10 
 
 
 
Chapter 2 
 
 
CONNECTION SYSTEMS USED FOR GRID 
SPATIAL STRUCTURES 
 
 
2.1 Introduction 
 
 From common spatial structures to the latest free-
form spatial structures, the connecting system is one of the 
most crucial points, not only for the accommodation of ge-
ometry but also for the local and global stability of the whole 
structure. The connectors for these structures are more 
complicated than ordinary framing systems because more 
members are connected to a single joint and the members 
are positioned in a three-dimensional space, which may 
cause complexities in the mechanism of force transfer [Lan 
1999]. In addition, assembling and geometrical procedure 
should be well accommodated not only to save cost and 
time of construction but also to adjust the building site as 
effectively as possible.  
 To provide proper solutions in connection systems on 
the spatial structure considering structural and geometrical 
requirments, many companies and researchers have provi-
ded different types and forms in the past decades. One of 
the related sources reported that over 250 different types of 
connecting systems have been suggested or used in practi-
ce, and there are around 50 commercial firms which have 
tried to specialize in the manufacture of proprietary connec-
tion systems for spatial structures [Lan 1999], each with its 
own types and forms that are difficult to compare.  
 Since the early age of architecture, designers have 
tried to describe the details of jointing, and the type of join-
ting depends mainly on the connecting technique, whether 
it is bolting, welding or applying special mechanical connec-
tors (Figure 2.1). For instance, the Eiffel tower, which was 
built in Paris for the 1889 exhibition by the French engineer 
Alexandre Gustave Eiffel, demonstrates the complexity of a 
Figure 2.1: 
Details of joint and strut described by 
a French architect Violet-le Duc  
[Makowski 2002]  
 
11 
 
three-dimensional joint in the age of gusset plates and rive-
ting (Figure 2.2). In the mid-20th century, Konrad Wachs-
mann designed various nickel steel node connectors, as 
shown in Figure 2.3, which were partially welded, used for  
long spanned spatial structures, such as a aircraft hangar 
projects [Rudolf 1988]. It is likewise influenced by the shape 
of the members. This usually involves a different connecting, 
depending on whether the members are circular or square 
hollow sections or rolled steel sections. Table 2.1 through 
2.3 show comprehensive summeries of the jointing systems. 
All the connection systems in these tables can be divided 
into three following main catagories: 
 
 with a node, 
 without a node, 
 with prefabricated units 
 
 Based on the tables and previous research, it is ne-
cessary to mention the most popular prefabricated connec-
ting systems in order to understand details in the connecti-
ons. Most of all, it is very meaningful to identify and compa-
re the characteristics of connection systems which are used 
in spatial and free-form structures and to detect their in-
fluence on the structural integration of the system. Thus, in 
the next section, more detailed characteristics of various 
connection systems will be mentioned.  
  
 
Figure 2.2: 
Connection details of Eiffel tower  
[Casas 2003]  
Figure 2.3: 
Mobilar node connector detail of Kon-
rad Wachsmann [Rudolph 1988]  
Figure 2.4:  
Aircraft hangar designed by Konrad Wachsmann [Rudolph 1988]  
12 
 
 
Table 2.1:  
Connecting types with nodes  
[Gerrits 1996][Lan 1999] 
13 
 
 
Table 2.2:  
Connecting types without nodes  
[Gerrits 1996][Lan 1999] 
Table 2.3:  
Connecting types with prefabrica-
ted units [Gerrits 1996][Lan 1999] 
 
14 
 
2.2 Connection systems for double layer space  
      structures  
 
The Mero system  
 The connection system Mero, which was introduced 
in 1942 by Dr. Mengeringhausen, has been very popular 
and has been used for numerous industrial buildings, chur-
ches, assembly halls and domes. The connecting system is 
made of tubular members with threaded ends which are 
connected to a steel sphere node with tapped bores to fill 
up eighteen members. Bolts are tightened by means of a 
hexagonal sleeve and dowel pin arrangement (Figure 2.5). 
The manufacturer can produce nodes of different size with 
diameter ranging from 46.5 mm to 350 mm, and the 
corrsponding bolts are M12 to M64 with a maximum allo-
wable force of 1413 kN. The Mero connection has the ad-
vantage that the axes of all members pass through the cen-
ter of the node, eliminating eccentricity loading at the joint; 
therefore the joint is only under axial forces. Tensile forces 
are then carried along the longitudinal axis of the bolts and 
resisted by the tube members through the end cones [Lan 
1999] [Makowski 2002]. The size of the connecting bolt of 
compression members, based on the diameter estimated 
from internal forces, may be reduced by 6 to 9 mm. The 
diameter of a steel node may be determined by the follo-
wing equations [Lan 1999] [Chen et al 2005]: 
 
           (2.1) 
 
 
 To satisfy the requirements of the connecting face of 
the sleeve, the diameter should be checked using the follo-
wing equation [Lan 1999] [Chen et al 2005]: 
 
                (2.2) 
 
 
 
Figure 2.5: 
Dimensions of spherical node of Mero 
system [Borrego 1968][Lan 1999]  
2
1
2
2
11
2 )2cot(
sin
ddddD  

 
2
1
2
2
1
2 )cot(
sin
dddD 
 

 
15 
 
D

21dd


where 
       = diameter of steel ball (mm) 
       = the smaller intersecting angle between two bolts (rad) 
       = diameter of bolts (mm) 
       = ratio between the inserted length of the bolt into the  
          steel ball and the diameter of the bolt 
       = ratio between the diameter of the circumscribed   
          circle of  the sleeve and the diameter of the bolt 
 
 The value of and                may be determined by the de-
sign of tension or compression bolt strength, but the values 
are 1.1 and 1.8, respectively.  
  
Bowl node (type NK)  
 Figure 2.6 shows the bowl type of node which con-
sists of a hemispherical node connecting top chord and dia-
gonal structural members. To connect the node and mem-
ber, a single bolt is generally used. The top chord members 
are square or rectangular sections and can be loaded in 
shear and are fitted flush to the nodes. Bowl nodes are 
used for double layer curved surfaces, in particular irregular 
plan or pyramid shape. The diagonal and lower chords are 
constructed in an ordinary Mero system with circular tubes 
and spherical nodes [Lan 1999]. This node connector was 
 
 
Figure 2.6:  
Details of bowl node developed by new 
Mero system (type NK) [Lan 1999]  
Figure 2.8: Geometry of Eden project, England [Knebel et al 2001]  
Figure 2.7: 
Details of bowl node connector for 
Eden project, England [Knebel et al 
2001] 
16 
 
used for the roof design of the Eden project, England 
(Figure 2.7 and 2.8 ) and the free-formed envelopes for the 
esplanade theatres in Singapore (Figure 2.9 and 2.10).  
 
 The Space Deck system  
 Around 40 years ago the connecting system Space 
Deck was introduced in the United Kingdom. It was almost  
completely used for industrial space frames and factories 
by repetitive application of units. The basic unit is an inver-
ted square on a base of pyramid shaped units with an angle 
top tray and four diagonal or bracing members. The units 
are interconnected by bolting their top layer members and 
interconnecting the lower chord node points by means of 
high tensile steel tie bars (Figure 2.11) [Borrego 1968].  
 The Space Deck system is used with members of  
less than 40 m span with a standard module depth of 1.2 m. 
The minimum structural depth is 0.75 m. In order to take a  
higher design load with a large span, alternative modules of 
1.5 m and 2.0 m are applied using the same depth.  
 
The PYRAMITEC system  
 After the Space Deck system was introduced to the 
space frame structures, the idea of prefabricated pyramidal 
units has been further developed by many other designers, 
although the details of the connections were different. The 
PYRAMITEC connection system, which the French desig-
Figure 2.9: Esplanade theatres in Singapore [Klimke et al 2002]  
Figure 2.11: 
Detail and application of Space Deck sys-
tem [Borrego 1968]  
 
Figure 2.10:  
Detail of connection system for espla-
nade theatres in Singapore [Klimke et 
al 2002] 
17 
 
ner M. S. Du Chateau developed, is one of the examples of 
this. This system consists of prefabricated three-
dimentional pyramids. The pyramids consist of welded fra-
mes made of steel angles with steel tube diagonals connec-
ting to an apex piece, which in turn receives the adjustable 
tie bars [Borrego 1968]. While the Space Deck systems is 
using only the square-based pyramids, the PYRAMITEC 
system employed triangle based pyramids as well as hexa-
gonal based pyramids (Figure 2.12). 
   
The UNISTRUT system  
 Developed in 1955 by Charles W. Attwood with the 
help of the Engineering Research Institute of the University 
of Michigan, the UNISTRUT connector consists of pressed 
steel plate produced automated in a special tooling machi-
ne, ensuring an extremely high precision in manufacture Figure 2.13: 
Details and prototype of UNISTRUT sys-
tem [Borrego 1968]  
Figure 2.12: Three basical configurations of PYRAMITEC system grid [Makowski 2002]  
(a) Triangular base (b) Hexagonal base (c) Square base 
18 
 
and very low cost though mass production. The structures 
of UNISTRUT are usually composed of framing struts, all 
of the same length for top and bottom layers as well as the 
diagonals. The struts are connected at the center of the 
joints by only one bolt to the specially shaped pressed-
steel plate (Figure 2.13) [Makowski 2002]. 
 
 The Triodetic system  
 The node connection system Triodetic was develo-
ped by a Canadian company S. Fentiman. It consists of an 
extruded aluminium node connector hub with serrated 
keyways. As shown in Figure 2.14 and 2.15, the end of 
each member is manufactured to be inserted into the hub. 
This connection system was originally developed only for 
aluminium structures, but Triodetic framing is now avai-
lable in galvanized steel, stainless steel, mill finish alumi-
num or anodized aluminum. Each variety serves special 
service environments. Factory finishes include polyester, 
powder-coating, chromating and kynar, offering a range of 
added aethetics and durability.  
Figure 2.15:  
Detail of Triodetic system [Makowski 
2002] [Borrego 1968] 
 
Figure 2.14:  
Application and details of Triodetic system  [Borrego 1968] 
19 
 
Figure 2.16:  
Detail of MURJ-3D system  
[Bardell et al 1997]  
Post 
Cube 
Arch 
Runner 
 The majority of structures utilize powder-coated 
galvanized steel or anodized aluminum for most envi-
ronments including salt and chlorine atmospheres. 
Stainless steel is required for highly corrosive conditi-
ons (e.g. potash processing). As a result, steel space 
frames could be erected without any electrolytic difficul-
ties [Makowski 2002].  
 As for the transmission of inner force, the tube 
section dimension at each connection is increased in 
the plane of maximum bending, and the tight keyway 
connection in the node prevents slippage, providing inc-
reased bending strength with no loss of axial capacity. 
To resist the rotation about the minor stress plane, si-
multaneous failure mode of all members at the connec-
tion would be needed, which is physically impossible 
given that they radiate at different angles, carry diffe-
rent loads and in many cases have different section 
property [Borrego 1968].  
 
The MURJ-3D System   
 In order to consider modular, universal and recon-
figurable connecting characteristics, the Department of 
Mechanical Engineering at the University of Southamp-
ton, England, developed an experimental node jointing 
system MURJ-3D in 1996. This system is constructed 
of four basic components, namely cube, post, arch and 
runner (Figure 2.16). Commencing with the Cube, a 
Connector Block is added to it by means of two screws 
which will transmit tension and compression loads. As 
many Runners as required may then be added to the 
octant, moved into position, and then secured. The enc-
losed “surface” of the basic octant is bounded by a 
spherical triangle – thus, the Runner, which is con-
centric to the octant, may be traversed anywhere over 
the surface of the spherical triangle [Bardell et al 1997]. 
 After sizing exercises were finished, comprehen-
sive test programs of both static and cyclic fatigue loa-
ding were performed to verify that the joint possessed 
enough strength and endurance to be implemented in 
20 
 
an real space-frame structure. In one typical loading test, 
for example, the suggested model was configured as a sin-
gle octant bisected by the Runner. A tensile test of 5 kN 
was gradually introduced (over a 30 second interval) 
through the mid-point of the Runner (θ=45°). The load-
displacement behavior is linear stiffness progress with 4 
mm at 5 kN [Bardell et al 1997].  
 
The UNIBAT System  
 About 25 years ago, the French connecting system 
UNIBAT was developed by S. du Chateau. This connection 
system consists of modular pyramidal units that are bolted 
only at their corners to the following units using high tensile 
bolts. Their lower layer is provided by tubular members 
which are flattened at the nodes and jointed to the pyramids 
by only one vertical bolt [Makowski 2002]. In fact, the UNI-
BAT had no prefabricated standard joint and thus was not 
limited by normal constrains imposed by the connector as 
to plan form or architectural layout. It could be used in vari-
ous types of structural sections, hollow sections or rolled 
sections, seperately or combined. The clear spans possible 
with the UNIBAT system are not limited as they usually are 
 
Figure 2.17:  
Prototype of MURJ-3D system [Bardell et al 1997] 
Figure 2.18:  
Details of UNIBAT system [Makowski 
2002] 
21 
 
in other systems, i.e. by the node connector, but simply by 
the maximum size of structural section available (Figure 
2.18). Theoretically, UNIBAT can be used for double– or 
multi-layer structures.  
 
The NODUS System  
 The Tubes Division of the British Steel Corporation 
introduced the nodal system NODUS in 1972. This joint 
system is a typical example of a mechanical connector. In 
the center of connector, there is a body divided into two half 
cased enclosures that are combined by a high strength fric-
tion bolt. 
 The bolt head is accommodated in a hexagonal re-
cess in one half casing, thus leaving the exterior of the joint 
flush with the outside of the chord member so that cladding 
can be fixed directly onto the chords. The half casting has 
four drilled lugs for connecting to the diagonal members, 
which intersect usually at 45 degree angle to the chords, by 
means of the appropciate half castings. The horizontal 
chord members are butt welded to connectors having circu-
lar rings which close into corresponding grooves in the half 
casings [Makowski 2002]. The ends of the bracing mem-
bers are fabricated with forked connectors which can be 
connected to casings lugs by a fork pin protected with split 
cotter pins. In order to create a seal between the half ca-
sings a gasket is inserted in the casings and is clamped 
with the central bolt, which is screwed with a specific torque 
value (Figure 2.19). 
 
Node connection system for NS space truss  
 Figure 2.20 shows the detail of node connection sys-
tem for NS space truss. It was introduced around 1970 by 
the Nippon Steel Corporation for the huge roof at the sym-
bol zone of Expo´70 in Japan. The node connector consists 
of a thick spherical steel ball node opened at the bottom for 
bolt  insertion and assembly.  
 The structural members are steel hollow sections ha-
ving specially shaped end cones containing threaded bolt 
holes welded to both ends of the tube. Special high strength 
Figure 2.19:  
Detail of Nodus system [Makowski 2002] 
 
Figure 2.20:  
Detail of node connection for NS space 
truss [Makowski 2002] 
22 
 
bolts were used to connect the tubular members to the 
spherical node. Several members could be connected to 
the node from any direction and eccentricity of internal 
forces could be avoided [Lan 1999].  
 
The Temcor´s aluminum connection system  
 The American company, Temcor, has introduced ma-
ny aluminum spatial structures. Using the adavantages of 
aluminum, such as its high corrosion resistance, high 
strength-to-weight ratio and manufacturability, Temcor has  
completed many long span aluminum spatial structures. In 
order to realize in aluminum long span structures, Temcor 
has developed its own connection system.  
 Typical joint details are shown in Figure 2.21. To as-
sure high moment transfer at the joints, the beam elements 
are connected with top and bottom gussets. The structural 
beams are symmetrical “I” sections with extruded grooves 
for connection of an interlocking panel and batten system. 
The panel has no bending stiffness and transfer of the envi-
ronmental loads to the beam extrusion occurs through 
membrane action. The panel also stabilizes the top flange 
of the beams to prevent column buckling in the minor axis 
direction [Lopez 1997]. 
 
Figure 2.21:  
Details of Temcor aluminum connection  
system [Lopez 1997] 
a : Formed aluminum gusset 
b : Top chord, aluminum “I“ beam 
c : Bottom chord, aluminium “I“ beam 
d : Diagonal aluminum pipe member 
e : Insulated aluminum panel 
Figure 2.22:  
Typical double layer system with the Temco aluminum connecting sys-
tem [Lopez 1997] 
23 
 
The SDC system 
 
 The SDC node connection system developed by a 
French designer M. S. du Chateau is shown in Figure 2.23 
and 2.24. The node consists of two cast shells which could 
be welded together to provide six circular holes, allowing 
connection by welding six tubular units at the same nodal 
point. However, the connections were up to 13 struts inter-
section by welding (Figure 2.24). The tubular components 
can slide into the node which allows a certain amount of 
angular adjustment, permitting a gradual change of the 
curvature of the surface of the structure. This system was, 
as usual, used for three-way double-layer lattice space 
grids or three-way single-layer grids [Borrego 1968] 
[Makowski 2002].  
Figure 2.23:  
Three way double-layer grid with SDC system [Borrego 1968] 
Figure 2.24:  
Details of SDC system [Borrego 1968] 
24 
 
Wachsmann and Smith system 
 
 In 1968, Wachsmann and Smith produced an inte-
resting design intented to overcome a limited degree of 
member angle variability to a three-dimentional node. 
Even though it is still based on the orginal presumption 
that all the member forces are coinciding, this design utili-
zes two concentric spherical layers, each consisting of four 
seperate mantles which arranged a central ball. The mant-
les, which contain the member attachment points (Figure 
2.26a and 2.26b), are then sealed to the ball by two he-
mispherical caps which are jointed to form a tension-
resisting outer case, with an allowance of movement of the 
incoming members over a limited range of angles (Figure 
2.26c). 
 This sophisticated internal arrangement of the joint 
gives it four main connections lying in the x-y-z ± 10° di-
rections (Figure 2.26a), and four secondary, variably orien-
ted, connections each capable of movement though a radi-
al arc of some 75°. This trial to utilize connectric spheres 
as the means to increase the scope for member attach-
ment locations, therefore ensuring the member forces 
pass through the center of the sphere, represented a novel 
and radical departure from the Mengeringhausen concept
[Bardell et al 1997].   
 
(a) The primary member attachments and    
      their mantles 
(b) The secondary member attachments   
     and their mantles 
(c) The complete joint, showing the tensi- 
      on resisting outer case 
Figure 2.26:  
Detail of Wachsmann and Smith joint  
[Bardell et al 1997]  
Figure 2.25:  
Skatch of Wachsmann and Smith detail principles [Borrego 1968]  
25 
 
2.3 Connection systems for single layer grid shells 
 
 Based on the recent architectural demand for transpa-
rent surface structure, single layer enveloped structures are 
becoming more popular. To fulfill their structural and geo-
metrical requirements of the whole single layered structure, 
many node connection systems have been developed. Mo-
reover, since free-form or complex-shaped buildings has 
been introduced to the field of architecture, the develop-
ment of appropriate node connection system has become  
an essential part of whole structural stability. Contrary to 
double layered structures, the connector must bear not only 
axial force but also bending moment to ensure structural 
integration. In this section, the author would like to introdu-
ce several node connection systems that were used in sin-
gle layer spatial structures, in order to determine the impor-
tance of the node connection system for the structural in-
tegration of the whole structure. 
 
Splice node connection  
 Mainly, there are two characteristics of splice node 
connector. At first, the contact surface between the node 
and the connected structural member goes along splice pla-
tes in the longitudinal axis of the member. According to the 
connecting style, one or two contact surfaces, which the 
shear force would be transferred, can be presented. Se-
condly, the connecting can be assembled as a bolted splice 
with shear-stressed bolts or by welding [Stephan et al 
2004]).    
 
Splice node connection SBP-1  
 Figure 2.27 shows one of splice node connection 
SBP-1 which was developed by Schlaich Bergermann & 
Partner, Stuttgart, Germany in 1988. The end of the beam 
is fabricated as half of a fork-shaped flat plate to be connec-
ted with a splice by two or more bolts, so that it has a single 
shear plane in the connection. Through the central bolt the 
horizontal angles between beam members can be adjusted.  
 
Figure 2.27:  
Assembling procedure of connectors 
SBP-1 [Heinle 1996] [Fischer 1999]  
26 
 
 As for the vertical angles, the splice plate has to be 
folded. Twist angles can be controlled only in a very restric-
tive range. Consequently, the low section height may cause 
a low transfer of bending moment [Stephan et al 2004]. This 
connector system SBP-1 was adopted in several single lay-
er reticulated domes, such as the courtyard roof of the City 
History Museum in Hamburg (Figure 2.28) and the roof of 
the indoor swimming pool in Necharsulm in Stuttgart, Ger-
many [Schlaich et al 1992].  
 
Splice node connection SBP-2  
 The splice node connector SBP-2 is shown in Figure 
2.30. This node connector is modified from the previous 
version of SBP-1. The end of beam is fabricated in one of 
two types. The first is a typical fork-shaped end of beam 
and the other is an opposite method of fabrication in which 
two splice plates can be attached on both the top and un-
derside of the beam. They are all connected by two or more 
bolts in double shear surfaces. The applying limitation for 
the horizontal, vertical and twist angles are almost same as 
previous version SBP-1. Due to the double shear sufraces 
in the joint, this node connector system can bear higher 
bending moments than the one of SBP-1 [Stephan et al 
2004]. Figure 2.29 shows the application of the node con-
nection system SBP-2 in the roof structure of the railway 
station Berlin-Spandau [Schlaich et al 1999]. 
 
Figure 2.28:  
City History Museum in Hamburg  
[Heinle 1996] 
Figure 2.30:  
Connection system SBP-2  
[Fischer 1999]  Figure 2.29: Railway station of Berlin-Spandau used SBP-2  
27 
 
 
Splice node connection POLO-1  
 Figure 2.31 shows a splice node connector POLO-1 
developed by Polonyi & Fink, Cologne, Germany. This con-
nector consists of a cylindrical or prismatic core and up to 
six vertical splice plates. The end of beam was fabricated 
as a fork-shaped form to be welded to two steel plates, and 
then the splice of the node is inserted to the end of the 
beam and connected by two or more bolts. Horizontal, verti-
cal and twist angles of the structural members can be ad-
justed by changing the geometry of the splice plates. This 
connection system can transfer a high bending moment. 
The canopy roof of the railway station in Cologne used this 
node connection system [Stephan et al 2004].  
 
End-face node connection   
 The chief identifying characteristic of the end-face 
connection system is that the connection surface between 
the node and the end-face of the connected member is 
transverse to the longitudinal axis of the element member 
using pretension bolts or welding [Stephan et al 2004]. The-
re are, of course, many end-face connection systems which 
are used in free form spatial structures, several of which will 
be mentioned here.  
 
End-face connection MERO disc node (type TK)  
Although the Mero system was originally developed for 
the pin-connected and double layered structures, recently, 
a modification of the shape of the end pieces welded to the 
tubular members allows the members to resist bending mo-
ments in addition to axial forces [Makowski 2002]. 
 Originally, the Mero system was developed for double 
layer grids. However, the increasing requirement of non-
planar roof forms brought the usage of the load-bearing 
space frame integrated with the cladding element. A new 
type of jointing system was named the Mero Plus System, 
which is able to express a variety of curved and folded 
structures. These new node connection system could trans-
fer shear force, resist torsion and bending moment in speci-
Figure 2.32: 
Details of disk node developed by new 
Mero system (type TK) [Lan 1999]  
Figure 2.31:  
Node connection POLO-1 [Stephan et al 
2004]  
28 
 
al cases [Lan 1999] [Makowski 2002]. 
 As shown in Figure 2.32, this type of node connector 
is a planar ring-shaped node connecting with 5 to 10 mem-
bers of square or rectangular sections. Only a single bolt 
was used to connect the node and structural member and 
depth of the node is the same as the depth of the member 
section. The load transmission is for the shear force and 
rotation. In terms of accommodation for local angles, the 
horizontal angle could be accommodated from 30° to 80°, 
and the vertical one can vary from 0° to 10°. For application 
in a global spatial structure, this system is suitable for latti-
ced shells consisted of triangular meshes under pin-jointed 
conditions [Lan 1999]. 
 
End-face connection MERO cylinder node (type ZK)  
 The basic principle of the type ZK is based on the sa-
me one as the disk node type TK. This type consists of a 
cylinderical node with a multiple bolted connection. The im-
portant point is that bending moment could be transmitted 
by these multiple bolts. As in type TK, 5 to 10 square or rec-
tangular sections can be connected to the cylinderical node 
to transfer loading. Connection angle varies 30° and 100° 
for the horizontal angle, while for the vertical angle, from 0° 
to 10° is possible. Cylinderical node connectors are used 
for single and double curved surfaces of lattice shells with 
trapezoidal mesh, for which the flexural rigid connections 
are needed [Lan 1999] [Makowski 2002]. 
 
End-face connection MERO block node (type BK)  
 The block node, type BK, is shown in Figure 2.34. 
Each structural member is connected to the block node by 
one or two bolts, which are mounted from inside the structu-
ral member. Thus, the member section must be hollow. As 
an alternative solution, the members can be welded to the 
node. In terms of fabrication, the node is cut from a thick 
steel plate [Stephan et al 2004]. The horizontal angle could 
 
Figure 2.34:  
Detail of block node developed by new 
Mero system (type BK) [Stephan et al 
2004]  
Figure 2.33: 
Details of cylinder node developed by 
new Mero system (type ZK) [Lan 1999]  
29 
 
be accommodated range from 70° to the maximum of 120°. 
The vertical angle is able to be controlled by 10°. This con-
nector system can be applied both to single and double cur-
ved surfaces with the pin and rigid joint where the number 
of members is small [Lan 1999]. Usually, this node connec-
tor is suitable for use with a simple geometry and a small 
structural dimension. 
 
End-face node connection SBP-4  
 The end-face node connection SBP-4 is shown in Fi-
gure 2.35. This connecting system was developed by 
Schlaich Bergermann & Partner for the Schlueterhof courty-
ard roof of the German Historical Museum, Berlin in 2002 
(2.36). Two cross-shaped plates composed the main node. 
For the structural beam, four plates are welded together to 
make a hole box-shaped in cross-section. The structural 
beam members are then connected to the node end-faces 
with butt welds. In order to erect, each member can be pro-
visionally connected to the node end-faces using bolts 
[Stephan et al 2004]. To strengthen the overall structural 
capacity, two cables pass through in the node connection 
and are secured using a clamp for the cable bracing.  
 In terms of geometrical accommodation, horizontal 
angles of each structural member at this node are determi-
 
Figure 2.35:  
End-face node connection system SBP-4  
[Schlaich et al 2003] 
 
Figure 2.36:  
Schlueterhof courtyard roof of the German Historical Museum, Berlin 
30 
 
Figure 2.38:  
Cutting of nodes of WABI-1 out of steel 
plate 180 mm with milling machine 
[Sischka et al 2001]  
Figure 2.37:  
End-face connection WABI-1 with various 
horizontal angles [Sischka et al 2001] 
Figure 2.39:  
Simulation of the roof in the British Museum in London [Sischka et al 2001]  
ned by the prefabricated geometry of the two cross-shaped 
plates. The vertical angle can be achieved through the spe-
cific handling; for example, cutting the node face. However, 
twist angle can be limited in the certain range. As for the 
structural capacity of this end-face node connector, due to a 
sufficient height of cross section, high bending moments 
can be transferred to the full member strength [Stephan et 
al 2004].  
 
End-face connection WABI-1  
 Figure 2.37 presents one of the welded end-face con-
nector WABI-1, which was developed by Waagner-Biro AG, 
Vienna in Austria. This system was used in the courtyard 
roof of the British Museum in London (Figure 2.39) 
[Anderson 2000] [Sischka et al 2001]. The node is a star-
shaped plate with 5 or 6 arm plates. Due to the milling ma-
chine, the entire node can be fabricated by cutting a thick 
steel plate, and the end faces of the structural members are 
milled to have a double mitre to match with the correspon-
ding node gap between arms (Figure 2.38). The cross secti-
on of each member is higher than the node. The top and 
bottom surfaces of the node plates are welded using fillet 
welding, and the side surfaces are connected by butt welds. 
As for the horizontal, vertical and twist angles, the structural 
 
31 
 
Figure 2.40:  
End-face node connection OCTA-1  
[Ramaswamy et al 2002] [Stephan et al 
2004]  
members at the node can be adjusted by the geometry of 
the double mitre cuts at the end of the beam members. 
High bending moments can be transferred to the full mem-
ber strength [Stephan et al 2004]. 
 
End-face connection OCTA-1  
 The end-face connector OCTA-1 was introduced by 
Octatube Space Structures BV, Delft, Holland [Ramaswamy 
et al 2002]. This system consists of a hollow spherical node 
with structural beam member. Each structural member is 
connected to the node sphere by two bolts, the assemby of 
which can be accomplished from inside the hollow sphere. 
To control the angles of geometry, two bolt holes for each 
member should be accommodated (Figure 2.40) [Stephan 
et al 2004]. 
 
End-face node connection MERO-4  
 Figure 2.41 and 2.42 show the end-face node con-
nector MERO-4. The firm MERO developed this node con-
nector for the free-form roofs over the Central Axis and the 
Service Center of the New Fair in Milan, Italy (Figure 2.43). 
Basically, the node consists of two dish nodes, one for the 
top chord of the structural member and the other for the 
bottom chord at the end of each member. The structural 
beam members meet at the end-face of the node and are 
connected to both nodes by bolts or welding. The middle of 
the dish nodes are fabricated with a circular hole to enable 
assembly in-situ. As for the angles of structural members, 
all of them can be pre-fabricated by the geometry of the 
machined plane surfaces at the nodes to adjust complex-
 
Figure: 2.41  
End-face node connection MERO-4 [Stephan et al 2004]  
Figure 2.42: Inside of connector MERO-4   
[Knobel 2004]  
32 
 
Figure 2.43:  
Free form surface of the New Fair in Milan, Italy [Schober et al 2004] 
shaped surfaces for the project.  
 Based on the mentioned connection systems, Figure 
2.44 through 2.48 show the adaptibility of accomodation for 
various local angles and the transferability of internal force 
of various connection systems [Stephan et al 2004]. The 
node connection systems HEFI-1 and SBP-3 were not men-
tioned in this chapter, however the explanation of geometri-
cal form will be introduced in the next chapter to understand 
their specific characteristics.  
 Generally speaking, there has been not enough re-
ported to compare connection systems, especially as used 
for the single-layer grid shell or free-form spatial structure, 
because there are so many systems that have geometrical 
characteristics which differ too greatly to compare exactly. 
Despite this, K. Fischer introduced a comparison of node 
connections for single layer structures in 1999 [Fischer 
1999] and S. Stephan introduced the relative comparison of 
connection systems used in single-layer reticulated structu-
res in 2004. 
 In general terms of adaptability in accommodating of 
various local angles, when the angles could be adjusted by 
the node´s accommodation, the applicabilities of angles are 
better than those controlled by the end of member.  
 Concerning the transferability of internal forces, the 
end-face node connections show better capabilities than 
33 
 
Figure 2.44:  
Adaptability of accommodation for  
horizontal angle [Stephan et al 2004]  
Figure 2.45:  
Adaptability of accommodation for  
vertical angle [Stephan et al 2004]  
splice connections, relatively; that is, the more closed faces 
between node and end of beam, the better the transferred load 
to the structural member. In the case of a connector having on-
ly one shear surface, for example SBP-1, the capability of loa-
ding transfer is lower than for those which consist of at least 
two shear surfaces. 
34 
 
Figure 2.46:  
Adaptability of accommodation for  
of twist angle [Stephan et al 2004]  
Figure 2.47:  
Transferability of axial force  
[Stephan et al 2004]  
Figure 2.48:  
Transferability of bending moment  
[Stephan et al 2004]  
35 
 
2.4 Recent connection system used for free   
      form grid spatial structures  
 
The node connection system for the free-form roof 
Westfield in London, England   
 In 2007 the Buchan Group International and Be-
noy designed a shopping center in London. To cover the 
mall area, they created a 17,000 m² of free-formed glass 
roof (Figure 2.51). Knippers Helbig Consulting Engi-
neers, Stuttgart and the fabricator Seele cooperated on 
the engineering design [Knippers et al 2008]. As shown 
in Figure 2.49, they developed a node connection sys-
tem which would both implement complex-shaped cur-
vature and fulfill required loading capacity.  
 The jointing principle here is a bolt connection of a 
hollow beam to the node where the end faces meet per-
pendicularly (Figure 2.49a). The node consists of twen-
ty-six different elements to create the perpendicular sur-
face and different connection geometries (Figure 2.49b). 
This node connector has a high structural capability and 
satisfies the architectural requirements, because there 
is no gap between nodes and beams which make the 
force transfer of external loads very effective. Figure 
2.50 shows the final check of the node connectors to 
ensure geometrical accuracy. 
(a) 
(b) 
Figure 2.49:  
End-face node connector for the free-
formed glass roof for Westfield, London  
[Knippers et al 2008]  
 Figure 2.50: Milling of connector (a) and final check of geometrical accuracy (b) [Knippers et al 2008]  
(b) (a) 
 
(c) 
36 
 
The node connection for free-form glass roof My Zeil in 
Frankfurt, Germany  
 Figure 2.52 shows details of node connection system 
used in the free-form glass roof of My Zeil in Frankfurt, Ger-
many, completed in 2008. The complex building was de-
signed by Italian architect Massimilano Fuksas and structu-
ral design performed by Knippers Helbig Consulting Engi-
neers in Stuttgart, Germany. An approximately 13,000 m² 
area of free-form glass roof covers this building. 
 Related to the solution of the connection system, the 
manufacturer Waagner-Biro, Wien, suggested a welded no-
de construction. A star-formed steel node was introduced 
as the center of the node where the end of each beam 
could be connected by welding. In order to implement the 
required complex geometries at the node, ten percent of the 
total number of node (2,500) had to be made of steel plates 
[Knippers et al 2008].  
 For the beam section, a welded hollow steel box sec-
tion with a standard dimension 120 mm × 60 mm was used. 
The thickness of each plate was calculated to be fulfilled 
with their static stress. As shown in Figure 2.53, the beam 
section and node were designed to overlap so that the 
treatment of the welding joints between flange and web 
would not be necessary.  
 The overlapped connections were designed more on 
 
 Figure 2.51: Grid for structural analysis (a) and interior view of Westfield (b) [Knippers et al 2008]  
(a) (b) 
Figure 2.52:  
End-face node connection for the free-
formed glass roof for My Zeil, Frankfurt  
[Knippers et al 2008]  
37 
 
the divided edge, where the beams could be followed 
smoothly (Figure 2.54 and 2.55) [Knippers et al 2008] 
[Hwang et al 2009]. Thus far, based on the reported literatu-
res, the overview of connection systems used for double 
layer space structures, single layer grid shells and recent 
free-form grid spatial structures has been introduced to 
describe the general characteristics of connection systems. 
In order to detail the simulation of the structural integration 
of the aforementioned connection systems into the whole 
global structure, four connection systems will be selected to 
represent the main characteristics of the connection sys-
tems in Chapter 4.  
 
Figure 2.55:  
Inside of My Zeil  
Figure 2.54:  
Marginal designing condition of grid generation for My Zeil  
[Knippers et al 2008] 
Figure 2.53:  
Mock-up design of connector