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ABSTRACT
Most of the design codes for the composite columns including American Concrete Institute do not account for the concrete confinements offered by the steel cores encased in the concrete section. However, the flexural capacities of the axially and laterally loaded composite columns were substantially underestimated as the axial load increases if the concrete confinement provided by a steel core is not considered. The aim of this study was to identify the structural gains of the composite columns with the cross-, H- and T-shaped steel cores encased in the concrete when the concrete confinement provided by the steel cores is taken into consideration. The formulation of the flexural strength considering the confining effects provided by the transverse reinforcements and cross-shaped steel cores for the maximum load limit state was presented with a 50% axial load of the nominal column capacity. The formulation for an ultimate load limit state with a 40% axial load of the nominal column capacity is listed in the Appendix. The design charts were presented for the strain ranges between 0.001 and 0.01, leading to gaining the strengths of the composite columns that have been lost when the confining effects provided by the steel cores were ignored.
Nomenclature
| Ari | = | area of the rebar layer i (i=1-4), mm2; |
| Asi | = | area of the part i of H-steel section, mm2; |
| B | = | width of the concrete section, mm; |
| Bi | = | width of the unconfined, equivalent confined concrete area (i =1 - 2), mm; |
| ci | = | height of the concrete compression zone of unconfined, equivalent confined concrete area (i =1 - 2), mm; |
| Cci | = | compressive force given by unconfined, equivalent confined concrete area (i=1,2), kN; |
| C’c1 | = | compressive force given by the equivalent confined concrete area inside, kN; |
| D | = | height of the concrete section, mm; |
| di | = | distance from the rebar layer i (i=1-4) to top of the concrete section, mm; |
| dc | = | distance from the centroid to top of the concrete section, mm; |
| ds | = | distance from the top flange of H-steel to top of the concrete section, mm; |
| dsi | = | distance from the force given by the part i of the H-steel to top of the concrete section, mm; |
| Es | = | Young’s modulus of steel, MPa; |
| Er | = | Young’s modulus of rebar, MPa; |
| Fri | = | force given by rebar layer i (i=1,4), kN; |
| Fsi | = | force given by part i of H-steel section (i=1,8), kN; |
| εcmi | = | strain at fiber of the unconfined, equivalent confined concrete area (i =1- 2); |
| εyR | = | yield strain of the rebar; |
| εyS | = | yield strain of the steel; |
| εri | = | strain of the rebar layer i (i=1-4); |
| εsi | = | strain respect to the part i of the H-steel section; |
| fyR | = | yield strength of the rebar, MPa; |
| fyS | = | yield strength of the steel, MPa; |
| f’c | = | compressive strength of the unconfined concrete, MPa; |
| f’cc | = | compressive strength of the equivalent confined concrete, MPa; |
| fc1 | = | concrete compressive stress in term of the concrete strain of the unconfined area, MPa; |
| fc2 | = | concrete compressive stress in term of the concrete strain of the equivalent confined area, MPa; |
| h1 | = | depth of the vertical H-steel section part of the cross-shape steel section, mm; |
| h2 | = | depth of the horizontal H-steel section part of the cross-shape steel section, mm; |
| Kh | = | confinement factors for the highly confined concrete; |
| Kp | = | confinement factors for the partially confined concrete; |
| Ke | = | confinement factors for the equivalent confined concrete; |
| tf11 | = | top flange thickness of the vertical H-steel section part of cross-shape steel section, mm; |
| tf12 | = | bottom flange thickness of the vertical H-steel section part of cross-shape steel section, mm; |
| tf21 | = | top flange thickness of the horizontal H-steel section part of cross-shape steel section, mm; |
| tf22 | = | bottom flange thickness of horizontal H-steel section part of cross-shape steel section, mm; |
| tw1 | = | web thickness of the vertical H-steel section part of the cross-shape steel section, mm; |
| tw2 | = | web thickness of the horizontal H-steel section part of the cross-shape steel section, mm; |
| x1 | = | distance from the edge of the concrete equivalent confined areas to the top of the concrete section, mm; |
| w1 | = | width of the vertical H-steel section part of the cross-shape steel section, mm; |
| w2 | = | width of the horizontal H-steel section part of the cross-shape steel section, mm; |
| αi | = | stress factors for the concrete areas i (i=1,2); |
| α’1 | = | stress factors for the concrete areas inside; |
| γ i | = | centroid factor for the concrete areas i (i=1,2); |
| γ’ 1 | = | centroid factor for the concrete areas inside; |
Author contributions
Won-Kee Hong conceived the idea; Won-Kee Hong and Dinh Han Nguyen derived the equations; Won-Kee Hong wrote and prepared the original draft; Won-Kee Hong and Dinh Han Nguyen reviewed & edited the manuscript.
Disclosure statement
The authors declare that they have no conflict of interest.
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.
Additional information
Funding
Notes on contributors
Dinh Han Nguyen
Dinh Han Nguyen is currently enrolled as a Ph.D. candidate in the Department of Architectural Engineering at Kyung Hee University, Republic of Korea. His research interests include precast composite structures.
Won-Kee Hong
Won-Kee Hong is a Professor of Architectural Engineering at Kyung Hee University. Dr. Hong received his Masters and Ph.D. degrees from UCLA, and he worked for Englelkirk and Hart, Inc. (USA), Nihhon Sekkei (Japan) and Samsung Engineering and Construction Company (Korea) before joining Kyung Hee University (Korea). He also has professional engineering licenses from both Korea and the USA. Dr. Hong has more than 30 years of professional experience in structural engineering. His research interests include new approaches to construction technologies based on value engineering with hybrid composite structures. He has provided many useful solutions to issues in current structural design and construction technologies as a result of his research combining structural engineering with construction technologies. He is the author of numerous papers and patents, both in Korea and the USA. Currently, Dr. Hong is developing new connections that can be used with various types of frames, including hybrid steel–concrete precast composite frames, precast frames and steel frames. These connections would contribute to the modular construction of heavy plant structures and buildings as well. He recently published a book titled as “Hybrid Composite Precast Systems: Numerical Investigation to Construction” (Elsevier).