Dimensionering av en bÃ¥gbro i trÃ¤ - Konstruktionsteknik - Lunds ...

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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
Keywords: Arch bridge, timber bridge, stress laminated timber deck, FEM, handcalculation, plate model, shell element, frame element & solid element.4
Page 7 and 8: Nyckelord: Bågbro, träbro, tvärs
Page 10 and 11: Rapportmall Konstruktionsteknik, LT
Page 12: Rapportmall Konstruktionsteknik, LT
Page 15: 1.2 SyfteSyftet med den här studie
Page 19 and 20: egränsande dimensioner vilket medf
Page 22 and 23: 4 TräRapportmall Konstruktionstekn
Page 24: Rapportmall Konstruktionsteknik, LT
Page 27 and 28: Figur 8. Plattelement med 4 noder,
Page 29 and 30: av att kunna använda tidigare skri
Page 31 and 32: Lastkombination 6.10a:(2)Lastkombin
Page 33 and 34: där α qi är en anpassningsfaktor
Page 35 and 36: Lastmodell 4 består av en utbredd
Page 37 and 38: Styvhet för materialet Tvärsnitt
Page 39 and 40: Figur 15. Deformation av ett elemen
Page 41 and 42: Figur 17. Exempel på infästning m
Page 43 and 44: Det kräver inte stora förspännin
Page 45 and 46: Figur 22. Glidning mellan lamellerD
Page 47 and 48: Figur 24. Lokalt brott på grund av
Page 49 and 50: De 300 mm helgängade skruvarna med
Page 51 and 52: Figur 28. Mått på sekundära syst
Page 53 and 54:
Figur 30. Mått på huvudbärare52
Page 55 and 56:
Figur 32. Bågens längd och höjdF
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Tabell 8. Antal lastfält oh deras
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Figur 34. Hjulyta och avstånd för
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(19)(20)Även längden på lastspri
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Figur 40. Upprepning av procedur vi
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Trafiklasten är placerad ut på de
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Figur 47. Resultat av moment (väns
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Från den kritiska knäcklasten kan
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(33)Genom komposanterna kan en resu
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eräkningsmetoden går ut på att b
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Figur 57. Diagram från handbok "By
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7.4.5.2 Kontroll 2 - Handberäkning
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Då körbanan modelleras som ett ba
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Tabell 10. Värden på den kritiska
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7.5 Hållfasthetskontroll av bågeI
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(67)(68)(69)(70)(71)7.5.2 Hållfast
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(80)7.5.2.4 Interaktion mellan drag
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Figur 66. Spänning i linjär- och
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Figur 70. Maximal nedböjning för
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Figur 73. Körbanans influenslinje
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Figur 76. Spänningsfördelningen i
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(83)Där b eff är den effektiva br
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8 Resultat och jämförelseResultat
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9 Diskussion och slutsatsResultaten
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102
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104
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Thelandersson, S. (2001), Stålkons
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(94)(95)12.1.1.2 Kontroll 2Den dime
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(112)(113)12.1.2 Knäckning i plan
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(127)(128)(129)(130)(131)12.1.3 Kn
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Figur 81. Mått och dimensioner fö
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De totala yttröghetsmomenten för
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12.1.4 knäckning ut ur plan med k
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(186)(187)(188)12.2 Beräkning av s
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