Space frames and connection node arrangement for them

A node connector in a double layer grid-type of space frame preferably is an extrusion which includes an open-ended tubular portion for snugly at least substantially encircling a frame chord member of desired cross-sectional configuration which is disposable in the passage. The node connector has fixed external elements which extend along the connector parallel to the passage. Those elements define facing parallel flat surfaces arranged in at least two pairs of such surfaces. The surfaces of each pair lie equidistantly from a center plane between them. Each center plane is parallel to the passage axis and preferably includes the passage axis. Each pair of facing flat surfaces of the node connector can cooperate closely with opposite flat surfaces at the end of each of other frames framing member placed between the facing surfaces. The node connector can be secured to a chord member in its passage and to ends of other framing members by shear pins which have zero clearances in node connector holes and in holes or passages through the respective framing members. The space frame can be a movable armature for a curved solar reflector, the space frame having a V-shaped major surface.At least some of the framing members can be thin wall tubes modified to have opposing, flat-exterior wall zones along the length of each tube and in which the wall thickness is locally increased and through which shear pin holes are defined.

FIELD OF INVENTION

This invention pertains to structural space frames. More particularly, it pertains to other-than-shell space frames and to connection node arrangements and other structural elements for such frames.

BACKGROUND OF THE INVENTION

A space frame is a network of structural framing members, such as tubes, interconnected at multi-member connection points (commonly called “nodes”) in such a way that the whole structure behaves as one structural element. By contrast, in the typical framing of beams and columns, as in buildings, structural elements often act independently of each other and can have completely separate force paths.

Two broad classes of space frames are recognized in the art. They are single layer grids and double (multiple) layer grids (DLGs). A single layer grid is a network (arranged on a triangular, rectangular or other geometric scheme) of node structures and structural members of desired cross-sections and sizes. A single layer grid achieves its structural strength by locating the grid elements in a curved surface. Thus, single layer grids are most commonly used to define domes, vaults, and other constructions having simple or compound curvature.

Double layer grids, as the name implies, are space frames in which the nodes are located in two separate surfaces which commonly are flat and in parallel spaced relation to each other; vaulted DLGs having curved parallel spaced surfaces also are known. In a double layer grid (DLG), the nodes are interconnected in each surface by straight structural elements called chords; the chords in each surface are arranged in repeating geometric patterns which usually are squares, but triangles and rectangles also can be defined by the chord array in each surface. The squares (or other geometric shapes) defined by the chords in the principal surfaces of a DLG normally are of the same size throughout the structures. The two surfaces of a DLG are interconnected by further straight structural elements which are referred to herein as struts to distinguish them from the chord elements which lie in the principal surfaces of a DLG. The nodes in a top surface of a DLG are located so that the centroid of the area of the square, e.g., they define is located over a node in the bottom surface of the DLG, and struts are connected from each of those top surface nodes to that bottom surface node. As a result, the struts in a DLG which extend between the principal surfaces of the DLG are oblique to the principal surfaces.

Space frames are routinely used as static structures, i.e., structures which are mounted on and supported by fixed supports or foundations. DLG structures which are square or rectangular in overall plan view (i.e., as seen from a vantage point on a line perpendicular to the DLGs principal surfaces) can be supported at the ends of the structure or at the mid-length, e.g., of the structure. However, it is known to use space frames as movable covers over sports arenas and stadiums, in which case the space frame supports are carried on roller or trolley units which are movable along horizontal tracks; space frames used in such situations are fundamentally static structures because the movement of such a space frame does not significantly alter the frame loads due to gravity.

The connections of framing members to nodes in a single layer grid rarely are anything other than rigid connections defined by bolting, riveting or welding of the associated framing members to each other or to other node elements at a node. Such rigid connections of framing members at grid nodes enables the connections to transmit to the nodes, and to other members at the node, moment loads on the framing members; moment loads are loads which act on a framing member in ways which cause the framing member to tend to rotate or pivot relative to the node. In modern double layer grids, on the other hand, the connections of the framing members to the nodes rarely are moment connections; they are connections which either are true pinned connections or are connections which are modeled as pinned connections. In a double layer grid, loads on the overall grid which would tend to produce rotational movements of framing members relative to the nodes are resisted by tensile or compressive forces which act in the framing members along their lengths, i.e., axially of the framing members. The reason for the use of pinned connections in DLGs is the cost and difficulty of assembling such grids having moment connections of the framing members at or to the nodes.

A true pinned connection of a DLG framing member at a node is a simple connection to define and to make. Such a connection typically is made by passing a bolt or a pin through aligned holes in a framing member and in a node connector arrangement to which that framing member and other framing members are pinned. To the extent that strut axes do not intersect the axes of the chords at the node (or the axis of a major chord at the node), the node is said to have eccentricity. Eccentricity at a DLG node causes the node to have moment loads or other undesired loads applied to it. The presence of moment loads at nodes of a DLG requires that at least some of the components of the grid be heavier than if no moment loads were present. Load eccentricity at a DLG node can be caused by imperfections in the alignments of the framing member coupled to the node, and framing member misalignments can be produced by clearances in the pinned connections at the node. Clearances at pinned connections in a DLG also can cause the grid framing members to have effective lengths between nodes which deviate from design lengths, thereby affecting the magnitudes of the actual loads in the framing members as compared to design load magnitudes. The solution to the existence of (or potential for) differences between actual and design framing member loads is to make the framing members heavier.

It is apparent, therefore, that existing structures and techniques for establishing connections of framing members to nodes in DLGs have deficiencies which adversely affect the load carrying capacities of an overall DLG and of the framing members present in it. Needs exist for structures and procedures by which pinned connections at nodes in DLGs can be made with reduced or no eccentricity and with minimal effects of clearances at the pinned connections. Meaningful satisfaction of any or all those needs can result in DLGs which make more efficient use of their framing members and so permit weights of framing members to be reduced, along with other consequent benefits and advantages. The principal factors effecting the cost of a given DLG are primarily the cost of the materials used to define the grid components and secondarily the cost of labor to assemble those components. Material cost is a function of material weight. Labor costs are a function principally of the man-hours needed to assemble a DLG.

SUMMARY OF THE INVENTION

The invention beneficially addresses the needs identified above. It does so by providing structural arrangements and procedures which described in detail below, along with descriptions of the several benefits and advantages of those structures and procedures. Principal aspects of the invention as claimed are summarized next below.

This invention provides a node connector structure which is useful in defining interconnections of plural framing members at a node in a double layer grid type of space frame. The node connector comprises a cylindrical base portion defining a passage having an axis. The passage is sized and shaped for snug slideable substantially axial insertion into it of an elongate chord framing member, the chord member having an axis along its length which is substantially alignable with the passage axis upon insertion of the chord member into the passage. The passage is configured to substantially enclose the chord framing member and to hold the framing member axis in alignment with the passage axis upon insertion of the framing member into the passage. The node connector carries substantially along the length of and externally of the base portion plural fixed structural elements which define at least two pairs of parallel, spaced, opposing substantially flat surfaces. The surfaces of each pair are spaced equidistantly from a center plane between then; the center plane is parallel to and substantially intersects the passage axis. At least one pair of holes is defined in the base portion; those holes are aligned on a line which transverses the passage axis and is normal to it. At lease one pair of further holes is defined through the elements which define each pair of parallel spaced opposing surfaces; those holes are aligned on a line which is normal to that pair of surfaces.

This invention also provides a pinned connection of a framing member in a double layer grid-type of space frame at a node of the frame via a node connector having elements which define a pair of spaced parallel substantially flat opposing surfaces. The framing member has at an end thereof, between the node connector opposing surfaces, its own substantially flat and substantially parallel opposite exterior surfaces which are spaced to have low clearance of the framing member end between the opposing node connector surfaces. A pin receiving passage is formed through the framing member along a line which is substantially normal to the framing member's parallel exterior surfaces. A pair of holes are formed through the node connector elements on a line substantially normal to the pair of opposing surfaces defined by those elements. A pin is insertable through the holes and the passage upon suitable placement of the framing member and between the opposing surfaces of the node connector. In that context, the pin is defined to have substantially an interference fit within the holes and the passage upon insertion of the pin into the holes and the passage.

This invention also provides a tubular structural member which has substantially constant cross-sectional size and configuration along its length. The member has a pair of parallel oppositely aligned flat areas in its exterior surface. The tubular member has a predetermined substantially uniform wall thickness except in a selected portion of each of the externally flat areas where the wall thickness is a selected amount greater than the predetermined wall thickness. A respective one of a pair of aligned holes is defined through the tube in each of the selected portions of greater tube wall thickness.

Also, this invention provides a movable support armature for a curved reflector of electromagnetic radiation. The armature is defined substantially as a double layer grid space frame having nonparallel major surfaces. The armature is comprised by plural parallel major chord framing members each of which has an elongate axis and is disposed in a frame major surface. Each major chord member extends parallel to an elongate extent of the frame. The major chord members include a pair of bottom major chord members essentially in a bottom one of the frame major surfaces, and three upper major chord members. The upper major chord members include a central chord member which is located between two outer chord members. The outer chord members lie in respective ones of two planes which also include the center chord member. The planes intersect at the center chord member at an oblique included angle which is concave away from the frame bottom plane. Node connector structures are connected to each major chord member at spaced locations along each member. Minor chord members are connected between corresponding nodes on the major chord members defining the respective planes described above to define rectangular arrays of major and minor chord members in each plane. Strut framing members are interconnected between nodes in different ones of the planes. Bracing framing members are connected between diagonally opposite nodes in each rectangular array.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a perspective view of a portion of a rectilinearly subdivided DLG space frame10. Frame10is composed of framing members which are disposed to define top11and bottom12layers of the frame and to interconnect those layers in an arrangement which causes frame layers11and12to be in spaced parallel relation to each other. Layers11and12can also be called grids, hence the name double layer grid (DLG) for the type of space frame shown inFIG. 1.

The framing members of DLG10are comprised by chords which are interconnected to define top and bottom layers11and12of the DLG which has an end13and opposite sides14and15. The chords which extend along the length of the DLG can be and preferably are continuous (subject to limitations on the lengths available) and, for present purposes, are called major chords. Thus, DLG10includes upper major chords16and lower major chords17. In each layer of DLG10, the upper and lower major chords are interconnected and spaced by upper18and lower19transverse minor chords, each of which has a length equal (or essentially so) to the spacing between the major chords which they interconnect. The major and minor chords of DLG10are aligned to be parallel to respective orthogonal directions, i.e., the length and the width, of the DLG. In each layer, the major and minor chords are interconnected at junction points which are commonly called nodes. Thus, DLG10has upper nodes20and lower nodes21. As is common in DLG, the distance in each layer between adjacent parallel minor chords is equal to the distance between adjacent parallel major chords, and so the upper nodes20and the lower nodes21are located at the corners of aligned rows and columns of squares bounded by the major and minor chords; each top layer square corresponds to a bay of the DLG; the chords in the bottom layer of frame10also define square bays. Thus, consistent with the foregoing, DLG10has constant square bay spacing.

If the spacing between adjacent parallel minor chords of a DLG is more or less than the spacing between adjacent major chords in a layer, the DLG is described as having constant rectangular bay spacing.

Chords16and18of DLG10can be said to be in (or to define) a top surface of the DLG; similarly, chords17and19are in (define) a bottom surface of the DLG. The top and bottom surfaces of DLG10are parallel.

The top and bottom layers of DLG10are spaced from and supported relative to each other by further diagonal framing members22called struts each of which extends between a top layer node20and a bottom layer node21. In order that the upper and lower grids may be stiffly fixed relative to each other by the struts, the upper major and minor chords are offset relative to the lower major and minor chords in such manner that the lower nodes21are located vertically below the centers of the square openings defined by the chords of the upper grid; upper nodes20are located vertically above the centers of the openings defined by the chords of the lower grid. Thus, the struts are disposed in planes which are inclined relative to the top and bottom surfaces of frame10. As shown inFIG. 1, within the boundaries of the frame, there are four struts22connected to each upper node20and to each lower node21. As a result, the struts are disposed in two sets of parallel planes, one set parallel to and intersecting one upper major chord and one lower major chord, and one set parallel to and intersecting one line of upper minor chords and one line of lower minor chords. Along the ends and sides of frame10, there are two struts22connected to each upper node20, and the frame end and side surfaces (strut planes) slope down and inwardly between the top and bottom surfaces of the frame.

In the classic frame10shown inFIG. 1, there are fewer squares in bottom layer12than there are in top layer11. As frame10is depicted inFIG. 1, the frame is six squares (bays) wide in its top layer and five squares (bays) wide in its bottom layer, while the length of the frame as depicted is indefinite. Such a DLG frame can be described by the notation 6×n/5×(n−1) in which 6×n denotes a top grid 6 bays wide by n bays long, and the notation 5×(n−1) denotes a bottom grid 5 bays wide by (n−1) bays long.

The description of frame10to this point has pertained to geometrical aspects of the frame, to the linear structural framing members which comprise the frame, and to the nodes where the lines (axes) of the different framing members intersect each other in an ideal frame. That description is a background and foundation for the following descriptions of actual frames and of the structures which are employed to interconnect framing members at nodes in those frames. The following descriptions include descriptions of node connector arrangements which enable the design and construction of DLG-type space frames having advanced properties and benefits.

FIG. 2is a perspective view of a DLG-type space frame25in the form of a truss of inverted equilateral triangular cross-section. Using the notation described above, frame25is a 1×8/0×0 DLG frame. Frame25has two upper major chords26and one lower major chord27, all of which extend along the full length of the frame.

FIGS. 3 and 4show a node connector28of frame25. Because the cross-sectional configuration of frame25is that of an equilateral triangle, a single basic node connector configuration can be used at all nodes in the frame. The framing members of frame25preferably are square tubes, the major chords preferably having cross-sections larger than the cross-sections of the other framing members (minor chords, struts, and torsion braces) present in the frame; the other framing members preferably are of the same cross-sectional dimensions. The frame material preferably is an extrudable aluminum alloy, and the framing members preferably are extruded aluminum tubes. Also, the node connectors28preferably are defined by extrusions of the same aluminum alloy.

FIG. 4shows the pinned connection of two struts30to a node connector28which has a pinned connection to lower chord27; a connection of struts to a node connector on either of the upper major chords would have substantially the same appearance as shown inFIG. 4except that the upper major chords actually are turned about their longitudinal axes visualize thatFIG. 4is rotated 120° in either direction.

Node connector28has a chord-receiving base channel portion31which has a flat base32and two parallel spaced flanges33perpendicular to the base. The spacing between opposing faces of flanges33is slightly greater than the exterior width of a major chord, and the height of the flanges from the base31preferably is equal to the height of a major chord. Node connector28also carries along the exterior of the channel portion, in directions parallel to the length of the connector's channel portion, plural fixed structural elements (flanges or ribs)34which define two pairs of parallel spaced opposing and substantially flat surfaces35and36. Surfaces35and surfaces36are spaced a distance which is slightly greater than the width of the extrusion from which the struts, minor chords and torsion braces of frame25are defined. Further, surfaces35are spaced parallel to and equally from opposite sides of a plane37which passes through the structural neutral axis of bottom chord27as received in and secured in the channel portion31of node connector28as shown inFIG. 4. Because chord27is defined by an extruded square tube of uniform wall thickness, the location of the neutral axis of the chord is coincident with the centroid of the cross-sectional area of the tubular chord. Similarly, surfaces36are spaced parallel to and equally from opposite sides of a plane38which passes through the neutral axis of chord27as received and secured in node connector28. Thus, regardless of the angularity of a strut30, as pinned to the node connector, relative to the length of the node connector, axial forces (tensile or compressive) in the truss are aligned with and pass through the neutral axis of the chord to which the node connector is fixedly (rigidly) mounted as by the use of shear pins. That is, because flanges34are parallel to the length of the node connector and have the described geometrical relations to the channel portion of the node connector, the assembled node connection is free of eccentricities regardless of the angularities of the pertinent struts relative to the chord.

Node connector28preferably is doubly pinned to chord27by use of shear pins40and clip retainers41as depicted inFIGS. 11 and 12. Double pinning of the connector to chord27provides a rigid connection between them; in a DLG a rigid connection of a node connector to at least one of the framing members engaging that node connector is important. To enable the node connector28to be doubly pinned to chord27, the connector has two sets of shear pin holes42formed through channel portions flanges33at spaced locations along the length of the connector. The two holes42in each hole set are centered on a line which is normal to the length of the node connector and passes through the neutral axis of the chord27as secured in node connector. Similar shear pin holes are formed through the walls of chord27on a line perpendicular to the chord's length and passing, preferably, through the neutral axis of the chord. If the length of truss10exceeds the length at which chords26and27can be obtained or conveniently handled, node connectors28can be used to make splices between aligned chord member lengths. Splicing is accomplished by making a splicing node connector of extended length, and by doubly pinning the adjacent ends of two chord member lengths to the node connector.

In like manner, shear pin holes43are formed through node connector flanges34for each other framing member which is to be connected to that node connector in completed frame25. In this instance, because each other framing member is simply (singly) pinned to the node connector, one hole43per each framing member to be connected to the connector is formed in each relevant flange34, and the two holes in the coacting flanges are centered on a line which is perpendicular to flange surfaces35or36. Similarly, two aligned shear pin holes are formed through the walls of each other framing member; they are located on a line perpendicular to the length of the framing member and passing, preferably, through the neutral axis of that member.

As shown inFIG. 2, upper major chords26and lower chord27of frame25are of equal length; compare the different lengths of major chords16and17in frame10shown inFIG. 1. Upper major chords26are located in spaced parallel relation to each other by minor chords44which are parallel to each other and perpendicular to the major chords, and so the upper major chords mount (as described above) node connectors28at their ends and at opposed locations spaced along their lengths. To afford connection points for the diagonal struts30in frame10, node connectors28are fixedly mounted to lower chord27at locations between the ends of that chord which are, respectively, midway along the distance between corresponding upper minor chords44. Also, to accommodate the mounting of frame support fittings45to the opposite ends of frame25, an end node connector28is fixedly mounted to each end of lower chord27.

As to each of node connectors28located between, rather than at, the ends of lower chord27, four struts30are pinned to each connector; two of those struts have their ends snugly yet movably received between surfaces35of the connector so that the opposing flat exterior surfaces of the strut substantially register with surfaces35, and another two of those struts have their ends snugly yet moveably received between surfaces36of the connector so that the opposing flat exterior surfaces of those struts substantially register with surfaces36. The ends of struts30are pinned to the connectors28with which they cooperate by use of shear pins40passed through the strut-end holes and through holes43of the connector. All shear pins are held in place by connection of clip retainers41to the pins; each retainer cooperates with its pin in a circumferential recess (groove)47defined in the round pin shank adjacent a distal end of the pin which is opposite from an enlarged head48at the other end of the pin. Two struts30are connected from the node connector at each end of lower chord27to a corresponding frame end connector at the adjacent ends of upper major chords26; seeFIG. 2.

Further, to make frame25stiff against torsional or wracking loads imposed upon it in use, frame25includes a torsion brace framing member49in each bay of the frame; a bay of frame25is the opening bounded by the upper major chords26and two adjacent upper minor chords44. Each torsion brace is connected between the node connectors at the diagonally opposite corners of a bay. The torsion braces lie in the plane of the upper minor chords, and so the torsion brace ends are simply (singly) pinned between the same surfaces35or36of each affected node connector between which an end of an upper minor chord44is similarly pinned. In the portion of frame25between its end bays, the torsion braces49alternate in the directions in which they are skewed to the length of the frame.

Attention is drawn to the node connectors denoted28′ and28″ inFIG. 2; they are at the opposite ends of a single upper minor chord44. In addition to being associated with an upper major chord26, connector28′ has associated with it two struts30, an upper minor chord44, and two torsion braces49. Struts30can be received between surfaces35of connector28′ and framing members44(one) and49(two) can be received between surfaces36of that connector. By contrast, node connector28″ has associated with it an upper major chord, a minor chord44, and two struts30. To accommodate those differences in the number of connections to them, connector28′ has a length greater than that of connector28″ by an amount adequate to accommodate the ends of three framing members between surfaces36of connector28′. That connector length difference is easily handled by making connector28′ from a longer length of the connector extrusion than the length of the extrusion section used to make connector28″ , and by drilling three sets of holes43through the flanges forming surfaces35rather than one set of such holes.

It is a feature of frame25that all of the shear pin holes formed in each node connector28have the same design diameter (and preferably actual diameter) as the diameter of the cylindrical shanks of the shear pins to be inserted into those holes, and that the shear pin holes formed in all framing members of frame25also have the same design (also preferably actual) diameter as the shank diameter of the shear pins used to pin them to node connector28. That is, each shear pin has zero clearance relative to the node connector and framing member holes through which its shank will be inserted to connect the relevant framing member to the relevant node connector. Such zero clearance means, as a practical matter, that each shear pin has an interference fit in each of the holes with which it coacts when installed in the frame. Such zero clearance of shear pins in connector and framing member holes means that frame25can be built with great precision and has no play or looseness in any of its connections. As noted above, the lack of play or looseness in the framing member connections in a space frame means that each framing member will experience and transmit loads which very closely correspond to design loads, and that all framing members will effectively share and correctly transmit loads and load forces within the frame. There will be minimal instances of some framing members carrying more or less of the fraction of the total loads they were designed to carry. Consequently, lower safety factors can be used in the design of frame25and correspondingly lighter framing members can be used than if the frame connections have play or looseness, without compromising safety or structural adequacy.

An inspection ofFIG. 2will reveal that it has 8 bays along its length, i.e., 8 intervals between 9 spaced upper minor chords44. Such inspection ofFIG. 2will reveal that the 4 bays in the mid-length of the frame are of the same length, which length is less than the equal lengths of the other 4 bays of the frame. Thus, frame25has variable bay spacing; bay spacing in frame25can be defined as the distance along the length of the frame between the centroids of the rectangular areas on opposite sides of a minor chord. Variable bay spacing means that some node connectors are closer to each other along a given major chord than are others of the node connectors along that major chord. Because of the natures of the node connectors28as described above, all of the node connectors along that major chord can be (preferably are) made with the same transverse cross-sectional configuration, i.e., made by use of different pieces cut from a single extrusion. Variable bay spacing is possible with node connectors28because, in all of the node connectors, the elements of the connectors which define surfaces35,36are arranged to be parallel to the length of the portion of the connector which cooperates with the major chord of the frame which can (preferably does) extend continuously through the connector. Variable bay spacing is easily achieved in frame25by varying the lengths of struts30and of torsion braces49as needed.

It is preferred that the node connectors and framing members of frame25be defined of the same material so that they all have the same coefficient of thermal expansion, thereby resulting in a frame which develops minimal stresses in it with temperature change and does not deflect or distort due to temperature changes. The preferred material for definition of the node connectors and framing members of frame25is an aluminum alloy, and those frame elements preferably are made by extrusion processes. Shear pins used in the connections within the frame can be made of aluminum or of stainless steel.

However, it is within the scope of this invention that the node connectors and framing members of frame25, or of other frames according to this invention, can be made of other materials. If steel is the material of choice, it will be apparent that the node connectors can be fabricated out of discrete components preferably welded together into integral articles of manufacture. Pultruded materials such as fiber reinforced plastics (synthetic resins) can be used; in that connection, pultruded components are regarded as equivalents of extruded components. Both extruded and pultruded components can be used in a given frame according to this invention. Node connectors can be made by other fabrication processes such as casting or machining.

Regarding frame25, it was noted that, because the overall cross-section configuration of the frame is that of an inverted equilateral triangle, all node connectors in the frame can have the same cross-sectional configuration. If the frame cross-sectional configuration were that of an isosceles triangle, then two different cross-sectional configurations would be needed for the node connectors. Similarly, if the frame configuration were to be that of a triangle having no equal included angles, three different node connector cross-sections would be required. The principles used in the design of node connectors28can be used in the design of node connectors for DLG-type space frames having other configurations than trusses of triangular cross-section. Square-section box trusses can be defined by a variation of node connectors28in which the central planes between surfaces35and36intersect each other at a 90° angle rather than a 60° angle. Moreover, a truss designed and constructed according to this invention can be disposed vertically to serve as a tower. Different node connector cross-sections are readily accommodated in the practice of this invention, as made more clear by the following descriptions.

FIG. 5is an end view of another space frame50according to this invention. Frame50is a double layer grid (DLG) frame which has a flat bottom surface defined by two bottom major chords51,52and bottom minor chords53which extend transversely of those major chords. The upper surface of frame50is not flat, but instead has the contour of a shallow V (oblique included angle) which is concave upwardly away from the frame's bottom surface; the frame is substantially symmetrical about a bisector plane of that included angle. The upper surface is defined by two planes54,55which intersect at the axis of an upper central major chord57. Two upper outer major chords58,59are located equidistantly from and on opposite sides of center chord57and lie, respectively, in planes54and55. Upper center major chord57is positioned centrally above and parallel to bottom major chords51,52by central struts60of equal length. Each of upper outer major chords58,59is positioned relative to the upper central major chord and to the adjacent bottom major chord by upper minor chords61and by struts62which are longer than central struts60. The major chords of frame50preferably are defined by round tubes. The minor chords, struts, torsion braces and auxiliary framing members (see the following descriptions) preferably are defined by square tubes. The tubes (round and square) preferably are defined by aluminum extrusions, as are all of the three different styles of node connectors at which the framing members of frame50are interconnected.

The intended use of frame50is as a movable support armature for an elongate preferably cylindrically curved mirror64in a solar power generation facility; the position of a mirror64relative to the frame is shown inFIG. 5. To enable the frame to serve in that capacity, the frame is designed and constructed to carry a mounting and torque transmitting arm65at each of its ends, and to carry supports66for tubes through which a liquid is circulated to be heated by solar radiation reflected by the mirror. The complete mirror and mirror support frame assembly has a center of gravity and a center of rotation which are coincident at67in arms65.

In light of the foregoing descriptions of truss frame25and its node connectors28, it will be apparent that frame50includes three styles of node connectors which cooperate respectively with bottom major chords51,52, with upper center major chord57, and with upper outer major chords58,59. Those three styles of node connectors are shown, respectively, inFIGS. 6 and 7, inFIGS. 8 and 9, and inFIG. 10.

Bottom major chord node connectors69have the cross-sectional configuration shown inFIG. 6. Unlike node connectors28in frame25, node connectors69are configured for cooperation with a major chord framing member which is defined in the form of a round tube. A node connector69has a base circularly cylindrical chord engaging portion70which defines a round circumferentially closed passage71which extends along the length of the connector. The diameter of passage71is slightly greater than the outer diameters of the bottom major chords of frame50so that each connector enables a chord tube to be snugly and slidably inserted into and through the node connector. At least one pair (preferably two pairs) of holes72, aligned on a diameter of passage71, are formed through the connector's chord engaging portion to enable shear pins (preferably zero-clearance shear pins as described above) to be used with cooperating holes in the pertinent major chord tube to fixedly mount the connector to the chord tube. In other respects, however, node connectors69, as well as upper central node connectors74(FIGs. 8 and 9) and upper outer chord node connectors75(FIG. 10) of frame50, are sufficiently similar to node connectors28that, in view of the content ofFIGs. 6-10, extended descriptions of frame50's node connectors are not needed for an understanding of them by a person skilled in the art.

Therefore, briefly noted, each of major chord node connectors69,74and75carries along its length and externally of its tubular chord engaging base portion70a plurality of fixed structural elements77which define plural pairs of parallel spaced opposing substantially flat surfaces78,79,80(FIG. 6as to connector69),81,82,83,84(FIG. 8as to connector74), and85,86and87(FIG. 10as to connector75). The facing ones of surfaces78-87afford snug yet movable registration with oppositely facing flat exterior surfaces of the minor chords and other framing members of frame50upon insertion of ends of those framing members between those facing surfaces as frame50is assembled (seeFIGS. 13-24). Aligned pairs of holes89are formed through elements (flanges)77at suitable locations in each particular node connector to enable the insertion of zero-clearance shear pins through them and through holes formed through the ends of the relevant framing members, as described above concerning frame25.

FIGS. 6,8and10show that certain ones of flanges77can be branched at their outer ends in order to define facing surface pairs78-87in which, in each pair, the surfaces are parallel to and equidistantly from corresponding central planes which include the axis of that node connector's chord receiving passage71and the neutral axis of the round tubular major chord received in that passage.

That is, in the node connector shown inFIG. 6, the connector elements77which define adjacent ones of surfaces78and79, and which define adjacent one of surfaces79and80, are not connected directly to the exterior of tube portion70. Instead they are carried at the ends of ribs which are connected directly to the exterior of tube portion70. The ribs preferably are disposed in planes which intersect the connector passage axis. This feature of a node connector allows connection to the connector of framing members lying in planes which have relatively small angular separation between them at the node connector while enabling the neutral axes of those framing members to have the desired intersection with the neutral axis of a framing member (chord, e.g.) located in the passage71of that node connector. The movement of the shear pin locations outwardly from the tube portion of the node connector is not a disadvantage.

The structure of completed frame50will become apparent from an understanding ofFIGS. 13-24which depict consecutive steps in the assembly of the frame from its component round and square tubular framing members and its node connectors69,74and75. The first of those steps is shown inFIG. 13. Node connectors69are engaged around the preferably tubular round member which defines bottom major chord52and are secured to it at the ends and the center of that chord. Each prefabricated node connector of frame50can bear coding notations which inform those persons assembling the frame where each node connector is to be placed in the frame and what directionality it is to have relative to the ends of its major chord member. Then, as shown inFIG. 14, three node connectors69are similarly engaged around and secured to bottom major chord51.

As shown inFIG. 15, a third step in the frame assembly process can be the mounting of five node connectors74in the proper sequence on upper center major chord57and the pinning of them to the chord. In that process, a plate90is mounted to the chord in association with the central node connector, which plate will later have connected to it a support66. Note that node connectors74are not uniformly spaced along chord tube57; see alsoFIG. 19where the reason for that connector spacing is made apparent. Fourth and fifth steps in the frame assembly process can be the placement of node connectors75on each of outer central major chord tubes58and59and the pinning of those connectors to those tubes; seeFIGS. 16 and 17.

FIG. 18illustrates a sixth step in the frame assembly process, namely, the interconnection of bottom major chord tubes51and52by bottom minor chords53, torsion bracing members92and additional elements of the frame, using zero-clearance shear pins to make all connections to node connectors. The major chords51,52and the minor chords53define two rectangular bays in the bottom layer (surface) of frame50. Those major chords are shorter in length than upper major chords57-59. Compensation for that major chord length difference is achieved by connecting to each end of each bottom major chord tube an additional preferably square framing member93. At each end of the bottom layer assembly, the other ends of transversely adjacent members93are doubly pin-connected or bolted (a stiff connection) to a coupling fitting94to which an end of a frame torque arm65later will be secured.

The upper central major chord subassembly (FIG. 15) can be connected in place relative to the bottom major chord assembly (FIG. 18) as depicted inFIG. 19as a seventh step in the assembly process. Central struts60are pinned between the node connectors69on the bottom major chords and the end node connectors74on the central chord, and the two other connectors74which are on opposite sides of the center of upper center chord57. Two further framing members95are pinned between center node connector74on upper chord57and the respective center node connectors69on bottom chords51,52. Plate90can then be secured, as by bolting or riveting, to the ends of members95which are pinned to center node connector74. Plate90can be further fixed in its desired position by connecting braces96between the central part of the plate and framing members95as shown inFIG. 19. The completion of this assembly step causes torque arm connection fittings94to be located substantially below the opposite ends of upper central major chord57.

Eighth and ninth steps in the assembly of frame50can be the pinned connection of upper outer major chords59,58to bottom major chords52,51, respectively, via longer struts62and node connectors69and75. SeeFIGS. 20 and 21.

A tenth step in assembly of frame50can be the interconnection of the upper outer major chords58,59to upper central major chord57, and the connection of auxiliary framing members to chords58and59. Such a step is depicted inFIG. 22which shows upper minor chord framing members61pinned between center chord node connectors74and laterally adjacent outer chord node connectors75; in the interest of clarity of illustration, frame elements located below the top of the frame are not shown inFIG. 22. Torsion braces92are disposed (one in each of the six bays defined by members57,58,59and61) diagonally between the chord members so that, on each side of center chord57, the torsion braces alternate in the ways which they are skewed relative to the length of the frame. As connected between major chords57,58and59, upper minor chords61can carry inverted U-clips98at selected locations along their lengths for later connection to them of longitudinal mirror mounting tubes99(seeFIGS. 23 and 24). Clips98function as risers from the flat upper surfaces of frame50to conform to the curvature of the focusing reflector which the frame supports in use. Also, square extension tubes100(akin to frame outriggers) can be rigidly connected between surfaces87of each of node connectors75. Each tube100can carry an inverted U-clip at its unsupported end. Thus, at each transverse station of frame50corresponding to the locations of upper minor chords61, the frame can include six clips98as features which facilitate the connection of mirror64to the frame.

Attention is directed to node connector74on upper center major chord57between plate90and the left end of the frame as depicted inFIGS. 21,22and23. In addition to major chord57which extends continuously (preferably) through that node connector, there are ten further framing members which have an end pinned to that node connector, namely, four central struts60having end surfaces registered with node connector surfaces81and82, two torsion braces92and one upper minor chord61having end surfaces registered with connector surfaces83, and two torsion braces and one upper minor chord61having end surfaces registered with connector surfaces84. That plurality of framing member connections to that node connector illustrates one form of the versatility of node connectors according to this invention.

The presence of mirror support outriggers100in frame50illustrates another form of the versatility of this invention's node connectors, namely, the ability of the node connectors to function as connectors for elements which are auxiliary to but not part of the relevant space frame as such.

FIGS. 23 and 24show a plurality of mirror support tubes99, disposed on parallel lines along the length of the frame, connected either directly to frame50or to inverted U-clips98which are connected to the frame. The mirror support tubes99preferably are aluminum extrusions with a cross-sectional configuration which includes a rectangle or a square with upper and lower external flanges. The mirror support tubes conform to a curved line which is, in essence, the curvature of the reverse side of concave mirror64.

FIG. 23is a top plan view of frame50with mirror support tubes mounted to it.FIG. 23is a good illustration of the benefits of using extruded or pultruded elements of constant cross-section and indefinite length as sources for node connectors of specified cross-section but of different lengths. For example, inFIG. 23there are four node connectors75carried on each of major chords58and59; on each of those chords, the node connectors are of three different lengths determined, principally, by the number of other framing members which are connected to them.

A torque arm65for mirror support frame50is shown inFIG. 25. Closely adjacent to its upper end, a large aperture102is formed through the plate for cooperation with a frame drive shaft (not shown) which can pass through that aperture to a suitable mechanism for controllably rotating the shaft. The plate provides a mechanism for connecting a frame50to such a drive shaft for movement of the frame with the shaft. Plate65also includes a smaller hole103through it below aperture102, but near the upper end of the plate, for receipt of an end of frame upper central major chord57. A cross piece104can be connected to the lower end of the plate and to define a pair of holes via which the plate can be bolted, e.g., to a coupling fitting94of frame50.

As noted above, all framing members (major chords, minor chords, struts, torsion braces, and other components) and node connectors of frame50preferably are made of the same type of aluminum. Thus, all of those frame components are affected equally by temperature changes. Also, all pinned connections in frame50preferably are defined by use of the zero-clearance shear pin technique described above. Precision fabrication of the components of frame50for field assembly, including cutting extrusions to desired lengths and the drilling (or other hole formation operations) of holes in those extrusion lengths at precise locations can be facilitated by the use of precision jigs and fixtures and the use of appropriate shop practices. As a result, frame50can be constructed to very small tolerances which produce a very rigid, comparatively lightweight, and temperature-insensitive support for mirror64which manifests essentially no deflection as the frame is turned about its mounting axis and experiences changes in the way gravity acts on the frame.

Worked skilled in the art will appreciate that the cross-sectional configurations of node connectors having chord-retaining tubular portions, such as portions70of node connectors69,74, and75, can be varied to define passages conforming to the cross-sectional shapes of non-round tubular members or of non-tubular members having standard shapes (e.g., channels) or custom shapes. Those workers also will appreciate that transverse chords, struts, and torsion braces can be square or other even-sided polygons, ovals with flats, or rolled shapes having flat and parallel exterior surfaces.

The zero-clearance shear pins described above (seeFIG. 11) can be installed, to make desired connections, either by driving them axially into place through the relevant holes in node connectors and framing members, or by turning them into place. If the pertinent framing member has its pin receiving holes formed in relatively thick-walled portions of the member, then the zero-clearance shear pin can be installed by axially driving it, as by lightly hammering on the head of the pin; the pin shank preferably is lubricated before its installation is started. However, if the framing member is a thin walled tube, e.g., driving a zero-clearance shear pin into place through those holes may produce dimpling (or other undesired permanent distortion) of the framing member in the vicinity of those holes. In that situation, the preferred procedure for installing a lubricated zero-clearance shear pin in to turn it into position, as by use of a wrench engaged with a non-round shear pin head, while applying axial force to the pin. In the latter situation, the threadless shank of the shear pin “self-threads” its way into and through the framing member holes without causing dimpling or other distortion of the framing member in ways which can reduce the force transmitting ability of the member as connected to its node connector.

A space frame, once assembled, rarely has any of its connections disassembled and removed. This invention affords the ability to disassemble and to reassemble a space frame having interconnections using zero-clearance shear pins. An example of such a disassembable space frame is scaffolding, and in such space frames (as well as others) the configuration of zero-clearance shear pin110shown inFIG. 26can be used to advantage. Pin110has a non-round head111at one end of an unthreaded round shank112, so that the pin can be driven or turned to install it in or to remove it from a pinned connection. Rather than being of constant diameter along its length (save for the presence of a circumferential clip retainer groove) as in pin40shown inFIG. 11, the shank112of pin110is of non-constant diameter. Shank112has a relatively short portion113of relatively large diameter adjacent to its head111, and a relatively longer relatively small diameter portion114along the balance of its length to a tapered distal end115of the pin. A circumferential clip retainer groove116is formed in shank position114near the distal end of the shank. Preferably, the intersections of the groove walls with the shank's cylindrical surface are chamfered, as at117, to make easier the insertion and removal of pin110into and from thin-wall framing members. It will be apparent that use of pin110requires that the pin receiving holes in the end of a framing member be of different diameters, one having a diameter equal to the larger diameter of the pin and the other having a smaller diameter equal to the smaller diameter of the pin. The difference between the larger and smaller diameter of pin shank112preferably is slight (e.g., on the order of 0.015 inch) so that the shear resisting capacity of the pin is not meaningfully reduced in its smaller diameter portion, and so that the bearing area of the pin for a framing member connected by it is not meaningfully reduced. An advantage of pin110is that its small diameter shank portion does not encounter a receiving hole of that diameter, in the course of being installed, until about the same time as the large diameter portion of the shank encounters a receiving hole of that larger diameter. Installation of the pin to make a pinned connection is easier and faster. Also, in removing the pin from a zero-clearance pinned connection, both pin shank portions become free from their receiving holes at substantially the same time, making pin removal easier and faster. A further benefit is the pin shank and the pin receiving holes in framing members are subjected to significantly reduced episodes of wear of the pin and holes which can cause their effective sizes to change as pinned connections are repeatedly made and disassembled over time. Thus, the benefits of zero-clearance pinned connections can be achieved over longer times in scaffolding and ethef in space frames which are subject to disassembly and reassembly.

Overall weight of a DLG-type space frame often is a significant design problem, especially where the frame is to be subject in use to significant loads, static or dynamic. The use of thin wall framing members suggests itself as a solution to the weight problem. However, where framing members can be subject to meaningful axial loads and pinned connections are to establish framing member interconnections, the use of thin wall framing members can be problematic and troublesome. The reason is that thin wall tubular framing members, because of the thinness of their walls, afford only small areas of the member cross-sections for bearing against shear pins, and for transfer of axial loads in the framing member to a node connector via the shear pins. Those small bearing areas mean that axial forces in the framing member are concentrated in those small areas as they transfer from the member to the shear pin, and that stresses in the members are highest in those areas. Those stresses can reach sufficiently high levels that the framing member crumples, tears or otherwise very adversely deforms at its pin receiving holes, thereby enlarging the effective diameter of those holes. Enlargement of the diameter of a shear pin receiving hole in a framing member of the space frame has the effect of changing the working length of the member, and that means that the member no longer can carry or transmit the loads applied to it in the space frame. That, in turn, causes other framing members in the space frame to be subjected to increased loads, which can cause their pin receiving holes to enlarge as those other framing members tear or crumple at those holes. The result can be a catastrophic failure of the space frame.FIG. 27 and 28depict a solution to the problem of the use of thin wall tubes as framing members in reduced weight space frames.

FIG. 27is a transverse cross-sectional elevation view of a non-round (oval) thin wall structural tube120, preferably an extrusion. Over most of its circumference, tube120has a relatively small wall thickness t1. Tube120has orthogonally related (perpendicularly oriented) axes of symmetry X-X and Y-Y (or X and Y axes). The tube dimension along the Y axis is less than its dimension along the X axis. The tube cross-sectional shape is arranged so that the tube has opposite walled flat exterior surface portions121which are centered on and extend across the member's Y axis and are parallel to axis X, and in the width of each of those surface portions121the wall thickness of the framing members is increased (preferably inwardly) to thickness t2. That is, the spacing of the inner surface of the tube from its outer surface increases from t1to t2across the width of each surface portion121. As a result, tube120has increased bearing areas against a shear pin passing through pin receiving holes122formed through the tube in alignment with the Y axis. The increased bearing areas means that the tube can carry and transmit to the shear pin axial loads in the tube of magnitude greater than would cause a tube having uniform wall thickness t1to crumple or tear at holes122.

In tube120, zones121of increased wall thickness extend along the entire length of the tube. It will be apparent that if the tube were defined with uniform wall thickness around its circumference, the section modulus of the tube (and its resistance to bending) about the tube's Y axis would be greater than the section modulus of the tube (and its resistance to bending) about the tube's X axis. It is also apparent that, because the wall thickness of tube120is increased in the portions of the tube's circumference where the exterior surfaces of the tube are flat and parallel to the tube's X axis, tube120has a section modulus about the X axis which is greater than the X axis section modulus of a tube of the same exterior contour and dimension having uniform wall thickness t1about its circumference, and so tube120is more resistant to bending about the X axis than such comparable tube of uniform wall thickness t1. Thus, it will be apparent that by adjustment of the widths of tube zones121and the difference between tube wall thickness t1and t2, tube120can be defined to have a section modulus about the X axis which is equal to the tube's section modulus about the Y axis, so that the tube's structural performance abilities in bending are essentially the same as those of a round tube having a diameter equal to the X axis dimension of tube120and having uniform wall thickness t1. The thin wall tube120has enhanced ability to carry and transmit axial loads (tension or compression) because of its increased wall thickness at holes122. Tube120also has enhanced column properties (notably resistance to buckling when subjected to compressive loads) because of its enhanced section modulus about its X axis. These benefits are obtained with minimal increase in the weight of the tube over one of uniform wall thickness t1because the adjustments to wall thickness are made in small sections of the tube circumference where they are most effective. The presence of oppositely facing aligned, flat areas in the exterior of tube120adapts tube120to effective use in node connectors of this invention because those flat tube surfaces can register closely with facing flat surfaces of a node connector where the tube can be pinned to the node connector. The ability to use thin wall tubes, modified according to the principles illustrated inFIG. 27, in a space frame having pinned connections means that the weights of framing members (major chords, minor chords, struts, torsion braces, and the like) in such frames can be reduced without reducing the load carrying capacity of the frame. Reductions in the weight of space frame components produce reductions in the costs of the frame components.

FIG. 28is a transverse cross-section view of another non-round (rectangular) thin wall structural tube125which has its wall thickness increased to t2from t1in central zones126of its greater dimension (width along the tube's X axis, as compared to its height along the Y axis.) The increased wall thickness preferably is manifested in the inner surfaces of tube125. Shear pin receiving holes127are formed through the tube walls in its zones of increased wall thickness, preferably centered on the Y axis, adjacent each end of the tube so that the tube can be pinned to a node connector according to this invention in a space frame of reduced weight. Tube125, like tube120, can be used to define a major chord, a minor chord, a strut, or other component of the frame. Tube125can be defined to have equal section moduli about its X and Y axes, if desired, or unequal adjusted section moduli if that should be desired.

The node connectors69,74and75shown inFIGS. 6,8and10have tubular base portions70defining passages71which fully encircle the round tubular chords with which they cooperate. While it is desirable that the cross-sectional configuration of a node connector be such that, upon slidable insertion of a chord member into the connectors chord receiving passage, the connector and the chord member cooperate so that the chord member is held in the connector with its axis substantially aligned with the passage axis, that objective can be attained by a suitably designed node connector having a passage which does not fully circumferentially enclose the chord member. That is, the node connector's chord receiving passage need not fully enclose the chord member circumferentially in order that the node connector can receive the chord member from moving sideways in the node connector. That aspect of this invention is illustrated inFIGS. 29,30, and31.

FIG. 29is a transverse cross-section view of a node connector130which cooperates with a tubular chord member131of non-round cross-section. Chord member131is predominantly round in cross-section but has a lateral outward projection132which subtends about 90° of the circumference of the otherwise round chord member. The projection is comprised by a pair of short parallel outwardly extending flanges133which connect to the opposite ends of a flat web or bridge134. The cross-section of the chord member is symmetrical about a plane through the axis (center of curvature) of the round portion of the chord tube and perpendicular to the plane of the bridge at the mid-length of the bridge. The cross-sectional configuration of the preferably extruded node connector130has a base portion of tubular nature defining a passage135which is sized and shaped so that, upon insertion of chord member131endwise into the passage, the passage surfaces cooperate closely with the outer surfaces of flanges133and the round major portion of the chord adequately to hold the chord in the connector in the desired way. Thus, the node connector has spaced parallel outwardly extending ribs136which cooperate with the outer surfaces of projection flanges133, but between those ribs the passage has a lateral opening from it along its length to accommodate the chord member projection132. The ends of ribs136lie in the plane of the top of projection132when the node connector and the chord member are engaged with each other.

The node connector130can be secured rigidly to chord member by passing shear pins through them adjacent to and parallel to the bottom of the chord member's bridge133. Alternately, as shown inFIG. 29, the connection of the node connector to the chord member can be made by engaging bolts138through holes in the node connector ribs into tapped holes in the chord member flanges131.

Node connector130and chord member131can be components in the upper layer of a classic flat DLG space frame of the kind shown inFIG. 1, as in an application of the space frame where the frame is to support decking or a roof arrangement. In that application, the chord member, due to its upward projection132along its length, has enhanced resistance to bending and so has properties akin to that of a beam. For use in such an application, outwardly extending elements (flanges)77present along the length of the node connector can define pairs of facing spaced parallel flat surfaces140,141,142and143for receiving transverse chords and struts of the frame. In each pair of surfaces, the facing surfaces can be equidistant from opposite sides of a center plane which includes the axis of passage135. Surfaces140and141are parallel with respective ones of them coplanar; those surface pairs can receive and have pinned to them the adjacent ends of two co-linear transverse chords of the space frame. Surfaces142and143are angled out and down from each other; the elements defining those surface pairs can receive and have pinned between them ends of struts (two per surface pair) which interconnect to four different nodes in the other (bottom) layer of the space frame.

FIG. 30is a cross-section view of a node connector139which is a variant of node connector130and of a chord member131. It was noted above that node connector130has a plane of symmetry, namely a plane vertically through the center of curvature of the round portion of passage135as node connector130is depicted inFIG. 29. The variation of node connector139upon node connector130is that both have essentially the same cross-sectional configuration, but connector139is defined by two identical parts139A and139B which are connected together at the vertical plane of symmetry of connector139. To enable parts139A and139B to be bolted together, as by bolts140, each of parts139A and139B has an exterior flange or rib141, from which one of elements77is carried, having a mating surface on the plane of symmetry of the assembled connector139and in which holes for bolts140are formed. Because parts139A and139B are identical in cross-section, they can be made from a common extrusion. The two-part node connector139, e.g., is advantageous if the total cross-sectional area and dimension of the overall connector is large; there is a limited number of large extrusion presses in the world, and the two-part nature of connector139means that extrusions for use in its construction can be made on smaller extrusion presses of which there are many.

FIG. 31is a cross-section view of a node connector145and a tubular chord member146which cooperate with each other; connector145is a modest variant of connector139, and chord member146is a modest variant of chord member131. The difference between the cross-sectional configurations of chord members131and146is that chord member146includes an external radial rib148along its length. The rib is centered on the plane of symmetry of the chord member. The difference between identical parts145A and145B of connector145relative to the parts139A and149B of connector139is that the ribs149of parts145A and145B are defined to mate with the opposite faces of chord member rib148rather than with each other. Because of the presence of its external rib148, chord member146has enhanced beam properties over chord member131.

Comment was made above that a variant of node connector130(FIG. 29), in which the passage through the length is a round circumferentially closed passage, can be used in the construction of a classic square frame (seeFIG. 1) in which the longitudinal major chords are round and other framing members can be square, oval with external flats, or otherwise consistent with the preceding descriptions. Such a variant of node connector130can be used to define the “free form” or laterally curved DLG space frame150shown inFIGS. 32(top plan view) and33(side elevation view), simply by making the upper and lower transverse chords151and152round and continuous through at least some of the frame nodes (splices may be needed) and by making the upper and lower longitudinal chord members153and154square and of lengths corresponding to the distance along a longitudinal chord line between adjacent nodes. The existence of an ability to construct such a laterally curved DLG space frame is shown byFIG. 33, a side elevation of such a frame, in which struts lie in diagonal planes extending across the width of the frame. The planes of the strut receiving surfaces142and143of such a node connector so disposed in the frame would be parallel to transverse chord lines, all of which are straight and uniformly spaced from each other along the length of the frame. Struts155connect between upper nodes156and lower nodes157. Struts connected to a given node can have unequal lengths to accommodate the lateral displacements of adjacent transverse chord members needed to produce the laterally curved plan shape of the frame shown inFIG. 32.

41It is apparent, therefore, that a node connector according to this invention, in which the parallel surfaces between which struts and discontinuous chord members are connected are surfaces which are parallel to the length of the passages in which a continuous chord member is received, is a node connector which can be used in a variety of differently configured DLG space frames, including frames which have uniform bay spacing longitudinally and transversely, space frames which have variable bay spacing longitudinally or transversely, and space frames in which longitudinal or transverse chord members are shifted laterally of each other as shown inFIG. 32.

Many benefits and advantages are afforded by this invention and its aspects and features described above. The node connectors enable certain chords of a DLG space frame to extend continuously though them. The node connectors can be used with space frame framing members of substantially any cross-sectional configuration desired; they are not limited to use with members having round or rectangular cross-sections. Node connectors and framing members can be extruded for low cost and dimensional precision. Node connectors and framing members can be made of materials having uniform metallurgical properties so that, among other benefits, space frames incorporating them are little affected dimensionally by temperature changes. The node connectors enable framing members of differing numbers, size and cross-sectional configuration to be effectively interconnected at a given node in a space frame. The node connectors can be defined to enable good, even ideal, positioning and alignment of framing members at a space frame node so that there are minimal or no eccentricities of framing member axes relative to each other at a node. The node connectors enable convenient use of variable bay spacing in a space frame, enabling the overall frame to efficiently carry design loads. The node connectors can be defined to provide interconnections between framing members in a diverse range of positions and numbers, thus enabling the use of DLG design and construction principles in more complex structures including non-static (movable) structures for electromagnetic radiation focusing applications such as movable mirror or reflector support armatures in solar power generation facilities and in radio and optical telescopes. Use-specific elements can be accommodated in space frames, such as mountings for solar reflectors, torque members, and other supports and accessories.

The zero-clearance shear pin connection aspects of this invention enable precision connections in space frames to be easily and inexpensively made, while also enabling other frame components to correctly perform assigned load carrying functions. Such connections can be disassembled and reassembled plural times while retaining desired levels of precision and tightness. The shear pins can be driven or turned into and out of installed positions in other members. Also, as explained with references toFIGS. 27 and 28, aspects of this invention enable minimum weight framing members to have enhanced axial load transmitting capabilities in pinned connections. The invention also enables a tubular structural element which is asymmetrical in X and Y directions to have equal (or other desired tailored) section moduli about those axes, thereby enabling weight saving thin wall tubes to be used to increased advantage in space frames.

The foregoing descriptions of depicted and other aspects of this invention are to be read as illustrative explanations to persons having skill in the relevant arts and technologies, not as an exhaustive catalog of all structural and procedural forms in which the invention can be embodied or used to advantage. Variations of the described structures and procedures can be used without departing from the fair scope of the invention.