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

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 9.0 cm. 1 hour 12.5 cm. 2 hours 16.0 cm. 3 hours

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.

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

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

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

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

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

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

Two slabs

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

Two slabs

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

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

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 , .

O.k.

O.k.

Ribbed Slab

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

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.

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

An Example for Ribbed slab Reinforcement