“A Comparative Study on

RC Flat Slab

&

Post-Tensioning Slab”

N.AjayResearch Scholar, Dept of Civil

Engg, BMSCE.And

S.Chethan Kumar J.Vittal. Kashyap

Structural Engineers, BBR INDIA PVT.LTD, Bangalore

OUTLINEINTRODUCTION

SCOPE OF STUDY

METHODOLOGY

ANALYSIS & DESIGN

RESULTS & CONCLUDING REMARKS

REFERENCES

INTRODUCTION BEHAVIOUR OF RCC AND PSC STRUCTURE

METHODS OF PRE-STRESS

PRE-TENSIONING POST-TENSIONING

(Reference : NPTEL Web site)

APPLICATION OF POST-TENSION

Cont..

BUILDINGS

SLAB ON GRADE PAVEMENTS

Why PT for Buildings?

Increased Clear Span. Thinner Slabs. Reduced Floor Loads, Lighter

Structures. Reduced Cracking and

Deflection. Reduced Storey Height. Rapid Construction. Large reduction in conventional

reinforcement.

SCOPE OF WORK Compare PT Flat slab and RC flat slab systems with respect to Strength

condition(moment carrying capacity),Service condition (long-term deflection) and Cost (Only Rebar Kg/Sq-m).

PANEL SIZE (m)

1 9 x 92 10 x 103 11 x 114 12 x 12

METHODOLOGY

Load Data:Super Impose Dead Load=3.0kN/Sq-m.Live load = 3.0 kN/Sq-m.Self-Weight of Slab= Actual.

Building Details:Type: Commercial Storey Height: 3.5 mNo of Bays: 4

Grade of Concrete: M-35.

Grade of Steel: Fe-500.

Post-Tensioning details:HT Strand for pre stressing: 12.7mmdia,7 ply Class II Area of strand: 98.7 mm2Design of PT Slab: Bonded system with Class-III

Structure (IS:1343-2012)Modulus of Elasticity: 1.95xE5MpaBreaking load: 183.7 kNUltimate Tensile Strength: 1860 MPaJacking force 75% UTS: 137.7 kNWedge draw-in slippage loss: 6 mm.Duct wobbles, K: 0.0020/m.Friction coefficient µ: 0.03 rad/m.Long term loss: 150 N/mm2 (For

creep/shrinkage/relaxation).

ANALYSIS Analysis by ADAPT-Builder Software.

Finite elements are automatically created by software. LOAD COMBINATIONS: Service(Total Load) :

1.0 x Selfweight + 1.0 x DL + 1.0 x LL+1.0 x PS Service(Sustained Load) :

1.0 x Selfweight + 1.0 x DL+ 0.3 x LL+ 1.0 x PS Strength:

1.50 x Selfweight + 1.5 x DL+ 1.5 x LL+ 1.0 x Hypostatic Initial:

1.0 x Selfweight + 1.15 x Prestressing.

Analyses of the both PT & RC slab floors are performed for the gravity load and the post tensioning forces.

DESIGN Design of slab by Strip Method (ACI and BS)- Column Strip and Middle Strip.

The column strip width is considered as 0.4x bay width and balance as middle strip (ref TR-43).

The design sections along the various design strips are checked for strength at service stage and ultimate stage conditions.

The sections are designed for ultimate stage with post tensioning steel considered as an internal resisting action.

Additional rebar is provided, if required, in the section to provide adequate strength. The section-designs are carried out internally by software.

Punching shear calculations are carried as per code provisions of IS:456, considering the vertical reactions and the moments transferred to the columns.

Check for Deflection of Slab as per IS:456-2000.

Check for Stresses of PT Slabs.

If provide Slab thickness satisfies Deflection & Stresses.

RESULTS

Moment Carrying Capacity in RC& PT slab in Column Strip Moment Carrying Capacity in RC& PT slab in Middle Strip

CONCLUDING REMARKS

RC slabs require more cross sectional dimensions compared to PT slabs.

The amount of concrete required for a floor is more for RC flat slab while compare to post-tensioned flat slab floor system.

Moment carrying capacity of PT Slabs is more than RC Slab with slender section when compared with RC Member.

PT slab provides a better serviceability than RC slabs.

The thickness of RC flat slab is 18.0% higher and cost is 13% more than the post-tensioned flat slab for 12 x 12 panel.

The quantity of steel per meter in RC Flat slabs are almost 45% higher than post-tensioned flat slabs for 12 x 12 panel.

Construction of PT Slab

ITPL- Bangalore ONE HORIZON CENTRE- Delhi

Photos : Courtesy by BBR INDIA PVT.LTD

WTT- Delhi Shangrila-Bangalore

Photos : Courtesy by BBR INDIA PVT.LTD

Marathon-Futurex-Mumbai

Photos : Courtesy by BBR INDIA PVT.LTD

1. Boskey Vishal Bahoria and Dhananjay K. Parbat,”Analysis and Design of RCC and Post-tensioned Flat Slab Considering Seismic Effect”, IACSIT International Journal of Engineering and Technology, Vol. 5, No. 1, PP10-13, February 2013.

2. Thayapraba M,” Cost Effectiveness of Post - Tensioned and Reinforced Concrete Flat Slab Systems”, International Journal of Innovative Technology and Exploring Engineering (IJITEE) ISSN: 2278-3075, Volume-3, Issue-12, PP107-109,May 2014.

3. Dr.Amlan.K.Sengupta&Prof.DevdasMenon,”Pre-stressed Concrete”, Indian Institute of Technology Madras, NPTEL.

4. Dr.Manamohan,R.Kalgal,”Post-tensioned Concrete in Building Sector”.

5. Martin Williams/ Sami Khan,” Post-Tensioned Concrete Floors”, Report, 1995.

6. Code of Practice for Prestressed Concrete Is: 1343 – 1980, BIS, Indian Standard Institution, New Delhi.

7. Plain and Reinforced Concrete Code of Practice Is: 456 - 2000, BIS, Indian Standard Institution, New Delhi.

8. Lin, T.Y., and Burns, N., 1981. “Design of Prestressed Concrete Structures”, John Wiley & Sons, New York.

REFERENCES

Thank you