Han, Wang, and Zhao 2008

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This paper presents the behavior of the composite frame with concrete-filled square hollow section (SHS) columns to steel beam. Finite element modeling (FEM) was developed using ABAQUS to carry out the behavior of the composite frames under a constant axial load on the columns and a lateral cyclic load on the frame. Accurate material and geometrical nonlinearities for confined concrete and steel were considered in the analysis. A damage plastic model for concrete and elasto-plastic model for steel were used respectively. Six composite frame tests were carried out to verify the FE model.

Experimental Study, Results, and Discussion

Solid elements were found to be more efficient in modeling the concrete and steel tubes were modeled with shell elements. A fine mesh of three-dimensional eight-node linear brick and reduced integration with hourglass control solid element (C3D8R) is used for concrete and four-node doubly curved general-purpose shell with finite membrane strain shell element (S4) is used for steel tubes and steel beam. It is found that a mesh size of 1 (length):1 (width):2 (depth) approximately for solid elements and 1 (length):1 (width) approximately for shell elements, can achieve accurate results. A typical joint, which consists of a concrete-filled steel tubular (CFT) column, a steel beam, and the outer ring is used in the analysis.

The elastic–plastic material behavior provided by ABAQUS (using the *PLASTIC option) allows a multi-linear or bilinear stress–strain curve to be used. The steel beam and SHS steel tubes were simulated by this model. The Mises yield surface is used to define isotropic yielding for steel material and the model for steel assumes associated plastic flow. An idealized multi-linear stress–strain model for cold-formed steel SHS steel tube is adopted in this paper. This paper used the material model developed by Han et al. (2007) to simulate the core concrete of the composite columns in a frame. The damaged plastic model is adopted to simulate the concrete provided by the ABAQUS library.

The contact between the concrete and the steel tube is modeled by interface elements. The interface elements consist of two matching contact surfaces of concrete and steel tube elements. The normal direction of the two surfaces is hard contact and the tangent contact is simulated by the Coulomb friction model. The interface element allows the surfaces to separate under the influence of a tensile force. However, the two contact elements are not allowed to penetrate each other. The I-shaped steel beam is welded from the three pieces of rectangular steel plate. The *TIE option in ABAQUS is used to simulate the welding lines of steel beam.

Six concrete filled SHS columns to steel composite frame specimens were tested under a constant axial load and a cyclically increasing lateral load. For each specimen, column height was 57.1 in. and the steel beam span was 98.4in. Frame specimens were designed using the concept of strong-column-weak-beam. Columns were filled with self consolidating concrete that was designed for compressive cube strength of 6.19 ksi. Several different I-beam and column dimensions were tested.

The lateral cyclic load was applied at the end of the steel beam for CFT frame specimens. The frame specimen was a sway frame with rigid connection to the foundation. The bottoms of two columns were fixed through the rigid foundation beam which was fixed to the floor with bolts. To prevent unexpected instability and lateral torsional buckling of the specimen, lateral braces were installed. The lateral loading history of the frame was generally based on ATC-24 guidelines for cyclic testing of structural steel components.

Test results indicated that the FE modeling developed was able to reasonably predict the lateral load versus lateral displacement relationship of composite frame and the ultimate lateral load carrying capacity.

References

  • Han, L.-H., Wang, W.-D., and Zhao, X.-L. (2008). "Behaviour of steel beam to concrete-filled SHS column frames: Finite element model and verifications," Engineering Structures, 30 (6), pp. 1647-1658. doi:10.1016/j.engstruct.2007.10.018