YS-RCS-BS-01

TWO WAY SLAB DESIGN

Problem

Design a grade 45 reinforced concrete slab subjected to 1.15kPa superimposed dead load and 1.50kPa live load. The dimension of slab is 4m x 5m x 150mm and cover to reinforcement is 25mm. The slab is continuous over one long edge and one short edge.

Solution

1. Check whether the long span to short span ratio does not exceed 2. The slab should be designed as one way spanning slab if the ratio is greater than 2.
2. Calculate the design load using load combination for ultimate limit state, as per Table 2.1, BS8110-1:1997.
3. Based on the slab edge continuities, determine the coefficient for design bending moment by referring to Table 3.14, BS8110-1:1997.
4. Calculate the design bending moment for all parts as per cl.3.5.3.4, BS8110-1:1997.
5. Arrange the reinforcement in slab section.
6. Determine the effective depth to tension reinforcement.
7. Determine whether singly reinforced section is sufficient as per cl.3.4.4.4, BS8110-1:1997. If doubly reinforced section is required, use greater slab section as it is impractical to provide compression reinforcement in slab.
8. Determine the lever arm of tension reinforcement in slab section using the formulation provided in cl.3.4.4.4, BS8110-1:1997.
9. Determine the area of reinforcement required based on cl.3.4.4.4, BS8110-1:1997. The area of reinforcement required should not be less than minimum requirement as stated in Table 3.25, BS8110-1:1997.
10. Determine the spacing of reinforcement to be provided. Check whether the provided reinforcement is sufficient.
11. Determine the coefficient for design shear force by referring to Table 3.15, BS8110-1:1997.
12. Calculate design shear force for all parts by using the formulation provided in cl.3.5.3.7, BS8110-1:1997.
13. Calculate design shear stress developed in slab section, as per cl.3.5.5.2, BS8110-1:1997.
14. Determine concrete shear strength based on the method provided in Table 3.8, BS8110-1:1997.
15. Check whether the concrete shear strength is adequate in resisting the design shear stress. If not, consider thicker slab since shear link may not be practical.
16. Based on the edge continuity conditions for all four slab corners, determine the area of reinforcement required to resist torsion and uplifting (cl.3.5.3.5, BS8110-1:1997).
17. Check whether the area of reinforcement provided fulfills the requirement calculated above.
18. Based on the short span support condition, determine the basic span to effective depth ratio by referring to Table 3.9, BS8110-1:1997.
19. Calculate the stress developed in reinforcing steel by referring to Table 3.10, BS8110-1:1997.
20. Determine the modification factor due to tension reinforcement based on Table 3.10, BS8110-1:1997.
21. Calculate length factor based on short span length, referring to cl.3.4.6.4, BS8110-1:1997.
22. Calculate the permissible span to effective depth ratio by multiplying the basic ratio with modification factor and length factor.
23. Check whether the actual span to effective depth ratio exceeds the permissible ratio.
24. Check whether it is necessary to perform rebar spacing check by assessing the fulfillment of criteria as stated in cl.3.12.11.2.7, BS8110-1:1997.
25. Determine the maximum allowable rebar spacing based on the formulation provided in cl.3.12.11.2.7, BS8110-1:1997.
26. Determine the minimum rebar spacing by referring to cl.3.12.11.1, BS8110-1:1997.
27. Check whether the actual rebar spacing lies between the minimum and maximum limits, as calculated in steps above.