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Abstract
A stub-girder floor system is a composite system constructed with a continuous
. . structural steel beam and a reinforced concrete slab separated by a series of short, typically wide, flange sections called stubs. Stubs are welded to the top of a continuous beam and attached to the concrete slab by shear connectors. Spaces between ends of stubs are used for installation of mechanical ducts and other utility systems and for placement of transverse floor beams that span between stub girders. The use of the stub girder floor
system generally reduces the amount of structural steel in the floor system by about 25% and the total cost of the floor system by about 15%. Moreover, the shallower depth of the main girders and the integration of the utility ducts and structural system result in the reduction of the building’s overall height.
To predict the reliable behavior and performance of stub-girder system in both elastic and plastic ranges, the Finite Element Method has been used in this study since the FEM is
”\ capable to represent the constituent parts, adopt adequate elements and use appropriate solution techniques. Moreover, the F.E model can be utilized to investigate aspects of behavior in far more detail than is possible in laboratory work. For instance, it permits the study of the sensitivity of response to variability of key components characteristics, including material properties, layout and shear stud response, allowing the investigation of partial interaction effects. Another important feature of the FE method is its ability to model the nonlinear behavior of the stub-girders. Also, it is fundamental that the interaction of all different components should be properly modeled as well as the interface behavior.
Two proposed models (2D and 3D FE models) were utilized in this study. These models contain all the main structural parameters and their associated nonlinearities (concrete slab, steel beam, stubs and shear connectors). In this model the shear connectors are modeled as springs to consider the geometry of studs in addition to the nonlinearity due to the interaction between the shear connector and the concrete. Test and numerical results available in the literature were used to validate both the 2D and 3D models.
According to the results of this research, it was found that the 2D model is more suitable to investigate the behavior of stub girder since it gives both less solution time and storage size without decreasing in the accuracy of the analysis when its results are compared with the results of the 3D model.
Based on the validated model, an extensive parametric study of stub-girders was performed. The present study shows how the behavior of the stub girder is affected by each of the concrete slab strength, steel strength, concrete slab depth, height of main girder
’1$ -md the length of exterior stub. Moreover, it was found that the ratio between the heights
:} of both the stub and the main girder is principle for achieving both high resistance and less
I material. Efficient values of this ratio were determined through the parametric study.
Finally, the study shows the effects of both the stiffuess and spacing of the shear connector upon the overall behavior of stub girder.