Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete

  • View
    39

  • Download
    0

Embed Size (px)

DESCRIPTION

Ground slab design, presetressed, post tensioned design, crack free ground slabs

Text of Presentation- Ground Slabs-Post-Tensioned Prestressed Concrete

  • 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-Tension