The light steel tube truss-webbed concrete composite bridge ,which adopts the light steel tube truss-webbed is used to support the concrete slab, and connects the spatial steel grid and the concrete faceplate to form a whole bridge through the shear connector. The application and research of this type of bridge is still in its infancy. In this paper, the basic mechanical properties and design methods are studied, the main contents as listed below:
1. The variation of mechanical behavior of the light steel tube truss-webbed concrete composite bridge with design parameters is studied, benchmark dimensionless weight analysis method based on orthogonal analysis is proposed, which can determine the optimum design parameters of the light steel tube truss-webbed concrete composite bridge, moreover, it can be widely applied to the optimization design of other similar structural parameters of bridges.
2. The research point out that the inclined steel web member has great influence on the ultimate flexural capacity and deformation of the composite girder. Based on the simplified assumption of stiffness equalization, the concept of ‘equivalent width of web member’ is defined. Further, the theoretical calculation formula of limit bending capacity and bending stiffness is established, The theoretical formula of shear stiffness of steel tube truss is deduced considering the shear deformation of steel tube truss,. Based on the existing experimental data and the finite element model, the flexural capacity and deformation formula is verified in this paper, which indicated that the formula has high precision.
3. A new typed K-shaped joint is presented which is applicable for the light steel tube truss-webbed concrete composite bridge, the bearing mode, failure mode, shear transfer mechanism and ultimate bearing capacity calculation method are studied through the model test.It indicate that the failure mode of K-shaped joint is the direct-shear failure in the joint area of the tube, and the main reason for the failure is the vertical shear in the joint area caused by the axial force difference of the chords．The shear capacity of the K-shaped joint is primarily contributed by concrete of the chords, the connecting bolts, the pin coupling bars and the PBL shear connectors. The simplified formula is established based on the failure mode of the joint，and a simplified formula for shear capacity of joint is proposed, which can guide the design and calculation of the K-shaped joints.
4. The direct shear tests of connecting bolts and pin coupling bars were carried out, multi-liners load-slip displacement curves of connecting bolts and pin coupling bars were proposed, which provides the basis for the finite element analysis of K-shaped joint. According to the mechanical model and parameters of the local connection, the three-dimensional refined K-shaped joint model is established, the calculated results can well reflect the failure mode and ultimate bearing capacity of the joint, morever, the calculated load- displacement curve also agrees well with the experimental results.
5. The shear lag effect is studied on the point supported concrete plate under uniformly distributed load, through the benchmark finite element model, it is put forward that the shear lag effect of point supported concrete plate is strong, and a zone of negative shear lag near the node is existence. Using the energy variational principle, a displacement function with undetermined power exponent is derived, the stress calculation formula of concrete plate is established with any power exponent, further longitudinal position correction factor β is introduced, and the calculation formula is amended, when the power exponent is 5 in displacement mode, and appropriate correction factor β is adopted, the results can be agreed well with the finite element value trend. The effective distribution width of concrete flange plate is calculated and compared with various codes, the results indicate that the calculation value of each code is generally large and unsafe.