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Spiral columns vs tied columns: how the design differs

For the same column section, the code gives different strength reduction factors and axial load limits for spiral and tied reinforcement. The reason lies in their confinement effect and failure mode.

ConceptsStructFlow R&D Team · SUHUL LLC・Published ・1 min read

1Different confinement effect

A continuous spiral wraps the core concrete evenly along the column, confining it better than discretely spaced ties; the core concrete keeps its strength at high compressive strains, so the column fails less abruptly.

2How the code treats them

Because spiral columns behave more ductilely, the code gives a higher strength reduction factor for compression-controlled sections and a higher axial load limit: 0.75 and 0.85 for spiral columns, against 0.65 and 0.80 for tied columns [4, 5].

3What it means for design

In columns with high axial load, these two differences show up directly in the design strength. Using a spiral for the same section raises the upper part of the P–M curve noticeably.

P–M interaction diagram of a circular column020406080100-400-200020040060080010001200M (tf·m)P (tf)Nominal strength Pn–MnDesign strength φPn–φMn
Fig. 1Nominal and design strength P–M curves of a circular (spiral) column (computed by the calculation core).

4Switch and compare in StructFlow

Both the circular column and rectangular column tools let you switch between spiral and tied directly, and the curves and check results update immediately.

References

  1. Mander, J. B., Priestley, M. J. N., & Park, R. (1988). Theoretical stress-strain model for confined concrete. Journal of Structural Engineering, 114(8), 1804–1826. doi:10.1061/(ASCE)0733-9445(1988)114:8(1804)
  2. Popovics, S. (1973). A numerical approach to the complete stress-strain curve of concrete. Cement and Concrete Research, 3(5), 583–599. doi:10.1016/0008-8846(73)90096-3
  3. Whitney, C. S. (1937). Design of reinforced concrete members under flexure or combined flexure and direct compression. ACI Journal Proceedings, 33(3), 483–498. doi:10.14359/8429
  4. ACI Committee 318. (2019). Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19). American Concrete Institute. doi:10.14359/51716937
  5. 內政部（Ministry of the Interior, Taiwan）. (2023). 建築物混凝土結構設計規範（Design Specifications for Concrete Structures of Buildings），112 年 8 月 10 日修正發布，113 年 1 月 1 日生效. nlma.gov.tw
  6. 內政部（Ministry of the Interior, Taiwan）. (2023). 建築物基礎構造設計規範（Design Specifications for Foundations of Buildings），112 年 6 月 20 日修正發布，113 年 1 月 1 日生效. nlma.gov.tw
  7. Mononobe, N., & Matsuo, H. (1929). On the determination of earth pressure during earthquakes. Proceedings of the World Engineering Congress, Vol. 9, Tokyo, 177–185.
  8. Sutherland, I. E., & Hodgman, G. W. (1974). Reentrant polygon clipping. Communications of the ACM, 17(1), 32–42. doi:10.1145/360767.360802
  9. National Center for Research on Earthquake Engineering (NCREE). 台灣新型高強度鋼筋混凝土（Taiwan New RC）專區. ncree.niar.org.tw/service/newrc
  10. Chiu, C.-K., Hung, C.-C., Lin, K.-C., Liu, K.-Y., Lee, H.-J., Cheng, M.-Y., et al. (2019). Design Guideline for Building of High-Strength Reinforced Concrete Structures (Draft), NCREE-19-001. National Center for Research on Earthquake Engineering.
  11. Hung, C.-C., & Li, S.-H. (2013). Three-dimensional model for analysis of high performance fiber reinforced cement-based composites. Composites Part B: Engineering, 45(1), 1441–1447. doi:10.1016/j.compositesb.2012.08.004
  12. Hung, C.-C., El-Tawil, S., & Chao, S.-H. (2021). A review of developments and challenges for UHPC in structural engineering: Behavior, analysis, and design. Journal of Structural Engineering, 147(9), 03121001. doi:10.1061/(ASCE)ST.1943-541X.0003073
  13. Shao, Y., Kuo, C.-W., & Hung, C.-C. (2021). Seismic performance of full-scale UHPC-jacket-strengthened RC columns under high axial loads. Engineering Structures, 243, 112657. doi:10.1016/j.engstruct.2021.112657
  14. Hung, C.-C., Kuo, C.-W., & Shao, Y. (2021). Cast-in-place and prefabricated UHPC jackets for retrofitting shear-deficient RC columns with different axial load levels. Journal of Building Engineering, 44, 103305. doi:10.1016/j.jobe.2021.103305
  15. Ou, Y.-C., Alrasyid, H., Haber, Z. B., & Lee, H.-J. (2015). Cyclic behavior of precast high-strength reinforced concrete columns. ACI Structural Journal, 112(6), 839–850. doi:10.14359/51687911
  16. Shen, W.-C., & Hwang, S.-J. (2023). Confinement reinforcement of high-strength reinforced concrete tied columns under high axial load. ACI Structural Journal, 120(3), 145–155. doi:10.14359/51738505

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