Post on 09-Oct-2015
description
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
1/50
Post-Tensioned
Prestressed Concrete
Post-Tensioned
Slab-on-Ground
Construction
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
2/50
Reinforced vs Plain Concrete
It is important to recognize the difference between
reinforced and plain concrete when referring to post-
tensioned or conventionally reinforced concrete slabs-
on-ground. The American Concrete Institute (ACI)
defines reinforcedconcrete as concrete designed to
satisfy the minimum requirements of the code. The
category of plain concrete was developed by ACI to
refer to concrete used in ground supported construction
where loads are light, stresses are low, life safety
concerns are minimal or non-existent and the minimumrequirements for reinforced concrete are not necessary.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
3/50
Occupancy Loads
Tension Tension
ft= Mc /I or M/Sb
How Prestressing Works
The Basics
Edge Lift Edge Lift
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
4/50
ft= M/Sb (P/A)
CompressionForce Force
How Prestressing Works
For Slabs-on-Ground
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
5/50
Advantages of Post-Tensioning
Inherent compressive strength of concrete
Less structural depth to achieve same design
strength
Economical use of building materials
Speed of construction
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
6/50
Single Family Residential
Multi-Family Residential
Commercial / Industrial
Sports Courts
Applications of Post-TensioningSlab-on-Ground Foundations
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
7/50
Post-Tension Steel
Tonnage Comparison
0
10000
20000
30000
4000050000
60000
70000
80000
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Buildings SOG Bridges R&S Anchors
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
8/50
Foundations TypesClassified by BRAB Report 33
In 1962, The Building Research Advisory
Board (BRAB) issued Report 33 which
classified residential foundations into fourdesign categories based upon the degree
of severity of the supporting soil:
Type I: Unreinforced
Type II: Lightly Reinforced
Type III: Reinforced and Stiffened
Type IV: Structural
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
9/50
The PTI design
procedure forexpansive soil is
based on a ribbed
slab layout.
PTI Design Procedure
Slab-on-Ground Foundations
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
10/50
The key-word
is Slab-on-GROUNDGROUND
Slabs-on-Ground are designed to meet aspecific set of soil parameters.
The performance of ANY foundation isdependent up on obtaining accurate soilinformation about the site.
Expansive Soils
Plasticity Index (PI) Greater than 15 Expansion Index (EI) Greater than 20
Em, Ym, Bearing Capacity
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
11/50
Site Inspection
Inspect site to look for unusual conditions
Drainage ditches or low areas that hold water
Trees that can influence soil moisture
Anythingthat appears out of the ordinary
Contact the geotechnical and structural engineerfor recommendations
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
12/50
Site Preparation
Strip Site of Organics & Trash
The site should be
initially stripped of all
surface vegetation and
other deleterious
material.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
13/50
Site Preparation
Recompact Scarified Surface Material
The exposed
subgrade shouldbe scarified and
recompacted.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
14/50
Site Preparation
Identify Voids & Recompact
Remove trees,
including theroot system
Proof roll the
site to identify
any loose soil
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
15/50
Site Preparation
Drainage
Grade the lot for
positive drainageaway from the
foundation during
and after
construction.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
16/50
Site Preparation
Compaction tests should be performed on all fill material used
during the site development phase. The quality, as well as the
compaction, of all fill material should be documented.
Fill should exhibit low expansion properties, be free of organicsand other deleterious material, and be compatible with the
existing soil characteristics.
READthe General Notes sheet prepared by the structural
engineer. This sheet may contain special instructions about
specific site preparation requirements.
Contact the structural engineer should anything be unclear or in
question.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
17/50
Components of an
Unbonded PT System
Unbonded Strand
Anchorages
Accessories
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
18/50
Unbonded P-T Strand
Corrosion Protection "Grease"
High Density
PolyethyleneSheathing
P-T Coating
7 wire Steel
Strand
Unbonded strand consists of
three main components:
Prestressing Steel
PT Coating
Sheathing
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
19/50
Anchorage System
Anchor
2-pc Wedge
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
20/50
Standard System
Fixed End Anchorage
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
21/50
Standard System
Stress End Anchorage
Anchor Pocket Former
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
22/50
Standard System Assembly
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
23/50
Stressing Anchorage
Incorrect Correct
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
24/50
Stressing Anchorage
Replace Sheathing
Tape
1 inch Rule
Tendon Sheathing Repair
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
25/50
Installation
Follow approved engineers drawings
Anchors are placed 6 inches from edge
Anchors are placed at T/2 or 3 below top of slab
Anchors are securelyattached to edge forms
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
26/50
Installation
Follow approved engineers drawings
Anchors are placed 6 inches from edge
Anchors are placed at T/2 or 3 below top of slab
Anchors are securelyattached to edge forms
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
27/50
Installation
Horizontal transitions
are smooth, clear all
openings by 3 inches
and are straight past
the opening
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
28/50
Chairs are placed
and tied at each
tendon intersection atless than 3-6
centers
Installation
Chair Placement
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
29/50
Installation
Chair Placement
IncorrectCorrect
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
30/50
Installation
Draped tendons are used in some designs to
provide compression in the bottom of beams
resisting tensile stresses caused from edge lift.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
31/50
Installation
Drops in Slabs
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
32/50
Plumbing Blockouts
Deflect tendons toavoid blockoutsthrough the slab.
Maintain minimum of3 concrete coverbetween tendon andblockout
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
33/50
Plumbing Blockouts
Corner blockouts
can cause
concreting
difficulties. Rebar
solutions can
alleviate the
congestion and
prevent cornerfailures
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
34/50
Anchorage Zone Penetrations
Penetrations through the anchorage zone
should be sleeved with schedule 40 pipe.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
35/50
Reentrant Corners
Initial curing tensile
stresses build-up at
reentrant (inside)corners causing
cracking to occur.
Rebar is typically
installed at these
locations.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
36/50
Stressing
Initial Concrete Strength (2,000 psi MIN)
Initial Marking (Elongations)
Calibration of Jack/Gauge
Stressing Force vs. Gauge Pressure
Final Elongation Measurement
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
37/50
Cutting Stressing Tails
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
38/50
Finishing Stressing Recess
Clean the pocket former recess of any
dirt, grit, oil or other material that will
prevent the grout from bonding to the
concrete
Grout pocket former recess with non-
shrink cement, sand and water mix that
will reach the minimum compressive
strength of the concrete slab.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
39/50
Inspections
Inspections should be conducted to insure
the quality of the construction.
Pre-pour: Installation of P-T and rebar
Pour: Placement of Concrete
Stressing: Tensioning of P-T Tendons
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
40/50
Pre-Pour Inspection
Check the tendon and bar count
Check the placement of the fixed-end anchors for
the required cover over the end of the steel
Check to be sure that the stressing ends are
securely nailed to the forms (2 nails) and that the
tendon is perpendicular to the anchor
Check to be sure that you have adequate
concrete cover over all of the steel
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
41/50
Pour Inspection
Do not add excessive water at the site
Place the concrete in one continuous
operation - NO COLD JOINTS
Consolidate (vibrate) the concrete around the
P-T anchors, especially in the corners where
multiple anchors are located.
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
42/50
Pour Inspection
DO NOTdisplace or walk on any of the reinforcement
- P-T or rebar
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
43/50
Post-Concrete Placement
Notify the P-T stressing company the day after
the concrete is placed to schedule stressing
Remove the forms - ALL OF THEM. Do thiswithin 3 days after the concrete is placed
Do NOT damage stressing tails in rough grade
Do NOT cover tendon tails with dirt or lumber
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
44/50
Trouble-Shooting
Honeycombs
Low strength and poor quality concrete
Plumbing mistakes
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
45/50
Trouble-Shooting
Correct Incorrect
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
46/50
Foundation Maintenance
Do not alter the drainage pattern of the site
Provide a minimum of 3%-5% of slope away fromthe foundation with the first 5 feet
Roof drains should not dischargewater at the perimeter of thefoundation
Do not plant trees within the trees drip line
Do not cut off natural moisture around thefoundation by constructing decks or pools
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
47/50
The long-term performance of any
slab-on-ground foundation is dependentupon good drainage and a moisture
maintenance program by the property
owner.
Performance
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
48/50
PTI Certification Program
Consistency of material quality
Quality of extrusion and fabrication process
Traceability of components
Stressing equipment calibration
Company commitment to the long termperformance of the system
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
49/50
Construction & Maintenance
More information concerning theconstruction & maintenance of post-tensioned slabs-on-ground, can be found ina manual published by the Post-TensioningInstitute.
The 3rdEditions is currently being reviewedby committee and will be available in thenext few months.
602-870-7540
www.post-tensioning.org
5/20/2018 Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete
50/50
Design Procedures & Code
602-870-7540
www.post-tensioning.org
New in 2005