3. RCC > PRESTRESS?
- Concrete structures were common by 1920’’s
- Concretes strength in compression and lack in tension was known.
In RCC reinforcement replaces tension.
- Thus transformation is due to development of cracks - Visible
- Not so visible
- This leads to :
- Loss of durability due to cracking
- Substantial deformations due to loss in section properties
This restricted the use to smaller spans
4. HISTORY OF PRESTRESSING
Initial Research and Development in Europe 1928-
1933.
Pioneers : - Freyssinet - France
Leonhardt - Germany
Magnel - Belgium
USA adopted this technology in 1949.
Reason for Development : Inability to increase spans of RCC Bridges.
First Bridge : - Choicy Le Ruy across Seine
Paris 1935 span 40m.
5. Prestressing is a tested, knowledge based Technology which
has withstood TEST OF TIME.
Live Technology : - Continuous State of Development.
Better, Stronger and improved
Materials
With matching Hardware.
2000T Capacity single Systems with steel strands.
1 T Capacity Carbon Fibre systems in Rehabilitation field
6. FROM BRIDGES TO PT SLABS
Prestress Developed initially for long span bridges.
First span was 40m. Now 1000m spans are planned
using cable stay technique which has same basic
principles, materials, hardware.
Technology was adopted later for many long span
structures like aircraft hangers.
Initial developments were all in Post Tensioning.
- i.e.. Concrete cast first and prestress applied later.
7. Later Pre Tensioning developed.
- i.e.. Concrete is cast around wires/strands already
tensioned .
- initially applied for standardized bridge girders.
- Then to precast building slabs and precast girders.
Advantages of PreTensioning
-- Product uniformity factory made.
-- Quick turnover with fast curing techniques.
Disadvantages
-- Transport, handling, multiple joints.
-- Profiling limitations hence span restrictions.
8. To Overcome above post tensioning of slab
developed.
Advantages
-- Reduction in number of joints
-- Mass pours
-- Quick removal of shutter possible to achieve same
speed
9. Developed initially in USA.
Being in use for last 50 years in various countries.
In Asian countries like Singapore, India in use for last 35
years.
In middle east last 15-18 years
In Oman last 5-6 years
Oman therefore is starting with
-- 50 years of knowledge
-- Benefits of all theoretical research and development.
-- Benefits of hardware development during period.
10. WHEN & WHY PT SLABS?
New buildings require
Large span structures, with flexible plans
Unobstructed space below sofit for services
Building height regulations : optimisation of storey ht
Possible only if
Beam less system is developed. 1) rcc flat slab
2) prestressed flat slab
11. It is also possible to have prestressed slabs in normal
slab and beam system, also allowing larger slab
spans.
Special Hardware suitable for slabs has been
developed
Flat Sheathings
20mm thk 45 to 70 mm wide for 12.7mm strand
--Rigid
--Flexible
Flat Anchorages
12. 12.7 mm HT Strand
Flat GI Duct
Flat Anchorage
Grout Vent Tube
16. MATERIALS USED IN PT
Concrete : Minimum C30 generally C35-C40
Reinforcing steel : Based on country wise availability
In Oman : 460 n/mm2
In India : 415 n/mm2
: 500 n/mm2
In Singapore : 500 n/mm2
Prestressing steel : Normal relaxation steel or grade I :
braking Load ~ 1750 n/mm2
: Low relaxation steel or grade II or
super grade ~ 1860 n/mm2
17. Sheathing : Galvanised Iron
Bright Metal
HDPE (Common in bridges).
Grout : Basic cement , water mixture with
admixture to fill the space between
sheathing and strands.
Grade should be same as concrete
slab
18. COMPARISON OF RCC AND PRESTRESSED
FLAT SLAB
RCC Flat Slab
1. Cracked section under service.
2. Excessive deformations or
increased thickness to control
deformations, due to cracked
sections.
3. Once cracked no closure of
crack removal of load.
4. Heavy reinforcement leads to
conjustion and concretability
parameters.
Prestressed Flat Slab
1. Uncracked section under service.
2. Deflections very much under
limit due to :
a) Prestress gives opposite initial
deformations
b) Gross properties reduce
deflections
3. Due to positive force on section
closure on removal of load.
4. No conjustion of steel.
19. COMPARISON OF RCC AND PRESTRESSED
FLAT SLAB
RCC Flat Slab
5 Excessive shrinkage cracks.
6. Shear performance -
Normal.
Prestressed Flat Slab
5. Early stressing of part of cables
reduce these substantially.
6. Since section is uncracked and
compressed enhanced shear
capacity by 30% or so.
20.
21. COMPARISON OF RCC & PT FLAT SLAB
ON REAL PARAMETERS
Take typical 9m x 9m grid Live load 4kn/m2 SDL 3 kn/m2
RCC flat slab
1. Slab thickness 300mm
2. HYSD 35 to 40 kg/m2
depending on size of dropcap
3. HTS Nil
4. Likely long term deflection
28-30mm
Prestressed flat slab
1. Slab thickness 220mm
2. HYSD 8 –– 10 kg/m2
depending
on dropcap
3. HTS ~ 4.5 kg/m2
4. Likely long term deflection
10-12mm
22. Cost Comparison
Project :Sohar Pearl
Office & Apparment Buildings City Mall
Alternative 1 : RCC Flat Slab Alternative 1 : RCC Flat Slab
For 8.5 x 8.3M Grid For 8.5 x 8.3M Grid
Slab thickness 300 MM Slab thickness 300 MM
Drop Cap 4000*4000*450MM Drop Cap 4000*4000*500MM
Materials Quantity Unit Price Amount Materials Quantity Unit Price Amount
Concrete 25.565 36.000 920.340 Concrete 24.365 36.000 877.140
Reinforcemen 2556.5 0.380 971.470 Reinforcement 2436.5 0.380 925.870
Shuttering 71.75 5.800 416.150 Shuttering 72.15 5.800 418.470
Total RO : 2307.960 Total RO : 2221.480
Alternative 2 : Post-tensioned Slab Alternative 2 : Post-tensioned Slab
For 8.5 x 8.3M Grid For 8.5 x 8.3M Grid
Slab thickness 200 Slab thickness 200 MM
Drop Cap 2800*2800*350 MM Drop Cap 2800*2800*350 MM
Materials Quantity Unit Price Amount Materials Quantity Unit Price Amount
Concrete 15.2 36.000 547.200 Concrete 15.2 36.000 547.200
Reinforcemen 634.95 0.380 241.281 Reinforcement 634.95 0.380 241.281
Shuttering 71.39 5.800 414.062 Shuttering 71.39 5.800 414.062
Post-tensionin 70.55 9.000 634.950 Post-tensionin 70.55 9.000 634.950
Total RO : 1837.493 Total RO : 1837.493
Savings 20.4% Savings 17.3%
23. Direct advantage Related further advantages
••Floor to floor height reduction
••Savings on total building height 1 floor can be gained for approx. each
20 floors
••Reduction of slab thickness leads to reduced energy needs
••Savings in columns and foundations costs
••Reduced formwork costs
••Increase in column of free space
••Flexible planning
••Improvement in durability
••Improvement in slab rigidity
Reduction in slab thickness DESIGN
Large spans
Limitation on crack widths
Reduction of steel ••Easier placing and handling of reinforcement
reinforcement and
arrangement simplification
••Large floor area can be tackled at a time
••Reduction in overall construction time
Less concrete volume per
pour
••Early formwork release.
••Reduction in total construction time.
••Reduction of formworks sets.
••Improvement in constructability. –– table forms.
Quick rotation of formwork
CONSTRUCTION
High deflection control ••Improvement in serviceability for all non-structural elements.
24. CRITICAL ISSUES : AS DESIGNER
If drop cap not available : Punching shear
problems.
or inadequate Limitations on max. shear
even with reinforcement.
RCC and PT Junctions.
Openings.
Shrinkage cracking.
Multi level propping.
Honeycombing near anchorages.
Breakage at passive anchors.
26. CRITICAL ISSUES : AS CONSTRUCTOR
Design of scaffolding system.
When can shutter be released?
Multilevel propping
27. SHARING OF DESIGN RESPONSIBILITIES
Globally ,PT is operated through special Agencies who have to
act in cooperation with main consultant and main contractor.
Necessary to DEFINE Responsibilities.
Framing Plan, Column Spacing - Main RCC consultant /
Architect / Owner
Global Analysis including
Lateral load analysis
Columns, footings, RCC areas -Main Consultant
Load bearing beams
Additions in slab for Global effects
28. SHARING OF DESIGN RESPONSIBILITIES
Slab Analysis ( Vertical Loads Only)- PT Consultant
Slab Drawings :
PT Layout & Elevations - PT Consultant
Reinforcement in slabs
Overall stability of structure - Main Consultant
29. Procedures /Work Methodology
Step-01: Tendon &Anchorage Installation
Step-02:Concreting/Casting of Slab
Step-03: Stressing of Cables
Step-04: Grouting of Cables
35. Project: Al Rawaq Building
Client: Suhail Bahwan Holdings
Consultant: Cowi & Partners LLC
Project: ASSAUD Business Centra
Client: Alia Properties
Consultant: Triad Oman Consultants
36. Project: 4 star Hotel Appartment at Al Qurum
Client: Mustafa Sultan Enterprises
Consultant: Al Hatmy Consultants
Project: Proposed Hotel Development at Azaiba
Client: Azaiba Hotel LLC
Consultant: Kadri Consultants
38. Project: Comm Bldg at MBD for Badrr Shipping
Client: Badrr Shipping Agencies
Consultant: EIDC
Project: Facility Building at KOM
Client: Oasis Development SAOC/PIEI
Consultant: Leeyanah Engg Consultancy
39. Project: Headquarters for MOD-Pension Fund
Client: MOD-Pension Fund
Consultant: Gulf Engg Consultancy
Project: Al Ruwad International School
Client: Muscat Int School
Consultant: Gulf Engg Consultancy
40. Project: Muscat International Airport-PkgIII
Client: Ministry of Transport& Communication
Consultant: Hill International
Contractor: Bechtel Enka Bahwan Consortium
Project: Comm Bldg at Bausher for Sk Salem Al
Areimi
Client: Sk Salem Al Areimi
Consultant: TRIAD Oman
41. Project: Bait Al Zubair –Ph04
Client: The Zubair Corporation
Consultant: Image Design/TRIAD Oman
42. Project: Residential development at Ruwi
Client: The Zubair Corporation
Consultant: NEO
Project: Residential development at Wadi Kabir
Client: Sk Salem Al Areimi
Consultant:TRIAD Oman
43. Project: Residential Building –Dar Al Maha-01
Client: Sohar Investment & Development
Consultant: EIDC
Project: Comm Res Bldg for Mr Dawood Al Futaisi
Client: Mr Dawood Al Futaisi
Consultant: Dawood Consultancy
44. Project: The Sultan centre at Azaiba
Client: The Sultan centre
Consultant: Cowi & Partners
Project: Al Maha Beach Restautant
Client: Al Rotana Hotels & Developments
Consultant: EIDC
48. THANK YOU ……
Corporate Address
Specialised Engineering LLC
PO Box 1020,Ruwi-112
Sultanate of Oman
Tel: 24713494
Fax:24713495
E-mail-info@spl-eng.com
Web:www.spl-eng.com
