2451 General Description

The jointing system is an extremely important part of a space frame design. An effective solution of this problem may be said to be fundamental to successful design and construction. The type of jointing

24.5 Jointing Systems depends primarily on the connecting technique, whether it is bolting, welding, or applying special mechanical connectors. It is also affected by the shape of the members. This usually involves a different connecting technique depending on whether the members are circular or square hollow sections or rolled steel sections. The effort expended on research and development of jointing systems has been enormous, and many different types of connectors have been proposed in the past decades.

The joints for the space frame are more important than the ordinary framing systems because more members are connected to a single joint. Furthermore, the members are located in a three-dimensional space, and hence the force transfer mechanism is more complex. The role of the joints in a space frame is so significant that most of the successful commercial space frame systems utilize proprietary jointing systems. Thus, the joints in a space frame are usually more sophisticated than the joints in planar structures, where simple gusset plates will suffice.

In designing the jointing system, the following requirements should be considered. The joints must be strong and stiff, simple structurally and mechanically, and easy to fabricate without recourse to more advanced technology. The eccentricity at a joint should be kept to a minimum, and yet the joint detailing should provide for the necessary tolerances that may be required during the construction. Finally, joints of space frames must be designed to allow for easy and effective maintenance.

The cost of the production of joints is one of the most important factors affecting the final economy of the finished structure. Usually, the steel consumption of the connectors will constitute 15 to 30% of the total. Therefore, a successful prefabricated system requires joints that must be repetitive, mass produced, simple to fabricate, and able to transmit all the forces in the members interconnected at the node.

All connectors can be divided into two main categories: the purpose-made joint and the proprietary joint used in the industrialized system of construction. The purpose-made joints are usually used for long-span structure where the application of standard proprietary joints is limited. An example of such a joint is the cruciform gusset plate for connecting rolled steel sections shown in Figure 24.28.

A survey around the world will reveal that there are over 250 different types of jointing system suggested or used in practice, and there are some 50 commercial firms trying to specialize in the manufacture of proprietary jointing systems for space frames. Unfortunately, many of these systems have not proved to be very successful mainly because of the complexity of the connecting method. Table 24.6, Table 24.7, and Table 24.8 give a comprehensive survey of the jointing systems all over the world. All the connection techniques can be divided into three main groups: (a) with a node, (b) without a node, and (c) with prefabricated units.

24.5.2 Proprietary System

Some of the most successful prefabricated jointing systems are summarized in Table 24.9. This is followed by further description of each system.

FIGURE 24.28 Connecting joint with cruciform gusset plate.

TABLE 24.6 Connection Types with a Node

Node

Connector Member Cross-section

Examples

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