YS-RCS-BS-05

COLUMN DESIGN

Problem

Design grade 45, 200mm x 200mm x 3.5m height braced reinforced concrete column. The column is subjected the following initial design forces:

Axial 250kN, bending moment about major axis at the top -5kNm, bending moment about major axis at the bottom 10kNm, bending moment about minor axis at the top -4kNm, bending moment about minor axis at the bottom 12kNm.

Let the cover to reinforcement as 25mm.

Solution

1. Arrange the reinforcement in column section. Make sure the number of rebar provided fulfills the requirement as per cl.3.12.5.3, BS8110-1:1997.
2. Determine whether the provided area of reinforcement fulfills the limiting values as per Table 3.25 & cl.3.12.6.2, BS8110-1:1997.
3. Calculate the spacing of rebar and check it against cl.3.12.11.1, BS8110-1:1997.
4. Provide the link in column in accordance with cl.3.12.7.1, BS8110-1:1997.
5. Determine the top and bottom end conditions about both major and minor axes, based on Table 3.19 & Table 3.20, BS8110-1:1997.
6. Calculate the effective height of column by referring to cl.3.8.1.6.1, BS8110-1:1997.
7. Calculate the column slenderness ratio based on cl.3.8.1.7 & cl.3.8.1.8, BS8110-1:1997.
8. Determine the type of column in accordance with cl.3.8.1.3, BS8110-1:1997.
9. Calculate the minimum eccentricity based on cl.3.8.2.4, BS8110-1:1997.
10. Calculate the minimum design moment due to eccentricity based on cl.3.8.3.2, BS8110-1:1997.
11. Determine initial design moment by referring to cl.3.8.3.2, BS8110-1:1997.
12. For slender column, carry out calculation as per step 13 to 18. For short column, proceed to step 19.
13. Calculate the ultimate capacity of column when subjected to only axial load, as per cl.3.8.3.1, BS8110-1:1997.
14. Calculate the axial capacity of the column under balanced section condition, as per cl.3.8.1.1, BS8110-1:1997.
15. Determine the column deflection reduction factor in accordance with cl.3.8.3.1, BS8110-1:1997.
16. Determine βa based on cl.3.8.3.1, BS8110-1:1997.
17. Determine the deflection of slender column by referring to cl.3.8.3.1, BS8110-1:1997.
18. Calculate the additional moment due to slender column deflection, as stated in cl.3.8.3.1, BS8110-1:1997.
19. Determine the design moment about the target axis, referring to Figure 3.20, BS8110-1:1997.
20. Determine h' and b', as defined in Figure 3.22, BS8110-1:1997.
21. Calculate the ratio of Mx/h' and My/b'.
22. Calculate N/bhfcu.
23. Determine the value of β as per Table 3.22, BS8110-1:1997.
24. For biaxially bent column, determine design equivalent uniaxial bending moment by referring to cl.3.8.4.5, BS8110-1:1997.
25. Develop axial and bending interaction curve about both axes for column, based on cl.3.4.4.1, BS8110-1:1997 and Appendix A, BS8110-3:1985. Click here for detailed steps.
26. Plot the design axial and bending moment on interaction curve and evaluate the column design. The design is inadequate if the point lies outside the envelope of curve.