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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     The invention relates generally to hoarding assembled around construction sites. 
     DESCRIPTION OF THE PRIOR ART 
     Hoarding is used to prevent pedestrians from entering a construction site and to prevent debris from escaping the site. Hoarding may also be used as temporary barriers to control pedestrian traffic during special events and out door activities. Basic hoarding is essentially a fence formed of wood beams or rectangular frames nailed together to serve as structural members, and wood cladding panels nailed to the structural members. Such hoarding often includes a covered walkway that usually consists of more wood beams nailed together to define a roof framework, and wood panels or boards laid on the framework. Such a walkway ensures that passers-by are protected against in jury from materials and debris accidentally dropped from a building. 
     There are several shortcomings to such prior practices. Assembly of a hoarding requires considerable time and labour and some measure of carpentry skill. Disassembly of the hoarding not only involves considerable time, and the beams and panels of the hoarding are discarded as waste. It would be desirable to provide a hoarding system which is not subject to such waste. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a modular hoarding comprising vertical posts and horizontal cross-members, preferably formed of tubular steel. The posts are positioned around the perimeter of a construction site by location in post holes, fastening to concrete surfaces, or other appropriate ways. Mounting features are provided to releasably secure the cross-members to the posts in a generally horizontal orientation. Panel structures are provided, preferably rectangular steel frames in which wood panels are permanently mounted. Mounting features are provided to secure each panel structure to the horizontal cross-members at a selectable height, accommodating variations in the surface on which the hoarding is erected. The mounting features preferably include a mounting structure fixed to each panel structure and formed with a set of vertically spaced openings. A removable mounting member may then be provided which has a key portion shaped to fit and lock into any of the openings, as by rotation between insertion and locking orientations, and which has a body portion shaped to extend rearward and downward about one of the cross-members. 
     In another aspect, the invention provides a covered walkway structure that can be incorporated into the basic fence structure defined by the modular hoarding. The walkway structure includes a set of uprights, each comprising a vertical support and a transverse bracket which has one end fixed to the support and an opposing free end. The support and bracket are preferably steel members welded or otherwise permanently fixed to one another at a predetermined angle. The free end of each bracket is releasably secured to one of the posts of the basic fence structure. In that regard, each bracket is associated with mounting features, preferably a vertical sleeve fixed to the free end of the bracket, and dimensioned to slide about any of the vertical posts. Panels or boards are placed on the brackets to serve as a roof, protecting the pedestrians from falling debris or construction materials dropped from above. The brackets are preferably angled downward from their respective vertical supports so that falling objects roll back into the construction site. Mesh and releasable cross-members may be fastened between the vertical supports of walkway structure to impart structural rigidity and to confine pedestrians to the covered walkway. 
     In another aspect of the invention, a method of erecting a modular hoarding is provided. The method comprises the steps of providing a plurality of vertical posts, securing the posts to the ground, securing a plurality of cross-members to the posts in a substantially horizontal orientation, and securing a plurality of panel members to the horizontally oriented cross-members. The cross-members are secured to the posts in a manner which permits the cross-members to be disassembled for later re-use. Also, the panels are secured to the cross-members in a manner which allows the panels to be disconnected from the cross-members so that the panels may be reused. 
     The invention permits basic fence-type hoarding and hoarding with covered walkways to be assembled and disassembled quickly by relatively inexperienced workers. It also reduces the risk of damage to hoarding components, allowing repeated use at different construction sites. The term “modular” as used in this specification in respect of hoarding should be understood as meaning a hoarding which is assembled from sets of standard prefabricated components and which can be expanded or reduced in size by adding or eliminating a number of these components. 
    
    
     Particular aspects of the invention have been summarized above. Others will be apparent from the drawings and a description of a preferred embodiment set out below, and will be more specifically defined in the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood with reference to drawings in which: 
     FIG. 1 is a fragmented perspective view of a hoarding system which defines both a fence and a covered walkway; 
     FIGS. 2-4 are fragmented rear, front and side views of the fence; 
     FIG. 5 is a fragmented side view of the junction between adjacent horizontal cross-members used to support wall panels in the fence; 
     FIG. 6 is a fragmented perspective view of a panel mounting assembly on one wall panel; 
     FIGS. 7 and 8 are fragmented perspective and elevational views showing how components of the panel mounting assembly interlock; and 
     FIG. 9 is an exploded side elevation showing an upright used to construct the walkway in which the upright is mounted to a post associated with the fence. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is made to FIGS. 1-3 which illustrate a modular hoarding  10 . The hoarding  10  includes a fence  12  which extends about the perimeter of a construction site and a covered walkway  14 . The fence  12  is formed with modular components adapted to assemble and disassemble easily: tubular steel posts, tubular cross-members, wall panels, and releasable mounting assemblies that join the various components. The fence  12  may be assembled in straight line segments at each side of a construction site. Corner structures are generally not required where sections of the fence  12  meet. 
     The fence  12  is assembled in sections. Fence posts are installed at intervals along the perimeter of the site, such as the three such posts  16 ,  18 ,  20 , apparent in FIG. 1 (posts  16  and  18 ) and FIG. 2 (posts  18  and  20 ). In most instances, holes will be dug to receive the posts, but the posts may be formed with apertured flanges for fastening to pavement or other durable surfaces. In some instances, the fence posts may be driven into the ground. Two posts  18 ,  20  associated with a particular section of the fence  12  are apparent in FIG. 2. A pair of conventional pipe clamp fasteners  22 ,  26  are mounted to one post  20  and another pair of fastener  24 ,  28 , to the other post  18  in order to releasably mount horizontal cross-members  30 ,  32 . The fastener  26 , which is typical, is further detailed in FIG. 4 where it may be seen to comprise two sleeves  36 ,  38  aligned along axes that are offset horizontally and mutually perpendicular. The sleeve  36  is located vertically about the post  18 , and split so that it can be tightened with a bolt to secure the fastener  24  at a desired height relative to the post  18 . The other sleeve  38  is oriented horizontally to receive and support the cross-member  32 . The upper cross-member  30  is simply slipped horizontally through the upper fasteners  22 ,  24 , and the lower cross-member  32 , through the lower fasteners  26 ,  28 , where the cross-members  30 ,  32  respectively constitute part of upper and lower rails  40 ,  42  on which panels are suspended. 
     The injunction  44  between two cross-members  32 ,  46  in the lower rail  42  is detailed in the enlarged view of FIG. 5. A conventional pipe connecting sleeve  50  is used to join the adjacent cross-members  32 ,  46 . The sleeve  50  is obtained circumferentially pinched, which causes the sleeve  50  to fit tightly about a pipe inserted into either end of the sleeve  50  and displaced substantially to the center of the sleeve  50 . The sleeve  50  is simply fitted over the end of one cross-member  32 , and the adjacent end of the other cross-member  46  is simply inserted into the sleeve  50 . Such joining of cross-members causes the sections of the fence  12  to act together as a unitary structure. 
     A typical wall panel  58  includes a rectangular frame  60  formed of angled-iron, and a wood panel  62  fastened to the outer planar face of frame  60 . These components are apparent in FIGS. 2-4, and detailed in the fragment view of FIG.  6 . The wood panel  62  is fastened to the rectangular frame  60  with self-tapping screws (like the screw  66  associated with the adjacent panel  70 ) which are screwed at intervals along the frame  60 . 
     Special mounting assemblies are used to fasten wall panels to the cross-members of the hoarding  10 . The mounting of the panel  58  is typical, and general aspects of such mounting will be apparent with reference to FIGS. 1 and 2. An upper pair of mounting assembles  76 ,  78  secures the panel  58  to the upper cross-member  30 . A lower pair of mounting assembles  80 ,  82  secures the panel  58  to the lower cross-member  32 . 
     The mounting assembly  76  associated with the panel  58  is typical and detailed in FIGS. 6-8. It includes a mounting plate  84  welded to the frame  60  of the panel  58  and facing rearward from the panel  58 . The mounting plate  84  has a set of four slots  86 ,  88 ,  90 ,  92  that are vertically aligned and spaced-apart. The mounting assembly  76  also includes a removable mounting member  94 . The removable mounting member  94  includes a key portion  96  and a body portion  98  angled essentially to define a hook. The key portion  96  is generally planar with a thickness less than width of the slots  86 - 92 , and has an elongate head  100  and a narrow neck  102  dimensioned to rotate within, for example, the slot  88 . The key portion  96  is essentially shaped to insert in a predetermined angular orientation relative to the slot  88 , with the mounting member  94  essentially horizontal, as shown in FIG. 7, until the neck  102  of the key portion  96  locates within the slot  88 , and the head  100 , behind the mounting plate  84 . The mounting member  94  is then rotated downward through 90 degrees to an operative vertical orientation about the cross-member, as shown in FIG.  2 . The head  100  then bears against the back of the mounting plate  84  to resist removal, and the body portion  98  extends rearward from the panel  58  and then downward about the cross-member. The mounting member  94  is secured to the mounting plate  84  with a threaded fastening assembly  104 . The fastening assembly  104  consists of a bolt  106  and a nut  108 . The body portion  98  of the removable mounting member  94  is formed with a slot  110  positioned to align with the slot  90  of the mounting plate  84 , immediately below the slot  88  through which the key portion  96  of the removable mounting member  94  is inserted. The bolt  106  is simply extended through the aligned slots  90 ,  106 , and the nut  108  is rotated to draw the body portion  98  of the removable mounting member  94  securely against the cross-member  30 . 
     In practice, the upper and lower rails  40 ,  42  set the general height of all wall panels. The mounting assemblies, however, permit the height of individual panels to be adjusted to accommodate irregularities in site surfaces. For example, as shown in FIG. 3, the wall panel  58  is raised relative to adjacent panels  70 ,  112  to accommodate a local rise  116  in the supporting surface. 
     The walkway  14  has a modular construction which includes standard uprights, such as the uprights  120 ,  122  apparent in FIGS. 1 and 9. The upright  120  which is typical includes a vertical support  124  and a transverse bracket  126  welded to the support  124 . The support  124  is a steel pipe but the bracket  126  has a truss construction to impart greater rigidity. A brace  125  is welded at an angle between the support  124  and the bracket  126  to further reduce sagging. In practice, the support  124  may be sunk in the ground, or a circular flange  127  with clearance holes (not shown) may be welded to the lower end of the support  124  to permit fastening to pavement. The bracket  126  inclines downward at a predetermined angle (roughly 15 degrees) from its fixed end  128  at the support  124  to its free end  130  distant from the support  124 . 
     The bracket  126  of the upright  120  is mounted releasably to the post  16  of the fence  12 . The mounting assembly  132  includes a sleeve  134  dimensioned to locate about the fence post  16  (or any other fence post in the fence  12 ). The sleeve  134  is welded in a vertical orientation to the free end  130  of the bracket  126 . During assembly, the upright  120  is raised, as shown in FIG. 9, to align the sleeve  134  with the post  16 , and then lowered to locate the sleeve  134  about the post  16 . A set screw  136  threaded into the sleeve  134  can be rotated to bear against the post  16 . Each upright is mounted to a different fence post in a similar manner. The mounting arrangement is not only simple, but permits manual rotation of the uprights  120 ,  122  about their associated posts to adjust spacing during connection of cross-members between the supports. A typical cross-member  138  is shown in FIG.  1 . It consists of length of steel or aluminum tube  140 , and conventional pipe fasteners  142  mounted at opposing ends of the tube  140  and adapted to fasten about the adjacent supports. Such cross-members add structural rigidity and also define a horizontal rail. Conventional wire mesh or other fencing material (not shown) may be extended between the uprights  120 ,  122  and fastened with wire ties to both the uprights  120 ,  122  and cross-member  138  to further enhance the rigidity of the walkway and to constrain pedestrian movement. 
     In the hoarding section illustrated in FIG. 1, the transverse brackets associated with the uprights  120 ,  122  align to define a, roof supporting structure. The mounting of roof materials is less critical than that of the wall panels. Wood boards  146  are simply laid over the brackets, and wood panels  148  are rested on the boards  146 . The angular inclination of the brackets, downward toward the interior of the construction site, ensures that rain and materials dropped onto the walkway  14  roll toward the interior of the construction site. 
     The hoarding  10  is very simply assembled. The fence posts are erected at intervals and exact spacing is not critical. The pipe clamp-type connectors are then mounted on the posts at desired heights, and the cross-members are slipped through the connectors. Adjacent ends of the cross-members are joined to define continuous upper and lower rails from mounting of wall panels. The wall panels are simply butted against the outer surfaces of the horizontal cross-members, and secured by inserting, rotating and fastening the removable mounting members. The uprights are then installed with their mounting sleeves located about the fence posts. The uprights may be rotated about the axes of their respective fence posts to adjust relative spacing and facilitate installation of cross-members. The set screws associated with the mounting of the uprights may be set, and post holes may be filled (or connecting flanges may be fastened to pavement). Roofing materials are then placed on the aligned braces. The hoarding  10  is disassembled by essentially reversing the series of assembly steps. The various joints and mounting assemblies permit easy releasing of component without damage. Standard components can be added or removed to accommodate different sites. 
     It will be appreciated that particular embodiments of the invention have been described and that modifications may be made therein without departing from the spirit of the invention or necessarily departing from the scope of the appended claims.

Summary:
A modular hoarding includes vertical posts secured to the ground. The vertical posts are spaced apart. Detachable, horizontally oriented cross-members are secured to the vertical posts. Detachable wall panels are secured to the horizontally oriented cross-members. The wall panels are secured in abutting positions to form a modular wall structure. The cross-members and wall panels are secured to the posts and cross-members respectively so that the cross-members and panels may be detached after use. The cross-members may be secured at various selected positions along the vertical posts. Similarly, the wall panels may be secured to the cross-members at various selected positions relative to the cross-members.