Stålförstärkning av limträbalkar för att öka hållfasthet och styvhet

Sammanfattning: In today’s housing market, open house plans are requested increasingly. This puts a demand on the beams being used to manage longer spans and is therefore exposed to larger loads. To manage these larger loads, one solution is to increase the beam dimensions. Because of demands to fulfill standardized measurements for doors, ceiling heights and roofing heights, there is not always room for the beam dimensions required. Another option is to reinforce the beams with another material to maintain the smaller dimensions. This report aims to examine the strength and stiffness of steel reinforced glulam beams and which dimensions and placement of the steel that is most beneficial for increasing strength and stiffness. This was accomplished by calculating strength and stiffness according to Bernoulli-Euler beam theory and by bend testing eighteen beams with four different configurations: one without reinforcement, one reinforced in the bottom, one reinforced on the top and one with reinforcement on both top and bottom. The results from the bending tests showed an increase of 33 – 77 % in bending strength and 70 – 95 % improvement in stiffness, depending on the configuration. This improvement correlates relatively well with the produced result from the calculations, even though some differences could be found. The most beneficial configuration, with regards to strength, was steel on the top, but the configuration with steel on the top as well on the bottom came a very close second. This beam should produce better results according to the calculations. On the other hand, configurations with steel on the bottom or the top correlated well with the calculations. At testing, the configuration with steel on the bottom showed marginally better strength results. This is however difficult to statistically determine because few beams were tested.