Connectors for geodesic dome structures

Connectors for joining struts used to form geodesic domes have first and second sets of semicylindrical portions located alternately on opposite sides of the longitudinal centerline of the connector. In the assembled joint, the first and second sets of adjacent connectors are interleaved and secured by pins or bolts forming hinge-like interconnections.

The present invention pertains to the construction of geodesic domes and, 
more particularly, to connectors for joining the framing members of such 
domes. 
BACKGROUND OF THE INVENTION 
Geodesic domes are generally constructed either of preformed triangular 
panels which are bolted together to form the dome or of individual 
structural members which are joined together during construction of the 
dome to form a space frame which is subsequently covered. In the space 
frame construction method it is necessary to connect as many as six 
structural members at a common point. Mitering of the individual members 
so that the members interfit at the common point is a costly process, 
requiring precise woodworking and skilled assembly. In order to simplify 
dome construction, a number of connectors have been proposed in the prior 
art. Among these are the connectors shown in U.S. Pat. Nos. 3,186,522, 
McCauley; 3,486,278, Woods; 3,635,509, Birkemeier et al; 3,810,342, Scott; 
3,844,074, Ahern; 3,990,195, Gunther; and 4,262,461, Johnson et al. Many 
of these prior art connectors require the use of a central hub member 
which is of relatively complex and, accordingly, expensive construction. 
Others of the prior art connectors are suitable only for use where the 
angular relationships of the structural members are precisely uniform, a 
condition that frequently is not present in actual construction 
situations. 
It is the primary object of the present invention to provide an improved 
connector for use in space frame geodesic dome construction which is 
characterized by its simplicity, permitting inexpensive construction and 
facilitating the dome assembly. 
It is a further object of the invention to provide a connector for use in 
space frame geodesic dome construction which is readily adaptable to 
accomodate variations occuring during dome construction. 
SUMMARY OF THE INVENTION 
The above and other objects of the invention which will become apparent 
hereinafter are achieved by the provision of a connector element for 
geodesic dome structural members which element has a portion adapted to be 
secured to the structural member and, extending from the end of the 
member, first and second sets of semicylindrical portions located 
alternately on opposite sides of the longitudinal centerline of the 
member. When adjacent structural members are assembled to form a joint, 
the first set of semicylindrical portions of the connector element 
attached to one structural member are interleaved with the second set of 
semicylindrical portions of the connector element attached to the adjacent 
structural member. Each such hinge-like interconnection is secured by a 
bolt or pin passing through the semicylindrical portions. 
For a more complete understanding of the objects and advantages of the 
present invention reference should be had to the following detailed 
description and the accompanying drawings wherein preferred embodiments of 
the invention are described and shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1-3, the connector element designated generally by 
the reference numeral 10 is of single piece construction, preferrably 
being formed from a steel strip. The connector element has parallel side 
portions 12, 14 spaced apart by a distance equal to the thickness of the 
structural member 16 to which the connector element is attached. Aligned 
holes 18 in the portions 12, 14 are provided for bolting the element 10 to 
the structural member 16. The intermediate portion 20 of the element 10 
which connects the side portions 12, 14 is provided with three parallel 
slots dividing this portion into four sections 22, 24, 26, 28. Each 
section includes a semicylindrical portion 30 extending tangentialy from 
one of the side portions 12 or 14 and a diagonal portion 32 extending to 
the other of the side portions. The sections are formed so that alternate 
semicylindrical portions are on opposite sides of the longitudinal 
centerline of the connector element and, as can be seen from FIG. 2, the 
outer faces of the semicylindrical portions are tangent to this 
centerline. 
As was discussed above, a typical geodesic dome joint comprises six 
structural members extending at generally uniform angular spacing from a 
common point. The assembling of such a joint with the connector elements 
10 is shown in FIGS. 3 and 4. Each structural member 16, which may be a 
wooden strut, has a connector element 10 attached to the end thereof and 
secured by any suitable means such as bolts 34 and nuts 36. Adjacent ones 
of the connector elements are positioned so that the semicylindrical 
portions of the connector elements are interleaved, forming a hinge-like 
knuckle joint. A pin or bolt 38 secures each joint. When the six 
structural members are so interconnected, the resultant ring-like 
configurations formed of the interlocking semicylindrical portions of the 
connector elements provides a structural joint transferring the loads 
between the structural members. 
It will be apparent that only a minimum of preparation of the structural 
members is required as no mitering or other precision fitting of the 
members is necessary. The hinge-like interconnections of the connector 
elements allows the joint to compensate for variations in the angular 
relationships of adjacent structural members, the joint being capable of 
accomodating an angular variation of 10.degree.-12.degree. between 
adjacent members. 
While the joint assembly of FIG. 3 connects six framing or structural 
members, the most commonly encountered joint in geodesic dome 
construction, the connector elements of the present invention are equally 
usable in assembling joints involving a greater or lesser number of 
framing members. Four and five member joints are shown in FIGS. 5 and 6, 
respectively. 
In the construction of geodesic domes, it is sometimes necessary to remove 
or omit a structural member, for example, to provide an opening for the 
installation of a door or window. A bridging connector element 40 for use 
in such situations is shown in FIGS. 7 and 8. The element has a pair of 
flat plate or wing portions 42, 44 angled relative to one another by an 
angle equal to approximately twice the angle between adjacent structural 
members of the joint. 
Thus, when the bridging element is to be used in place of one structural 
member in a six member joint, the angle between the wing portions is 
approximately 120.degree. and, preferrably, 124.degree.. At the 
intersection of the wing portions, the bridging connector is formed with 
first and second pairs of semicylindrical portions 46, 48 arranged in the 
same manner as the semicylindrical portions of the connector elements 10. 
As will be seen from FIG. 9, the bridging connector element 40 serves to 
complete the circle of interleaved semicylindrical portions. The wing 
portions of the element 40 bear against the sides of the portions 12, 14 
of the connectors 10 attached to the structural members on opposite sides 
of the opening formed by omitting a structural member. 
A modified connector element 50 is shown in FIGS. 10 and 11. This connector 
element has an elongated plate-like portion 52 provided with bolt holes 54 
and, at one end, first and second pairs of knuckles 56, 58. This connector 
element is secured to the framing member 60 by inserting the same into a 
slot 62 extending inwardly from the end of the member on the longitudinal 
centerline thereof and is secured by bolts 64. As with the previously 
described embodiment, the joint is formed by interengaging the knuckles 
56, 58 of adjacent connector elements and securing the same with bolts or 
pins 66. 
A further modification of the connector element is illustrated in FIGS. 12 
and 13 and comprises a plate portion 72 having bolt holes 74 and provides 
on opposite edges thereof with first and second pairs of knuckles 76, 78. 
This connector element is designed to be attached to the end of a framing 
member 80 and secured thereto by lag bolts 82. 
While preferred embodiments of the invention have been illustrated and 
described, it will be understood that changes and additions may be made 
therein. Accordingly, reference should be had to the appended claims in 
determining the scope of the invention.