Dimensionering av en bågbro i trä - Konstruktionsteknik - Lunds ...

AbstractRapportmall Konstruktionsteknik, LTHIn the past it was common to build in timber but in the last 150 years, steel andconcrete in particular have been the dominating material in bridge-buildings. This ismainly due to not having mastered the timber construction to the same extent as steeland concrete. Nowdays the interest in timber bridges have increased and the technicalsolutions have been greatly developed in the last 15 years.The purpose of this study is to provide an insight of how a design of an arch bridge intimber is according to Eurocode can be done. For the report the design will be checkedwith hand calculations and with commercial FEM software, SAP2000. When handcalculations have been too time consuming or not possible for the authors toimplement FEM have been used for the design values.The case study is based on an existing arch bridge with a stresslaminated timber deckin Norway which was designed by the old Norweigan standards. The results from thehand calculations gave a lower strength compared to methods based on the finiteelement method. The difference between the two methods were not very large, handcalculation are about 20 % lower than the methods which were calculated by FEM.For out of plane buckling the bracing stiffnes at the attachment points have a greatinfluense on the strength of the arch. In reality the hinged attachment points is not rigidat the transverse direction and should be considered when designing the bridge. Thebuckling load can vary between 1 and 45 MN but make the greatest contributionbefore the out of the plane stiffness reaches 10000 N/mm.Bending stresses in the transverse direction is a big problem for the deck. The materialutilization of the deck was calculated to 565 % of the recommended pre-stress level of1 MPa. Both compression and tension are the same in the deck but with opposite signs,this may be because the modeling is done with shell elements.When comparising the authors' plate model with Ekström in Chap. 9.6.1 it can be seenthat the solid elements provide a different stressdistributions at the top and bottom ofthe deck. The tensile stresses are less than the compressive stresses in the solid platemember, this is due to the maximum compression stresses that are obtained directlyunder the load which generates an "disrupted zone" of the stresses. When modelingwith shell elements the gap between the laminations can’t be taken into account,therefor no accurate representation of the results are obtained when modelizing theplate member in SAP2000.Although the calculations shows that the bridge lacks strength at some points, we mustnot forget that this is an existing functional bridge in Norway. The bridge is designedfor old standards according to Norwegian regulations and has probably passed therequirements. This is a sign that the new Eurocode is much more stricter than previousstandards.3