temporary or permanent molds into which the cementitious material and/or the backfill material is deposited. Further, the formwork may be supported by falsework. The falsework may include temporary structures commonly used in construction to support permanent structure(s) until construction has sufficiently progressed for the permanent structure(s) to be supported/self-supporting. In particular, in certain embodiments, pillars act as falsework to support stackable formwork to facilitate near continuous production of the backfilled void. In other embodiments, the formwork may be printed and take the form of a cast or shell for receiving cementitious material and/or backfill material. 
     For example, in an embodiment, manufacturing the tower structure may include positioning a cast-like printed formwork (herein referred to as a “cast component”) to define the access opening and/or the backfilled void before, during, or after printing the portion of the tower structure around the access opening and/or the void. The cast component may be left permanently embedded in the printed portion of the tower structure as the tower structure is built up, or the cast component may be printed in place, used, and removed from the printed portion of the tower structure as the tower structure is built up. In particular, in certain embodiments, the cast component includes a different cementitious material composition than the composition of the cementitious material to be introduced into the cast component or to be used for printing the remainder of the tower structure. 
     As used herein, the term “cast component” generally refers to a type of pre-fabricated component, and the term “pre-fabricated component” generally refers, but is not limited to: (1) cast components that are printed in situ during printing of the tower structure; (2) cast components that are pre-printed separately from the tower structure; (3) pre-fabricated door assemblies and pre-fabricated foundation assemblies; and (4) equivalent structures described in further detail herein. 
     Thus, the methods described herein provide many advantages not present in the prior art. For example, the additively-manufactured structures described herein may include the necessary reinforcement to strengthen the overall structure in the region of the access opening, thereby simplifying the process of reinforcement placement (which is relatively complex around the access opening). Thus, the overall load bearing capabilities of the additively-manufactured structure at and about the access opening can be improved. Moreover, the present disclosure may permit on-site printing of structures having any desirable size, thereby enabling the construction of large tower structures and wind turbines. Accordingly, the structures manufactured using methods of the present disclosure may be formed without requiring a tall crane. The methods of the present disclosure may also increase design flexibility, eliminate overall size restrictions, and permit the formation of structures having any desirable profile and cross-sectional shape. The additive printing device may also utilize any suitable number of variable width printer heads to decrease manufacturing time and/or to create gaps or voids during continuous printing, for example. Moreover, the present disclosure is configured to minimize cold joint formation and provide solutions to minimize the effects and influences of cold joints where such joints unavoidably might develop. 
     Referring now to the drawings,  FIG.  1    illustrates a perspective view of one embodiment of an additively-manufactured structure of the present disclosure, specifically, a wind turbine  10 . As shown, the wind turbine  10  includes a tower  12  extending from a foundation  15  or support surface with an access opening  17  and a nacelle  14  mounted atop the tower  12 . A plurality of rotor blades  16  are mounted to a rotor hub  18 , which is in turn connected to a main flange that turns a main rotor shaft. The wind turbine power generation and control components (not shown) are typically housed within the nacelle  14 . Moreover, as shown, the tower  12  may also include a base portion  19  below the access opening  17 . In an embodiment, the base portion  19  of the tower  12  below the access opening  17  may be manufactured differently than the portion  21  of the tower structure  12  surrounding and/or including the access opening  17 . Similarly, the portion  23  of the tower structure  12  above the access opening may be manufactured differently than the base portion  19  and/or the portion  21 . 
     The view of  FIG.  1    is provided for illustrative purposes only to place the present invention in an exemplary field of use. It should be appreciated that the invention is not limited to any particular type of wind turbine configuration. In addition, the present invention is not limited to use with wind turbine towers but may be utilized in any application having concrete constructions and/or tall tower structures in addition to wind towers, including for example homes, bridges, tall towers, building construction, and other aspects of the concrete industry. Further, the methods described herein may also apply to manufacturing any similar structure that benefits from the advantages described herein. 
     Referring now to  FIG.  2   , the tower structure  12  of the wind turbine  10  of  FIG.  1    is described in more detail according to an embodiment of the present disclosure. Specifically,  FIG.  2    illustrates a partial, cross-sectional view of one embodiment of the tower structure  12  of the wind turbine  10  according to the present disclosure. As shown, the tower structure  12  defines a generally circumferential tower wall  20  having an outer surface  22  and an inner surface  24 . Further, as shown, the circumferential tower wall  20  generally defines a hollow interior  26  that is commonly used to house various turbine components (e.g., a power converter, transformer, etc.). In addition, as will be described in more detail below, the tower structure  12  is formed using additive manufacturing. 
     Moreover, as shown, the tower structure  12  is formed of one or more cementitious materials  28  that is reinforced with one or more reinforcement members  30  ( FIG.  2   ), such as elongated cables or wires, helical cables or wires, reinforcing bars (also referred to as rebar), mesh reinforcing fibers (metallic or polymeric), reinforcing metallic rings (circular, oval, spiral and others as may be relevant), and/or couplings. According to an embodiment, the cementitious material  28  may be provided through any suitable supply system  32  (see, e.g.,  FIG.  4   ). Further, as shown in the generalized simplified illustration of  FIG.  2   , the reinforcement members  30  may be embedded in the cementitious material  28  during the printing process, as described in more detail below. As used herein, the cementitious materials  28  may include any suitable workable paste that is configured to bind together after curing to form a structure. Suitable cementitious materials include, for example, concrete, pitch resin, asphalt, geopolymers, polymers, cement, mortar, cementitious compositions, or similar materials or compositions. 
     According to an embodiment of the present disclosure, an adhesive material (not shown), a cold joint primer (not shown), and/or steel/metal/alloy/composite frame(s) or end cap(s) in the form of C-shaped frames, for example, (not shown) may also be provided between one or more of the cementitious materials  28  and the foundation  15 , the cementitious material  28  and reinforcement members  30 , or multiple layers of the cementitious material  28  and reinforcement members  30 . Thus, these materials may further supplement interlayer bonding between materials, facilitate integration or use of pre-fabricated components or formwork, or simply provide aesthetic benefits by capping off the rough edges of an additively-manufactured wall of cementitious material  28  in a tower structure  12 , for example. 
     The adhesive material described herein may include, for example, cementitious material such as mortar, polymeric materials, and/or admixtures of cementitious material and polymeric material. Adhesive formulations that include cementitious material are referred to herein as “cementitious mortar.” Cementitious mortar may include any cementitious material, which may be combined with fine aggregate. Cementitious mortar made using Portland cement and fine aggregate is sometimes referred to as “Portland cement mortar,” or “OPC.” Adhesive formulations that include an admixture of cementitious material and polymeric material are referred to herein as “polymeric mortar.” Any cementitious material may be included in an admixture with a polymeric material, and optionally, fine aggregate. Adhesive formulations that include a polymeric material are referred to herein as “polymeric adhesive.” 
     Exemplary polymeric materials that may be utilized in an adhesive formulation include may include any thermoplastic or thermosetting polymeric material, such as acrylic resins, polyepoxides, vinyl polymers (e.g., polyvinyl acetate (PVA), ethylene-vinyl acetate (EVA)), styrenes (e.g., styrene butadine), as well as copolymers or terpolymers thereof. Characteristics of exemplary polymeric materials are described in ASTM C1059/C1059M-13, Standard Specification for Latex Agents for Bonding Fresh to Hardened Concrete. 
     Referring now generally to  FIGS.  3  through  5   , an additive printing device  40  is described according to an embodiment of the present disclosure. Notably, all or part of tower structure  12  may be printed, layer-by-layer, using the additive printing device  40 , which may use any suitable mechanisms for depositing layers of additive material, such as concrete, to form tower structure  12 . Additive manufacturing, as used herein, is generally understood to encompass processes used to synthesize three-dimensional objects in which successive layers of material are formed under computer control to create the objects. As such, objects of almost any size and/or shape can be produced from digital model data. It should further be understood that the additive manufacturing methods of the present disclosure may encompass three degrees of freedom, as well as more than three degrees of freedom such that the printing techniques are not limited to printing stacked two-dimensional layers but are also capable of printing curved and/or irregular shapes. 
     It should be further understood that the additive printing device  40  described herein generally refers to any suitable additive printing device  40  having one or more nozzles for depositing material (such as the cementitious material  28  or the backfill material which is not shown) onto a surface that is automatically controlled by a controller to form an object programmed within the computer (such as a CAD file). More specifically, as shown in  FIG.  3    and described below, the additive printing device  40  includes one or more printer heads  42  having any suitable number of nozzles  44  and being independently movable to simultaneously print layers of the tower structure  12 . 
     Referring still to  FIGS.  3  through  5   , the additive printing device  40  is described in more detail according to an embodiment of the present disclosure. As illustrated, the additive printing device  40  may include a vertical support structure  50  which is generally configured for suspending one or more of the printer heads  42  above tower structure  12  during the printing process. In this regard, the vertical support structure  50  may extend from the ground or from foundation  15  upwards substantially along a vertical direction V to a position at least partially above a top  52  of the tower structure  12  (e.g., and also above foundation  15  before the first layer is printed). 
     As illustrated, the vertical support structure  50  may include a plurality of support towers  54  and one or more gantry beams  56  that extend between at least two of the support towers  54 . Although two support towers  54  and a single gantry beam  56  are illustrated in the  FIGS.  3  through  5   , it should be appreciated that any suitable number and position of support towers  54  may be used according to alternative embodiments. In addition, the support towers  54  and the gantry beams  56  are illustrated as being truss-like structures (e.g., similar to a tower crane), but could be formed in any other suitable manner or have any other configuration according to alternative embodiments. 
     In addition, although the vertical support structure  50  is illustrated as being positioned on the outside of the tower structure  12 , it should be appreciated that according to alternative embodiments, the vertical support structure  50  may be positioned inside the tower structure  12 . According to still other embodiments, the vertical support structure  50  may include the support towers  54  positioned both inside and outside of the tower structure  12 . In addition, the additive printing device  40  may be suspended from the vertical support structure  50  using any other suitable system or mechanism. 
     Notably, during the additive printing process, the top  52  of tower structure  12  is built layer-by-layer, rising along the vertical direction V. Therefore, the vertical support structure  50  may be an expandable support structure which may be raised along with the height of tower structure  12 . In this regard, the vertical support structure  50  may be formed from a plurality of stacked segments  60  which are positioned adjacent each other along the vertical direction V and joined to form the rigid vertical support structure  50 . Thus, when the tower structure  12  approaches the top  58  of the vertical support structure  50 , additional segments  62  may be added to stacked segments  60  to raise the overall height of vertical support structure  50 . 
     Referring specifically to  FIG.  3   , additional segments  62  may be combined with stacked segments  60  to raise the vertical support structure  50  using a jacking system  64 . In general, as shown, the jacking system  64  may be positioned proximate foundation  15  and is configured for raising the vertical support structure  50  (e.g., including the stacked segments  60  and the gantry beams  56 ) and inserting additional segments  62 . Specifically, a separate jacking system  64  may be positioned at a bottom of each support tower  54 . 
     According to an embodiment, the jacking system  64  may include a jacking frame  66  and a jacking mechanism  68  which are positioned at the bottom of stacked segments  60 . The jacking mechanism  68  described herein may generally be any suitable hydraulically, pneumatically, or other mechanically actuated system for raising the vertical support structure  50 . Accordingly, when additional segments  62  need to be added, a dedicated jacking mechanism  68  simultaneously raises each of the support towers  54  such that additional segments  62  may be inserted. Specifically, the jacking frame  66  may support the weight of the vertical support structure  50  as additional segments  62  are positioned below the lowermost stacked segments  60 . Additional segments  62  are joined to stacked segments  60  using any suitable mechanical fasteners, welding, etc. This process may be repeated as needed to raise the total height of the vertical support structure  50 . 
     In certain situations, it may be desirable to protect the tower structure  12  and components of the additive printing device  40  from the external environment in which they are being used. In such embodiments, the tower cover  70  may generally be any suitable material positioned around the vertical support structure  70 . For example, the tower cover  70  may be a fabric-like material draped over or attached to the vertical support structure  50  (e.g., over the support towers  54  and/or the gantry beams  56 ). 
     As mentioned briefly above, the vertical support structure  50  is generally configured for supporting one or more of the printer heads  42  and or other modules which facilitate the formation of the tower structure  12 . Referring specifically to  FIGS.  3  through  5   , the additive printing device  40  may further include one or more support members, such as support rings  80 , that are suspended from the vertical support structure  50 , or more specifically from gantry beams  56 , above the tower structure  12 . For example, as illustrated, the support ring  80  is mounted to the gantry beam  56  using a vertical positioning mechanism  82 . In general, the vertical positioning mechanism  82  is configured for adjusting a height or vertical distance  84  measured between the gantry beam  56  and a top of support ring  80  along the vertical direction V. For example, the vertical positioning mechanism  82  may include one or more hydraulic actuators  86  extending between gantry beam  56  and support ring  80  for moving support ring  80  and printer heads  42  along the vertical direction V as tower structure  12  is built up layer-by-layer. 
     As illustrated, the hydraulic actuators  86  are configured for adjusting the vertical distance  84  to precisely position nozzles  44  of the printer heads  42  immediately above top  52  of the tower structure  12 . In this manner, the additive printing process may be precisely controlled. However, it should be appreciated that according to alternative embodiments, the vertical motion of the printer heads  42  may be adjusted in any other suitable manner. For example, according to an embodiment, the support ring  80  may be rigidly fixed to the gantry beam  56  while the support ring  80  and/or the printer heads  42  are used to facilitate vertical motion to precisely position nozzles  44 . For example, the printer heads  42  may be slidably mounted to the support ring  80  using a vertical rail and positioning mechanism to adjust the vertical position relative to the support ring  80  and the tower structure  12 . 
     According to the illustrated embodiment, the printer head(s)  42  is movably coupled to the support ring  80  such that the nozzles  44  may deposit cementitious material  28  around a perimeter of tower structure  12  while the support ring  80  remains rotationally fixed relative to gantry beam  56 . In this regard, for example, a drive mechanism  100  may operably couple the printer head(s)  42  to the support ring  80  such that printer head(s)  42  may be configured for moving around a perimeter  102  of the support ring  80  (e.g., about a circumferential direction C) while selectively depositing the cementitious material  28 . One exemplary drive mechanism  100  is described below and illustrated in the figures, but it should be appreciated that other drive mechanisms are contemplated and within the scope of the present disclosure. 
     As best shown in  FIG.  4   , for example, the drive mechanism  100  may include a ring gear  104  that is positioned on the support ring  80  and a drive gear  106  that is rotatably mounted to printer head  42 . Specifically, as illustrated, the ring gear  104  is defined on a bottom  108  of the support ring  80 . Thus, when printer head(s)  42   42  is mounted on the bottom  108  of support ring  80 , drive gear  106  engages ring gear  104 . The drive mechanism  100  may further include a drive motor  110  that is mechanically coupled to the drive gear  106  for selectively rotating the drive gear  106  to move printer head(s)  42  around a perimeter  102  of the support ring  80 . In this manner, the support ring  80  may remain stationary while printer head(s)  42  moves around the support ring  80  while depositing the cementitious material  28  to form a cross-sectional layer of tower structure  12 . 
     Although the drive mechanism  100  is illustrated herein as a rack and pinion geared arrangement using drive gear  106  and ring gear  104 , it should be appreciated that any other suitable drive mechanism  100  may be used according to alternative embodiments. For example, the drive mechanism  100  may include a magnetic drive system, a belt drive system, a frictional roller drive system, or any other mechanical coupling between printer head(s)  42  and support ring  80  which permits and facilitates selective motion between the two. 
     In addition, in an embodiment, the support ring  80  may generally have a diameter that is substantially equivalent to a diameter of the tower structure  12 . However, it may be desirable to print the tower structure  12  having a non-fixed diameter or a tapered profile. In addition, as illustrated for example in  FIG.  5   , the tower structure  12  may include an outer tower wall  120  spaced apart along a radial direction R from an inner tower wall  122 . For example, the outer tower wall  120  may be printed to define a mold for receiving poured concrete, e.g., to decrease printing time and total construction time. 
     Thus, as shown, the additive printing device  40  may include a plurality of concentric support rings  80  and printer heads  42  for simultaneously printing each of the outer tower wall  120  and the inner tower wall  122 . Specifically, as illustrated, an outer support ring  124  may be positioned above the outer tower wall  120  and have a substantially equivalent diameter to the outer tower wall  120 . Similarly, the inner support ring  126  may be positioned above the inner tower wall  122  and have a substantially equivalent diameter to the inner tower wall  122 . It should be appreciated that as used herein, terms of approximation, such as “approximately,” “substantially,” or “about,” refer to being within a ten percent margin of error. According to this embodiment, each of outer support ring  124  and inner support ring  126  may include dedicated printer heads  42  and/or other modules for facilitating the printing process of outer tower wall  120  and inner tower wall  122 , respectively. 
     Referring again to  FIG.  4   , the printer head(s)  42  may include mechanisms for adjusting the position of nozzles  44  on printer head(s)  42 . For example, printer head(s)  42  may include a radial adjustment mechanism  130  that is configured for moving print nozzle  44  along the radial direction R. Specifically, according to the illustrated embodiment, radial adjustment mechanism  130  includes a slide rail  132  mounted to a bottom  134  of printer head  42 . The slide rail  132  extends substantially along the radial direction and is configured for slidably receiving the nozzle  44 . 
     The radial adjustment mechanism  130  may further include an actuating mechanism  136  that moves print nozzle  44  along the radial direction R within the slide rail  132 . For example, the actuating mechanism  136  may include any suitable actuator or positioning mechanism for moving nozzle  44  within the slide rail  132 . In this regard, for example, the actuating mechanism  136  may include one or more of a plurality of linear actuators, servomotors, track conveyor systems, rack and pinion mechanisms, ball screw linear slides, etc. 
     Referring still to  FIGS.  3  and  4   , the additive printing device  40  may include any other suitable number of subsystems or modules to facilitate and improved printing process or improved finishing of tower structure  12 . For example, as best illustrated in  FIG.  4   , the additive printing device  40  may include a reinforcement module  140  which is movably coupled to the support ring  80  and is configured for embedding one or more support members  142  at least partially within tower structure  12 . In this regard, for example, the reinforcement module  140  may be similar to the printer head(s)  42  in that engages the support ring  80  and may move around a perimeter  102  of the support ring  80  while depositing the support members  142 . 
     For example, according to an embodiment, the support members  142  may be reinforcement bars (i.e., rebar), tensioning cables, or any other suitable structural support members, as explained briefly below. For example, as shown in  FIG.  2   , the reinforcement module  140  may embed one or more reinforcement members  30  at least partially within one or more of portions of the tower structure  12 . In this regard, the reinforcement module  140  positions reinforcement members  30  at least partially within the tower structure  12 . It should be understood that such reinforcement members  30  may extend along the entire height of the tower structure  12  (e.g., as shown in  FIG.  2   ) or along only a portion of the tower height. 
     Similarly, referring still to  FIGS.  3  and  4   , the additive printing device  40  also may be configured to supply backfill material, for example, via a mechanism movably coupled to the support ring  80  and configured for depositing backfill material and/or any other material as described herein. In this regard, for example, such a mechanism may be similar to the printer head(s)  42  and/or reinforcement module  140  in that it engages the support ring  80  and may move around a perimeter  102  of the support ring  80  while depositing a backfill material  229  (see e.g.,  FIGS.  14 ,  18 - 21   ). For example, according to an embodiment, the backfill material  229  described herein may include any suitable workable paste that is configured to bind together after curing to form a structure. Suitable materials include, for example, concrete, pitch resin, asphalt, clay, cement, mortar, cementitious compositions, geopolymer materials, polymer materials, or similar materials or compositions. 
     According to an embodiment, as the tower structure  12  is being built up, the additive printing device  40  can alternate between depositing reinforcement members  30  using the reinforcement module  140 , printing the cementitious material  28  using printer heads  42  and nozzles  44 , and backfilling a void using the backfill module. Alternatively, as illustrated in  FIGS.  3  and  4   , the reinforcement module  140  may be positioned adjacent the printer heads  42  and configured for unwinding or unrolling the reinforcement members  30  or rebar into the print area prior to depositing cementitious material  28  such that the reinforcement members  30  becomes embedded within or printed over with cementitious material  28 . Alternatively, the additive printing device  40  may include any other suitable features for compressing or embedding tensioning cable into cementitious material  28  before it has solidified or cured. In alternative embodiments, the additive printing device  40  is configured to eject the cementitious material  28  with short polymer and/or metallic fibers or rings as reinforcements to improve the structural strength of the tower structure  12 . 
     Furthermore, the reinforcement members  30  may generally be configured for ensuring that the stresses in the cementitious material  28 , e.g., concrete, may remain largely compressive. Thus, the reinforcement members  30  may be pretensioned in the cementitious material  28  and may be printed around the reinforcement members  30  or the printing process may define holes or voids throughout the tower structure  12  through which the reinforcement members  30  may be placed after curing or for backfilling, and thereafter post-tensioned. In addition, the reinforcement members  30  may be cables, tendons (e.g., external vertical pretensioned tendons), and/or subsequently grouted into place. In alternative embodiments, the additive printing device  40  may be configured to provide tension to the reinforcement members  30  during printing of the tower structure  12 . In such embodiments, additive printing device  40  may vary a tension of the reinforcement members  30  as a function of a cross-section of the tower structure  12  during the printing process. Thus, such reinforcement members  30  are configured to manage tensile stresses of the tower structure  12 . 
     In another embodiment, the tower structure  12  may include, for example, a plurality of reinforcing bars that form a metal mesh (not shown) arranged in a cylindrical configuration to correspond to the shape of the tower structure  12 . Further, the cylindrical metal mesh can be embedded into the cementitious material  28  of the tower structure  12  before the material  28  cures and periodically along the height of the tower  12 . In addition, the additive printing device  40  is configured to print the cementitious material  28  in a manner that accounts for the cure rate thereof such that the tower wall  20 , as it is being formed, can bond to itself. In addition, the additive printing device  40  is configured to print the tower structure  12  in a manner such that it can withstand the weight of the wall  20  as the additively-formed cementitious material  28  can be weak during printing. 
     In addition, although the description herein refers to the tower structure  12  being printed from a single material, e.g., concrete, it should be appreciated that the tower structure  12  may be printed using any suitable material, even if different from other sections. In addition, the tower structure  12  may have any suitable cross sectional profile. In this regard, as illustrated, the tower structure  12  may be substantially cylindrical or have a circular cross section. However, according to still other embodiments, the tower structure  12  may be polygonal, elliptical, oval, square, teardrop, airfoil, or any other suitable shape. In addition, according to still another embodiment, the tower structure  12  may be tapered or vary in cross-sectional area depending on the vertical position along the tower structure  12 . 
     Referring now to  FIG.  6   , a block diagram of an embodiment of a controller  190  of the additive printing device  40  is illustrated. As shown, the controller  190  may include one or more processor(s)  192  and associated memory device(s)  194  configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). Additionally, the controller  190  may also include a communications module  196  to facilitate communications between the controller  190  and the various components of the additive printing device  40 . Further, the communications module  196  may include a sensor interface  198  (e.g., one or more analog-to-digital converters) to permit signals transmitted from one or more sensors or feedback devices to be converted into signals that can be understood and processed by the processor(s)  192 . It should be appreciated that these sensors and feedback devices may be communicatively coupled to the communications module  196  using any suitable means, e.g., via a wired or wireless connection using any suitable wireless communications protocol known in the art. 
     As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. The processor  192  is also configured to compute advanced control algorithms and communicate to a variety of Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.). Additionally, the memory device(s)  194  may generally include memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s)  194  may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s)  192 , configure the controller  190  to perform the various functions as described herein. 
     Referring now to  FIG.  7   , a perspective view of an embodiment of an additively-manufactured structure  12  having an access opening  17  with a pre-fabricated component(s)  90  formed therein is illustrated. The pre-fabricated component(s)  90  described herein may include any suitable pre-fabricated component formed in a number of ways. For example, in particular embodiments, as described in detail herein, the pre-fabricated component  90  may be a pre-fabricated door assembly  92  of the tower structure  12 . In particular, as shown, the pre-fabricated door assembly  92  has a door frame  93  defining an access opening  95  and a door for moving between an open position that exposes the access opening  95  and a closed position that covers the access opening  95 . In such embodiments, as shown in the inset of  FIG.  7   , the reinforcement members  30  are arranged within the composite material  34  around the access opening  95 . More particular, in certain embodiments, as shown, the reinforcement members  30  may be arranged within the composite material  34  at a plurality of different angles with respect to the access opening  95 . 
     In certain embodiments, the pre-fabricated door assembly  92  is derived/produced by position or printing a cast component (not shown) to define the access opening  95  and then depositing cementitious material within the cast component to complete production of the pre-fabricated door assembly  92 . In such embodiments, the cast component is an integral part of the pre-fabricated door assembly  92  and is left permanently embedded in the tower structure  12  as the tower structure  12  is built up. In particular, in certain embodiments, the cast component for the pre-fabricated door assembly  92  may be formed of a different material composition than the composition of the material introduced into the cast component for completing the pre-fabricated door assembly  92  or used for printing the remainder of the tower structure  12 . 
     Referring now to  FIG.  8   , as mentioned, the pre-fabricated component  90  may also be a pre-fabricated foundation assembly  94 . Further, as shown, the pre-fabricated foundation assembly  94  may include a plurality of foundation segments  97 . Thus, in certain embodiments, the method of the present disclosure may include arranging the plurality of foundation segments  97  together to form a foundation of the tower structure  12 . In such embodiments, as shown, a gap  98  exists between each of the plurality of foundation segments  97  with the portions  38  of the reinforcement members  30  protruding from the foundation segments  97  within the gaps  98 . Moreover, in certain embodiments, the pre-fabricated component  90  also is derived/produced by position or printing a cast component (not shown). In particular, in certain embodiments, the cast component for the pre-fabricated foundation assembly  94  may include a different material composition than the composition of the material introduced into the cast component for completing the pre-fabricated foundation assembly  94  or used for printing the remainder of the tower structure  12 . 
     As such, such pre-fabricated components  90  can be constructed prior to printing the tower structure  12  such that the components  90  can be easily incorporated therein, or the pre-fabricated components  90  can be constructed in situ during printing of the tower structure  12 . For example, in an embodiment, the pre-fabricated components  90  may be formed via casting both on or off site. In alternative embodiments, the pre-fabricated components  90  may be formed via the additive printing device  40 , i.e., by printing and depositing the cementitious material  28  via the printer head(s)  42  to form the pre-fabricated component  90  prior to positioning the component  90  adjacent to the support surface  15  of the tower structure  12  for printing remaining portions of the structure  12 . 
     Referring now to  FIGS.  9 - 11   , illustrated is an embodiment of an additively-manufactured structure  212  having a reinforced access opening  217  with a backfilled void  202  and a pre-fabricated door assembly  92  according to the present disclosure. The backfilled void  202  described herein may include any suitable backfilled void  202  formed in a number of ways. For example, in a particular embodiment, as shown in  FIGS.  13  and  15   , the backfilled void  202  may be formed all at once by forming/building up the tower structure  12  to define a void  201  and leaving the void  201  to be backfilled with the help of one-piece formwork  204 , for example, and then backfilling the void  201  all at once after the one or more reinforcement members  30  are placed into/through the void  201 . 
     In another embodiment, as shown in  FIGS.  14  and  16   , the backfilled void  202  may be formed incrementally with continuous or near continuous forming of the tower structure  12 , continuous or near continuous expansion of the void  201  from the backfilled void  202  portion, and continuous or near continuous backfilling of the expanded void  201  via stackable formwork  205 , for example. As such, in certain embodiments, the backfilled void  202  is not formed all at once but instead is formed continuously or near continuously during continuous or near continuous printing of the tower structure  12 , which helps to prevent or significantly reduce cold joint formation between the older backfilled void  202 , the newer backfilled void  202 , and the surrounding tower structure  12 . In a different embodiment, and as mentioned herein in detail, the backfilled void  202  may be formed by position or printing a printed formwork (not shown) to define the void  201  and then depositing cementitious material to complete production of the printed formwork such that it can be used for completing production of the backfilled void  202 . As such, in certain embodiments, the formwork  204  remains an integral part of the tower structure  12  even after the void  201  is backfilled and, therefore, the formwork  204  is left permanently embedded in the tower structure  12  as the tower structure  12  is built up. 
     Moreover, and still referring to  FIGS.  9 - 11   , the portions of the reinforcement members  30  protruding from the pre-fabricated door assembly  92 , and the portions of the reinforcement members  30  extending across the backfilled void  202  are configured to reinforce the cementitious material around the access opening  217 . In certain embodiments, as shown in  FIGS.  9 - 11   , the reinforcement members  30  are incorporated into the backfilled void  202  and the backfilled void is incorporated into the surrounding tower structure  12  above the access opening  217  to reinforce the access opening  217 . In particular, as shown in  FIGS.  10 - 11   , the reinforcement members  30  may be arranged within the backfilled void  202  at a plurality of different angles with respect to the access opening  217 . For example, in one embodiment, the reinforcement members  30  are arranged within the backfilled void  202  in a grid. In another embodiment, the reinforcement members  30  are extended horizontally across the void  202 , and the reinforcement members  30  are extended vertically across the void  202 . In another embodiment, the reinforcement members  30  may be arranged to take a plurality of different angles with respect to the access opening  217  when placed into the backfilled void  202 . The reinforcement member  30  may take the form of a U-shaped reinforcement member (see e.g.,  FIGS.  10 - 11   ) but may also be L-shaped, T-shaped, E-shaped, etc. 
     Referring now to  FIG.  12   , a flow diagram of one embodiment of a method  300  for additively-manufacturing a structure with a reinforced access opening is provided. In particular, the method  300  can be used to form the tower structure  212  of  FIGS.  9 - 11    using the additive printing device  40  of  FIGS.  3 - 5   , or to form any other suitable structure, tower, or tall structure using any other suitable additive printing device. In this regard, for example, the controller  190  of  FIG.  6    may be configured for implementing the method  300 . However, it should be appreciated that the method  300  is discussed herein only to describe aspects of the present disclosure and is not intended to be limiting. 
     Further, though  FIG.  12    depicts a control method having steps performed in a particular order for purposes of illustration and discussion, those of ordinary skill in the art, using the disclosures provided herein, will understand that the steps of any of the methods discussed herein can be adapted, rearranged, expanded, omitted, or modified in various ways without deviating from the scope of the present disclosure. Moreover, although aspects of the methods are explained with respect to the tower structure  212  and the additive printing device  40  as an example, it should be appreciated that these methods may be applied to the operation of additive printing device to form any suitable tower structure. 
     Furthermore, as described herein, it may be advantageous to incorporate one or more backfilled void(s)  202  into the tower structure  212  to yield a reinforced access opening  217  or any opening or aperture through or partially through the tower wall  20 . Accordingly, the method  300  described herein provides a method for manufacturing a tower structure  12  that incorporates such backfilled void(s)  202 . In particular, as shown at ( 302 ), the method  300  includes printing, via an additive printing device  40  having at least one printer head  42 , a portion of the tower structure  212  adjacent to a support surface  15  of a cementitious material. In such embodiments, the printed portion of the tower structure  212  defines an access opening  217 . For example, the additive printing device  40  of  FIGS.  3 - 5    and one-piece formwork (see e.g.,  FIG.  15   ) or stackable formwork (see e.g.,  FIGS.  14  and  16   ), for example, can be used to complete the method  300  described herein. Thus, as previously explained, the method  300  may include positioning the vertical support structure  50  above the support surface  15  of the tower structure  212 , suspending a support member from the vertical support structure  50  (such as support ring  80 ), and movably coupling the printer head(s)  42  to the support member. 
     Referring back to  FIG.  12   , and as shown at ( 304 ), the method  300  also includes providing a void  201  of the cementitious material at a top boundary of the access opening  17 . The void  201  may be formed all at once by forming/building up the tower structure  12  to define the entire intended void  201  and leaving the void  201  to be backfilled with the help of one-piece formwork  204 , for example. The void  201  also may be formed incrementally by continuous or near continuous expansion of the void  201 , and continuous or near continuous printing of the tower structure  212  around the void  201  and defining the expanding void  201 , for example, such that the void  201  has older and newer defined space. The void  201  also may be formed by position or printing a printed formwork (not shown) to define the void  201 , such that the formwork  204  remains an integral part of the tower structure  212  and is left permanently embedded in the tower structure  212  as the tower structure  212  around the void  201  and defining the void  201  is built up. In certain embodiments, the void  201  may be provided before positioning any pre-fabricated component(s)  90 , significant formwork  204 , or cast component(s) (not shown) (see e.g.,  FIG.  15   ). In other embodiments, the void  201  may be provided before positioning any significant formwork  204  or cast component(s) (not shown), but after positioning of any pre-fabricated component(s)  90  (see e.g.,  FIG.  14   ). In some embodiments, the entire intended void  201  may be provided only after positioning of the pre-fabricated component(s)  90 , any significant formwork  204 , or cast component(s) (not shown) (see e.g.,  FIG.  16   ). 
     Referring back to  FIG.  12   , as shown at ( 306 ), the method  300  also includes placing one or more reinforcement members  30  in the void  201  such that the one or more reinforcement members  30  extend across the void  201 . In particular, the one or more reinforcement members  30  may be arranged within the void  201 , i.e., prior to the void  201  being backfilled or during continuous or near continuous backfilling of the void  201 —at a plurality of different angles. For example, in one embodiment, the reinforcement member(s)  30  are arranged within the void  201  in a grid. In another embodiment, the reinforcement member(s)  30  are extended horizontally across the void  202 , and the reinforcement members(s)  30  are extended vertically across the void  202 . In another embodiment, the reinforcement member(s)  30  may be arranged to take a plurality of different angles with respect to the access opening  217  when placed into the backfilled void  202 . Depending on the embodiment, the form, shape, and structure of the reinforcement member(s)  30  (e.g., U-shaped, L-shaped, T-shaped, E-shaped), and depending on the presence of pre-fabricated component(s)  90 , any significant formwork  204 , or cast component(s) prior to ( 306 ), the method  300  at ( 306 ) may include placing the reinforcement member(s)  30  in the void  201  and extending the one or more reinforcement members in the void in whatever direction is not obstructed by either the pre-fabricated component(s)  90 , the formwork  204 , or the cast component(s) (see e.g.,  FIGS.  13 - 16   ). 
     As shown at ( 308 ), the method  300  also includes continuing to print the printed portion of the tower structure  212  around the void  201  to build up the tower structure  201 . The additive printing device  40  of  FIGS.  3 - 5    and the one-piece formwork (see e.g.,  FIG.  15   ) or the stackable formwork (see e.g.,  FIGS.  14  and  16   ), for example, may be used. 
     As shown at ( 310 ), the method  300  also includes backfilling the void  201  with the backfill material  229  to incorporate the reinforcement member(s) within the void  201  into the printed portion of the tower structure  212 . In particular, in an embodiment, ( 310 ) may include depositing or backfilling, via the additive printing device  40 , for example, a backfill material  229  into the currently available void  201  of the tower structure  212 . Again, and for example, the additive printing device  40  of  FIGS.  3 - 5    and one-piece formwork (see e.g.,  FIG.  15   ) or stackable formwork (see e.g.,  FIGS.  14  and  16   ), for example, can be used. “Currently available void” as used herein refers to continuous or near continuous manufacturing situations to distinguish between the older backfilled void  202 , which is void  201  that has been backfilled earlier in time and prior to the continued expansion of the void  201 —and the newer backfilled void  202 —which is void  201  that has been backfilled later in time after the continued expansion of the void  201 . Therefore, and returning to ( 310 ) of method  300 , the backfilled void  202  may be formed by backfilling the currently available void  201  all at once after the reinforcement member(s)  30  are placed into/through the currently available void  201 . 
     In another embodiment, the backfilled void  202  may be formed incrementally with (1) continuous or near continuous forming of the tower structure  12 , (2) continuous or near continuous expansion of the void  201  (from what may have be currently available for backfilling earlier in time, or from what may have been backfilled earlier in time), and (3) continuous or near continuous backfilling of the expanded void  201  beyond what was the previous currently available void  201 , which helps to prevent or significantly reduce cold joint formation between the older backfilled void  202 , the newer backfilled void  202 , and the surrounding tower structure  12 . 
     Referring now to  FIG.  13   , a schematic diagram of an embodiment of a sequence  400  by which the tower structure of  FIGS.  9 - 11    is manufactured is illustrated. As shown at ( 402 ) of the sequence  400 , a portion of the tower structure  212  is printed of a cementitious material  28  to define the access opening  217 . Next, as shown at ( 404 ) of sequence  400 , a formwork  204   a  is positioned and installed along the printed portion of the tower structure  212  defining the access opening  217 . 
     As shown at ( 406 ) of sequence  400 , a void  201  of the cementitious material  28  is provided at a top boundary of the access opening  217  by continuing to print the tower structure  212  up above the top boundary of the access opening  217  and the formwork  204   a . Also, as shown at ( 406 ) of sequence  400 , one or more reinforcement members  30   a —the same horizontal full ring rebar reinforcement members  30   a  incorporated and part of the printed portions of the tower structure  212 —are extended across the void  201  and, therefore, remain placed in the void  201  such that the one or more reinforcement members  30   a  extend horizontally across the void  201 . Also, as shown at ( 406 ) of sequence  400 , the formwork  204   a  facilitates the continued printing of the tower structure  212  above the top boundary of the access opening  217  (by helping to support the one or more horizontal reinforcement members  30   a ) and facilitates the continued printing of the tower structure  212  above the top boundary of the access opening  217 . 
     Optionally, between ( 404 ) and ( 406 ) of sequence  400 , the sequence  400  may include placing a liner along formwork  204   a  at the top boundary of the access opening  217  on the inside surface of the void  201  to facilitate removal of the formwork  204   a  after formation of the backfilled void  202  at ( 414 ) of sequence  400 . 
     Still referring to  FIG.  13   , as shown at ( 408 ) of sequence  400 , one or more reinforcement members  30   b  are extended across the void  201  and, therefore, remain placed in the void  201  such that the one or more reinforcement members  30   b  extend vertically across the void  201 . Also, as shown at ( 408 ) of sequence  400 , the formwork  204   a  defines and obstructs the bottom of the void  201  and, therefore, the one or more vertical reinforcement members  30   b  are placed into the void  201  through the top or through the sides of the void  201 , in between the one or more horizontal reinforcement members  30   a , to form a grid of reinforcement members  30 . Also, as shown at ( 408 ) of sequence  400 , the formwork  204   a  facilitates formation of the backfilled void  202  of the tower structure  212  by helping to support the one or more vertical reinforcement members  30   b , the additional formwork  204   b , and the backfill material  229  at ( 414 ) of sequence  404 . 
     As shown at ( 410 ) of sequence  400 , a cold joint primer may also be applied to the void  201 . In addition, as shown at ( 412 ) of sequence  400 , a formwork  204   b  is positioned and installed along the open sides of void  201  of the tower structure  212 , which leaves the top of the void  201  open for backfilling. Next, at ( 414 ) of sequence  400 , the void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  within the void  201  into the printed portion of the tower structure  212  and to form the backfilled void  202 . 
     Referring now to  FIG.  14   , a schematic diagram of an embodiment of a sequence  500  by which the tower structure of  FIGS.  9 - 11    is manufactured is illustrated. In particular, the sequence  500  involves the use of stackable formwork  205  and continuous or near continuous printing techniques. As shown at ( 502 ) of sequence  500 , a portion of the tower structure  212  is printed of a cementitious material  28  to define the access opening  217 . As shown at ( 504 ) of sequence  500 , a formwork  204   a  is positioned and installed along the printed portion of the tower structure  212  defining the access opening  217 . 
     As shown at ( 506 ) of sequence  500 , a void  201  of the cementitious material  28  is provided at a top boundary of the access opening  217  by continuing to print the tower structure  212  above the top boundary of the access opening  217  and the formwork  204   a , and one or more horizontal reinforcement members  30   a  are extended across the void  201 . As shown at t ( 508 ) of sequence  500 , one or more vertical reinforcement members  30   b  are placed and extended across the void  201  to form a grid of reinforcement members  30  with the one or more horizontal reinforcement members  30   a , and a stackable formwork  205  is positioned and installed along the open sides of void  201  of the tower structure  212 , but also extending above the elevation of the void  201  or the printed tower structure  212 , which leaves the top of the void  201  open for backfilling, and which leaves more room for continued printing of the tower structure  212  along and above the elevation of the void  201 , and which allows for expansion of the void  201 . 
     As shown at ( 510 ) of sequence  500 , a first portion of the void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  within the first backfilled portion of the void  201  into the printed portion of the tower structure  212  and to form at least a portion of the backfilled void  202 . As shown at ( 512 ) of sequence  500 , the stackable formwork  205  facilitates the continuous or near continuous printing of the tower structure  212  above the top boundary of the access opening  217  and above the first backfilled portion of the backfilled void  202  to help expand the void  201 , and also helps mitigate against the effects of cold joint formation. Next, as shown at ( 514 ) of sequence  500 , the expanded void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  within the expanded void  201  into the printed portion of the tower structure  212  and to form a second, newer portion of the backfilled void  202 . 
     Referring now to  FIG.  15   , a schematic diagram of an embodiment of a sequence  600  by which the tower structure of  FIGS.  9 - 11    is manufactured is illustrated. In particular, the sequence  600  involves the use of one piece formwork  207 . As shown at ( 602 ) of sequence  600 , a portion of the tower structure  212  is printed of a cementitious material  28  to define the access opening  217 . As shown at ( 604 ) of sequence  600 , a falsework  209  is positioned and installed within the access opening  217  to provide support for the continued printing of the printed portion of tower structure  212  above the top boundary of the access opening  217 . Also, at ( 604 ) of sequence  600 , the tower structure  212  above the top boundary of the access opening  217  is continued to be printed to define the void  201  such that the one or more horizontal reinforcement members  30   a  of the printed portion of the tower structure  212  above the top boundary of the access opening  217  extend across the void  201 . 
     As shown at ( 606 ) of sequence  600 , one or more vertical reinforcement members  30   b  are placed and extended across the void  201  to form a grid of reinforcement members  30  with the one or more horizontal reinforcement members  30   a . As shown at ( 606 ) of sequence  600 , the falsework  209  is removed. Also, as shown at ( 606 ) of sequence  600 , as there is no formwork, falsework, or pre-fabricated components in the tower structure  212  to obstruct the bottom of the void  201 , the one or more vertical reinforcement members  30   b  may be placed in the void  201  through the bottom of the void  201 , in between the one or more horizontal reinforcement members  30   a , to form a grid of reinforcement members  30 , and fixed in placed via fixtures (see e.g.,  FIGS.  10 - 11   ) such that the reinforcement member grid  30  is tied in place. Also, at ( 606 ) of sequence  600 , the continued printing of tower structure  212  above the top boundary of the access opening  217  and the continued formation of the void  201  are paused. 
     As shown at ( 608 ) of sequence  600 , a formwork  204   a  is positioned and installed along the printed portion of the tower structure  212  defining the access opening  217 , and a one piece formwork  207  is positioned and installed along the open sides of void  201  of the tower structure  212 , but also extending above the elevation of the void  201  or the printed tower structure  212 , which leaves the top of the void  201  open for backfilling, and which leaves more room for continued printing of the tower structure  212  along and above the elevation of the void  201 . 
     Still referring to  FIG.  15   , as shown at ( 610 ) of sequence  600 , the currently available void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  within the backfilled portion of the currently available void  201  into the printed portion of the tower structure  212  and to form at least a portion of the backfilled void  202 . 
     As shown at ( 612 ) of sequence  600 , a cold joint primer is applied to the portion of the backfilled void  202  formed at ( 610 ). Also, as shown at ( 612 ) of sequence  600 , the one piece formwork  207  facilitates the continued printing of the tower structure  212  above the top boundary of the access opening  217  and above the portion of the backfilled void  202  formed at ( 610 ) that expanded the void  201 . As shown at ( 614 ) of sequence  600 , the expanded void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  into the printed portion of the tower structure  212 , and to finish forming the backfilled void  202 . 
     Referring now to  FIG.  16   , a schematic diagram of an embodiment of a sequence  700  by which the tower structure of  FIGS.  9 - 11    is manufactured is illustrated. In particular, the sequence  700  involves the use of stackable formwork  205  and continuous or near continuous printing techniques. As shown at ( 702 ) of sequence  700 , a portion of the tower structure  212  is printed of a cementitious material  28  to define the access opening  217 . As shown at ( 704 ) of sequence  700 , a falsework  209  is positioned and installed within the access opening  217  to provide support for the continued printing of tower structure  212  above the top boundary of the access opening  217 . Also, as shown at ( 704 ) of sequence  700 , the tower structure  212  above the top boundary of the access opening  217  is continued to be printed to define the void  201  such that the one or more horizontal reinforcement members  30   a  of the printed portion of the tower structure  212  above the top boundary of the access opening  217  extend across the void  201 . 
     As shown at ( 706 ) of sequence  700 , one or more vertical reinforcement members  30   b  are placed and extended across the void  201  to form a grid of reinforcement members  30  with the one or more horizontal reinforcement members  30   a . Also, at ( 706 ) of sequence  700 , the falsework  209  is removed. Also, as shown at ( 706 ) of sequence  700 , as there is no formwork, falsework, or pre-fabricated components in the tower structure  212  to obstruct the bottom of the void  201 , the one or more vertical reinforcement members  30   b  may be placed in the void  201  through the bottom of the void  201 , in between the one or more horizontal reinforcement members  30   a  to form the grid of reinforcement members  30 . Also, as shown at ( 706 ) of sequence  700 , the continued printing of tower structure  212  above the top boundary of the access opening  217  and the continued formation of the void  201  are paused. 
     As shown at ( 708 ) of sequence  700 , a formwork  204   a  is positioned and installed along the printed portion of the tower structure  212  defining the access opening  217 , and a first piece of stackable formwork  205   a  is positioned and installed along at least a portion of the open sides of void  201  of the tower structure  212 , which leaves the top of the void  201  open for backfilling, and which leaves more room for continued backfilling of the void  201  above the elevation of the first piece of stackable formwork  205   a  and for continued formation of the backfilled void  202 . 
     As shown at ( 710 ) of sequence  700 , a first portion of void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  within the first backfilled portion of the void  201  into the printed portion of the tower structure  212  and to form at least a portion of the backfilled void  202 . In addition, there may be a loop as needed between ( 710 ) and ( 708 ), wherein a second piece of stackable formwork  205   b  (and so on and so forth) is positioned and stacked above the first piece of stackable formwork  205   b , along the void  201  of the tower structure  212 , which leaves the top of the void  201  open for backfilling, and which leaves more room for continued backfilling of the void  201  above the elevation of the first piece of stackable formwork  205   a  and for continued formation of the backfilled void  202 , and then a second portion of void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  into the printed portion of the tower structure  212 . 
     As shown at ( 712 ) of sequence  700 , a depending on the number of loops between ( 708 ) and ( 710 ) needed, the stackable formwork  205  facilitates the continuous or near continuous printing of the tower structure  212  above the top boundary of the access opening  217  and above the first and second backfilled portion of the backfilled void  202  to help expand the void  201 , and also to help mitigate against the effects of cold joint formation. Also, as shown at ( 712 ) of sequence  600 , a cold joint primer may be applied to the portion(s) of the backfilled void  202  formed during the loop between ( 708 ) and ( 710 ). As shown at ( 714 ) of sequence  700 , the expanded void  201  is backfilled with the backfill material  229  to incorporate the one or more reinforcement members  30   a,b  into the printed portion of the tower structure  212 , and to finish forming the backfilled void  202 . 
     Referring now to  FIGS.  17 - 18   , provided are two simplified front views of an additive printing device having a printer head  40  having a variable width printer nozzle  41 , also known as a variable width printer head, that may be used to print the structures of  FIGS.  9 - 11   , in particular, to print a gap or void for the tower structure, according to the present disclosure. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     Clause 1. A method of additively-manufacturing a structure having a reinforced access opening, the method comprising: 
     printing, via an additive printing device having at least one printer head, a portion of the structure adjacent to a support surface of a cementitious material, the printed portion of the structure defining an access opening; 
     providing a void of the cementitious material at a top boundary of the access opening; 
     placing one or more reinforcement members in the void such that the one or more reinforcement members extend across the void; 
     continue printing the printed portion of the structure around the void to build up the structure; and 
     backfilling the void with a backfill material to incorporate the one or more reinforcement members within the void into the printed portion of the structure. 
     Clause 2. The method of clause 1, wherein the at least one printer head is a variable width printer head, the method further comprising adjusting the variable width printer head to provide, at least in part, the void at the top boundary of the access opening. 
     Clause 3. The method of claim  1 , further comprising positioning a pre-fabricated door assembly defining the access opening adjacent to the support surface before printing the portion of the structure, then printing the portion of the structure around the pre-fabricated door assembly such that the printed portion of the structure comprises the pre-fabricated door assembly. 
     Clause 4. The method of any of the preceding clauses, wherein printing the portion of the structure defining the access opening comprises positioning formwork or a cast component to define the access opening before printing the portion of the structure, then printing the portion of the structure defining the access opening, at least in part, along the formwork or the cast component. 
     Clause 5. The method of clause 4, wherein providing the formwork or the cast component comprises printing, via the additive printing device having the at least one printer head, the formwork, or the cast component adjacent to the support surface to define the access opening. 
     Clause 6. The method of any of the preceding clauses, wherein printing the portion of the structure comprises printing a base portion of the structure below the access opening by placing one or more ring-shaped reinforcement members atop the support structure and printing one or more layers of the cementitious material upon the one or more ring-shaped reinforcement members. 
     Clause 7. The method of any of the preceding clauses, wherein printing the portion of the structure comprises printing a door sub-portion by printing one or more walls of the cementitious material to define a boundary of the access opening, and wherein continuing to print the printed portion of the structure around the void to build up the structure comprises placing one or more ring-shaped reinforcement members above the void and printing one or more layers of the cementitious material upon the one or more ring-shaped reinforcement members. 
     Clause 8. The method of any of the preceding clauses, wherein the at least one printer head comprises a variable-width printer nozzle, wherein providing the void of the cementitious material at the top boundary of the access opening comprises: 
     printing, via the variable-width printer nozzle, one or more layers of the portion of the structure with the void formed therebetween. 
     Clause 9. The method of any of the preceding clauses, wherein providing the void of the cementitious material at the top boundary of the access opening comprises: 
     providing the formwork or the cast component at the top boundary of the access opening to define the void adjacent to the access opening; and 
     continue printing the printed portion of the structure around the formwork or the cast component at the top boundary of the access opening. 
     Clause 10. The method of clause 9, wherein providing the formwork or the cast component comprises printing, via the additive printing device having the at least one printer head, the formwork, or the cast component to define the void adjacent to the access opening. 
     Clause 11. The method of any of the preceding clauses, wherein placing the one or more reinforcement members in the void comprises arranging a plurality of reinforcement members in a grid pattern within the void. 
     Clause 12. The method of clause 11, wherein arranging the plurality of reinforcement members in the grid pattern within the void comprises horizontally extending the plurality of reinforcement members across the void and vertically extending the plurality of reinforcement members across the void. 
     Clause 13. The method of any of the preceding clauses, wherein placing the one or more reinforcement members in the void comprises horizontally extending the one or more reinforcement members across the void and extending and anchoring load-bearing suspension cables across the void. 
     Clause 14. A structure, comprising: 
     a support surface; 
     a printed portion formed from a cementitious material adjacent to the support surface, the printed portion comprising a pre-fabricated door assembly to define, at least in part, an access opening; and 
     a backfilled void at a top boundary of the access opening, the backfilled void comprising backfilled cementitious material, the backfilled void comprising one or more reinforcement members embedded within the backfilled cementitious material and extending across the backfilled void such that the one or more reinforcement members are incorporated into the printed portion of the structure. 
     Clause 15. The structure of clause 14, further comprising a cast component at the top boundary of the access opening defining, at least in part, the backfilled void. 
     Clause 16. The structure of any of clause 14-15, further comprising a base portion comprises one or more layers of cementitious material and one or more ring-shaped reinforcement members. 
     Clause 17. The structure of any of clause 14-16, wherein the printed portion of the structure comprises at least two walls formed of the cementitious material and adjacent to and supporting the pre-fabricated door assembly. 
     Clause 18. The structure of any of clause 14-17, wherein the backfilled void comprises a plurality of reinforcement members arranged in a grid pattern. 
     Clause 19. The structure of any of clause 14-18, wherein the plurality of reinforcement members arranged in the grid pattern comprises horizontally extending reinforcement members and vertically extending reinforcement members across the void. 
     Clause 20. The structure of any of clause 14-19, wherein the backfilled void comprises horizontal reinforcement members and one or more anchored load-bearing suspension cables. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.