This paper presents the first and recent results of some parametric studies on multiplanar K-joints with gap made of circular hollow sections. In several figures, the steps towards determination of a suitable model are presented. Comparisons between tests and finite elements results confirm the procedure. With these models, parametric studies have been performed so that at the completion of this work, formulae for strain concentration factor (SNCF) as a function of the geometric parameters ß1 = b1/b0; τ = t1/t2 and gap parameter g" = g/t0 (see fig. 1 for symbols) can be presented. As far as possible design graphs are also to be given.
Nearly all the tests on the fatigue behaviour of hollow section joints published in the last few years were carried out using uniplanar test specimens Regarding the multiplanar K-joints, there have only been a few experiments carried out in different countries. In almost all the cases, the tests were performed under static load. The first fundamental investigations on multiplanar joints made of circular and square hollow section under fatigue load have been carried out in the Netherlands (Delft University of Technology and TNO Building and Construction Research, Rijswijk) and in Germany (Karlsruhe University) sponsored by the ECSC (Puthli, R. S., 1988–1991, Mang, F., 1988–1991, Mang, F., 1991–1). In this programme joints in multiplanar girders have been tested (Delft) as well as isolated joints (Karlsruhe). The fundamental investigations incorporated static measurements, where the strain concentration factors SNCF are determined in the critical areas by means of strain gauges. In a program sponsored by the Deutsche Forschungsgemeinschaft (DFG) (Mang, F., 1994), these investigations have been further researched numerically, using the Finite Element Method. The measurements mentioned above and also additional tests as part of the DFG research project contain the basic reference data for the determination of a suitable model for multiplanar K-joints with gap made of circular hollow sections (CHS).
