Welded KK-joints of circular hollow sections in highway bridges

摘要

Over the last 15 years steel-concrete composite highway bridges comprising spatial trusses made of Circular Hollow Sections (CHS) have become an innovative and aesthetic alternative to the conventional all-steel bridges in Europe. The so-called KK-joint is a major detail of the above mentioned trusses that normally consist of two planes of rising and falling (not crossing) braces and a continuous bottom chord forming together a KK at the intersection. From the viewpoint of economics and ease of construction the braces are preferred being welded directly on the bottom chord. To verify a welded spatial tubular truss against fatigue failure the well-known S-N method is not sufficient anymore due to the complexity of the welded joint geometry. The more sophisticated hot-spot stress approach has to be applied. In general, stress concentration factors are used in order to compute the hot-spot stresses at the truss joints. Unfortunately, the available SCF-values are not applicable to highway bridge geometries. In particular, the low γ-values (chord slenderness) being typical of highway bridges make an application of the existing SCF-values impossible. This paper aims to show the first results of a still on-going research project for developing recommendations concerning the fatigue design and construction of welded KK-joints in highway bridges.