"Behavior and Design of Concrete-Filled Beam-Columns" is the next in the Research to Practice Webinar Series co-produced by the Network for Earthquake Engineering Simulation (NEES) and the Earthquake Engineering Research Institute (EERI). There is no cost to attend this webinar. You may register online at this link. PDHs will be available from EERI after the webinar for $30.
In recent years, numerous innovative structural systems have evolved where structural steel and reinforced concrete have been combined to produce a building having the advantages of each material. Composite construction exploits the synergistic action in a single structural member of steel in tension and shear and concrete in compression. Additional constructional advantages for composite construction accrue from the fact that concrete has relatively low material costs, good fire resistance, and is easy to place, while the steel offers high ductility, toughness and high strength-to-weight and stiffness-to-weight ratios.
Typically, the use of composite columns in the United States has been limited to mega-columns or perimeter frames in tall buildings in seismic or hurricane areas where lateral drift controls design. In these cases, the steel column is often used to carry the gravity loads during construction, and is later encased or filled with concrete to provide lateral stiffness. Composite columns also represent a very attractive option to increase of building strength, stiffness and deformation capacity in structures subjected to large man-made and natural lateral loads.
Until recently, it was difficult to predict the maximum structural response of a frame system that includes composite beam-columns based on typical frame analysis and design strategies. The problems were two-fold. First, there was insufficient high quality experimental data to calibrate models for combined axial and flexural loads under complex loading regimes. Second, there was scant evidence to justify the system factors to be used in seismic analysis, the values of member stiffness to be used in lateral load design, and the applicability of general stability approaches such as the direct analysis method to buildings incorporating composite columns.
A multi-institution combined experimental/computational NEES research program was undertaken in 2009 comprised (a) experiments on 18 full-scale slender concrete-filled steel tube beam-columns, (b) the development of new finite element formulations that enable accurate representation of the seismic response of three-dimensional composite braced and unbraced frame structures; (c) extensive use of these models in FEMA P695 studies to reevaluate the seismic performance factors of ASCE 7-10, and (d) the development of design recommendations for composite structures within the context of the AISC Specification for Structural Steel Building. The results of the investigation indicate that concrete-filled beam-columns are extremely tough and ductile elements, capable of maintain their load-carrying capacity and stiffness through very severe cyclic load histories. In addition, the advanced models indicate that structural systems with these types of members provide superior performance under nonlinear time-history analyses. The results have provided additional data to improve the design provisions for composite columns and beam-columns in both the AISC Specification and the AISC Seismic Provisions.
Credits and References
Presented by: Roberto T. Leon, Virginia Tech; Jerome F. Hajjar, Northeastern University; Larry Griffis, Walter P. Moore
Co-produced by: The Network for Earthquake Engineering Simulation (NEES) and The Earthquake Engineering Research Institute (EERI)
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