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Design of Concrete Structure I

Dr. Ali Tayeh First Semester 2009. Design of Concrete Structure I. Lecture 12. One Way Slab Part 1. Slab – Minimum thickness. One-Way Slab Design. Thickness of One-Way Slabs. Fire Rating. This is equal to the number of hours for unexposed surface to rise a set amount usually 120 o C.

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Design of Concrete Structure I

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  1. Dr. Ali Tayeh First Semester 2009 Design of Concrete Structure I

  2. Lecture 12 One Way Slab Part 1

  3. Slab – Minimum thickness

  4. One-Way Slab Design Thickness of One-Way Slabs Fire Rating This is equal to the number of hours for unexposed surface to rise a set amount usually 120 o C 9.0 cm. 1 hour 12.5 cm. 2 hours 16.0 cm. 3 hours

  5. Cover for Slab Reinforcement ACI Sec. 7.7.1 (min. cover for corrosion protection) ( 1.) Concrete exposed to earth or weather. < f16 = 4.0 cm > f16 = 5.0 cm ( 2.) Concrete not exposed to earth or weather. < f32 = 2.0 cm Min. covers for fire ratings should also be considered.

  6. Minimum Reinforcement • According to ACI-Code 7.12.2.1 and for steels yielding at , the shrinkage reinforcement is taken not less than 0.0018 of the gross concrete area, or

  7. Solid slab Two way slab One-way slab Ribbed Slab Two way slab One-way slab

  8. One-Way Solid Slab Design Reinforcement Typical Reinforcement in a one-way slab:

  9. One-Way Solid Slab Design Cutoffs If requirements for use of ACI Moment Coefficients:

  10. One-Way Solid Slab Design Need to confirm thickness is adequate for one-way shear. Difficult to place shear reinforcement in a slab. Minimum area of shear reinforcement required in slabs if Usual use

  11. Moment Diagram: Approximate Method of Continuous Beams and One-Way Slabs: More than two slabs

  12. Two slabs

  13. Shear Diagram: Approximate Method of Continuous Beams and One-Way Slabs: More than two slabs

  14. Two slabs

  15. Summary of One-way Solid Slab Design Procedure • Select representative 1-m wide design strip/strips to span in the short direction • Choose a slab thickness

  16. Calculate the factored load by magnifying service dead and live loads according to this equation . The dead load includes own weight of the slab in addition to the covering materials it supports. The live load is dependent on the intended use of the slab. • Draw the shear force and bending moment diagrams for the strip

  17. Example 1 Using the ACI-Code approximate structural analysis, design for a warehouse, a continuous one-way slab supported on beams 5.0 m apart as shown in Figure ‎. Assume that the beam webs are 30 cm wide. The dead load is 3 kN/m2 in addition to the slab own weight, and the live load is 2 kN/m2. Use , .

  18. O.k.

  19. O.k.

  20. Ribbed Slab

  21. One-way Ribbed Slab Design Notes • According to ACI-Code 8.11.6.1, topping slab thickness is not to be less than 1/12 the clear distance between ribs, nor less than 5.0 cm. • According to ACI-Code 8.11.8, shear strength provided by rib concrete Vc may be taken 10 % greater than those for beams. It is permitted to increase shear strength using shear reinforcement or by widening the ends of ribs • Ribs are designed as rectangular beams in the regions of positive moment between the supports and as T-shaped beams in the regions of negative moments at the supports. Effective flange width beff is taken as half the distance between ribs, center-to-center

  22. Summary of One-way Ribbed Slab Design Procedure • The direction of ribs is chosen. • The overall slab thickness h is determined based on deflection control requirement. • The factored load on each of the ribs is computed. • The shear force and bending moment diagrams are drawn. • The strength of web in shear is checked. • Design positive and negative moment reinforcement.

  23. Example 2 Design a one-way ribbed slab to cover a 4 m x 10 m panel, shown in Figure below. The covering materials weigh 2 kN/m2, the live load is 2 kN/m2

  24. An Example for Ribbed slab Reinforcement

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