Structural Timber System for Medium-to-Long Spans: The HB System Revisited

The evolution of long-span timber structures during the last centuries has been driven by technological developments that are associated with materials, joints, and manufacturing. Many extraordinary structural solutions have been developed, some of which have been very advanced in their time and have been replaced by new ones, typically because of the advent of new manufacturing methods or, at times, due to new technological innovations. This study examines the Hilding Brosenius (HB) system, which was developed in the 1940s as a versatile wooden frame solution for medium-to-long spans. The HB system is based on an I-shaped cross section where the web consists of two diagonal board layers, and the flanges are assembled from boards by nailing and gluing. This study presents and discusses the main structural components of the system from the perspective of structural mechanics, current design requirements, and manufacturing technologies. As a practical application example, the structural system will be examined in the renovation project of an HB portal frame from the 1950s. The main findings of this study are: (1) the HB system has certain features that would make it worthwhile modernizing and reusing it more widely; and (2) the HB system design principles lead to a safe and robust yet light and optimal structure.