Abstract
Steel-concrete composite beams both have the advantages of steel structure and concrete structure.And it has been used in lots of engineering in our country,such as Nanbu Bridge and Yangbu Bridge in Shanghai[1].There are a large number of scholars at home and abroad having studied the mechanic properties[2-5]and durability[6-9]of steel-concrete composite beams.In this paper,the static test and finite element simulation analysis of the positive and negative bending moment of the stud corroded steel-concrete composite beams are carried out.
A constant current was used in the test to accelerate the corrosion,and the studs with different degrees of corrosion were energized at dif ferent time.Through the static test(Figure 1 and Figure 2),the overall bearing capacity,the relative slip between the materials,the development of inter-span deflection,and other mechanical properties of composite beams of the positive and negative bending moment were studied before and after the stud corrosion.The finite element analysis software ABAQUS was used to model the composite beams,and the deflection of the composite beams before and after the coring of the studs was analyzed and compared with the experimental values.
Figure 1 Loading diagram of positive bending moment
Figure 2 Loading diagram of negative bending moment
During the monotonic loading of the test,the composite beams all failed due to local buckling of the steel beams and cracking of the concrete slab,rather than the fracture of the shear joint(Figure 3 and Figure 4).
Figure 3 Concrete slab crushed
Figure 4 Steel beam local buckling
It can be seen from the experiment that under the positive and negative bending moment,the bearing capacity of the composite beam decreases with the increase of the corrosion rate of the studs,and the slip between the concrete slab and the steel beam increases with the increase of the corrosion rate of the studs,with the overall stiffness reduced.And the effect under the action of negative bending moment is more obvious.The reason is that the concrete slab is pulled under the action of negative bending moment,and the studs are subjected to a larger pulling force earlier.
In the simulation of ABAQUS,the concrete constitutive structure selects the concrete plastic damage model,and the steel constitutive structure uses the ideal elastoplastic model.The studs with different diameters are used to simulate the studs with different corrosion rates.T3D2 units are adopted to model steel bars and C3D8R units are adopted to model steel beams,concrete slabs and studs.The simulation of the composite beam support is the same as the test.The support is set at 100 mm from both ends of the beam.One end constrains U1,U2,and U3 to simulate the fixed hinge support,and the other end constrains U1 and U2 to simulate the sliding hinge support.The model is shown in Figure 5.
Figure 5 Finite element model of the com posite beam
Comparing the simulating results and test results,it can be seen that the stiffness and ultimate bearing capacity of the combined beam test results are different from the finite element values,but it is small.The ultimate bearing capacity of the finite element calculation is slightly smaller than the experimental value.It may be because the constitutive relation of the steel is selected from the ideal elastoplastic model,and the strengthening stage of the steel is not considered;the difference in the initial stiffness of the composite beam may be that there was a gap on the interface between the concrete slabs and steel beams due to the construction errors.