Frame structures

While timber construction often uses simple beam structures on pendulum supports with elaborate bracing, steel construction usually constructs halls as frame structures. A pity, really, as the frame structure is also an ideal construction method for timber construction.

A frame is a structural element composed of rods that are resistant to bending. The core element is the rigid connection, the so-called frame corner. The spatial bracing of the hall in the transverse direction is achieved directly via the frame. Only stiffening in the longitudinal direction is required; there is no need for a complex stiffening connection in the transverse direction of the building. A distinction is made between three-hinged and two-hinged frames. In the case of three-hinged frames, the frame corners are usually designed using a KZ joint if this is still possible for transportation reasons. In contrast to the two-hinged frame, the internal forces in the three-hinged frame cannot be influenced - the statically indeterminate two-hinged frame is much more interesting in terms of design.

The bending moment curve in the two-hinged frame can be optimized by a variable cross-sectional profile and by a controlled imposed deformation of the supporting structure (prestressing due to displacement of the support points). The aim is to reduce the bending moment of the corner in such a way that the connecting forces of the corner do not determine the beam dimension. The reduction in the corner naturally increases the bending moment in the center of the span. These measures made it possible, for example, to reduce the corner moments of the EIZ Frutigen frames from 950 kNm to 770 kNm.

Such optimizations are inconceivable without precise knowledge of the frame corner connections. The exact force progression as well as the stiffness and possible slippage of the connection must be known for the design. For transportation reasons, it must also usually be possible to assemble the frames on site. As such connections are rare in timber construction, the GSA LMV assembly connection was developed in collaboration with Professor Ernst Gehri and the n`H engineers. This is a pluggable, rigid connection of glulam elements, which can be used for straight beams, but especially in connection with beam buckling (frame corners). Specially shaped steel strips are glued into the timber using GS anchors. The steel strips can be connected to each other on site using a simple bolt connection. In addition to the high connection performance, the GSA LMV connection is characterized by its high rigidity, its appearance (steel part barely visible) and its simple, pluggable connection.