Tubular sections have become increasingly popular in recent years due to their superior performance as structural members (especially in compression and torsion) as well as their aesthetic appearance. However, if exposed to high local shear forces, e.g. at supports of long lattice girders, tubular joints perform less favourably due to punching shear. To increase the joint capacity of these joints ring-stiffeners can be used. So far, ring-stiffened joints can mostly be found in large scale buildings. Yet, theoretical research on ring-stiffened T joints with compression loading of the brace (Willihald et aL 1999) indicate that ring-stiffeners can also be useful for small chord diameters. An experimental study is presented and the results of the earlier work are verified. In addition, further Finite Element modelling has been carried out, to study the influence of ring-stiffeners in tubular Y joints with compression loading of the brace.
In recent years, the use of tubular sections as structural elements has steadily increased. A comanon application is found in lance girders. The efficiency of tubular sections in such structures is mainly influenced by the design of the brace to chord joints. At supports, problems can arise due to high forces transverse to the chord from the braces. Internal ring-stiffeners (flat plates) placed at the intersection of the chord and brace members are a possible simple solution (see Figure 1). Design guides and Codes (ClDECT/Wardenier et al., 1991, EUROCODE 3, 1994) do not include methods for dealing with this type of reinforcement. So far, ring-stiffeners can mainly be found in offshore structures, where they are used to reduce stress concentrations and therefore improve fatigue performance. Most research has therefore been concentrated in determining Stress Concentration Factors (SCF) for such joints.