U.S. patent application number 11/978859 was filed with the patent office on 2008-03-27 for tubular structural member with non-uniform wall thickness.
Invention is credited to Gary N. Curtis, Dean R. Hackbarth, Glenn A. Reynolds.
Application Number | 20080072516 11/978859 |
Document ID | / |
Family ID | 38626850 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080072516 |
Kind Code |
A1 |
Reynolds; Glenn A. ; et
al. |
March 27, 2008 |
Tubular structural member with non-uniform wall thickness
Abstract
A tubular structural member has substantially constant
cross-sectional size and configuration along its length between its
opposite ends. The member has a pair of parallel oppositely aligned
flat areas in its exterior surface. The member has substantially
uniform wall thickness except in a selected portion of each the
opposing areas where the member's wall thickness is a selected
amount greater than the uniform wall thickness. The increase wall
thickness preferably is manifested in the interior of the tubular
member. The cross-sectional area of the member can have orthogonal
neutral axes, and the exterior dimension of the member along one of
those axes can be greater than the exterior dimension of the member
along the other of those axes which is normal to the exterior flat
areas; the amount and distribution of the thickening of the
member's walls over the uniform thickness can be defined to cause
the section modular of the member about each of the neutral axes to
be substantially equal.
Inventors: |
Reynolds; Glenn A.; (Long
Beach, CA) ; Hackbarth; Dean R.; (San Pedro, CA)
; Curtis; Gary N.; (Anacortes, WA) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
38626850 |
Appl. No.: |
11/978859 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11525721 |
Sep 22, 2006 |
|
|
|
11978859 |
Oct 29, 2007 |
|
|
|
Current U.S.
Class: |
52/694 |
Current CPC
Class: |
E04H 12/00 20130101;
E04B 2001/1936 20130101; E04B 1/19 20130101; E04B 2001/1984
20130101; F24S 25/13 20180501; E04B 2001/1933 20130101; E04C
2003/0495 20130101; F24S 25/00 20180501; H01Q 15/18 20130101; Y02E
10/47 20130101; E04B 2001/199 20130101; E04B 1/1903 20130101; E04B
2001/1975 20130101 |
Class at
Publication: |
052/694 |
International
Class: |
E04C 3/02 20060101
E04C003/02 |
Claims
1. A straight tubular structural member of substantially constant
cross-sectional size and configuration along its length and having
a pair of parallel oppositely aligned flat areas in its exterior
surface, the tubular member having substantially uniform wall
thickness except in a selected portion of each of the opposing
areas where the wall thickness is a selected amount greater than
the uniform wall thickness.
2. A structural member according to claim 1 in which the
cross-sectional area of the member has orthogonal neutral axes, the
exterior dimension of the member along one of the axes being
greater than the exterior dimension of the member along the other
axis which is normal to the exterior flat areas.
3. A structural member according to claim 2 in which the amount and
distribution of thickening of the member walls to be greater than
the selected wall thickness is defined to cause the section modulus
of the member with respect to the one neutral axis to be
substantially equal to the section modulus of the member with
respect to the other neutral axis.
4. A structural member according to claim 3 in which the
cross-sectional shape of the member is rectangular.
5. A structural member according to claim 3 in which the
cross-sectional shape of the member is substantially oval.
6. A structural member according to claim 1 in which the increase
in wall thickness over the uniform thickness is manifested in the
interior of the tubular member.
7. A structural member according to claim 1 including a respective
one of a pair of aligned holes defined through the member wall in
each of the selected portions of greater wall thickness at least at
one of two opposite ends of the member.
8. A structural member according to claim 1 in which the holes of
at least one of the hole pairs are round and one of the holes of
that pair is of greater diameter than the other hole of that pair.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a division under 35 U.S.C. .sctn. 120 of
co-pending application Ser. No. 11/525,721 filed Sep. 22, 2006, and
claims the priority of only that Application and not the priority
of any application filed before application Ser. No.
11/525,721.
FIELD OF INVENTION
[0002] This invention pertains to tubular structural members. More
particularly, it pertains to tubular structural members having
non-uniform wall thickness having particular utility in pinned
connections.
BACKGROUND OF THE INVENTION
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] The solution to the existence of (or potential for)
differences between actual and design framing member loads is to
make the framing members heavier.
[0010] 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
[0011] The invention beneficially addresses the needs identified
above. It does so by providing structural arrangements and are
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.
[0012] Not used.
[0013] Not used.
[0014] This invention provides a tubular structural member which
has substantially constant cross-sectional size and configuration
along its length between its opposite ends. The member has a pair
of parallel oppositely aligned flat areas in its exterior surface.
The tubular member has a substantially uniform wall thickness
except in a selected portion of each of the opposing 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 member in each of the selected
portions of greater tube wall thickness at least at one of the ends
of the member.
[0015] Not used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The previously mentioned and other aspects of this
invention, and benefits, features and advantages of them, are more
fully described and noted in the following detailed descriptions
made with reference to certain structural and procedural
embodiments of the invention which are depicted in the accompanying
drawings in which:
[0017] FIG. 1 is a perspective view of a double layer grid (DLG)
space frame of indeterminate length and which has constant square
bay spacing;
[0018] FIG. 2 is a perspective of a simple DLG space frame, in the
nature of a triangular truss, which has variable bay spacing;
[0019] FIG. 3 is a perspective view of a node connector for the
space frame shown in FIG. 2;
[0020] FIG. 4 is a fragmentary end elevation view of the node
connector of FIG. 3 with connections of framing members to it in
the construction of the space frame shown in FIG. 2;
[0021] FIG. 5 is an end elevation view of a more complex DLG space
frame which is a movable support armature for a curved mirror and
is useful in a solar power generation installation;
[0022] FIG. 6 is an end view of a first node connector
configuration useful in the DLG shown in FIG. 5;
[0023] FIG. 7 is a perspective view of the node connector of FIG.
6;
[0024] FIG. 8 is an end view of a second node connector
configuration useful in the DLG shown in FIG. 5;
[0025] FIG. 9 is a perspective view of the node connector of FIG.
8;
[0026] FIG. 10 is an end view of a third node connector
configuration useful in the DLG shown in FIG. 5;
[0027] FIG. 11 is an elevation view of a shear pin useful in making
connections of space frame framing members to node connectors in
the practice of aspects of this invention;
[0028] FIG. 12. is a plan view of a known style of clip retainer
useful with the shear pin of FIG. 11;
[0029] FIG. 13 is a perspective view illustrating a first step in
the construction of the DLG of FIG. 5;
[0030] FIG. 14 is a perspective view illustrating a second step in
that same construction process;
[0031] FIG. 15 is a perspective view illustrating a third step in
that same construction process;
[0032] FIG. 16 is a perspective view illustrating a fourth step in
that same construction process;
[0033] FIG. 17 is a perspective view illustrating a fifth step in
that same construction process;
[0034] FIG. 18 is a perspective view illustrating a sixth step in
that same construction process;
[0035] FIG. 19 is a perspective view illustrating a seventh step in
that same construction process;
[0036] FIG. 20 is a perspective view illustrating an eighth step in
that same construction process;
[0037] FIG. 21 is a perspective view illustrating a ninth step in
that same construction process;
[0038] FIG. 22 is a perspective view illustrating a tenth step in
that same construction process, substantial parts of the previously
assembled space frame being deleted from FIG. 22 for enhanced
clarity of depiction of structure being added by step ten;
[0039] FIG. 23 is a top plan view which illustrates an eleventh
step in that same construction process;
[0040] FIG. 24 is a fragmentary end elevation view of a portion of
the structure shown in FIG. 23;
[0041] FIG. 25 is a perspective view of one of the two pivot
(torque transfer) arms which are components of the mirror support
armature of FIG. 5;
[0042] FIG. 26 is an elevation view of another shear pin useful in
the practice of aspects of this invention;
[0043] FIG. 27 is a cross-sectional elevation view of a DLG framing
member according to an aspect of the invention;
[0044] FIG. 28 is a cross-sectional elevation view of another DLG
framing member which uses the same design principles on the framing
member shown in FIG. 27;
[0045] FIG. 29 is a cross-sectional view of another node connector
according to the invention in which the connector's chord receiving
passage is not fully closed but is sufficiently closed that the
cooperation of the connector with a chord inserted axially into it
holds the chord so that its axis is aligned with the passage axis
and the chord can move only axially in the passage;
[0046] FIG. 30 is a cross-section view of a further node connector
which is a variant of the node connector shown in FIG. 29, the
variation being that the node connector is defined by two identical
parts, which preferably are extrusions, secured to each other and
to a frame chord;
[0047] FIG. 31 is a cross-section view of a still further node
connector according to the invention which is a variant of the node
connector shown in FIG. 30 and in which the chord includes an
external radial rib through which passes a bolt securing the
connector parts to each other and to the chord;
[0048] FIG. 32 is a schematic plan view of a "free form" DLG space
frame which can be constructed using node connectors according to
this invention; and
[0049] FIG. 33 is an elevation view taken along line 33-33 of FIG.
32.
DETAILED DESCRIPTION OF THE INVENTION
[0050] FIG. 1 is a perspective view of a portion of a rectilinearly
subdivided DLG space frame 10. Frame 10 is composed of framing
members which are disposed to define top 11 and bottom 12 layers of
the frame and to interconnect those layers in an arrangement which
causes frame layers 11 and 12 to be in spaced parallel relation to
each other. Layers 11 and 12 can also be called grids, hence the
name double layer grid (DLG) for the type of space frame shown in
FIG. 1.
[0051] The framing members of DLG 10 are comprised by chords which
are interconnected to define top and bottom layers 11 and 12 of the
DLG which has an end 13 and opposite sides 14 and 15. 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, DLG 10
includes upper major chords 16 and lower major chords 17. In each
layer of DLG 10, the upper and lower major chords are
interconnected and spaced by upper 18 and lower 19 transverse 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 DLG 10 are 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, DLG 10 has
upper nodes 20 and lower nodes 21. 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 nodes 20 and the lower nodes 21 are 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 frame 10 also define square
bays. Thus, consistent with the foregoing, DLG 10 has constant
square bay spacing.
[0052] 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.
[0053] Chords 16 and 18 of DLG 10 can be said to be in (or to
define) a top surface of the DLG; similarly, chords 17 and 19 are
in (define) a bottom surface of the DLG. The top and bottom
surfaces of DLG 10 are parallel.
[0054] The top and bottom layers of DLG 10 are spaced from and
supported relative to each other by further diagonal framing
members 22 called struts each of which extends between a top layer
node 20 and a bottom layer node 21. 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 nodes 21
are located vertically below the centers of the square openings
defined by the chords of the upper grid; upper nodes 20 are 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 frame 10.
As shown in FIG. 1, within the boundaries of the frame, there are
four struts 22 connected to each upper node 20 and to each lower
node 21. 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 frame 10, there are two
struts 22 connected to each upper node 20, and the frame end and
side surfaces (strut planes) slope down and inwardly between the
top and bottom surfaces of the frame.
[0055] In the classic frame 10 shown in FIG. 1, there are fewer
squares in bottom layer 12 than there are in top layer 11. As frame
10 is depicted in FIG. 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.times.n/5.times.(n-1) in
which 6.times.n denotes a top grid 6 bays wide by n bays long, and
the notation 5.times.(n-1) denotes a bottom grid 5 bays wide by
(n-1) bays long.
[0056] The description of frame 10 to 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.
[0057] FIG. 2 is a perspective view of a DLG-type space frame 25 in
the form of a truss of inverted equilateral triangular
cross-section. Using the notation described above, frame 25 is a
1.times.8/0.times.0 DLG frame. Frame 25 has two upper major chords
26 and one lower major chord 27, all of which extend along the full
length of the frame.
[0058] FIGS. 3 and 4 show a node connector 28 of frame 25. Because
the cross-sectional configuration of frame 25 is that of an
equilateral triangle, a single basic node connector configuration
can be used at all nodes in the frame. The framing members of frame
25 preferably 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
extrudible aluminum alloy, and the framing members preferably are
extruded aluminum tubes. Also, the node connectors 28 preferably
are defined by extrusions of the same aluminum alloy.
[0059] FIG. 4 shows the pinned connection of two struts 30 to a
node connector 28 which has a pinned connection to lower chord 27;
a connection of struts to a node connector on either of the upper
major chords would have substantially the same appearance as shown
in FIG. 4 except that the upper major chords actually are turned
about their longitudinal axes--visualize that FIG. 4 is rotated
60.degree. in either direction.
[0060] Node connector 28 has a chord-receiving base channel portion
31 which has a flat base 32 and two parallel spaced flanges 33
perpendicular to the base. The spacing between opposing faces of
flanges 33 is slightly greater than the exterior width of a major
chord, and the height of the flanges from the base 31 preferably is
equal to the height of a major chord. Node connector 28 also
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) 34 which define two
pairs of parallel spaced opposing and substantially flat surfaces
35 and 36. Surfaces 35 and surfaces 36 are spaced a distance which
is slightly greater than the width of the extrusion from which the
struts, minor chords and torsion braces of frame 25 are defined.
Further, surfaces 35 are spaced parallel to and equally from
opposite sides of a plane 37 which passes through the structural
neutral axis of bottom chord 27 as received in and secured in the
channel portion 31 of node connector 28 as shown in FIG. 4. Because
chord 27 is 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, surfaces 36 are spaced parallel to and
equally from opposite sides of a plane 38 which passes through the
neutral axis of chord 27 as received and secured in node connector
28. Thus, regardless of the angularity of a strut 30, 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 flanges 34 are 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.
[0061] Node connector 28 preferably is doubly pinned to chord 27 by
use of shear pins 40 and clip retainers 41 as depicted in FIGS. 11
and 12. Double pinning of the connector to chord 27 provides 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 connector 28 to be
doubly pinned to chord 27, the connector has two sets of shear pin
holes 42 formed through channel portions flanges 33 at spaced
locations along the length of the connector. The two holes 42 in
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
chord 27 as secured in node connector. Similar shear pin holes are
formed through the walls of chord 27 on a line perpendicular to the
chord's length and passing, preferably, through the neutral axis of
the chord. If the length of truss 10 exceeds the length at which
chords 26 and 27 can be obtained or conveniently handled, node
connectors 28 can 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.
[0062] In like manner, shear pin holes 43 are formed through node
connector flanges 34 for each other framing member which is to be
connected to that node connector in completed frame 25. In this
instance, because each other framing member is simply (singly)
pinned to the node connector, one hole 43 per each framing member
to be connected to the connector is formed in each relevant flange
34, and the two holes in the coacting flanges are centered on a
line which is perpendicular to flange surfaces 35 or 36. 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.
[0063] As shown in FIG. 2, upper major chords 26 and lower chord 27
of frame 25 are of equal length; compare the different lengths of
major chords 16 and 17 in frame 10 shown in FIG. 1. Upper major
chords 26 are located in spaced parallel relation to each other by
minor chords 44 which are parallel to each other and perpendicular
to the major chords, and so the upper major chords mount (as
described above) node connectors 28 at their ends and at opposed
locations spaced along their lengths. To afford connection points
for the diagonal struts 30 in frame 10, node connectors 28 are
fixedly mounted to lower chord 27 at locations between the ends of
that chord which are, respectively, midway along the distance
between corresponding upper minor chords 44. Also, to accommodate
the mounting of frame support fittings 45 to the opposite ends of
frame 25, an end node connector 28 is fixedly mounted to each end
of lower chord 27.
[0064] As to each of node connectors 28 located between, rather
than at, the ends of lower chord 27, four struts 30 are pinned to
each connector; two of those struts have their ends snugly yet
movably received between surfaces 35 of the connector so that the
opposing flat exterior surfaces of the strut substantially register
with surfaces 35, and another two of those struts have their ends
snugly yet moveably received between surfaces 36 of the connector
so that the opposing flat exterior surfaces of those struts
substantially register with surfaces 36. The ends of struts 30 are
pinned to the connectors 28 with which they cooperate by use of
shear pins 40 passed through the strut-end holes and through holes
43 of the connector. All shear pins are held in place by connection
of clip retainers 41 to the pins; each retainer cooperates with its
pin in a circumferential recess (groove) 47 defined in the round
pin shank adjacent a distal end of the pin which is opposite from
an enlarged head 48 at the other end of the pin. Two struts 30 are
connected from the node connector at each end of lower chord 27 to
a corresponding frame end connector at the adjacent ends of upper
major chords 26; see FIG. 2.
[0065] Further, to make frame 25 stiff against torsional or
wracking loads imposed upon it in use, frame 25 includes a torsion
brace framing member 49 in each bay of the frame; a bay of frame 25
is the opening bounded by the upper major chords 26 and two
adjacent upper minor chords 44. 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 surfaces 35 or 36 of each affected node connector between
which an end of an upper minor chord 44 is similarly pinned. In the
portion of frame 25 between its end bays, the torsion braces 49
alternate in the directions in which they are skewed to the length
of the frame.
[0066] Attention is drawn to the node connectors denoted 28' and
28'' in FIG. 2; they are at the opposite ends of a single upper
minor chord 44. In addition to being associated with an upper major
chord 26, connector 28' has associated with it two struts 30, an
upper minor chord 44, and two torsion braces 49. Struts 30 can be
received between surfaces 35 of connector 28' and framing members
44 (one) and 49 (two) can be received between surfaces 36 of that
connector. By contrast, node connector 28'' has associated with it
an upper major chord, a minor chord 44, and two struts 30. To
accommodate those differences in the number of connections to them,
connector 28' has a length greater than that of connector 28'' by
an amount adequate to accommodate the ends of three framing members
between surfaces 36 of connector 28'. That connector length
difference is easily handled by making connector 28' from a longer
length of the connector extrusion than the length of the extrusion
section used made connector 28'', and by drilling three sets of
holes 43 through the flanges forming surfaces 35 rather than one
set of such holes.
[0067] It is a feature of frame 25 that all of the shear pin holes
formed in each node connector 28 have 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 frame 25 also
have the same design (also preferably actual) diameter as the shank
diameter of the shear pins used to pin them to node connector 28.
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 frame 25 can 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 frame 25 and
correspondingly lighter framing members can be used than if the
frame connections have play or looseness, without compromising
safety or structural adequacy.
[0068] An inspection of FIG. 2 will reveal that it has 8 bays along
its length, i.e., 8 intervals between 9 spaced upper minor chords
44. Such inspection of FIG. 2 will 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,
frame 25 has variable bay spacing; bay spacing in frame 25 can 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 connectors 28 as 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 connectors 28 because, in all of the
node connectors, the elements of the connectors which define
surfaces 35, 36 are 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 frame 25
by varying the lengths of struts 30 and of torsion braces 49 as
needed.
[0069] It is preferred that the node connectors and framing members
of frame 25 be 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 frame 25 is 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.
[0070] However, it is within the scope of this invention that the
node connectors and framing members of frame 25, 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.
[0071] Regarding frame 25, 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 connectors 28 can 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
connectors 28 in which the central planes between surfaces 35 and
36 intersect each other at a 90.degree. angle rather than a
60.degree. 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.
[0072] FIG. 5 is an end view of another space frame 50 according to
this invention. Frame 50 is a double layer grid (DLG) frame which
has a flat bottom surface defined by two bottom major chords 51, 52
and bottom minor chords 53 which extend transversely of those major
chords. The upper surface of frame 50 is 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 planes 54, 55 which
intersect at the axis of an upper central major chord 57. Two upper
outer major chords 58, 59 are located equidistantly from and on
opposite sides of center chord 57 and lie, respectively, in planes
54 and 55. Upper center major chord 57 is positioned centrally
above and parallel to bottom major chords 51, 52 by central struts
60 of equal length. Each of upper outer major chords 58, 59 is
positioned relative to the upper central major chord and to the
adjacent bottom major chord by upper minor chords 61 and by struts
62 which are longer than central struts 60. The major chords of
frame 50 preferably 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 frame 50 are
interconnected.
[0073] The intended use of frame 50 is as a movable support
armature for an elongate preferably cylindrically curved mirror 64
in a solar power generation facility; the position of a mirror 64
relative to the frame is shown in FIG. 5. To enable the frame to
serve in that capacity, the frame is designed and constructed to
carry a mounting and torque transmitting arm 65 at each of its
ends, and to carry supports 66 for 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 at 67 in
arms 65.
[0074] In light of the foregoing descriptions of truss frame 25 and
its node connectors 28, it will be apparent that frame 50 includes
three styles of node connectors which cooperate respectively with
bottom major chords 51, 52, with upper center major chord 57, and
with upper outer major chords 58, 59. Those three styles of node
connectors are shown, respectively, in FIGS. 6 and 7, in FIGS. 8
and 9, and in FIG. 10.
[0075] Bottom major chord node connectors 69 have the
cross-sectional configuration shown in FIG. 6. Unlike node
connectors 28 in frame 25, node connectors 69 are configured for
cooperation with a major chord framing member which is defined in
the form of a round tube. A node connector 69 has a brace
circularly cylindrical chord engaging portion 70 which defines a
round circumferentially closed passage 71 which extends along the
length of the connector. The diameter of passage 71 is slightly
greater than the outer diameters of the bottom major chords of
frame 50 so 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 holes 72, aligned on a diameter
of passage 71, 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 connectors 69, as well
as upper central node connectors 74 (FIGS. 8 and 9) and upper outer
chord node connectors 75 (FIG. 10) of frame 50, are sufficiently
similar to node connectors 28 that, in view of the content of FIGS.
6-10, extended descriptions of frame 50's node connectors are not
needed for an understanding of them by a person skilled in the
art.
[0076] Therefore, briefly noted, each of major chord node
connectors 69, 74 and 75 carries along its length and externally of
its tubular chord engaging base portion 70 a plurality of fixed
structural elements 77 which define plural pairs of parallel spaced
opposing substantially flat surfaces 78, 79, 80 (FIG. 6 as to
connector 69), 81, 82, 83, 84 (FIG. 8 as to connector 74), and 85,
86 and 87 (FIG. 10 as to connector 75). The facing ones of surfaces
78-87 afford snug yet movable registration with oppositely facing
flat exterior surfaces of the minor chords and other framing
members of frame 50 upon insertion of ends of those framing members
between those facing surfaces as frame 50 is assembled (see FIGS.
13-24). Aligned pairs of holes 89 are formed through elements
(flanges) 77 at 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 frame
25.
[0077] FIGS. 6, 8 and 10 show that certain ones of flanges 77 can
be branched at their outer ends in order to define facing surface
pairs 78-87 in 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 passage 71 and
the neutral axis of the round tubular major chord received in that
passage.
[0078] That is, in the node connector shown in FIG. 6, the
connector elements 77 which define adjacent ones of surfaces 78 and
79, and which define adjacent one of surfaces 79 and 80, are not
connected directly to the exterior of tube portion 70. Instead they
are carried at the ends of ribs which are connected directly to the
exterior of tube portion 70. 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 passage 71 of that node connector. The
movement of the shear pin locations outwardly from the tube portion
of the node connector is not a disadvantage.
[0079] The structure of completed frame 50 will become apparent
from an understanding of FIGS. 13-24 which depict consecutive steps
in the assembly of the frame from its component round and square
tubular framing members and its node connectors 69, 74 and 75. The
first of those steps is shown in FIG. 13. Node connectors 69 are
engaged around the preferably tubular round member which defines
bottom major chord 52 and are secured to it at the ends and the
center of that chord. Each prefabricated node connector of frame 50
can 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 in FIG. 14, three node connectors 69
are similarly engaged around and secured to bottom major chord
51.
[0080] As shown in FIG. 15, a third step in the frame assembly
process can be the mounting of five node connectors 74 in the
proper sequence on upper center major chord 57 and the pinning of
them to the chord. In that process, a plate 90 is mounted to the
chord in association with the central node connector, which plate
will later have connected to it a support 66. Note that node
connectors 74 are not uniformly spaced along chord tube 57; see
also FIG. 19 where the reason for that connector spacing is made
apparent. Fourth and fifth steps in the frame assembly process can
be the placement of node connectors 75 on each of outer central
major chord tubes 58 and 59 and the pinning of those connectors to
those tubes; see FIGS. 16 and 17.
[0081] FIG. 18 illustrates a sixth step in the frame assembly
process, namely, the interconnection of bottom major chord tubes 51
and 52 by bottom minor chords 53, torsion bracing members 92 and
additional elements of the frame, using zero-clearance shear pins
to make all connections to node connectors. The major chords 51, 52
and the minor chords 53 define two rectangular bays in the bottom
layer (surface) of frame 50. Those major chords are shorter in
length than upper major chords 57-59. 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 member 93. At each end of the bottom layer assembly, the
other ends of transversely adjacent members 93 are doubly
pin-connected or bolted (a stiff connection) to a coupling fitting
94 to which an end of a frame torque arm 65 later will be
secured.
[0082] The upper central major chord subassembly (FIG. 15) can be
connected in place relative to the bottom major chord assembly
(FIG. 18) as depicted in FIG. 19 as a seventh step in the assembly
process. Central struts 60 are pinned between the node connectors
69 on the bottom major chords and the end node connectors 74 on the
central chord, and the two other connectors 74 which are on
opposite sides of the center of upper center chord 57. Two further
framing members 95 are pinned between center node connector 74 on
upper chord 57 and the respective center node connectors 69 on
bottom chords 51, 52. Plate 90 can then be secured, as by bolting
or riveting, to the ends of members 95 which are pinned to center
node connector 74. Plate 90 can be further fixed in its desired
position by connecting braces 96 between the central part of the
plate and framing members 95 as shown in FIG. 19. The completion of
this assembly step causes torque arm connection fittings 94 to be
located substantially below the opposite ends of upper central
major chord 57.
[0083] Eighth and ninth steps in the assembly of frame 50 can be
the pinned connection of upper outer major chords 59, 58 to bottom
major chords 52, 51, respectively, via longer struts 62 and node
connectors 69 and 75. See FIGS. 20 and 21.
[0084] A tenth step in assembly of frame 50 can be the
interconnection of the upper outer major chords 58, 59 to upper
central major chord 57, and the connection of auxiliary framing
members to chords 58 and 59. Such a step is depicted in FIG. 22
which shows upper minor chord framing members 61 pinned between
center chord node connectors 74 and laterally adjacent outer chord
node connectors 75; in the interest of clarity of illustration,
frame elements located below the top of the frame are not shown in
FIG. 22. Torsion braces 92 are disposed (one in each of the six
bays defined by members 57, 58, 59 and 61) diagonally between the
chord members so that, on each side of center chord 57, the torsion
braces alternate in the ways which they are skewed relative to the
length of the frame. As connected between major chords 57, 58 and
59, upper minor chords 61 can carry inverted U-clips 98 at selected
locations along their lengths for later connection to them of
longitudinal mirror mounting tubes 99 (see FIGS. 23 and 24). Clips
98 function as risers from the flat upper surfaces of frame 50 to
conform to the curvature of the focusing reflector which the frame
supports in use. Also, square extension tubes 100 (akin to frame
outriggers) can be rigidly connected between surfaces 87 of each of
node connectors 75. Each tube 100 can carry an inverted U-clip at
its unsupported end. Thus, at each transverse station of frame 50
corresponding to the locations of upper minor chords 61, the frame
can include six clips 98 as features which facilitate the
connection of mirror 64 to the frame.
[0085] Attention is directed to node connector 74 on upper center
major chord 57 between plate 90 and the left end of the frame as
depicted in FIGS. 21, 22 and 23. In addition to major chord 57
which 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 struts 60
having end surfaces registered with node connector surfaces 81 and
82, two torsion braces 92 and one upper minor chord 61 having end
surfaces registered with connector surfaces 83, and two torsion
braces and one upper minor chord 61 having end surfaces registered
with connector surfaces 84. That plurality of framing member
connections to that node connector illustrates one form of the
versatility of node connectors according to this invention.
[0086] The presence of mirror support outriggers 100 in frame 50
illustrates 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.
[0087] FIGS. 23 and 24 show a plurality of mirror support tubes 99,
disposed on parallel lines along the length of the frame, connected
either directly to frame 50 or to inverted U-clips 98 which are
connected to the frame. The mirror support tubes 99 preferably 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 mirror
64.
[0088] FIG. 23 is a top plan view of frame 50 with mirror support
tubes mounted to it. FIG. 23 is 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, in FIG. 23
there are four node connectors 75 carried on each of major chords
58 and 59; 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.
[0089] A torque arm 65 for mirror support frame 50 is shown in FIG.
25. Closely adjacent to its upper end, a large aperture 102 is
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 frame 50 to such a drive shaft for
movement of the frame with the shaft. Plate 65 also includes a
smaller hole 103 through it below aperture 102, but near the upper
end of the plate, for receipt of an end of frame upper central
major chord 57. A cross piece 104 can 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 fitting 94 of frame 50.
[0090] As noted above, all framing members (major chords, minor
chords, struts; torsion braces, and other components) and node
connectors of frame 50 preferably 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 frame 50
preferably are defined by use of the zero-clearance shear pin
technique described above. Precision fabrication of the components
of frame 50 for 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,
frame 50 can be constructed to very small tolerances which produce
a very rigid, comparatively lightweight, and
temperature-insensitive support for mirror 64 which manifests
essentially no deflection as the frame is turned about its mounting
axis and experiences changes in the way gravity acts on the
frame.
[0091] Worked skilled in the art will appreciate that the
cross-sectional configurations of node connectors having
chord-retaining tubular portions, such as portions 70 of node
connectors 69, 74, and 75, 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.
[0092] The zero-clearance shear pins described above (see FIG. 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.
[0093] 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 disassemble space frame is scaffolding, and in such space
frames (as well as others) the configuration of zero-clearance
shear pin 110 shown in FIG. 26 can be used to advantage. Pin 110
has a non-round head 111 at one end of an unthreaded round shank
112, 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 is pin 40 shown in FIG.
11, the shank 112 of pin 110 is of non-constant diameter. Shank 112
has a relatively short portion 113 of relatively large diameter
adjacent to its head 111, and a relatively longer relatively small
diameter portion 114 along the balance of its length to a tapered
distal end 115 of the pin. A circumferential clip retainer groove
116 is formed in shank position 114 near the distal end of the
shank. Preferably, the intersections of the groove walls with the
shank's cylindrical surface are chamfered, as at 117, to make
easier the insertion and removal of pin 110 into and from thin-wall
framing members. It will be apparent that use of pin 110 requires
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 shank 112 preferably 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 pin 110 is 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 other space frames which are subject to disassembly and
reassembly.
[0094] 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. FIGS. 27 and 28 depict a
solution to the problem of the use of thin wall tubes as framing
members in reduced weight space frames.
[0095] FIG. 27 is a transverse cross-sectional elevation view of a
non-round (oval) thin wall structural tube 120, preferably an
extrusion. Over most of its circumference, tube 120 has a
relatively small wall thickness t.sub.1. Tube 120 has 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
portions 121 which 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 portions 121 the wall thickness of the framing members is
increased (preferably inwardly) to thickness t.sub.2. That is, the
spacing of the inner surface of the tube from its outer surface
increases from t.sub.1 to t.sub.2 across the width of each surface
portion 121. As a result, tube 120 has increased bearing areas
against a shear pin passing through pin receiving holes 122 formed
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 t.sub.1 to crumple or
tear at holes 122.
[0096] In tube 120, zones 121 of 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 tube 120 is 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, tube 120 has 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 t.sub.1 about its circumference, and so tube 120 is more
resistant to bending about the X axis than such comparable tube of
uniform wall thickness t.sub.1. Thus, it will be apparent that by
adjustment of the widths of tube zones 121 and the difference
between tube wall thickness t.sub.1 and t.sub.2, tube 120 can 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 tube 120 and having uniform wall thickness t.sub.1.
The thin wall tube 120 has enhanced ability to carry and transmit
axial loads (tension or compression) because of its increased wall
thickness at holes 122. Tube 120 also 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 t.sub.1
because 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 tube 120 adapts tube 120 to 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 in FIG. 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.
[0097] FIG. 28 is a transverse cross-section view of another
non-round (rectangular) thin wall structural tube 125 which has its
wall thickness increased to t.sub.2 from t.sub.1 in central zones
126 of 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 tube
125. Shear pin receiving holes 127 are 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. Tube 125, like tube 120, can be used
to define a major chord, a minor chord, a strut, or other component
of the frame. Tube 125 can 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.
[0098] The node connectors 69, 74 and 75 shown in FIGS. 6, 8 and 10
have tubular base portions 70 defining passages 71 which 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 in FIGS. 29, 30, and
31.
[0099] FIG. 29 is a transverse cross-section view of a node
connector 130 which cooperates with a tubular chord member 131 of
non-round cross-section. Chord member 131 is predominantly round in
cross-section but has a lateral outward projection 132 which
subtends about 90.degree. of the circumference of the otherwise
round chord member. The projection is comprised by a pair of short
parallel outwardly extending flanges 133 which connect to the
opposite ends of a flat web or bridge 134. 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 connector 130 has a base portion of tubular nature
defining a passage 135 which is sized and shaped so that, upon
insertion of chord member 131 endwise into the passage, the passage
surfaces cooperate closely with the outer surfaces of flanges 133
and 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 ribs 136 which cooperate
with the outer surfaces of projection flanges 133, but between
those ribs the passage has a lateral opening from it along its
length to accommodate the chord member projection 132. The ends of
ribs 136 lie in the plane of the top of projection 132 when the
node connector and the chord member are engaged with each
other.
[0100] The node connector 130 can be secured rigidly to chord
member by passing shear pins through them adjacent to and parallel
to the bottom of the chord member's bridge 133. Alternately, as
shown in FIG. 29, the connection of the node connector to the chord
member can be made by engaging bolts 138 through holes in the node
connector ribs into tapped holes in the chord member flanges
131.
[0101] Node connector 130 and chord member 131 can be components in
the upper layer of a classic flat DLG space frame of the kind shown
in FIG. 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 projection 132 along 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) 77 present along the length of the
node connector can define pairs of facing spaced parallel flat
surfaces 140, 141, 142 and 143 for 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 passage 135. Surfaces 140 and 141 are 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. Surfaces 142 and 143 are
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.
[0102] FIG. 30 is a cross-section view of a node connector 139
which is a variant of node connector 130 and of a chord member 131.
It was noted above that node connector 130 has a plane of symmetry,
namely a plane vertically through the center of curvature of the
round portion of passage 135 as node connector 130 is depicted in
FIG. 29. The variation of node connector 139 upon node connector
130 is that both have essentially the same cross-sectional
configuration, but connector 139 is defined by two identical parts
139A and 139B which are connected together at the vertical plane of
symmetry of connector 139. To enable parts 139A and 139B to be
bolted together, as by bolts 140, each of parts 139A and 139B has
an exterior flange or rib 141, from which one of elements 77 is
carried, having a mating surface on the plane of symmetry of the
assembled connector 139 and in which holes for bolts 140 are
formed. Because parts 139A and 139B are identical in cross-section,
they can be made from a common extrusion. The two-part node
connector 139, 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 connector 139 means that extrusions for use in
its construction can be made on smaller extrusion presses of which
there are many.
[0103] FIG. 31 is a cross-section view of a node connector 145 and
a tubular chord member 146 which cooperate with each other;
connector 145 is a modest variant of connector 139, and chord
member 146 is a modest variant of chord member 131. The difference
between the cross-sectional configurations of chord members 131 and
146 is that chord member 146 includes an external radial rib 148
along its length. The rib is centered on the plane of symmetry of
the chord member. The difference between identical parts 145A and
145B of connector 145 relative to the parts 139A and 149B of
connector 139 is that the ribs 149 of parts 145A and 145B are
defined to mate with the opposite faces of chord member rib 148
rather than with each other. Because of the presence of its
external rib 148, chord member 146 has enhanced beam properties
over chord member 131.
[0104] Comment was made above that a variant of node connector 130
(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 (see FIG. 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 connector 130 can be
used to define the "free form" or laterally curved DLG space frame
150 shown in FIGS. 32 (top plan view) and 33 (side elevation view),
simply by making the upper and lower transverse chords 151 and 152
round and continuous through at least some of the frame nodes
(splices may be needed) and by making the upper and lower
longitudinal chord members 153 and 154 square 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 by FIG. 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 surfaces 142 and 143 of 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. Struts 155 connect between upper nodes 156 and
lower nodes 157. 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 in FIG. 32.
[0105] It 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 in FIG. 32.
[0106] 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
electro-magnetic 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.
[0107] 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 to FIGS. 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.
[0108] 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.
* * * * *