Stiffening of roof trusses due to lateral forces

Sammanfattning: This final thesis has its origin due to Derome trätekniks wish to investigate if it’s possible to ensure total stability of the roof construction for their future hall concept Deromehallen. The stabilization is either made with the help of diaphragm action or with a system of parallel trusses. In the background there are the stabilization problems with Lidl‐stores. These roofs were tiled roofs which were edified of roof cloth, ridges and bricks. The roof trusses showed buckling in top and sub frames, which in some occasions demanded action to prevent the roof from collapsing. The problem with these halls is that the lateral forces on the roof construction are big and have to be stabilized (this concerns only span lengths about 25 meters). This happens when the load from snow affect roof trusses top frames and creates large axial forces which on their hand gives lateral buckling. The ridges opportunities to absorb these forces by themselves are small. If a top frame buckles the ridge this will affect the next roof truss and this will buckle the next ridge force including its own which does that these forces are added for every roof truss. The result is that a small force fastly becomes a big one. Diaphragm action with help from trapezoidal corrugated sheets is designed after the presuppositions described in method part (see chapter 3.2) and roof sheet Plannja 70 were picked. Due to that this hall building is uninsulated but the choice of roof plate is not optimized with the motivation that it is an unsureness when diaphragm action and temperature movements coexists. The difference between roofs covered with tiles and cardboards is that the tiled roof has ridges instead of matchboards. The stabilization system consists of parallel trusses, wind straps, jack rafters and ridges or matchboards. Wind straps and jack rafters are designed according to BKR 03 while parallel trusses and ridges are designed according to Eurocode 5 part 1:1. This stabilization system skeleton (parallel trusses, wind straps, jack rafters and ridges or matchboards) is designed to hold expected forces and a construction is never stronger than it´s weakest link. All fasters and fastening details (nails and angels) have to be designed before the system are complete; this is not included in this final thesis.