Discuss precast concrete characteristics, advantages ... Total Precast Structures 081011... · Discuss precast concrete characteristics, advantages ... design team with its goals

Slide 1

Precast Structures and FramesMiles L. Blackman, P.E.

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Slide 2 Learning Objectives

• Discuss precast concrete characteristics, advantages and benefits, typical construction methods and construction applications.

• Understand precast applications and uses.

• Review typical precast building components.

• Learn about the manufacturing processes that give precast concrete its consistent high quality.

• Gain insight on technical considerations including connections, construction and erection.

• Understand the precasters role in assisting the design team with its goals.

• Access industry resources available to designers of precast structures.

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Slide 3 • The single most

important event that

led to the launch of

the prestressed

concrete industry in

North America was

the construction of

the technically

innovative, Walnut

Lane Memorial Bridge

in Fairmont Park in

Philadelphia,

Pennsylvania in 1949-

1950.

A Brief History

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Slide 4

• This prestressed concrete bridge

became a reality because of the

vision, persistence and courage

of a few extraordinary

individuals.

• Prof. Mangel described the

concept of pre-compressed

concrete to his students using

his well-known illustration of a

stack of books…

Prof. Gustav Mangel, University of Ghent, Belgium

A Brief History

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Slide 5

• The books on the

bottom are like pre-

compressed concrete:

using a compressive

force, they support

their own weight…

plus significant

superimposed loads,

represented by the

books on top.

A Brief History

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Slide 6 • Early innovations

included 7-wire

strand, long-line

casting beds; high-

quality, permanent

steel forms;

specialized chemical

admixtures; high

early-strength

concrete; accelerated

curing with heat; and

more…

7-Wire High Strength Strand

Long-Line Casting Beds

Permanent Steel Forms

Admixtures

High Early-Strength Concrete

Accelerated Curing

A Brief History

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Slide 7 • The combination of

high strength steel –

to resist tensile stress

– and concrete – to

provide compressive

strength

and durability – make

this composite

material adaptable to

many applications.

What is Precast/Prestressed Concrete?

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Slide 8 • Once the concrete is

cured, the strand

force is released from

the abutments. This

causes the steel

strands, which are

under high tension,

to try to return to

their original length.

A compression force

is created in the

bottom of the

component, and

camber.

PRESTRESS

FORCE

PRESTRESS

FORCECAMBER

Upward Deflection Created byPrestressed Strand is Camber


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Slide 9 • The compressive force

and upward force on

the concrete from the

strands helps offset

applied loads. The

combination of durable

concrete and high-

strength steel results in

a lasting strength that

ensures retention of the

component’s durability

throughout its lifetime.

PRESTRESS

FORCE

PRESTRESS

FORCE

LOADING

UPWARD FORCE EFFECT

DUE TO PRESTRESSING

The Effect of Camber Resists Downward

Deflection When Loads Are Applied


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Slide 10 PCI’s Dictionary of Terms….

Total Precast . . .

• Substantial core and shell of the structure are comprised of precast components.

• Many types of commercial applications.

• Allow for tailored design as necessary.

• Architectural choices are limitless.

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Slide 11 Applications

• Parking

Structures

• Residential

• Offices

• Manufacturing

• Institutional

• Others

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• Parking

Structures

• Residential

• Offices

• Manufacturing

• Institutional

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• Parking

Structures

• Residential

• Offices

• Manufacturing

• Institutional

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• Parking

Structures

• Residential

• Offices

• Manufacturing

• Institutional

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• Parking

Structures

• Residential

• Offices

• Manufacturing

• Institutional

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Slide 16

A. Load-bearing architectural spandrel

B. Exterior column

C. Double-tee or Hollowcore plank

D. Interior column

E. Inverted tee beam or composite beam

F. Shear wall

G. Stairs

A

A

B

F

C

C

E

D

G

B

F

C

C

E

D

Double-tee System

Hollowcore Plank System

Typical Precast Building Components

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Slide 17 Spandrel

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Slide 18 Interior Columns

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Slide 19 Exterior Columns

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Slide 20 Double Tees

• Double Tees derive their name from

their shape.

• The vertical elements are called “stems”

and the horizontal deck element is

called the “flange”.

• Economical spans start at approximately

50 ft. and can exceed 100 ft.

• Double tees are used for floors, roofs,

bridge members AND wall panels.

• Pre-topped tees are used in parking

structures with a thickened flange and

no field-poured topping.

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Slide 21 Hollow-Core Planks

•Hollow-core slabs can

simultaneously provide a

floor surface and a ceiling

surface which require very

little finish work.

•There are a variety of

manufacturers with

thicknesses ranging from 6

inches to 16 inches

•Maximum spans are about

60 ft. for typical residential

loading.

•Fire ratings up to 4 hours.

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Slide 22 Inverted tee beam

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Slide 23 Shear Walls

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Slide 24 Stairs and Landings

•Precast stairs,

stairwells and

landings are

erected with the

balance of the

structure, allowing

workers easy

access to all

working levels.

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Slide 25 Wall Panels

• Load-bearing walls

become perimeter

structural-gravity

support for floors

and roof

• Eliminates need for

perimeter structural

framing

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Slide 26 • Using precast concrete

components together as a

complete structural system

creates a design in which the

whole is greater than the sum

of the parts.

• For example, combining

precast/prestressed hollowcore

plank or double tees with

precast beams and columns

creates a durable, fire-resistant

structure that is quick to

erect and cost efficient due to

the compressed construction

schedule.

A Complete Structural System

Precast/Prestressed Structural Systems

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Slide 27 •All lateral loads are

transferred to a moment-

resisting frame that ties

beams and columns

together with rigid

connections.

•The need for shear walls is

eliminated.

Rigid Frame System


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Slide 28

•In general, an exterior

shear wall system permits

greater design flexibility

because it eliminates the

need for a structural core.

•By combining gravity load

bearing function with lateral

load resistance,

the exterior shear wall

system is also, in general,

more economical.

Exterior Shear Wall System


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Slide 29

•Lateral loads are

transmitted by floor

diaphragms to a structural

core of precast shear walls.

• The shear wall can be tied

together vertically and at

corners to form a structural

tube that cantilevers from

the foundation.

Interior Shear Wall System


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Slide 30 The Connections

•Connections: •Transfer Load

•Restrain Movement

•Provide Stability

•Design Must Include: •Adequate strength

•Ductility

•Proper detailing

•Account for tolerances

•Responsibility:•Typically provided by

the precast fabricator

based on loads or

forces provided by the

EOR.

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Slide 31 Manufacturing Process

• PCI-Certification…Insist on it!

– Ensures that plant has developed and

documented an in-depth, in-house quality

system based on time-tested, national

industry standards.

• Understanding the manufacturing

process will help you see how quality

control and efficiency are achieved.

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Long Line Forms

•Precast structural

elements are generally

prestressed.

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Panels are Set

•Architectural precast can

be conventionally reinforced

or prestressed.

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Slide 34

Place Concrete

Manufacturing Process

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Cure, then Strip Forms

•After the concrete

has cured, products

are removed from

the forms and

moved to the

storage yard.

•This is where post-

pour measuring,

cleaning, cutting,

special finishing,

etc. will take place.

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Slide 36 •Casting with a form liner

can create unique textural

effects. Form-liner designs

can be selected from a

broad range of inexpensive

stock liners, or a custom

style can be created from

existing materials or a

specific design.

Form-Liner Finish

Glaxo, Research Triangle Park, NC

Architectural Precast Wall Panels

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Slide 37 •Improvements in the

fabrication process have

created more refined

finishes. These range from

delicate finishes achieved

by surface acid etching or

light abrasive blasting to

bold textures and patterns,

created by using form

liners. Rich, colorful

textures also can be

produced by chemically

exposing colorful coarse

aggregates.

Special Finishes


ACID ETCHED SAND BLAST

RIBBED FORM LINER

EXPOSED

AGGREGATE

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Slide 38 •A designer can achieve

strikingly different colors

and textures from a single

precast mix simply by

varying the finish treatment.

The single mix shown here

has three different finishes.

This multiple-finish

technique offers an

economical yet effective

way to heighten aesthetic

interest.

Acid Etch Sandblast

Exposed

Aggregate


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Slide 39 •To create a flame-finished

granite appearance in

architectural precast, an

appropriately colored

precast-mix design needs

only to be sandblasted.

•In this comparison, the

sandblasted precast in the

foreground closely matches

the actual flame-finished

granite in the background.

Replicating Flame-Finished Granite

The Hearst Tower,

Charlotte, NC


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Slide 40 •Chemical surface retarders

effectively highlight the full

color and natural beauty of

the precast coarse

aggregate. Here, the

chemical retarder is being

removed with plain water

immediately after casting.

Chemical Retarders


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Slide 41 •These brick-faced precast

units can be erected quickly

as one large panel, at any

time of the year. This

application has become

more popular across the

country due to escalating

costs for field labor and the

scarcity of skilled masons.

Brick Faced Precast


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Slide 42 •Frequently, architects

encapsulate rigid insulation

within architectural precast

panels to generate higher

energy efficiency and

achieve additional

advantages.

•These panels consist of a

layer of precast that is

poured into the form, after

which the insulation is

placed and another layer of

concrete is added.

Encapsulated Rigid Insulation


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Slide 43 Construction and Erection Considerations

• By considering

construction and

erection as the job

is designed, cost

and schedule can

be positively

impacted.

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Slide 44 Construction and Erection Considerations

DO’s and DON’Ts

Some keys to economy …

•Fabrication

•Delivery

•Installation

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Slide 45

•Repetition is key to economy

Fabrication

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Slide 46 Keys to Fabrication Economy

•Many forms are made of

wood and can be expensive.

•Minimize number of

molds and maximize the

number of castings from

each mold.

Fabrication

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Slide 47 Delivery

• Must be able to deliver

and handle on-site

• Maximum Panel

Dimensions (Varies)– 12’ Tall x 40’ Long Preferred

• 14’ Maximum Width

• 50’ maximum length

– Maximum Panel Weight

• Common Payload of 40,000 lbs

• Affected by Local Conditions

• Limited by Regulatory

Agencies

• Permits and Escorts

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Slide 48

Properly Prepare Site

Delivery

•The site must be

properly prepared by

the Contractor to

allow truck and crane

access around the

site.

•Access roads?

•Staging areas?

•Crane pads?

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Slide 49

• Avoid Circumstances Requiring Double Handling.

•Must have close access for ease of erection

Installation

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Slide 50

•Plan for crane position

in the design stage

(Tower).

Installation

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Slide 51 Installation

• Anticipate crane size,

reach and erection

sequence to minimize

crane moves and set-

ups.

Sequence

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Slide 52 Design Considerations

•Get a Precaster involved

as early as possible to:

– Provide design &

engineering support.

–Provide value engineering

& cost support.

–Assist in material selection

& aesthetic considerations

–Generally, expedite the

project and save you money.

Early Design Involvement

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Slide 53 Responsibilities

• Engineer of Record (EOR)

– Define system concepts

– Define codes & design criteria

– Lateral stability analysis

• May be assigned to precaster

– Topping/Diaphragm Design

• Precast Engineer

– Individual Component designs

– Connection designs

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Slide 54 Specifications

• Clearly specify the code and code edition for

the project.

• Specify the loads and fire ratings required

• Specify connection forces where they cannot

be determined by the precaster.

• Clearly specify connection finishes required.

• Specify PCI certification.

• Specify the proper Quality Control.

– Structural elements with Arch finishes may

fall under MNL 116 rather than MNL 117.

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Slide 55 Serviceability

•Total Precast Structures are not as heavy as

perceived, perhaps less than 20% additional

weight over composite steel.

•Higher floor dead load can improve vibration

performance over steel–framed floors.

•Total Precast Structures feature “built-in” fire

resistance

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Slide 56 Green Design

• Re-usable Forms– Typically steel forms that are used over and over….

• Recycled Materials – Fly ash, Steel, Recycled aggregate

• Local & Renewable Materials– 85% of precast concrete is made up of naturally occurring and local

materials (sand and stone). Compared to other materials extraction requires low amounts of energy and they go directly into the finished product

• Transported and erected within 200 miles of plant.

• Thermal mass influences:– Heat absorption and loss

– Thermal lag

– Energy consumption

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Slide 57 Benefits

• Long clear spans

• High load capacity

• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 58 Benefits



• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 59 Benefits



• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 60 Benefits



• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 61 Benefits



• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 62 Benefits



• Fire resistance

• Durability

• Acoustical

performance

• Thermal mass

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Slide 63 Benefits

• Single source

• Speed of

construction

• All weather

construction

• Design flexibility

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Slide 64 Benefits

• Single source

• Speed of

construction

• All weather

construction


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Slide 65 Benefits

• Single source

• Speed of

construction

• All weather

construction


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Slide 66 Benefits

• Single source

• Speed of

construction

• All weather

construction


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Slide 67

PCI - Ongoing industry support

•Publications

PCI Design handbooks (6th)

Technical literature

Guide Specifications

PCI JOURNAL

ASCENT

•Website – www.pci.org

Resources

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Slide 68 Resources

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Slide 69 Questions?

This concludes the Presentation on Total Precast Structures and Frames. Thank you for your time!

PCMATexas.org PCI.org

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Documents

Discuss precast concrete characteristics, advantages ... Total Precast Structures 081011... · Discuss precast concrete characteristics, advantages ... design team with its goals