Masato NAGAI
Development of design of composite hybrid bridges
Supervisor Masatsugu NAGAI
In order to reduce the bridge construction cost, a composite two-I-girder bridge with a simple transverse stiffening system has been developed, and it has been recognized to be the most economical and powerful solution for the bridges with a span from 40 to 60 meters. In order to reduce the cost furthermore, we have been proposing the introduction of performance-based Limit State Design (PB-LSD) Method for the design of steel-concrete composite bridges. When the span exceeds 60 meters, most of bridges are PC bridges due to their economical advantage. In order to cope with this subject, our research group has been proposing double-composite type composite and composite hybrid bridges in combination with design method based on LSD. In this study, we studied applicability of composite hybrid bridge, and the followings are main findings from this study.
1) The possible combination using current material will be the material grade of SM570(S450) and SM490Y(S355).
2) If continuous composite non-hybrid-girder bridge with a span from 80 to 100 meters is designed based on LSD, the expected reduction of steel volume will be around 10% compared to that of the bridge based on ASD.
3) In case of hybrid girders with the same span, the reduction will be around 5%. This is because the stress level of hybrid girders has to be reduced in order to satisfy the required performance at serviceability limit.
4) However, the material cost of hybrid girder bridges will be 5 to 6% smaller compared to that of non-hybrid bridges.
5) When the post buckling strength is expected in hybrid girders, shear strength of it with a web material strength of S355 will be around 20% smaller than that of non-hybrid girder. This is not so prominent. However, if the post buckling strength is ignored, in case of thin web, the reduction of shear strength of hybrid girders is prominent.
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