Advanced analysis of steel-concrete composite frames

Abstract

Modern specifications such as AS4100 and AISC360-10 permit the design of steel frames by advanced analysis (second order nonlinear inelastic analysis). But the research on advanced analysis for steel-concrete composite frames with concrete-filled steel tubular (CFST) columns, composite beams, and composite connections is still in its infancy despite widespread application of such frames in modern construction. To conduct advanced analysis of composite frames, the best option is to adopt simplified numerical models because of the computational efficiency. However, it is very challenging to accurately capture the effects of composite action between different components of a composite frame using simplified models. This task initially requires the proper understanding of the fundamental behaviour of each component of composite frames. Therefore, 3D FE modelling was utilised to investigate the fundamental behaviour particularly for the CFST columns and composite beams with headed shear studs welded through profiled steel sheeting. Finally, a simplified tool to design composite frames by advanced analysis was developed. For CFST columns, simplified numerical models were developed using fibre beam element (FBE) models. The main challenging part of FBE modelling is to define accurate material properties because the FBE modelling cannot account for the interaction between the steel tube and concrete, which have significant effects on prediction accuracy. Therefore, the material models themselves should account for the interaction. Although a few material models for either steel or concrete are available in the literature for FBE modelling, such models cannot be used especially when considering the rapid development and application of high strength materials and/or thin-walled steel tubes. Therefore, versatile yet simple steel and concrete material models were developed in this study based on extensive regression analysis of data generated from 3D FE modelling. The FBE modelling results of circular CFST columns indicate that the proposed material models can be utilised for sufficiently wide practical ranges of such columns (concrete strength: 20 to 200 MPa, steel yield strength: 185-960 MPa, diameter to thickness ratio: 10-220). The full-scale experiments of composite beams are very expensive. Thus, FE modelling can be a viable alternative to investigate the fundamental behaviour of composite beams. But the FE models developed earlier have adopted various assumptions to simplify the modelling of some complex interactions such as the interaction between the shear studs and concrete. Accordingly, those FE models have limitations to capture certain types of failure modes. To address the above issues, a FE model for composite beams with profiled steel sheeting was developed. The realistic interaction between different components, including fracture of shear studs and profiled steel sheeting, along with concrete damage, has been considered in the FE modelling. The developed FE model successfully captured different types of failure modes of composite beams, such as shear failure of the studs, concrete crushing failure, steel beam failure and rib shear failure. Furthermore, the method to determine shear force (ð'‰s) âˆ'slip (ð>¿s) behaviour of shear studs in composite beams was introduced. Meanwhile, the contribution from profiled steel sheeting in carrying axial loads in composite beams can be quantified. The simplified numerical modelling for composite beams was developed utilising shell, beam, and connector elements representing the composite slab, steel beam, and shear studs, respectively. Similarly, the simplified models for composite beam-to-CFST column connections (blind-bolted flush and extended as well as through-plate connections) were developed where the connection behaviour was defined in terms of moment-rotation curves using connector elements. The simulation took just a few minutes for both composite beams and connections and the predictions are in well agreement with the test data. Finally, the proposed simplified numerical models of CFST columns, composite beams and composite connections were assembled together to conduct advanced analysis of steel-concrete composite frames. In particular, the proposed models were verified for composite frames with joints, such as welded external diaphragms and bolted endplate connections. The predictions obtained from simplified models of composite frames show very good correlation with test results and are computationally very efficient. Therefore, the proposed model can be efficiently used to conduct advanced analysis of composite frames. Then, a comparative study was conducted to investigate the differences between the traditional member-based design and design by advanced analysis of composite frames. The results indicated that the design based on advanced analysis was economical compared to traditional design method.

Date of Award	2018
Original language	English