Umm Al-Qura University Department of Civil & Structural Engineering 1 Design of reinforced concrete II Design of one-way solid slabs Lecture (1)

Umm Al-Qura University Department of Civil & Structural Engineering 2 Design of reinforced concrete slabs  Reinforced concrete slabs are used in floors, roofs and walls of buildings and as the decks of bridges  Concrete slabs behave primarily as flexural members and the design is similar to that for beams 1)the breadth of the slab is fixed and a unit breadth of 1 m is used in the calculations 2)the shear stresses are usually low in a slab except when there are heavy concentrated loads 3)compression reinforcement is seldom required

Umm Al-Qura University Department of Civil & Structural Engineering 3 Design of one-way spanning solid slabs  The slabs are designed as if they consist of a series of beams of 1 m breadth  The main steel is in the direction of the short span and secondary or distribution steel is required in the transverse direction  The main steel should form the out layer of reinforcement to give it the maximum lever arm

Umm Al-Qura University Department of Civil & Structural Engineering 4 Depth, bending, shear  To calculate the depth of the slab, the designer must first estimate the percentage of steel required in the slab for bending  Generally, most slabs will be lightly reinforced, i.e.  The percentage of reinforcement can be used, together with the support conditions, to select an appropriate span/depth ratio from Figure 6.3. (Check of deflection).

span/depth ratio from Figure 6.3. (Check of deflection). 5

span/depth ratio from Table

Umm Al-Qura University Department of Civil & Structural Engineering 7  According to clause 6.2.2, EC2, where the design shear force ( ) is less than the design shear resistance of the concrete alone ( ) no shear reinforcement need be provided  Where, shear reinforcement should be provided such that.

Umm Al-Qura University Department of Civil & Structural Engineering 8  The maximum transverse spacing of shear reinforcement should not exceed 1.5d  Due to practical difficulties concerned with bending and fixing shear reinforcement make it unlikely that shear reinforcement could be provided in slabs less than 200 mm thick.

Umm Al-Qura University Department of Civil & Structural Engineering 9 Reinforcement details for solid slabs Reinforcement areas (clause 9.3.1, EC2)  The maximum and minimum percentages of longitudinal steel permitted in beams and slabs are the same. Minimum Area = 0.13% of A C Maximum Area = 4% of A C  The area of transverse or secondary reinforcement should be

Umm Al-Qura University Department of Civil & Structural Engineering 10 Spacing of reinforcement  The clear distance between reinforcing bars should not be less than the following: 3)maximum aggregate size plus 5 mm (if the aggregate size exceeds 32 mm) 1)maximum bar size 2)20 mm  The maximum bar spacing in slabs,, for the main reinforcement should be and for secondary reinforcement:

Umm Al-Qura University Department of Civil & Structural Engineering 11 Anchorage and curtailment  For detailing the main reinforcement in slabs, the same provision outlined earlier for beams will apply.  EC2 requires that in slabs near end supports, half the calculated span reinforcement should continue up to the support and be anchored in accordance with Clause 8.4.4, EC2.

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