Project on Design and construction of post tensioning slab PRESENTING BY:- CH .Gopichand (10631A0110) D.Nagender (10631A0120) J.Paramesh (10631A0126) N.Prudhviraj (10631A0129) S.Sathyanarayana(10631A0147) CIVIL ENGINEERING 4 th YEAR SRI VENKATESWARA ENGINEERING COLLEGE INTERNAL GUIDE: Mrs.P.Jhansi
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Project on
Design and construction of post tensioning
slab
PRESENTING BY:-
CH .Gopichand (10631A0110)
D.Nagender (10631A0120)
J.Paramesh (10631A0126)
N.Prudhviraj (10631A0129)
S.Sathyanarayana(10631A0147)
CIVIL ENGINEERING
4th YEAR
SRI VENKATESWARA ENGINEERING COLLEGE
INTERNAL GUIDE:
Mrs.P.Jhansi
Objectives
The objective of the present report is
to summarize the experience available today in the field of
post-tensioning in building construction and in particular to
discuss the design and construction of post tensioned slab
structures, especially post tensioned flat slabs*
A detailed explanation will be given of the checks to be carried
out, the aspects to be considered in the design and the
construction procedures and sequences of a post-tensioned
slab. The execution of the design will be explained.
Prestressed concrete
PRINCIPLE – Using high tensile strength
steel alloys producing permanent pre-
compression in areas subjected to Tension.
A portion of tensile stress is counteracted
thereby reducing the cross-sectional area of
the steel reinforcement .
METHODS :- a) Pretensioning
b)Post-tensioning
PRETENSIONING :- Placing of concrete
around reinforcing tendons that have been
stressed to the desired degree.
POST-TENSIONING :- Reinforcing tendons
are stretched by jacks whilst keeping them in
serted in voids left pre-hand during curing of
concrete.
These spaces are then pumped full of grout
to bond steel tightly to the concrete.
STEEL BARS BEING
STRETCHED BY JACKS
Introduction
Methods of Pre-stressing
Pre-tensioning
Post-tensioning
Introduction
Pre-tensioning
• Steel tendons are stressed before the concrete is placed
at a precast plant remote from the construction site.
Introduction
Post-tensioning
• Steel tendon are stressed after the concrete has been placed and gained sufficient strength at the construction site.
Introduction
Post-tensioning Systems
Un-bonded Post-tensioning System
Bonded Post-tensioning Systems
Single strand
Multi strands flat duct
Multi strands round duct
Single strand
Design of PT Slabs
Flat Plate with Drop Panels
Common geometries*
• Two-way system
• Suitable span: 12.2 m
• Limiting criterion: Deflection
• Rebar**: 2.94 kg/m2
• PT: 3.87 kg/m2
* for typical office/residential buildings using
ACI/UBC requirements
** quantity assume no bottom reinforcement
Materiel properties
CONCRETE:Fc^28 → Compressive strength of concrete 28 days.Fcd → Design value for compressive strength on concrete.
→ 0.6 × fc^28 = 21 N/MM^2PRE STRESSING STEEL:
Ap → cross sectional area of pj steel 146 mm^2Fpy →yield strength of PT steel 1570 N/MM^2
Fpu → characteristic strength of PT steel 1770 N/MM^2
PRE-TENSIONING STEEL:Ep → modulus of elasticity of pre stressing steel 1.95 × 10^5 N/MM^2
(very low relaxation (3%)
Admissible stressing 0.75 fpu
Reinforcing steel:
Fsy →yield strength of reinforcing steel is 460 N/MM^2