Final thesis presentation.

Detailing for Post-Tensioning in Buildings
30th
January, 2014.
By
Md. Rashidul Islam.
Student ID :WUB 10/10/43/1306
Supervised by
Shekh Istiaq Ahmed
Lecturer
Department of Civil Engineering
WORLD UNIVERSITY OF BANGLADESH
Welcome To Thesis Presentation

When Eugene Freyssinet “invented” prestressed concrete it was considered to
be an entirely new material- a material which did not crack. Thus, during the
active development of prestressed concrete in the 1940’s and 1950’s the
emphasis was on elastic methods of analysis and design.
Shortly after the Second World War, Freyssinet designed a number of highly
successful bridges in France, which led to wide acceptance of prestressed
concrete (Collins and Mitchell 1997).
In 1956, the construction of the first high rise building to utilize post-tensioned
slabs began, namely, the Diamond Head Apartments in Honolulu, Hawaii. This
structure was 14 storey’s high with replicated floor plans for each level. It was
evident, even in this initial development in post-Tensioned slabs, that this
scenario was where post-tensioned slabs had a significant advantage. The cycle
of propping, pouring, stressing and back propping was simply repeated at each
level, with building services ensuing. Prop movement was simplified, with props
simply elevated each time they were required. The labor intensive and
potentially complex stage of stressing (timing and quantity of stressing) became
more efficient as a familiar construction routine emerged with time.)
INTRODUCTION

 The main benefits of Post-tensioned slabs are their ability to increase
construction Speed, reduce slab thickness and maintain minimal to No slab
deflections. Due to these benefits Post-tensioned slabs have become a very
popular and familiar form of construction for multistory buildings.
 Post-tensioning utilizes high quality high strength steel such that 1kg of post-
tensioning strand may replace 3 or 4 kg of ordinary non pre-stressed
reinforcement. This can reduce congestion in members. Under service load
conditions steel stresses should be limited to about 200 to 250MPa for crack
control. For every 1MPa of confinement stress about 4MPa of additional
compressive strength is produced. (Strain in the confinement reinforcement
should be limited to about 0.1% under ultimate loads).
 In 1939 Austrian H. von Emperger made the suggestion that limiting the
amount of prestressed wires, so asto allow minimal cracks to occur had
benefits. Allowing cracking under full design working load allowed sufficient
control over deflection and crack widths and hence achieved good service load
behaviour. This led to the use of the terms full prestressing and partial
prestressing, to distinguish between structures which respectively are not
designed to crack, and structures allowed limited cracking which gives greater
deflection control (Warner et al. 1998).

Advantage of Prestress Concrete
 The entire section of the concrete becomes effective in prestress
concrete, where as only the portion of section above neutral axis is
supposed to at in case of reinforcement concrete.
 The use of higher strength of the materials reduces the cross sectional
dimensions % hence its effect in weight saving.
 It is more economical for structures of long spans and those carrying
heavy loads.
 Prestressing reduces or eliminates cracks in concrete, which resists
corrosion and other chemical action.
 The use of corned tendons help to carry some of the shear.
 Prestressed structures are more slender. They field more clearance.
 Very large spans such as segmental bridge or cable-stayed bridges can
only be constructed through the use of prestressing.

Objectives
“Detailing for post-tensioning” addresses the important.
The objectives of this document are:
• To assist in producing better designs which are easier and
more economical to build.
• To provide previously unavailable background design
information regarding the more important anchorage:
• To be frank and open about what is actually being done
and to disseminate this knowledge: and
• To present a balanced perspective on design and correct
the growing trend of over analysis

Methodology & Study
• Due to the strong industry support for this Thesis, access to a
construction site incorporating Post-tensioning slabs was supplied at
the commencement of the Thesis. This allowed the experimental
component of this research to test and measure a wide range of
variables on site. The requirement for this project surfaced during the
design stages of Pacific blue jeans wear Ltd, a multistory building
constructed in 14, Gadda, Ulail, Savar, Dhaka, Bangladesh-1400. The
design project for Pacific blue jeans wear Ltd was particularly
complex due to a very ambitious construction timeline. Therefore, it
should be noted in this Thesis that reference to this building is
primarily name Al-Muslim Industrial Park is unavoidable due to the
timing of the Thesis. Seven out of the ten slabs being poured at Pacific
blue jeans wear Ltd utilized an identical two-way PPS slab
arrangement. Due to the large size of the slabs, each of the seven slabs
were poured in two sections. This gave the Thesis fourteen
opportunities to collect concrete samples directly from the
construction site at the time of pouring.

Pile Layout Plan of Pacific blue jeans wear Ltd.

Basement Re-bar placement and Water stopper settings .

TENDON LAYOUT PLAN DETAIL GROUND FLOOR SLAB

PC Strand check ( Size=12.70mm, grade 1860, ASTM A416-1996,
Mfg. Date e.t.c ) at practical field.

Anchorage Cone Setting at slab end portion.

Two duck pipe joint by duck socket (Coupler).

Profiles Setting at Column Direction & Checking by Drawing .

Profiles Setting at Slab middle Beam, Column point, Periphery Beam,
Under Top Re-bar and Grout vent Setting for Grouting.

Master Grip uses for anchorage gripping by Hydraulic Jack

Before tension we setup Hydraulic Pump carefully
(Left side Pressure vent & Right side Release vent)

Strand Tensioning, data calculated & check Elongation at field

Strand Tensioning Measured data calculated & check when Gripping
completed

Constituent materials (cement, water, admixtures) are carefully selected. We are checked for
compatibility with each other. Quantities of admixtures and water are optimized to provide stable,
low-bleed grouts which assure complete filling of the tendon ducts and an alkaline environment
for long-term protection of the tendon. Grout mixes consisting of selected Scan cements and
specific admixtures ( Civex-100) have been analyzes and optimized for exclusive use in.
Experience with grouted post tensioning tendons proven that a cementations grout can provide
excellent protection for the prestressing steel.Bonded internal tendons, slab tendons, developed a
full process dedicated to improving the quality of grouting activities on site and grouting materials,
under the trademark -HPI® (high performance injection).

Result & Discussion
Sub: Pre-Stress & RCC Building Cost Estimation Compare
Typical floor Estimation ( Floor Area 85,000 sft)
Pre-stress part
1 Strand 78 ton 78000 6084000
2 Sheat pipe 24000 m 25 600000
3 Anchorage 884 Nos 1400 1237600
4 Grout L/S 680000
5 Labor charge L/S 450000
Slab casting
Sl. No
Materials
description Qnty.
Unit
Rate Amount
1 R.C Volume 85000 cft 160 13600000
2 Re-Bar 102 ton 55000 5610000
Column+Lift+Stair
1 R.C Volume 8000 cft 160 1280000
2 Re-Bar 28 ton 55000 1540000
3 Civil work (89500 cft X 138/=) 12351000
Total Cost 43432600
Non pre-stress part
Slab casting
Sl. No Materials
description
Qnty. Unit Rate Amount
1 R.C Volume
12750
0cft 160 20400000
2 Re-Bar 550ton 55000 30250000
Column+Lift+Stair
1 R.C Volume 8000cft 160 1280000
2 Re-Bar 28ton 55000 1540000
Labor cost
1 Civil work (135500 cft X 110/=) 14905000
Total Cost 68375000
Finding :
Hence, Save Amount 42.57 % of PC slab than RCC Slab
So, Post-tensioning Slab will be economical & Safety.

Conclusion
 The experimental program performed in this Thesis allowed detailed monitoring of the
primary concrete material properties (fc, Ec and ft) at Pacific blue jeans wear Ltd. over
the time periods of 7, 14, 21 and 28 days. This monitoring was performed for site curing
conditions for 35N/mm² and 40 N/mm² concrete mixes. Secondary material properties
were obtained from independent testing performed by Concrete mix. The database
produced by the experimental program has produced a vital reference of onsite slab
performance for future projects.
 A statistical analysis performed on the experimental data provided this Thesis with a
detailed understanding of the statistical distribution of primary material properties for
concrete mix’s 35 N/mm² and 40 N/mm² concretes in AMG project. This statistical
analysis allowed this research to conclude that the variance of fc, Ec and ft does not
depend on age. However it does depend on curing conditions, although only slightly.
The variance of each material property does depend on concrete mix when a comparison
was made between 35 N/mm² and 40 N/mm² mixes.
 It was determined that the most appropriate current deformation prediction method was
the deflection and camber prediction methods proposed by Collins and Mitchell (1997).
However this numerical method does not consider the statistical distribution of concrete
material properties.

Strand Pressure Strand Placement

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